I just realised I don't really understand earth ground! - Page 1
Forum section: electronics / beginners

author: seb1982
author_rank: Regular Contributor
timestamp: April 03, 2013, 07:12:13 am
content: I was just browsing Ebay for a nice aluminium project case, and thinking, "ooh, I must get a cheap crimping tool so I can earth the chassis properly", when I realised there's s big thing I don't get about earth ground.As I understand it, current will always take the path of least resistance. But, I gather that all "earth ground" really is is a big copper tube sunk into the ground somewhere nearby. If I stuck both my multimeter probes in the ground, it would pretty quickly tell me that it had, effectively, "infinate" resistance. If I put both probes on my hand, it tells me I have a resistance of a few m-ohms or thereabouts. So, when a loose wire touches a metal chassis and makes it live, and I touch it, why would the electricity flow down to earth (massive resistance) rather than through me (less resistance)?Also, I think I remember someone saying that they'd connected their anti-static workbench mat to earth through a 1 ohm resistor, or something like that, and I really don't understand why you'd do that either.If anyone can help me understand what's going on, that'd be great! I really hate it when I suddenly realise that I don't understand something I always thought I did - there are enough things already on the list of things I *know* I don't understand!

author: gnif
author_rank: Unknown
timestamp: April 03, 2013, 07:20:33 am
content: Most housing here in AU has earth leakage detectors, so if your random bit of gear does short to ground and current flows it will trip and protect you. I think they trip at ~50ma.

author: peter.mitchell
author_rank: Super Contributor
timestamp: April 03, 2013, 07:51:36 am
content: That's why the earth electrode/stake/rod is quite large and driven quite deeply into the ground.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 03, 2013, 08:02:29 am
content: Quote from: gnif on April 03, 2013, 07:20:33 amIt's normally 30mA for fuseboard ciruit breakers.This little doover is good for knowing for sure how good your breaker is and if you've got any rouge things on your power circuit.http://www.jaycar.com.au/productView.asp?ID=QP2000

author: ludzinc
author_rank: Unknown
timestamp: April 03, 2013, 08:57:01 am
content: FYIThe mains Neutral and Earth are connected at the switchboard to your house.That is why a fault in equipment that shorts to 'earth' will complete a circuit and blow a fuse. 'Earth' is also known as 'Safety Earth' - it's there to carry current only in the event of a fault, with Neutral being the correct return path for current.The Earth stake is long and driven into the ground where it's wet and it's resistance isn't that high (wet soil is full of nice electrolytes). Again, this is for safety. If your house supply goes nuts and there's a big fault, current will go to ground. This little statement grossly oversimplifies how the Earth stake protects you - lots of good information here:http://en.wikipedia.org/wiki/Earthing_system

author: Rerouter
author_rank: Super Contributor
timestamp: April 03, 2013, 10:11:34 am
content: the earthing stake also helps equalize the ground potential across the grid, if every house was floating, your mains could be a few thousand volts below ground reference when a thunder storm is overhead,by everyone having a stake in the ground it dramatically minimizes this effect,

author: grumpydoc
author_rank: Super Contributor
timestamp: April 03, 2013, 10:41:16 am
content: QuoteCurrent takes all paths which complete a circuit, in inverse proportion to their resistance.QuoteAt the small test voltage your multimeter provides and the very small contact area that you will get with typical probes not much current will flow but the ground does, indeed, conduct fairly well - especially when damp or wet. However in the event of HV faults causing significant ground current to flow then it is possible to create large potential differences between points on the ground a few feet apart - google "step voltage" for details.

author: Monkeh
author_rank: Super Contributor
timestamp: April 03, 2013, 10:33:12 pm
content: Quote from: ludzinc on April 03, 2013, 08:57:01 amSuch a broad, sweeping statement. How would you describe TN-S or TT earthing?

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 03, 2013, 10:43:26 pm
content: http://www.mikeholt.com/technical.php?id=grounding/unformatted/Separatesystems&type=u&title=Separately%20Derived%20Systems%20%5BTransformers,%20Generators,%20etc.%5D%20(4-10-2K)

author: kaindub
author_rank: Regular Contributor
timestamp: April 07, 2013, 09:55:44 am
content: Are you talking about protective earth - rather than a circuit or ground earth?A protective earth is there to protect people - no other reason.I notice that you are from the UK. In the UK they use an earthed nuetral mains distribution system.'That means that at every switchboard, there is a link between the incoming nuetral connection and the earth connection. The earth connection goes to the big copper rod in the ground. The earth connection also is reticulated with the nuetral and active conductors.Every metal fitting associated with an electrical device, unless its double insulated, is connected to earth.So if there is a fault between active and metal, which a person could touch, the circuit breaker will trip. No current through one's body!If one touches for whatever reason an active conductor, and then an earthed meatla fitting, the the earth leakge part of the circuit breaker will tripSimple

author: Monkeh
author_rank: Super Contributor
timestamp: April 07, 2013, 10:59:58 am
content: Quote from: kaindub on April 07, 2013, 09:55:44 am*sigh*QuoteNo.QuoteWhat copper rod?QuoteIf only.

author: M. András
author_rank: Super Contributor
timestamp: April 07, 2013, 02:23:37 pm
content: copper would corrode over time in wet enviroment within the soil, ive only seen plated steel or stainless steel rods later only in small form factor dunno for what reason

author: sleemanj
author_rank: Super Contributor
timestamp: April 07, 2013, 02:59:25 pm
content: For bonus points and to really mess with your head thinking about the electrickery flowing through the earth under your feet you could consider the single wire earth return power distribution (seewikipedia)

author: Anson
author_rank: Regular Contributor
timestamp: April 07, 2013, 06:18:28 pm
content: Here in Florida we use a 110 volt system. The neutral and mains ground are connected in the interior panel box for the house and on the exterior panel. At the utility pole they drive in a 1" diameter 10ft solid copper pipe that serves as mains ground. It serves as safety only. Most small appliances have only a connection to positive and neutral. Only larger or higher current devices or devices sensitive to voltage spikes typically have a direct connection to mains earth ground.

author: MikeK
author_rank: Super Contributor
timestamp: April 07, 2013, 06:37:44 pm
content: Anson, Did you know you have your entire address in your profile?

author: darko31
author_rank: Regular Contributor
timestamp: April 07, 2013, 06:47:21 pm
content: I'm no expert, but as I understand it the earth is zero electrical potential (voltage, and to be more precise earth is reference point) and difference between electrical potentials make the current flow. So if for some reason you get 220V/110V on chassis and you touch it you will get shocked because you are also at zero potential because you are connected to earth. So protective earth acts like short circuit between mains and earth so someone wouldn't get shocked. The same principle applies to the use of the voltage tester, when you touch the top of it with your finger, you have connected the earth.Here's some wikipedia articles for some more help of understandinghttp://en.wikipedia.org/wiki/Ground_(electricity)http://en.wikipedia.org/wiki/Appliance_classes

author: Anson
author_rank: Regular Contributor
timestamp: April 07, 2013, 07:08:15 pm
content: Quote from: MikeK on April 07, 2013, 06:37:44 pmYes. It's fine. Nothing to hide nothing to steal even if they wanted too they'd die trying. I'm always home and I like target practice.I put it there in case someone wanted to send me something. I put an ad in the buy trade section for IC's I am disabled and on limited income so I was begging.Thought maybe some nice people would send me something to ease my boredom.

author: IanB
author_rank: Super Contributor
timestamp: April 07, 2013, 07:19:41 pm
content: Quote from: seb1982 on April 03, 2013, 07:12:13 amActually the current will try to flow through you on the way to earth if you happen to put your body in the current path. The earth pin of an electric socket has a very low return resistance to ensure sufficient current flows to blow the fuse in the event of a fault. If I connect a bulb between live and earth it glows at full brightness. This is one way to check that the earth connection is not faulty.However, the wet earth outside has rather less resistance than you imagine. If you happen to touch the live wire with one hand and put the other hand on the ground (don't try this!!!) you will get electrocuted. This is how so many electrical deaths and injuries occur when people are using garden tools like hedge trimmers or lawn mowers and accidentally cut the cord.

author: Matje
author_rank: Regular Contributor
timestamp: April 07, 2013, 10:23:52 pm
content: Quote from: seb1982 on April 03, 2013, 07:12:13 amA resistor of 1 MOhm.It's done for 2 reasons,1. safety: if the mat is connected directly to the protective earth wire there is a chance of electrocution, although modern mains wiring uses failure current fuses (or how these are called in english) which trip if significant current flows from hot to somewhere else than to neutral. So today dropping a hair dryer into the tub probably won't work.2. ESD protection: the thing that kills parts is not the voltage, it is the resulting current. To make sure the current flowing when you put a part charged to kvolts on the mat is limited there is a big resistor built in. Also to make sure *you* don't get zapped when you touch the mat - that would be nasty after all... ;-)If you want to get really, really, totally confused about earth - go read what the radio amateur guys have to say about it. Multiple earth points in an antenna system, selfmade earth points build from lots of radially layed out wires buried in the ground, high voltages between earth points due to thunder storms, the works.

author: seb1982
author_rank: Regular Contributor
timestamp: April 08, 2013, 12:54:40 am
content: Thanks for the replies, everyone.It seems (like so much else) to be a case of whenever you begin to understand something, you just end up with a bunch more questions!I think I'm slowly getting my head round it now, thanks. I certainly won't be playing with anything mains related (save for bog-standard transformers) any time soon - there's just too much I don't know if I don't know (if you'll pardon the Rumsfeld-ism!)

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 08, 2013, 06:38:24 am
content: Quote from: Anson on April 07, 2013, 07:08:15 pmI like that kinda thinkin'O0

author: ptricks
author_rank: Frequent Contributor
timestamp: April 08, 2013, 02:00:57 pm
content: To complicate things further, you can use the ground for a battery.http://en.wikipedia.org/wiki/Earth_battery

author: ejeffrey
author_rank: Super Contributor
timestamp: April 08, 2013, 05:49:50 pm
content: Quote from: seb1982 on April 03, 2013, 07:12:13 amPlanet earth has nothing to do with the normal use of 'grounded wiring' You never(*) rely on conduction through the earth for functionality of safety. This is because as you have noted, the earth resistance is normally quite large compared with a copper wire.If you look at your household wiring, you will see that the ground wire runs back and is connected to the neutral wire at your main breaker panel (in the US -- practices vary by country, but the idea is the same). The idea is that if a fault happens, the ground wire can safely carry enough current to trip the fuse or circuit breaker. This current flows through the 'ground wire', but at no point does a significant fraction of it flow through dirt. If you tried to to this, by e.g., running a two-conductor cable from the circuit breaker to the outlet and then connecting the ground pin to a separate grounding rod that would be a serious violation of electrical code and also unsafe in the event of a fault.Now for the earthing rod. There will be a separate wire running from the neutral bus of your main breaker box to an earth rod. Also, all structural metal in your house should be connected to ground directly or indirectly. This prevents large induced voltages from building up between the ground conductor and the earth. The currents involved are relatively small, but they can generate dangerous voltages if not neutralized.(*) Almost never. There are systems like single-wire earth return that use the earth as a conductor, but these are the exception, not the rule.

author: G7PSK
author_rank: Super Contributor
timestamp: April 09, 2013, 11:29:24 am
content: Earthing equipment has nothing to do with personal safety it is about protecting supply and distribution equipment. earthing dates back to the late 19th century when generating equipment was driven by steam engines that were connected to earth by all the pipes involved. I attach a PDF of a page from The electrical year book of 1951 which explains that very well.No way should you rely on an earth or any form of earth trip to protect you from harm, if you try to play the part of an HRC fuse you will only give yourself grief. The only thing that will prevent you from harm when working wit high voltage is that device between your ears.

author: seb1982
author_rank: Regular Contributor
timestamp: April 09, 2013, 12:25:19 pm
content: Thanks for that - yeah, there was a lot I didn't get! I blame my education! I always thought that its primary role was to prevent a massive potential difference between, say, the chassis of the item in question and a water pipe, for example, if you were to touch both simulatneously.Live and learn, eh! I'll be doing a lot of reading around this in the coming days.

author: IanB
author_rank: Super Contributor
timestamp: April 09, 2013, 01:39:23 pm
content: Quote from: G7PSK on April 09, 2013, 11:29:24 amThis statement is not at all correct. You have made here an error of fact, of logic and of comprehension.The book extract you attached says that earthing protects supply equipment in the event of fault conditions. The same reference saysnothing at allabout whether earthing also protects users of electrical equipment at the point of delivery. The first case is not exclusive of the second case and both may be true at the same time.In both cases the principle is to ensure that a fault condition where a live conductor connects to earth potential causes a fault current that will trip a breaker or fuse before harmful effects can occur. Such harmful effects might include equipment damage in some cases and human injury in others.

author: Monkeh
author_rank: Super Contributor
timestamp: April 09, 2013, 02:45:26 pm
content: Quote from: seb1982 on April 09, 2013, 12:25:19 pmThat's equipotential bonding, not earthing.However, one of the requirements for protective (earth) conductors is that they be large enough not to present a hazardous voltage in case of a short circuit before the fault clears (ie. the protective device trips).

author: Randall W. Lott
author_rank: Regular Contributor
timestamp: April 09, 2013, 02:53:08 pm
content: I may be a bit of a stickler, but current prefers the path of least impedance.

author: G7PSK
author_rank: Super Contributor
timestamp: April 09, 2013, 03:29:13 pm
content: Quote from: IanB on April 09, 2013, 01:39:23 pmI was trying to point out not to rely on earthing to protect you or others, If none of the system was earthed and there was no way that the live wires could connect to earth you would not need one, but as the text I attaching here says no insulation is perfect especially when this one was written (1921) I have some earlier stuff around but I have to dig that out.And yes earthing equipment will help to protect people but just don't rely on it to do so use your grey matter as you don't make a good fuse if you do the least is it hurts and the worst is your light's go out and that's not good your fuse is non serviceable.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 09, 2013, 09:32:27 pm
content: Grounding has more of a role to play in North America than some other countries that use only one voltage to the home. North American power is supplied to the home at 1-16KV through a center tapped step down transformer , often called a pig on a pole. Between the two outer secondaries is 240VAC and from either secondary to the center tap is 120VAC. The center tap is grounded at the transformer to establish the neutral point , it is like when you use a transformer with a center tap as ground and then the other secondaries to produce a + and - DC supply for powering opamps ,etc. Watch out for people that don't understand how this system works, even people who work in the field often refer to the system as having different phases, it is only single phase and has nothing in common with split phase power.

author: IanB
author_rank: Super Contributor
timestamp: April 10, 2013, 06:21:38 am
content: Quote from: ptricks on April 09, 2013, 09:32:27 pmTechnically, it does have two different phases though.In a normal three phase distribution system the three phases share a common neutral (assuming a wye configuration) and each phase is 120 degrees apart from the others. In this supply the phase to phase voltage is higher than the phase to neutral voltage (by a factor of 1.73). All of the three phases are "hot" compared to ground.In a typical US domestic supply there are two phases that share a common neutral and each phase is 180 degrees apart from the other. The phase to phase voltage is higher than the phase to neutral voltage (by a factor of 2). Each of the two phases is "hot" compared to ground.So in practical terms you have a two phase supply instead of a three phase supply. There is a similarity in kind that differs only in the details.

author: G7PSK
author_rank: Super Contributor
timestamp: April 10, 2013, 11:46:22 am
content: Are the two halves of the secondary wound in opposite directions then in order to get 2 phase. The only true two phase that I have seen requires a 4 wire system which is one reason the 3 phase system won out.If the two haves are 180 deg. apart. surely you would not have 240 voltage across the two live wires only 120 V. live to neutral as each half would equally oppose the other.With 3 phase here you have 230 phase to neutral and 415 phase to phase but it is still single phase using two live wires but at 415 instead of 230 volts but the resultant power is due to the phase angle being 120 degrees at 180 deg they are equal and opposite.

author: SeanB
author_rank: Super Contributor
timestamp: April 10, 2013, 07:40:46 pm
content: Yes, you have 240V between the 2 "hot" wires. You also get a 3 phase variant that has 115V between phase and neutral, but 208V between phases. Not seen in a residential install often, you will with a factory have 2 supplies fed from separate transformers. A 208V 3 phase and a 120V 2 phase supply, each with a separate meter. You also get a 277V supply often used for lighting purposes, as you can run a 1kW mercury lamp direct from this with only an inductive ballast. No need for an autotransformer HX or CWA ballast then with the additional capacitors and extra losses.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 11, 2013, 02:14:49 am
content: Quote from: IanB on April 10, 2013, 06:21:38 amThis is a common misconception about residential power in the USA. I think people confuse the measuring of the L1 or L2 to N and saying that is 2 phases but it is wrong to say that because it isn't 2 phases as would normally be considered in power distribution. That would be like me plugging in a power transformer into an outlet and saying because it has a center tap it is now 2 phase power.The 2 wires L1 and L2 are not separate phases, they are a single phase . Tapping the neutral which is the center tap of L1 to L2 results in half the voltage because it is only one half the winding. There are only 2 wires connected to the transformer that powers the home so only one phase can exist.L1+L2 = 240VAC , L1+N = 120VAC , L2+N = 120VAC , all are the same phase.This explains it better:

author: c4757p
author_rank: Super Contributor
timestamp: April 11, 2013, 02:27:40 am
content: Why does it matter how they are derived? One is 1/120Hz (180° of 60Hz) shifted relative to the other. Sounds like a "phase" to me.

author: David_AVD
author_rank: Super Contributor
timestamp: April 11, 2013, 02:34:17 am
content: I've heard this "it's not 2 phase" discussion several times over the years. I've always thought that if the 2 hot legs are not in-phase, then that's two phase. How they are derived is irrelevant I reckon.

author: c4757p
author_rank: Super Contributor
timestamp: April 11, 2013, 02:47:22 am
content: I think it would be correct to argue that split-phase isn't "two-phase", since that term has specific meaning for power distribution, but I don't think the minutiae of power distribution/electrician's terminology really matters when someone's just trying to explain the basics. Phase is just the frequency domain extension of a time offset, and it's perfectly valid for something to have a phase angle of 180°. Split-phase isn't "two-phase", but the two legs of it are most certainly phases.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 11, 2013, 03:06:17 am
content: The problem with using the word phase when talking about AC power is that you can't start calling every transformer with a tap as having multiple phases , there is only one wave of power moving through the coil from the start of the winding to the end of the winding, that is one phase, no matter how many taps you put on the winding you will still only have one phase moving through the winding till it reaches the end. The reason grounding is so important in these systems is that without it serious shock hazards exist and is why the first power systems were 2 phase or 4 wire systems.

author: JoeyP
author_rank: Frequent Contributor
timestamp: April 11, 2013, 03:11:48 am
content: Anyone know what the actual resistance of "Earth" is? Not talking about locally to a grounding rod. I know it varies considerably in a give location by soil type and moisture etc. I'm talking say Sydney to Los Angeles or North pole to South pole, excluding the resistance of the local connecting point.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 11, 2013, 03:17:15 am
content: Quote from: JoeyP on April 11, 2013, 03:11:48 amI don't know of anywhere that list a general all around number as it would vary a lot from place to place but you might want to read about how submarines communicated in the past. Submarines used ELF communications that required lines 32 + miles long to be buried in the ground due to the high resistance of the earth. They probably have more info on it than most.http://en.wikipedia.org/wiki/Communication_with_submarineshttp://en.wikipedia.org/wiki/Project_Sanguine

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 11, 2013, 03:24:13 am
content: It's magic.there are small dwarves that herd the electrons......no other way to explain it.read the section on split phase>http://members.dcn.org/jdnewmil/techinfo/Polyphase20051216.pdf

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 11, 2013, 03:27:40 am
content: Quote from: JoeyP on April 11, 2013, 03:11:48 amyou have to measure it.http://www.weschler.com/_upload/sitepdfs/techref/gettingdowntoearth.pdf

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 11, 2013, 03:40:57 am
content: And when I said measure it I literally meant you should measure it.I'm pretty sure no one knows, but with that book and some really long cables you might become famous.

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2013, 03:59:54 am
content: Quote from: ptricks on April 11, 2013, 02:14:49 amIt is exactly like that, because that is exactly what is going on!If you take the center tap from a transformer as a common reference and look at the voltages on the outer terminals you do indeed have two phases.The see the illustration below. In each case the phases are evenly distributed around the circle.

author: JoeyP
author_rank: Frequent Contributor
timestamp: April 11, 2013, 04:06:06 am
content: Quote from: 4to20Milliamps on April 11, 2013, 03:40:57 amI don't think the leads for my DMM are quite long enough. I thought maybe some really smart people had already calculated it from volume/resistivity of elements etc. Maybe it's the next final frontier. I should go get a big fat government grant...

author: G7PSK
author_rank: Super Contributor
timestamp: April 11, 2013, 05:16:57 pm
content: If the 2 halves of the transformer windings were 180 deg. apart both the halves would go positive or negative at the same time so if you connected to the 2 outer trappings without the neutral no power would flow, also there is only a single phase going into the transformer shown so the input is single phase.https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif

author: ivan747
author_rank: Super Contributor
timestamp: April 11, 2013, 09:27:06 pm
content: Since we are discussing grounding, I have a question. My house wiring is a mess. We are not sure if we have grounding, but after looking around, I figured the earth wires connected to our outlets join the Neutral at the service panel. This service panel is old, so it doesn't have terminals for ground, only for neutral.It took me a long time to figure out things because there's absolutely no consistent color coding on anything. Now, I know it is correct to join ground and neutral at the service panel, but I am still not 100% sure this is actually connected to earth with a grounding rod. There is a grounding rod outside the house, but color coding is not consistent (the wire is green, but so are both of the lines inside the service panel and possibly the neutral).Basically, we have no visual way to know if our earth terminals are actually connected to earth. We just know earth in our outlets join neutral at the service box and the current goes back to the 17kV-240V transformer outside somehow.How can I solve this?

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2013, 09:34:31 pm
content: One test would be to use a DMM to measure voltages. On an AC volts range, check that the measurement between neutral and ground in each socket is no more than a few mV, then check that the voltage between the circuit ground and metal objects like water pipes and gas pipes is also no more than a few mV. If you really want to get creative, drive a metal stake into the ground and measure between that and the circuit ground in electrical sockets. That also should be close to zero.This is not a guarantee that everything is good, but it will certainly give you an indication if things are bad.

author: ddavidebor
author_rank: Super Contributor
timestamp: April 11, 2013, 09:34:42 pm
content: Call someone with an earth tester, an insurance company and a church because is better that you make peace with god before go in the sky because you don't have working protection in your home.

author: ivan747
author_rank: Super Contributor
timestamp: April 11, 2013, 09:45:08 pm
content: Quote from: ddavidebor on April 11, 2013, 09:34:42 pmThe scary thing is that there's a water heater with the earth lead directly connected to the water pipes inside it. An electrician came to install a ground lead yesterday, and he bolted it to the service box chassis, but the service box chassis is floating. He says it is grounded because it is embedded into the concrete wall but I wouldn't trust in that (that's not an Ufer ground by any means). The box is floating because the neutral terminals are isolated with a plastic separator.Quote from: IanB on April 11, 2013, 09:34:31 pmI just measured earth and neutral at an outlet far away from the service panel against the grounding rod, it's around 300mV AC on both cases. We use PVC pipes for water and gas pipes are not grounded because in this country you just pay for a propane gas tank and when it's empty you pay to get it swapped. They are not bolted to the floor or anything.The closest thing to earth potential is the grounding rod and I measured 360mV between this and the earth pin on the socket. Maybe if I used a low impedance multimeter it would drop down further.

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2013, 09:51:18 pm
content: I don't think ~300 mV is alarming. I have a faulty ground connection in one of my sockets and it measures about 60 V with induced voltages from nearby cables.The main reason for a good ground rod connection is protection against electric shock; it prevents touchable items in the home floating at voltages significantly above ground.

author: ivan747
author_rank: Super Contributor
timestamp: April 11, 2013, 11:10:34 pm
content: I tried testing for continuity, but the beeper in the multimeter would turn on and off like 4 times a second. It wasn't an overload, I'm sure. Must be some residual voltage playing up on me.Now the only thing that remains is the color mess we have in the service panel. I think tomorrow a real electrician is coming over to check the grounding issue with the heater, but I would like him to check if everything related to electricity is OK because I have lots of concerns. For starters, there's a power inverter wired in a dangerous way, the service box is floating, certain cable's gauge seem too small for the circuit breaker capacity (I saw 60A breakers used with gauge 10 wire, should be 6), split phase 240V outlets might be unfused and with 1 line wired to the power inverter and finally, the color coding (I'm sure that will never get fixed, though).This is electric hellI don't even want to touch it, such a mess.

author: c4757p
author_rank: Super Contributor
timestamp: April 11, 2013, 11:13:30 pm
content: Quote from: ivan747 on April 11, 2013, 09:45:08 pmAn electrician? No, an "electrician".

author: Things
author_rank: Regular Contributor
timestamp: April 12, 2013, 03:29:42 am
content: I don't think the earth ground is meant to carry full short circuit current if something does short out to a case for example, just enough that it stops mains devices floating like IanB said, say, during a thunderstorm and induced current, but allow enough current to flow to trip a GFI.Although it probably would have a low enough resistance given a rod deep enough into the ground, it'd only take like 8KOhms resistance to trip a 30mA GFI on 240V, and wet soil is well and truly lower than 8K.

author: Monkeh
author_rank: Super Contributor
timestamp: April 12, 2013, 03:32:35 am
content: Quote from: Things on April 12, 2013, 03:29:42 amYes it bloody well is.QuoteAnd when you don't have a 'GFI'?

author: Things
author_rank: Regular Contributor
timestamp: April 12, 2013, 03:39:10 am
content: QuoteThen usually you don't have a ground pin on your sockets at all - very common in the US in older homes.

author: Monkeh
author_rank: Super Contributor
timestamp: April 12, 2013, 03:41:32 am
content: Quote from: Things on April 12, 2013, 03:39:10 amUh, right, okay...The CPC has nothing to do with the operation of an RCD.

author: IanB
author_rank: Super Contributor
timestamp: April 12, 2013, 03:56:59 am
content: Quote from: Monkeh on April 12, 2013, 03:32:35 am"Things" is not talking about the earth return in the circuit wiring, he is talking about the impedance of the literal earth beneath your feet. If you stick two metal poles in the ground there won't be a low impedance between them, especially in dry soil.

author: Monkeh
author_rank: Super Contributor
timestamp: April 12, 2013, 04:00:22 am
content: Quote from: IanB on April 12, 2013, 03:56:59 amThat's your interpretation.And yes, I know about earth impedance.

author: c4757p
author_rank: Super Contributor
timestamp: April 12, 2013, 04:14:07 am
content: Quote from: Things on April 12, 2013, 03:39:10 amMost US homes don't have GFCIs on most outlets - just ones near water. Most US homes are fully outfitted with grounded sockets.

author: c4757p
author_rank: Super Contributor
timestamp: April 12, 2013, 04:21:06 am
content: Quote from: IanB on April 12, 2013, 03:56:59 amMaybe so, but in this specific case, that impedance is being depended upon to carry protective earth currents. Shoving a box in concrete and saying it's earthed means you're depending on the path through the concrete and all the way around to the distribution board to neutralize any faults.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 12, 2013, 04:36:07 am
content: Surprising that this discussion keeps lingering on, there's a reason some appliances don't have a ground connection.http://en.wikipedia.org/wiki/Appliance_classesWe have a laboratory here that tests and labels things called underwriter's laboratory, everything has to be listed and labeled.All modern electrical installations have a three wire grounding type receptacle, the equipment grounding conductor is sized according to the over current protection device<fuse, breaker, whatever.http://www.stabiloy.com/NR/rdonlyres/19FC4111-742D-47B7-9A28-06DF8AB4023D/0/EquipmentGroundingConductor.pdfelectrical systems have become much more safe over the years, equipment grounding is used to clear faults on the equipment, ground fault protection is used to prevent electrocution for personnel.http://en.wikipedia.org/wiki/Residual-current_device

author: Monkeh
author_rank: Super Contributor
timestamp: April 12, 2013, 04:37:41 am
content: Quote from: 4to20Milliamps on April 12, 2013, 04:36:07 amAll conductors are sized to suit the protective device, and it's a bit more involved than 'this carries 20A without getting warm', too.

author: IanB
author_rank: Super Contributor
timestamp: April 12, 2013, 05:02:59 am
content: Quote from: ptricks on April 11, 2013, 03:06:17 amYou forget that polarity reverses if you swap the measurement points. With the neutral as the center tap on the transformer winding you will get opposite polarities if you measure up to one end of the winding or down to the other end. With a regular sine wave symmetry means that a reversal of polarity corresponds to a 180 degree phase shift. This is illustrated in the diagram below:

author: megajocke
author_rank: Regular Contributor
timestamp: April 12, 2013, 06:13:18 am
content: The problem with calling that configuration 2-phase, even though it might make sense, is that this term is already understood to mean something different:http://en.wikipedia.org/wiki/Two-phase_electric_powerThe configuration is therefore called split phase (or single-phase 3-wire):http://en.wikipedia.org/wiki/Split-phase_electric_powerOne important distinction is that 2-phase is a true polyphase system which can create a rotating magnetic field and will deliver non-pulsating total power to a linear symmetric load. Converting between different split-phase systems (for example 2,3 or maybe even 5-phase) can be done using nothing but transformers.Single phase (whether split or not) can not be converted to polyphase power using only transformers.

author: IanB
author_rank: Super Contributor
timestamp: April 12, 2013, 06:29:54 am
content: I see, so it's a matter of terminology rather than mathematics. In engineering terms two phase power refers back to a system where the two phases were 90 degrees apart rather than 180 degrees with split phase. But awkwardly, the 90 degree configuration does not have the nice symmetrical properties that the split phase or three phase systems have, such as non-pulsating power delivery and the ability to eliminate the neutral wire with balanced loads (the Wikipedia article referenced above says that two phase power pulsates at twice the line frequency).I am still going to say there are two phases present in a split phase system since there is a phase angle, even if electrical engineers don't want to call it two phase power for historical reasons.

author: G7PSK
author_rank: Super Contributor
timestamp: April 12, 2013, 11:13:31 am
content: Quote from Wikipedia "Three-wire, 120/240 volt single phase power used in the United States and Canada is sometimes incorrectly called "two-phase". The proper term is split phase or 3-wire single-phase. The two live outputs of a 3-wire single phase transformer secondary winding are properly called "legs".And as show in the wave form diagrams kindly provided by IanB the two halves of the split phase add up to a single phase at twice the voltage.

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2013, 03:45:06 am
content: Quote from: G7PSK on April 12, 2013, 11:13:31 amNote carefully from my earlier diagram it is not thesumof the phases in a split phase supply that gives a single phase at twice the voltage, it is thedifferencebetween them. When you put your voltmeter between L1 and L2 and see 240 V you are measuring the difference between the two 120 V legs.This is illustrated in the diagram below, with a comparison to the three phase case. In the three phase case the difference between two phases gives 1.732 times the line voltage (208 V in the case of 120 V line voltage). The value 1.732 is of course the square root of 3.

author: iamnothim
author_rank: Regular Contributor
timestamp: April 13, 2013, 04:44:06 am
content: epic

author: G7PSK
author_rank: Super Contributor
timestamp: April 13, 2013, 09:39:05 am
content: I understood that the US domestic voltage is 120 and 240 indicating that there is no phase difference between the transformer taps or legs, certainly that is what I have seen when in the US. Also the pole transformers are single phase input with one live wire input and a common neutral earth which is also shared with the LT side of the transformer, on occasions the 120/240 wires are tied onto the neutral/ earth for support. I took some photographs of this in 2001 when I first visited the US I have seen much the same setup in all the parts I have visited. How do you get two phases out with only one phase in.

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2013, 10:09:17 am
content: Quote from: G7PSK on April 13, 2013, 09:39:05 amSometimes US electrical arrangements can look pretty hokey, can't they?QuoteIt's because the phase of an AC voltage is inverted (or shifted 180 degrees) if you reverse the connections. With a centre-tapped transformer secondary as seen in the US you have your common neutral/ground reference in the middle. Then if you go "up" one leg you get a phase angle of 0 say, and when you go "down" the other leg you have reversed direction giving you a voltage that is 180 degrees out of phase. You can see this in my picture in post #63 where the red wave between L2 and N is "upside down" compared to the black wave between L1 and N.If you wanted two voltages that were exactly in phase you would have to take one between L1 and N and the second between N and L2 (going "down" a leg each time). But this arrangement would not give you a common neutral and would not provide a single grounding point. To get two outputs with the same phase and a common neutral you would have to do something like this:You could no longer connect between L1 and L2 to get twice the voltage, but now you could put L1 and L2 in parallel to get twice the current. This is not how things are usually arranged in power distribution transformers, but it is sometimes seen in low voltage applications.

author: G7PSK
author_rank: Super Contributor
timestamp: April 13, 2013, 11:13:15 am
content: I have a site transformer which gives 110 volts on the secondary with an earthed center tap so that you have 55 V + 55 V I will put it on the scope and have a look but I am pretty certain it is only a single phase output.Even if the US transformers give 2 phase out puts they are only used as single phase of either 120 or 240 surely where would 2 phase be in actual use.

author: johnwa
author_rank: Frequent Contributor
timestamp: April 13, 2013, 01:51:42 pm
content: Quote from: IanB on April 12, 2013, 06:29:54 amI don't think this is quite right about the non-pulsating power supply. I believe a two phase supply at 90 degrees will give a continuous flow of power (into a suitably balanced load), since sin^2(x) + cos^2(x)=1. This is the property that allows conversion between polyphase systems with transformers that megajocke referred to.A true polyphase system can deliver power continuously, while a single or split phase supply gives power intermittently in pulses. Therefore, in order to synthesize three phase power from single (or split), some form of energy storage is required - big capacitors in a VFD, or the inertia of a rotary phase converter.You are right about the neutral current not cancelling in a two phase system IanB. Three phase is the lowest number that gives continuous power and no neutral current.

author: G7PSK
author_rank: Super Contributor
timestamp: April 13, 2013, 04:48:48 pm
content: I have realised that there is an anomaly created by the scope connections if you put the earth connection on the center tap and the probes on the two end taps you have inversion of on or other of the halves, if the scope earth is connected to say the bottom leg and the probes to the next two legs the waveforms are in sync. I am not sure why this perhaps someone with more scope experience can throw some light on this and explain the correct way to connect in such cases.I am attaching some photos (not very good exposures are slow).

author: megajocke
author_rank: Regular Contributor
timestamp: April 13, 2013, 05:15:34 pm
content: Quote from: IanB on April 12, 2013, 06:29:54 amYes, it's most definetely only a matter of terminology.Actually, that article on Wikipedia says "Power transfer in a three-phase system with balanced loads is constant, whereas it pulsates at twice the line frequency insingle-phasesystems.", so that statement is actually not about two-phase (90 degree) systems. Two-phase has nonpulsating power as can be seen from sin^2(x) + cos^2(x)=1 as johnwa wrote.If you want to be mathematically consistent, it might make sense to call split-phase (the center tapped transformer) 2-phase just as you want, and rename the traditional configuration known as 2-phase to "4-phase without neutral".

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2013, 05:18:08 pm
content: Quote from: G7PSK on April 13, 2013, 04:48:48 pmYes! That is exactly what I have been saying in all the posts above. It is not an anomaly, it is exactly what is expected. Look at the picture in Reply #63 above. It shows exactly what your scope shows.It is because when you measure from B to A you are going "up" the winding and have positive polarity. But when you measure from B to C you are going "down" the winding and have therefore reversed the polarity of what you are measuring. Because you are going down the winding the AC waveform is turned upside down.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 05:35:49 pm
content: Quote from: IanB on April 13, 2013, 10:09:17 amSometimes?

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2013, 05:49:46 pm
content: Quote from: johnwa on April 13, 2013, 01:51:42 pmYes, I agree. Two sine waves of the same frequency when combined at any phase angle will produce another sine wave of the same frequency.QuoteInteresting. I didn't notice it before, but if you consider power to be proportional to the square of the voltage, then a three phase supply does deliver perfectly continuous power, as does a two phase supply with a 90 degree phase angle.To synthesize one phase from another you need to be able to combine phase angles in a suitable way to get the new angles. If you only have 0 degrees and 180 degrees to start with you can't combine them in any way to get new angles. But if you start with 0 degrees, 120 degrees and 240 degrees you can obtain other multiples of 30 degrees by appropriate manipulations.QuoteIt only doesn't cancel in a four wire system with 90 degree phase angle.It does cancel just like three phase if you have two symmetrical phases 180 degrees apart (this is exactly what happens with 120/240 split phase systems) as illustrated below: (however this arrangement does not give continuous power as three phases do)

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 09:38:05 pm
content: Quote from: ivan747 on April 11, 2013, 09:45:08 pmI have heard a lot of reasons for not not grounding something, but concrete grounds it ? that is a new oneThe important thing is that you don't have multiple grounding points to earth ground. There should be 1 location for the ground rod and everything else coming from that location. In the USA some areas no longer allow water pipes as a grounding point because of the use of non metal pipes or if someone inserts a connection in the piping it could break the electrical connection to ground.My advice is to find a copy of your areas electrical code and read through the requirements.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 09:39:18 pm
content: Quote from: ptricks on April 13, 2013, 09:38:05 pmBwahahaha, seriously, where'd you pull that from?Please, don't touch electrical installations. Ever.

author: c4757p
author_rank: Super Contributor
timestamp: April 13, 2013, 09:41:19 pm
content: Quote from: Monkeh on April 13, 2013, 05:35:49 pmWell, those pictures are pretty bad. Most of the wiring where I live (New York State) isn't half as ugly and bodgey-looking as that is.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 09:49:11 pm
content: Quote from: Monkeh on April 13, 2013, 09:39:18 pmI am licensed in the USA to do all the way up to industrial installations.The rule comes from the NEC2011 code book .You never want more than 1 ground point if possible because multiple ground points create a differential between the points. Some installations require multiple ground rods , only because there is rock or something else preventing the normal ground rod installations.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 09:56:50 pm
content: Quote from: ptricks on April 13, 2013, 09:49:11 pmWhich is why you have to use a sufficiently large conductor to make the connection. It's often impossible not to have conductive materials in contact with the earth, and they introduce a potential if youdon'tconnect them.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 10:01:29 pm
content: Quote from: Monkeh on April 13, 2013, 09:56:50 pmYou use the conductor size specified for the service load. You shouldn't have conductive materials in contact with the earth that are also connected to the service ground, doing so can cause the grounding system to resort to shunting the current through that pathway vs the established grounding point.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 10:03:38 pm
content: Quote from: ptricks on April 13, 2013, 10:01:29 pmSo, let's just leave that pipe or steelwork with a potential on it relative to the distributed ground, okay.And people wonder why I despair at American electrics.Also, what current? It's ground, not neutral.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 10:15:39 pm
content: Quote from: Monkeh on April 13, 2013, 10:03:38 pmItems that contact or go into the the ground because removing is not feasible, or in things such as a metal building are grounded differently depending on the site. Each site is unique , but in a residence , like the question that was asked, it is uncommon to find multiple grounded conductors contacting the earth ground. I don't know why you despair at American electrics, I suggest you pick up a copy of the NEC 2011.The ground not neutral comment ,I don't understand, the purpose of grounding is so that any dangerous voltages contacting a metal surface by a person will have the current sent to ground vs into and through the person. The current from the shock hazard doesn't differentiate between ground or neutral, it will take whatever is the least path of resistance.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 13, 2013, 10:16:06 pm
content: wow, this where proper training and continuing competency comes in."Section 250.104(A) requires a metal water piping system installed in or attached to a building to be bonded back to the electrical service. The metal water pipe can be bonded to the electrical service enclosure, the grounded conductor at the service, the grounding electrode conductor where it is of sufficient size, or to one or more of the grounding electrodes for the service.The main purpose of this bond is to ensure that the metal water pipe is at the same zero voltage to ground as the service grounded conductor. A secondary purpose is to ensure that there is a path back to the service for electrical current flow if the metal water pipe becomes energized."http://www.ecmag.com/section/systems/bonding-water-piping

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 10:20:50 pm
content: Quote from: ptricks on April 13, 2013, 10:15:39 pmSure, I'll just drop by the local bookshop and grab a copy, it's certainly more useful to me than anything else I could spend £60 on.QuoteA grounding conductor within an installation should not have any significant current on it except during fault conditions, which areto be cleared within very specific time limits. There should be no hazard potential during this period. It does not matter whether it goes through your 'established grounding point' or the old metal water pipe so long as it goes and the fault clears in a timely fashion. And itwill not gothrough the water pipe in a TN-C-S system anyway.Quote from: 4to20Milliamps on April 13, 2013, 10:16:06 pmTo whom was that addressed?I'm guessing not me, seeing as it basically agrees with me, except it seems to oddly specify a metal water supply pipe only.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 13, 2013, 10:29:12 pm
content: Quote from: Monkeh on April 13, 2013, 10:20:50 pmnope not you.telling everyone you are licensed "up to the industrial installations" doesn't add up, you're either a journeyman , a master, or have a residential license.either way understanding impedance is kind of important, and electricity follows all paths, not just the path of least resistance.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 10:32:30 pm
content: Quote from: 4to20Milliamps on April 13, 2013, 10:29:12 pmWhich is why having the lowest impedance, most reliable earth connection you can achieve, via any reasonable (and permanent, water supply pipes need not apply) method, is critical.Obviously when designing a system to have multiple dedicated earthing connections, there are considerations. Just whacking a rod down on every corner of the building may not work as well as you think. Lunacy to suggest that it's to be avoided without proper consideration, however.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 13, 2013, 10:37:27 pm
content: you have to test it to make sure it meets the code requirements but never more than two are required.http://www.mikeholt.com/videodisplaynew.php?pageid=4134

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 10:39:52 pm
content: Quote from: 4to20Milliamps on April 13, 2013, 10:37:27 pmRequired by those regs, anyway. I, personally, would do my best to get it down a hell of a lot further than 25 ohm.Mind you, I would also try and get a PME system installed.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 10:40:59 pm
content: Quote from: 4to20Milliamps on April 13, 2013, 10:29:12 pmIt does add up, if you want to get technical it is referred to as High Voltage Electrician , it is required to work for a major power producer in the USA as an electrical engineer. You can't design systems if you don't know how they are implemented in the field. Well you can, but it isn't fun for the parties involvedImpedance is very important and in some of the industrial installations it can cause some very weird changes in the wiring that otherwise wouldn't have been allotted for if impedance were not taken into account.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 13, 2013, 10:43:44 pm
content: very rarely is it above 25 ohms, when we did ground grids for the telephone company it had to be below 3 ohms, and we had to chemically treat the ground rods to get it. Before we started we did site survey and used the fall of potential method, documented it and the engineer reviewed it. Some sites had 10 or so 10 foot long stainless ground rods welded together with 4/0 copper.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 13, 2013, 10:45:27 pm
content: Quote from: ptricks on April 13, 2013, 10:40:59 pmso you're an engineer that doesn't have a master's license?

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 10:45:38 pm
content: Quote from: 4to20Milliamps on April 13, 2013, 10:43:44 pmMeanwhile, the 'ground' in my property should be well below 0.5 ohm. No rods, no mats, just some bonding.Ahh, the wonders of a proper network.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 10:56:32 pm
content: Quote from: 4to20Milliamps on April 13, 2013, 10:45:27 pmIt isn't done through the same paths that an electrician would follow where they have to work so many hours at each level. This is certification that you know all the rules, codes, and procedures for those trades along with the high voltage stuff, it is about an additional year of time if you have a degree in EE, and then intern for 2000 hours with another person who has already achieved the certification. You could go through the journeyman stages and move up that way but then it wouldn't do you much good because you would still need the engineering degree and the high voltage stuff. Generally it is designed for people that don't have to physically go out and do the work on a daily basis but would design the products that would be implemented at the sites.The reason I made a point about the 1 grounding site is because we have over the last couple years seen an increasing number of residences that have ground issues, not because the electrician did something wrong but because the utilities like phone or cable have done something wrong. It isn't unusual to find sites that have the ground from the cable system to the home connected to something metallic that isn't part of the homes grounding or to find ground rods , 1ft long, yes 1 ft, driven in the ground for the cable system because the tech didn't want the work of running a proper ground.edit:If anyone in the USA is interested in where you can get the high voltage training, some of it overlaps so you need to work with your employer and some are required to be onsite at your place of employment. Overall though a great place to look into for training.http://www.nttinc.com/content/grounding-and-bonding-electrical-systems-hazardous-locationshttp://www.nttinc.com/content/nfpa-70earc-flash-electrical-safety-electric-power-generation-transmission-and-distributionhttp://www.nttinc.com/content/2012-nfpa-79-electrical-standard-industrial-machineryhttp://www.nttinc.com/courses/national-electrical-code/2011-national-electrical-code%C2%AE-nfpa-70e-awareness-and-grounding-and

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 11:13:58 pm
content: Quote from: ptricks on April 13, 2013, 10:56:32 pmOkay, that's a different thing entirely. Muptiple ground rods, properly connected = fine. Multiple unbonded ground sources = not so fine. And yes, bodges by telecoms and cable companies are a problem everywhere. I grow most tired of seeing unarmoured coax just laid down the edge of a driveway..

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 13, 2013, 11:14:25 pm
content: I see, I have worked for a lot of utility engineers and every one has been great to work with.In Colorado the utilty company's concern stops at the meter, I'm surprised they are complaining about a problem that's technically not yours.

author: Monkeh
author_rank: Super Contributor
timestamp: April 13, 2013, 11:21:01 pm
content: Speaking of non-electricians not doing things right:

author: ptricks
author_rank: Frequent Contributor
timestamp: April 13, 2013, 11:27:26 pm
content: Quote from: 4to20Milliamps on April 13, 2013, 11:14:25 pmWe provide insurance for home owners against surges for appliances and such and we often have to deny claims when we send out an inspector and see the reason the tv no longer works is because the cable guy did the grounding wrong . In such cases we tell them to get a lawyer and sue the cable guy.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2013, 12:04:30 am
content: Quote from: ptricks on April 13, 2013, 10:56:32 pmI imagine the cable ground has potential ground loop issues, though? For instance, is the coax shield on the cable a signal ground or a protective ground? And if it is a protective ground, whose ground is it bonded to--the origin or the destination? And if both, what is to prevent loop currents flowing along the coax due to potential differences at each end? I suppose if everything is earthed to the actual ground at multiple points along the line the problem is minimized?

author: ptricks
author_rank: Frequent Contributor
timestamp: April 14, 2013, 12:33:26 am
content: Quote from: IanB on April 14, 2013, 12:04:30 amIt is to be grounded at both ends. The idea is to protect from induced voltages. Loops do occur quite a bit and you can find lots of pages on google on how some people have solved them. The easiest would be isolation transformers on the line but those can be problematic as well. Most homes will not have a problem with the grounding but there are always exceptions.

author: Monkeh
author_rank: Super Contributor
timestamp: April 14, 2013, 01:23:43 am
content: I've seen coax turn into white smoke because of ground loops. They should be isolated at the point of installation. But that would cost money...

author: TerraHertz
author_rank: Super Contributor
timestamp: April 14, 2013, 02:10:10 am
content: Quote from: Monkeh on April 13, 2013, 11:21:01 pmHa ha! Lawnmower bait.Because there's not enough confusion in this thread already, everyone should google 'global earth electric currents'.Current, current everywhere! It's in the air, it's in the ground and oceans... And the entire planet is one plate of a giant capacitor, with the ionized solar wind forming the other conductor. And sometimes, so some people theorize, the planets develop enough voltage differential to arc directly across space between them. There are even claims that has happened within distant human history.I'd like to see that. While watching from about a light-day away.

author: Monkeh
author_rank: Super Contributor
timestamp: April 14, 2013, 02:11:52 am
content: Quote from: TerraHertz on April 14, 2013, 02:10:10 amNot so much, it was originally under 4" of concrete step. Still not where it should be. Now it's under about 3" of block paving.

author: xrunner
author_rank: Super Contributor
timestamp: April 14, 2013, 02:20:16 am
content: Quote from: TerraHertz on April 14, 2013, 02:10:10 amI am finding some of this information shocking!

author: c4757p
author_rank: Super Contributor
timestamp: April 14, 2013, 02:34:39 am
content: Quote from: TerraHertz on April 14, 2013, 02:10:10 amA "capacitor" is an abstraction, there is capacitance between every two conductive points in the universe.QuoteThat seems a bit hokey. Any information on that worth reading?QuoteFor an arcbetween planets? I want more distance than that.

author: ivan747
author_rank: Super Contributor
timestamp: April 14, 2013, 02:41:03 am
content: Quote from: ptricks on April 13, 2013, 09:38:05 pmSure, I'm in the look for a copy of the Dominican electrical code... oh wait, it doesn't existBut since we are using the American voltage, frequency, outlets and wiring techniques, I assume we follow NEC.

author: TerraHertz
author_rank: Super Contributor
timestamp: April 14, 2013, 04:04:07 am
content: Quote from: c4757p on April 14, 2013, 02:34:39 amThis abstraction works remarkably well in a practical sense though, if one 'point' is a sphere weighing 5.972 E24 kg, and the other 'point' is a conductive layer around it (the ionosphere) of surface area: 4 pi [Earth's radius: 6,371 km + atmosphere thickness: 480Km]^2 = 589E6 square Kilometers.Hmm.... What's the Earth to Ionosphere capacitance in Farads?http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capsph.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/electric/diverg.html#c1http://en.wikipedia.org/wiki/Relative_permittivityhttp://hyperphysics.phy-astr.gsu.edu/hbase/tables/diel.htmlTaking the permittivity of the atmosphere as 1 (dielectric constant of air is very nearly equal vacuum), and working in mks (not 100% confident there) that's 1.143 x 10^9 Farads.Oh yeah, I definitely would like to whack a screwdriver across that abstraction's terminals. Or a 'space elevator' cable, ha ha.The net stored charge is a result of integration of long term changes in the flux density of the solar wind, the resulting charge input to the upper atmosphere of solar ions, cosmic rays, and small solid bodies (hundreds of tons of tiny icy and stony meteors each year, all of which carry some charge they accumulated from the solar wind and cosmic rays), and also the overall atmospheric dielectric leakage rate. The pissy little local discharges we know as lightning are just small side effects of this system.It's worth bearing in mind that electrostatic forces are about 10^36 times stronger than gravity, for equivalent amounts of involved nuclear mass/charge.QuoteNot if you want the effortless 1 minute reading version.Book: Thunderbolts of the Gods, by David Talbott and Wallace Thornhill.I guess as a last resort you could try googling something like 'electrical discharges between planets' or 'electric universe'.One link collection here:http://everist.org/archives/links/!_Electric_Universe_links.txt

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2013, 09:17:06 am
content: NASA did release an article about the biggest lightning discharge they have seen in a galaxy recently.......

author: G7PSK
author_rank: Super Contributor
timestamp: April 14, 2013, 09:47:27 am
content: I am still thinking about the phase relationship in a center tapped transformer, if you think of the ac power as a rotating battery or rather in this case a pair of rotating batteries going around so first you have positive on top and then negative, if you have a connection between each cell as well as one at the positive and one at the negative you get V1 and V2 you can either run a load at V1 or V2 or a load at V1+V2 now if one of the batteries was 180 degrees out in polarity compared to the other you could still load them at V1 or V2 but if you connected so that you had V1+V2 you would now have positive connected to positive with the result that no power would flow.The only way that I can square this in my mind with what is being shown on a scope is the scope is not right or rather not being used right, on one or the other trace you need to use the invert button.Also if you think about the current flow as generated by the magnetic field in the transformer and apply the hand rule to that you realise that unless one half of the center tapped transformer is wound in the opposite direction from the other the power has to all flow in one direction. so the bottom leg at any one moment is at one potential the middle is at a higher potential than the bottom leg but lower than the top leg.

author: johnwa
author_rank: Frequent Contributor
timestamp: April 14, 2013, 11:36:46 am
content: Quote from: IanB on April 13, 2013, 05:49:46 pmI agree, the 180 degree case ("split phase" or whatever you want to call it) will reduce/cancel the neutral current. It is possible to run a three wire 90 degree two phase system - this will reduce the current in the neutral, but cannot cancel it entirely (down from 2 * Ip to 1.4142 * Ip IIRC)Quote from: G7PSK on April 14, 2013, 09:47:27 amThe situation as you describe is correct for the first half-cycle G7PSK.(middle circuit diagram). In this state, there is already effectively 180 degrees phase shift, because one supply has its 'negative'/neutral connected to the common neutral, while the other one has its 'positive'/phase connected. On the second half cycle, V2 reverses polarity, as you have drawn in your bottom circuit. But V1 also reverses, so the voltages still sum.Quote from: G7PSK on April 14, 2013, 09:47:27 amIt's not so much a matter of the direction they are wound in, as the way they are connected. One method of manufacture is to wind half of the secondary and bring the wire out to a tap. Then, without cutting the wire, take it back and keep winding the other half of the secondary in the same direction.Alternatively, you can just have two separate and identical secondaries (possibly both wound at the same time), giving you four ends of the windings. Two of these are connected together, and depending on which two, the voltage at the ends of the combined winding will either add or cancel.Anyway, it appears that the discussion has been sidetracked into the benefits of various earthing systems. All we need now is for someone to come out in favour of using a floating distribution system, and the sparks will really start to fly!

author: Monkeh
author_rank: Super Contributor
timestamp: April 14, 2013, 11:38:48 am
content: Don't tempt me.

author: G7PSK
author_rank: Super Contributor
timestamp: April 14, 2013, 12:18:48 pm
content: In my thought experiment both batteries would turn what I was showing in the third drawing is how the voltage would add up if they were 180 deg. apart.I have now connected up my scope with small capacitors in the circuit to isolate the earth clips so that I can show all the phase correctly with both halves and the two combined I get a photo showing all three traces at once with all the phase in sync.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2013, 02:40:23 pm
content: Quote from: G7PSK on April 14, 2013, 09:47:27 amYou can test this for real with your multimeter using actual batteries. You don't need to imagine the batteries turning; DC will work fine to illustrate polarity.Place two batteries in series as in your second drawing. Take the middle terminal as the common (neutral or ground) reference point. Measure up to the top battery. Then measure down to the bottom battery. Remember that voltages have a direction (that is what polarity is), so it matters which way round you connect the meter leads. You always want to connect the black lead to the ground point if you are comparing voltages against a common reference.What you will see is you have a positive voltage and a negative voltage. The difference between the positive and negative voltages is the total voltage. This makes sense because the voltage measured between two points is always a voltage difference, and difference means to subtract.(If you put the ground point instead at the negative terminal of the bottom battery then the voltage difference would be 3 V - 0 V = 3 V giving the same total difference as you would expect.)

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 14, 2013, 03:03:49 pm
content: not only do we have split phases we also have a split forum topic going.with AC flowing through a coil the magnetic field expands and contracts according to the amplitude, splitting the coil in half is no different than taking a rotating string and making another node in the middle, the two halves will rotate opposite one another.

author: G7PSK
author_rank: Super Contributor
timestamp: April 14, 2013, 03:41:05 pm
content: Hard to do when your battery is spinning around the junction of the two poles. What I was trying to illustrate with the second battery was if you connected them thus (180deg reverse) no power would flow between the end contacts only between one or other end and the center. The same would happen if both halves of the transformer secondary were at opposite by 180 deg power could only flow with the neutral connected and that would have ti be 1.4 times bigger than the other legs, when operating 240 volt equipment the neutral center is not used and therefore you would have a wattless power situation.Have the same situation in small generators when configuring for 110/220 volts where the windings are switched series/parallel get one winding the wrong way around in 220 configuration and there is no power out get it wrong in 110 and and only smoke comes out.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 14, 2013, 03:52:52 pm
content: A battery is designed to have an excess or depletion of electrons based on the materials it's made of, a coil of wire isn't, turn it any way you want the only thing that determines it's polarity is the ground connection.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2013, 04:01:11 pm
content: Quote from: G7PSK on April 14, 2013, 03:41:05 pmBut did you see my picture? Is it showing up OK?What I showed with the batteries is what happens with the centre tap on a transformer. The batteries don't have to be spinning at all. You can do that experiment with two 1.5 V batteries sitting on your bench. Try it and see, connecting your DMM as I showed. You will find the top battery measures 1.5 V and the bottom battery measures -1.5 V (which is why the trace appears upside down on the oscilloscope in your other experiment). Yet, obviously if you measure the outer terminals of the batteries you will get 3 V.

author: Unknown
author_rank: Unknown
timestamp: April 14, 2013, 04:13:49 pm
content: Quote from: 4to20Milliamps on April 14, 2013, 03:03:49 pmQuote from: 4to20Milliamps on April 14, 2013, 03:52:52 pmOK. Explain this circuit to me:SourceIf polarity does not matter and they will always have 180° phase shift, how does the parallel circuit work? Would reversing the connections of one of the secondaries have any effect?

author: G7PSK
author_rank: Super Contributor
timestamp: April 14, 2013, 04:40:38 pm
content: If the phase is 180 deg out compared to the other half of the winding (in other words reversed or opposite in polarity) that means that when the top half is on a positive excursion so is the bottom half with the negative excursions both being the center tap yet you have power at double voltage between the top connection and bottom connection with half voltage on the center.https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif

author: Unknown
author_rank: Unknown
timestamp: April 14, 2013, 04:54:28 pm
content: So parallel operation is impossible? Or you can connect the windings in parallel regardless of their relative orientation?

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2013, 05:05:57 pm
content: Quote from: G7PSK on April 14, 2013, 04:40:38 pmThe polarity depends which way round you measure it.Get a battery, get your DMM. Measure the battery with the red lead on (+) and the black lead on (-). The meter says 1.5 V (ish), right? Now put the red lead on (-) and the black lead on (+). Now what does the meter say? What changed? Did the battery suddenly reverse its polarity, or did you just change how you measured it?If you swap the connection between two terminals you reverse the polarity. This is the same with a battery as with a transformer winding.I drew you a picture. I don't know how to make it any clearer.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 14, 2013, 05:10:39 pm
content: positive in......positive out, no matter which way you turn the current transformer.http://en.wikipedia.org/wiki/Dot_conventionnow add a ground connection and that changes things.

author: G7PSK
author_rank: Super Contributor
timestamp: April 14, 2013, 05:47:41 pm
content: Yes ground the center leg and the outer legs go higher and lower than ground potential power will still flow from one outer leg to the other without using a connection to the center Ie. two wires single phase at the higher voltage orbiting around earth potential, (whatever that is). All I am trying to get my mind around is what is shown on the scope is not all that it seems, for a start the scope only shows 2 dimensions and in reality the power is in 3 dimensions and what appears as a nice wavy line is a spiral.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2013, 07:28:53 pm
content: Quote from: G7PSK on April 14, 2013, 05:47:41 pmWith the two batteries and the centre tap, the voltage is positive when you go up a leg and negative when you down a leg. The negative voltage is still 1.5 V but it is inverted.Similarly with the centre tap on the transformer. The scope trace is upright when you go up a leg, and upside down (inverted) when you go down a leg.The situation with the transformer is just the same as with the batteries. Forget three dimensions, spirals, orbiting Earth, all that nonsense. It is not important to the question.Here's another picture:

author: David_AVD
author_rank: Super Contributor
timestamp: April 14, 2013, 09:15:34 pm
content: The only thing that baffles me is that some people can't see a obvious phase relationship between the ends of a centre tapped transformer!

author: G7PSK
author_rank: Super Contributor
timestamp: April 14, 2013, 09:23:13 pm
content: I can see that if you use the scope to measure the two halves that one end is high and the other will be low I cannot see how the power can be 180 deg out of phase on each half and still have power flowing between the outer leads unless I have a different understanding of 180 degrees which to me means opposite direction and to me to opposite halves do not make a greater whole and most certainly do not make a two phase system out of single phase.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2013, 09:30:23 pm
content: Quote from: G7PSK on April 14, 2013, 09:23:13 pmOK, look. Suppose you dig a hole 6 ft deep in the ground. The bottom of that hole is 6 ft below ground level, is it not? We can say the bottom of the hole is at an elevation of -6 ft compared to ground level.Now climb 6 ft up a ladder next to the hole. Your elevation will be +6 ft from ground, yes?So now suppose you jump off the ladder into the hole. How far will you fall? Assuming you don't miss the hole it will be 12 ft.But how can this be? Surely +6 ft plus -6 ft equals zero, does it not? What explains this contradiction?It is explained because you don'taddthe elevations, you find thedifferencebetween them. We have (+6 ft) - (-6 ft) = 12 ft.Just think of voltages as elevations above or below ground and you will get the picture.

author: c4757p
author_rank: Super Contributor
timestamp: April 14, 2013, 09:34:24 pm
content: Quote from: G7PSK on April 14, 2013, 09:23:13 pmNo, it means a delay by 180/360 = 1/2 of the period of the waveform. If you take a sine wave and invert it, and you take another sine wave and push it half a sine wave forward, you'll be unable to tell them apart, it's the same effect. That's why an inverted AC voltage is a 180° phase difference.

author: David_AVD
author_rank: Super Contributor
timestamp: April 14, 2013, 10:40:20 pm
content: As a tangent on Ian's ladder / hole explanation, imagine you had a tall ladder. If you climbed up and down from the 8' mark to the 12' mark you'd be moving 4' each time. Again, it was the difference between the two heights (12-8), not the addition of them (12+8) that gave the "amplitude".In this new case however there is a"DC offset" (the 8'). This could represent a DC bias, as was used on a valve amplifier in another thread.

author: MasterOfNone
author_rank: Regular Contributor
timestamp: April 14, 2013, 11:00:02 pm
content: I believe G7PSK thinks of the phase in terms of the direction the current is flowing in the winding of the transformer. So for him a three phase supply must have three windings each with a 120 degrees phase shift, and a two phase supply must have two windings and the current in each winding must be out of phase.In the US it seems that the current flows through both windings in the same direction, regardless of how you measure the tap-off voltages, so for him it isn’t a two phase supply.I believe the reason he keeps mentioning zero power is because if both halves of the winding had current flowing in the opposite direction then the L1 to L2 measurements would be zero. See my battery example below (he posted a similar drawing in one of his posts).Of course he could mean something else.

author: TerraHertz
author_rank: Super Contributor
timestamp: April 15, 2013, 04:57:27 am
content: Good grief.It's lucky transformers have no egg-like characteristics, otherwise people would be arguing over whether the small or large end was the 'right phase'.

author: G7PSK
author_rank: Super Contributor
timestamp: April 15, 2013, 08:00:28 am
content: Thank you masterOfnone you see what I mean single phase is single phase and not polyphase. If you stand on your head that does not mean you are in Australia (Unless you are when you invert yourself) it also does not make the world turn upside down it only alters your point of view. I am certainly looking at it from a power point rather than a signal point where yes you can have currents flowing in all directions but when it comes to 50 or 100 kva that will only end in grief.I have proved at least to my own satisfaction that earthing a center tap does not alter one half in relationship to the other if looked at the right way, I connected my scope up using capacitors to isolate and keep the current down on the earth leads of the probes (only needed on earth leads as internal ones for ac on center of probe leads) earthed the center tap separately. Before some calls foul I used identical capacitors on all leads to keep things even as capacitor will introduce some shift. I then fixed the probes onto the transformer connection progressively from top to bottom and had all three wave forms all lined up so that they could all overlay each other. Three traces were bottom leg to center leg-center leg to top leg and bottom leg to top leg the transformer was 12 volts with a center tap that I connected to earth as I had negated the scope earth with the capacitors. I have to go out today but I will up load photographs of the set up as soon as possible.

author: IanB
author_rank: Super Contributor
timestamp: April 15, 2013, 08:35:41 am
content: Quote from: G7PSK on April 15, 2013, 08:00:28 amBut the point of view is everything. In science, everything is relative to how you look at it. That's what the theory of relativity is all about. What you measure depends on your frame of reference.Go back to the two batteries in series in Reply #115. Obviously the current is flowing in the same direction through both batteries. It must, or they wouldn't be in series and the voltages wouldn't add up. It's just the same with the two halves of the transformer winding. The current has to flow the same direction in both at the same time or you wouldn't get 240 V out of the two 120 V halves.But, and this is the important thing, the phase of the voltage depends on which way round you make the connections. If you put the ground lead of your oscilloscope on the centre tap and measure an outer tap you will get one phase. If you reverse the connections to the oscilloscope you will invert the phase. The wave will appear upside down, or alternatively it will appear shifted by 180 degrees (it is the same thing).This is all just the same as with a battery. If you swap the red and black leads on the meter the voltage will appear negative instead of positive. The battery hasn't changed, but what you see has changed because you changed your point of view.You don't need to post any pictures to show this. We know exactly what you are seeing.

author: G7PSK
author_rank: Super Contributor
timestamp: April 15, 2013, 08:56:35 am
content: Right so its single phase then. Or at least it is single phase power. I agree that if you look at it with a scope in the manner one would normally the lower half is reversed or 180 deg out. as power and that is how I look at it in this context it is single phase by everything I know, i have been building power plant for over 40 years started as a hobby while at school and commercially for 30 years and i would only recognise that configuration as split single phase.As for relativity that is exactly that relative. I go by what you first see is not necessarily what you are looking at so like to dig deeper, so my apologies for putting you through the hoops.https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif

author: Tepe
author_rank: Frequent Contributor
timestamp: April 15, 2013, 02:02:59 pm
content: Quote from: G7PSK on April 15, 2013, 08:56:35 amNo

author: G7PSK
author_rank: Super Contributor
timestamp: April 15, 2013, 03:08:58 pm
content: http://en.wikipedia.org/wiki/Split-phase_electric_powerIts a split single phase Not a polyphase system of any description.http://en.wikipedia.org/wiki/Two-phase_electric_powerhttp://en.wikipedia.org/wiki/Polyphase_system

author: Tepe
author_rank: Frequent Contributor
timestamp: April 15, 2013, 04:57:08 pm
content: Quote from: G7PSK on April 15, 2013, 03:08:58 pmOh, an article with issues :-)With its missing references for the terminology it could even have been written by somebody with a bee in his bonnet.I think we can all agree that -sin(x)=sin(x+180°) and if it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.Quote from: G7PSK on April 15, 2013, 03:08:58 pmAn article about an historical system with a 90 phase difference. What's its relevance, apart from repeating the wrong terminology claim?

author: c4757p
author_rank: Super Contributor
timestamp: April 15, 2013, 05:11:37 pm
content: I don't understand how you don't see that two halves of one split phase themselves are phases. Just like how "2" is a number, and if you split it into 1 and 1, those are still both numbers! Maybe not in electrician's/power distribution terms, buy hey, this ain't the PDVblog forum!

author: G7PSK
author_rank: Super Contributor
timestamp: April 15, 2013, 05:17:27 pm
content: With split phase power supplies you require a starting circuit on any electric motor as there is no rotating field produced naturally.http://www.programmablepower.com/support/FAQs/DF_AC_Distribution.pdfThis one explains that the transformers are specially wound to give 180 degree phase difference. But it is still single phase when taking power of the two legs to give 240 volts just as it is single phase to take 415 volts of 2 legs of a three phase 415 /240 4 wire system in the UK you have 240 and 415 single phase or three phase with or without neutral as required.http://www.anoldman.com/power_systems/understanding_residential_ac_phases

author: Tepe
author_rank: Frequent Contributor
timestamp: April 15, 2013, 05:22:26 pm
content: Even better, put the center tap transformer in a black box with the two phases coming out of the box. How is a consumer supposed to tell that the phase difference wasn't produced by a suitably constructed two-phase generator?

author: Tepe
author_rank: Frequent Contributor
timestamp: April 15, 2013, 05:26:47 pm
content: Quote from: G7PSK on April 15, 2013, 05:17:27 pmOf course, after allsin(x) - sin(x+180°) = 2 sin(x)

author: c4757p
author_rank: Super Contributor
timestamp: April 15, 2013, 06:06:46 pm
content: You're saying that "phase" implies a rotating field. Maybe to electricians, but when I hear that, it sounds like someone who works a lot with LCDs saying something's not a square wave because it's not quite right for driving an LCD. Maybe when you're specifically talking to people who specialize in power distribution it's useful to use a different definition than the rest of us, but - welcome to the rest of us!

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 15, 2013, 11:01:56 pm
content: This probably won't help any, but it's worth a try.http://www.thecoffeebrewers.com/electricity.html

author: IanB
author_rank: Super Contributor
timestamp: April 15, 2013, 11:14:39 pm
content: <nitpicky>The peak voltage would be 170 V, not 120 V</nitpicky>

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 15, 2013, 11:22:12 pm
content: I don't care as long as it makes coffee

author: TerraHertz
author_rank: Super Contributor
timestamp: April 16, 2013, 12:06:49 am
content: This is so entertaining. Classic case of placing too much importance on labels, while not being careful to make sure everyone has the same definitions of what the labels mean.Phase: the angular offset of one repetitive signal, relative to another similar signal.Phase - voltage or current?: Can be used to refer to either, but if not specified is generally considered to be referring to voltage.Reference point: when discussing the phase angles of multiple signals, it's pointless unless the same reference is used for all measurements.The argument over whether a mains output transformer with a grounded center tap, has one output phase or two... so funny.I guess if you're happy with saying that simply inverting a sine wave's voltage creates a 'shifted phase', then fine.Personally, I'd put the origin of labeling those two AC supply lines as different 'phases', down to someone needing to come up with a way to make the dumbest hick electricians remember that connecting them together is a bad idea."Joe, you can't connect these two wires, they are DIFFERENT PHASES, OK?"Where the word 'phases' provides the magic handwaving, for someone who doesn't really understand.It'd be much more interesting to look into the origins and reasoning behind that center tapped pole transformer system.So OK, the US street distribution is several KV, to minimize resistive power loss in the distribution system, for a given amount of copper used. But then there's all the copper required in the transformers... I wonder how that works out, overall? Did they actually need less copper in the end, with that system? As opposed to the more direct system like in Australia, where the street level distribution is the same as the household voltage - three phase wires plus a multiply grounded neutral return, and premises directly tapping the street wires, for one, two or three phases as required.With the US system, I presume the street distribution does actually have three high voltage phases (120 deg apart), and if premises need true three phase power for rotational machinery, they can have a true 3-phase street transformer installed. The output of that would be star config, with grounded center point, I suppose? Of course in such installations there's no question, those really are three different phases, and electricians call them so.Then with premises that only have small power requirements, they get a pole transformer with only one or two outputs. With only one HV source phase, so of course the two outputs are just that phase. Except electricians don't care about terminology precision, so they call the two opposed polarity outputs 'phases'.

author: c4757p
author_rank: Super Contributor
timestamp: April 16, 2013, 12:21:15 am
content: Quote from: TerraHertz on April 16, 2013, 12:06:49 amYeah, except it's the electricians saying that the split rails arenotphases.QuoteKnowing our general efficiency levels,no.QuoteDepends on the street. Mine does not have three phases, but I'm in a very sparse area with nobody around who needs three-phase power (middle of the forest). In the city, that's usually how it works, AFAIK.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 16, 2013, 04:25:44 am
content: Some apartments in the US are wired 3 phase (120/208), though each unit generally can only access 1 or 2 of the phases.Any reason why most residential neighborhoods aren't wired like that? I see that as helping balance out the load. (So a house with an unusually large or small load would likely be spread out over 2 phases instead of being concentrated on one phase.)Also, if you took a 3 phase motor and wired each stator coil to a separate H bridge (so you have 6 wires from the motor going into 3 H bridges), would that be 6 phase or split 3 phase?

author: G7PSK
author_rank: Super Contributor
timestamp: April 16, 2013, 07:19:37 am
content: Quote from: NiHaoMike on April 16, 2013, 04:25:44 am3 phase 6 wire used where reversing is required or for starting purposes as star delta connection. starting is on star and switch to delta when up to speed helps to stop the lights going out during starting on line with big motors.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 16, 2013, 11:59:49 am
content: Quote from: TerraHertz on April 16, 2013, 12:06:49 amIn the US and many other countries, copper is not used for transmission lines, it isn't strong enough, it stretches over time and causes line sags, it hasn't been used in a very long time. Steel coated aluminum is used now for transmission lines, it is strong enough to not break and cost is low. One item to remember is that the USA was, it isn't now, one of the countries to pioneer technology when it was invented. The USA was one of the first to have a large electricity roll out and they made a lot of mistakes. Other countries that provided service later could benefit from not having to make those mistakes. Lots of areas were wired for single phase because it was the cheapest way to wire at the time. Later when industry wanted 3 phase it tended to cluster in areas that were lots of industries but few homes.QuoteIn the US most lines coming to the home are single phase because 3 phase isn't needed or 50 years ago the area was single phase and cost prohibits changing that. 3 phase terminates at the distribution sub station and then one of the phase is sent to a different section of homes. 3-phase power can be extremely expensive to have added to a site because it often means stringing new lines all the way back to the sub station. The nearest 3 phase connection that I could tap is about 5 miles away, at over $20k per mile that is an install cost of $100k.QuoteElectricians in the US do not call the single phase (split phase) output two phases because they know that would confuse itself with the distribution 2 and 3 phase installs.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 16, 2013, 12:10:53 pm
content: Quote from: NiHaoMike on April 16, 2013, 04:25:44 amIt really depends on what the load average is for the area. Sometimes all you can get is single phase and rather than string new lines all the way from the sub station it is cheaper to just upgrade the single phase line capacity. Load calculations have some pretty high margins, 300A allotted for each home when only 200A is possible because of the mains breaker of the home limit, to prevent overload so spreading out the load over lots of single phases really isn't needed near the homes. Homes are supplied with lines all the way up to 35KV @ 2-500A which are fed by 50KV@10KA so balancing the load isn't too much of an issue except when areas sustain a heavy build up of new homes or business and the capacity wasn't designed for that increase. A typical single phase line can supply 360 homes easily.

author: SeanB
author_rank: Super Contributor
timestamp: April 16, 2013, 06:01:00 pm
content: Originally power distribution was done with DC voltage, and the substation in the street provided 100VDC on 2 power rails from motor generators running either on steam or from a higher voltage DC supply fed in from a larger power station. Thus one side had +100V and another -100V as a supply, with higher loads being supplied by using the 2 100V lines to give 200VDC as power. The wiring was done to reduce the size of the common conductor, as it normally only has to handle the imbalance current between houses, not the whole street load, which are handled by the 2 line wires, at half the current.When AC was being introduced, the motor generator sets were replaced by transformers and mercury arc rectifiers, still keeping the 2 power rails so as not to have to replace all the infrastructure in a district when upgrading. When finally the switch was made to AC distribution the mercury arc rectifiers were simply removed and the transformers were simply switched to supply the power rails, as all these substations either had 3 sets of gear if they had a 3 phase supply, or had 2 sets if single phase. The load output was simply rearranged to use a single phase, as again it was desired to not have to rewire the streets and houses, with the AC voltage being chosen to work with older equipment in houses at the time.Thus the 2 phase is cast in stone. In the UK and elsewhere they had chosen a higher voltage in the beginning, typically 200-250VDC and had thus only a single wire pair along the street, as the insulation of the time was problematic at higher voltages, and winding the motors and transformers for higher voltage was more difficult, so they just supplied full current ( same current as the US on the lines as well, but capable of higher power to loads) to the lines. When they changed to AC it was merely a wiring change.

author: G7PSK
author_rank: Super Contributor
timestamp: April 16, 2013, 09:35:32 pm
content: The UK was lucky with the early decisions on power distribution, it started with Ferranti then in the 30's they started on closing all the small local town plants and building the national grid then we really lucked out with free demolition by the luftwaffe so we had to build all new.https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gifI walked trough our village looking at the power distribution as that is overhead lines and noted that it is pretty well every other house is on another phase in order to keep things balanced. Four wires plus earth strung on poles so fairly easy to spot which line the connection is.

author: IanB
author_rank: Super Contributor
timestamp: April 17, 2013, 12:49:57 am
content: Quote from: TerraHertz on April 16, 2013, 12:06:49 amWith the typical "pole pig" transformer used in the USA the secondary is not copper wire but rolled up aluminium sheet. There are actually only just a few turns on the secondary side, maybe a dozen or so (but a lot of cross sectional area per turn). When people say the the mains supply has effectively zero impedance they are not kidding...

author: SeanB
author_rank: Super Contributor
timestamp: April 17, 2013, 04:05:17 pm
content: Most have copper windings, though you do get a lot of the smaller units using aluminium strip as wiring. The cores though are run at a very low power level, along with having a large cross section of the wiring, mostly to reduce the off load losses in the core to as low a level as possible, as the transformer is always running at low power levels with only short duration of full power operation during peak hour. Often you find it only has a 20C rise over ambient, with possibly only a 40C rise at full load. oil cooling on all of them, though the oil is more there as an insulator, but it keeps hot spots from forming in the inner windings. Bigger ones that are doing distribution down from the grid though often have forced cooling, as the power levels are high enough that they have oil pumps and thermostatically controlled fans to cool the unit when it reaches full load. Those that are that big have a conservatory tank with a pipe connecting it with a flow switch, which trips out the transformer if there is a sudden flow of oil into the tank, which means the transformer is arcing over internally.

author: c4757p
author_rank: Super Contributor
timestamp: April 17, 2013, 04:14:41 pm
content: Curious question relevant to the US using so many damn transformers: What is the typical efficiency of one of those? How does the power loss in the transformer compare to the power saved by the higher voltage lines?

author: IanB
author_rank: Super Contributor
timestamp: April 17, 2013, 04:20:50 pm
content: Here is a video showing how those "little" pole mounted transformers are made. Fascinating for anyone who likes power electronics:It's a "little" transformer, because those things are still huge and need a fork lift to move them when you see them on the ground instead of stuck up a wooden pole...

author: G7PSK
author_rank: Super Contributor
timestamp: April 17, 2013, 05:13:13 pm
content: Is that number on the outside the rating, some had 25 and others 50, so I wondered if that was KVA.

author: IanB
author_rank: Super Contributor
timestamp: April 17, 2013, 06:15:20 pm
content: I don't know, but I would guess the "25" is 25 kVA and the "14.4" is 14.4 kV.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 18, 2013, 04:33:34 am
content: Quote from: G7PSK on April 16, 2013, 07:19:37 amI was thinking more along the lines of using an industrial 3 phase motor in a homemade EV. You'll almost surely wire it for delta (with paralleled windings if applicable) in order to reduce battery voltage requirements.But an EV requires a lot of power, so those DIY inverters out there need a bank of IGBTs on each phase. So you decide to "open up" the delta and connect each of the three windings to its own pair of IGBT banks, in order to ensure current sharing. You now have 3 windings connected to their own H bridges.And now you realize that rather than create 3 sine waves 120 degrees out of phase, you create 6 sine waves 60 degrees out of phase, so that each winding of the motor is connected across two phases 180 degrees out of phase. Now your battery voltage requirements go down a bit (or you can get a little more horsepower for the same voltage).Would that (6 waves 60 degrees out of phase) be called 6 phase or split 3 phase? If it's the latter, what would true 6 phase look like?

author: G7PSK
author_rank: Super Contributor
timestamp: April 18, 2013, 09:56:07 am
content: The windings will only give you 3 pairs of poles or 6 pairs depending on the speed rating however you use the connections as one set of windings will be on top of the other.