Difference between main earth reference and real Earth ground? - Page 1
Forum section: electronics / beginners

author: AzzyAsi
author_rank: Newbie
timestamp: January 26, 2017, 12:17:58 am
content: I just looked on an older video about how not to blow your oscilloscope and saw the big problem with reference main earth products and remembered I have an adjacent dilemma to shed some light on.The problem I have and seek an answer for long time is the following:Is the main earth reference (3rd pin in mains outlet) any different than real Earth (like a metal pole stuck in the ground) ?The background story:I have a large cast iron heating radiator behind my desk (with steel pipes all around, interconnected throughout the whole building 10 floors, all the way to ground) and the computer keyboard has metal frame on the back.The problem is that I get a mild shock whenever I touch the radiator and anything earthed through mains earth pin. (like the metal on the said keyboard, end of usb leads, chassis of computer, shroud of ports on any device like tv, printers, metal casings of appliances like a fridge, etc.Got me curious and measured with my crude multi-meter (china export, very cheap but auto-scaling) and between computer chassis and said radiator says 220V AC. But the amps are not there since i could get comfortable with that tickle if it's not concentrated in one tiny point of contact. So it's hard to feel when touching full hand each object, but very tickley if only the tip of the finger is held on one object.Anyway.. how can I have 220V between a radiator and 3rd earth pin? Is this a design feature I don't know? or maybe earthings are not done correctly at one end (the building is very old, and i really don't know if the radiators have any connection with the earth, but after all, the pipes go for hundreds of meters underground, all metal, or the electrical mains earth is gone bad?). Or do i have a neighbor with faulty appliance that leaks voltage into the earth pin (or radiator.. idk, just saying it is possible)Now whatever the reason, the problem was there for the past 15 years, the solution was wrapping a cable from my mains outlet to the radiator (the ground one, of course).. but I wonder the reasons I got this weird thing. Unfortunately, further testing can't be done since the radiator got recently isolated with pexal pipes in several places and removing this problem altogether, but still wonder about it.Can't really test it because real Earth ground is hard to reach from 10th floor where I live.

author: Ian.M
author_rank: Super Contributor
timestamp: January 26, 2017, 12:46:29 am
content: Real Earth isn't so hard to reach for a brief test. You just need a bit over 30m of wire, + a metal rod you can pound into the ground. I would suggest using thin enamelled copper wire, and lowering it out of the window with a small padded weight on the end one dark evening, so no one notices it and hassles you. You could also use ordinary hookup wire but there's more chance of it being noticed and its a bigger investment. Make sure that you aren't touching any metal object while lowering the wire. Rig a reel holder with a light friction drag so you can pull more wire from below. Once it touches down, go down, connect it to the spike and ground it in the nearest accessible earth surface. You can then measure voltages between that wire, Mains Earth and also any building metalwork. A few volts difference wouldn't be unusual but if you get a high voltage, it would indicate a dangerous fault with your building's ground conductor. If there is an earthing fault, you could also get dangerous relative voltages between Mains Earth and any telephone, cable TV or aerial distribution system cabling. Remove the wire before anyone notices and complains . . . .CAUTION: If your apartment is equipotential bonded to the Mains Earth and there is an earthing fault, a dangerous voltage may exist between any object in it (including you) and the wire. Handle the wire as if it was live until you know the voltage difference is minimal.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 26, 2017, 01:06:04 am
content: Depending on where you are you can find huge voltages between the third pin and earth ground. The most I have observed steady state in a US site is over 50 VAC. This type of situation arises due to either failures in bonding, or more commonly just old wiring practices where bonding to earth ground was not required.If you are in an environment where heavy loads are switched (welding, large motors on and off, HVAC, etc.) you can get brief transients far larger than that, even when properly bonded.The key is to remember that ground is a circuit all its own, with resistance, inductance and capacitance along with various sources of voltage and current. The challenge is that it is difficult or impossible to know all of the traces in this circuit.

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2017, 05:29:43 am
content: Everything *should* be bonded to the same grounding rod(s) stuck in the ground outside, at least that's how it's done in the US. If you have a significant voltage on any exposed metal items or the ground pin on receptacles then something is wrong. You should never receive a tingle from touching exposed metal.

author: neil t
author_rank: Regular Contributor
timestamp: January 26, 2017, 06:26:42 am
content: It was common practice here in Australia to bond all housing Earths to the Water pipes, Only last year the house i'm renovating had a ground rod installed,as I pointed out to the electrician, if you didn't like your neighbour it would be an easy way to electrocute someone (accidently of course).p.s All the houses around me built around the same time are still Earth bonded to the water pipes.

author: AzzyAsi
author_rank: Newbie
timestamp: January 26, 2017, 07:18:10 am
content: I'm not in US, but in Europe, Romania.Here we use the CEE7 non-polarized plugs, 220V 50Hz 16A for outlets, 10A for lighting, 25A combined for the home user and 380V tri-phase for industrial users. (and the home user actually gets a phase out of a standard 380V 3phase)The building is only with apartments. No industrial environment.I bet grounding practices were not the best. I have exactly two grounded outlets in the house, the rest are unearthed. (and the actual grounding for the building.. I don't know where it is or if in good function)Now the computer is grounded in one of those outlets. The fridge, washing machine, are all earthed. The tingle I get is not from randomly touching the case, but touching the case and the heating radiator at the same time. Every time has the same intensity, and every time I touched those two objects at the same time I got a tingle.So I guess the culprit was whatever was hooked to the pipes, and leaking volts into the radiator. (i think that earthing from outlet is still usable since the electrical company is doing maintenance now and then.. but i don't thing anyone ever checked how a radiator is grounded.)Fortunately, the problem is gone now since the said radiator is isolated electrically now from the rest of the building and pipes have been changed with pexal tubing in more places in building and is totally possible to have disconnected the problem.later edit: just checked with a multimeter the mains voltage: phase to null 219V, phase to ground pin 219V, null to ground pin 0V. So from this I conclude the earth pin is good, and the radiator was the culprit, I guess it's a weird connection to a radiator in this building expecting the radiator to be sort of ground, and clearly was not.

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2017, 08:35:00 am
content: I always like hearing how these sort of mundane (to most people) things are done in other parts of the world. I had the opportunity to replace the main panel, consumer unit I think he called it in a friend's shop when I visited the UK. Very different from the systems I was familiar with. The single ended pure 240V and the concept of ring mains took some getting used to. After extensive discussions neither of us can decide on a clear winner but both the US and UK systems have their advantages.At one time using the water pipe as ground was common practice here too. I'm not sure when the code changed to require a separate grounding rod but I suspect it was when galvanized pipe started to be replaced by plastic from the meter to the shutoff in the house. Galvanized pipe made a decent ground rod but obviously plastic doesn't.

author: Brumby
author_rank: Unknown
timestamp: January 26, 2017, 02:00:00 pm
content: Quote from: neil t on January 26, 2017, 06:26:42 amThis practice is no longer permitted for new installations - but existing installations exist all over.The electrical risk to plumbers is well known in the trade - and there are guidelines that have been set down. For example, I had a leaky main tap (next to the water meter) that had to be replaced. Since the electrical path through the plumbing was going to be broken, when the plumbers came to fix it, the first thing they did was to affix solid electrical connections either side of the section to be worked on. A shorting strap was connected between them and a meter was monitoring the situation. As I understand it, if the meter shows there is a voltage above a certain threshold at any time during the work, the plumbers are to walk away immediately until an electrician has resolved the cause.The logic is simple and the risk, deadly.If there were an earth leakage current on a property without an RCD breaker and a pipe earth, the current would very likely use the pipes as a return circuit, rather than the soil surrounding it. Break the pipe circuit and you have a potentially lethal voltage, just waiting to pass through the unsuspecting plumber should he holds both sides of the break during his work.What should be earthed and what is properly earthed aren't always the same. I would suggest anyone should treat earth connections with suspicion - until you have demonstrable proof they are OK.

author: Seekonk
author_rank: Super Contributor
timestamp: January 26, 2017, 03:04:21 pm
content: Our college had a carrier current radio station. The ground from one building to another was about 17V and you could make a little arc with it there was so much current. In rural areas they sometimes use a single HV wire to feed a local transformer and use the earth as a return path. This can set up rivers of current. Dairy farmers often have ground surveys done, voltage potential between two ground rods. Cows won't drink enough water if they get a zap on their lips. Let alone if you apply it to their nipples.Ground isn't that low a resistance. A main feature is that it brings the ground ( the stuff you walk on) to the same potential as the frame of some device you might be toughing when a fault occurs.

author: dimkasta
author_rank: Regular Contributor
timestamp: January 26, 2017, 03:36:36 pm
content: Keep in mind that getting advice for Mains voltages on a forum is a big NONONO. In fact, some other forums I am participating in prohibit such discussions.First of all, no-one knows the exact scheme your installation follows or the local regulations and practices.And to be honest, when it comes to mains, if you have to ask, then you should probably call a professional.I mean no disrespect to you or anyone trying to help, I am just raising a friendly red flag.We cannot be too cautious about mains.

author: HoracioDos
author_rank: Frequent Contributor
timestamp: January 26, 2017, 03:58:52 pm
content: Quote from: Brumby on January 26, 2017, 02:00:00 pmSame here in Argentina. Also one of the few countries that adopted Plug Type I and dropped Type C.

author: Seekonk
author_rank: Super Contributor
timestamp: January 26, 2017, 04:06:29 pm
content: That advice would apply to most forum subjects.If interested in just how bad the electric grid can be in some counties, watch "Power Trip" (2003)

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2017, 05:06:30 pm
content: Quote from: dimkasta on January 26, 2017, 03:36:36 pmSince when? You do realize this is an engineering forum and many of us design and/or build products that are mains voltage or higher?Yes you should always check the local laws and regulations and don't go modifying the wiring based solely on advice in a forum but to prohibit discussion of mains voltage is condescending and frankly ridiculous.

author: Vtile
author_rank: Super Contributor
timestamp: January 26, 2017, 05:36:45 pm
content: If you get zapped in regular basis in your home, there is something wrong and should fixed or atleast the root cause analysed by competent professionals. Static buildup should be taken account though, but in home in same place everytime should ring the bells.I started to get shocks from my car after every short driving in winter, after I changed my shoes from ESD rated to regular market models, very annoying. I did change shoes again, car is still the same.Where I live the words "I just got zapped from the X and Y device on my home" while calling the electrician usually results of swearing, a broken coffee cup sounds and worldrecord 1000 meter run results if it is their own previous work, which should tell the seriousnes level. <- Ok, that is a myth, but "I have no time now" will turn to "I'm there in a minute".One thing also might want to test is to measure voltage between your computer and ground. If something is not grounded or wrongly wired they might build up condensator like system and discharge every time you touch them if you have any reference to ground, which shouldn't be acceptable either.I just few days ago found out that my table fluerescent lamp (20+ years in use before noticing it) on my electronic workdesk do build up 50V charge to its leg, low energy one fortunately (seen on 1MOhm meter, but not with 20k AVO8 ), but still it will be drawn out of service, just in case. Will be interesting teardown when I get a new one in a few days to replace it. I don't know the structure of it, but I suspect a capacitive coupling through wire insulation.PS. It wouldn't be a terribly bad idea check the groundings and wirings every time you move a new home. The older the building or area is the more changes there are that there is really weird problems. The buildings in general since they might be seen the coming of the light bulb and every style of wiring there have been and repaired and extented by several generations of electricians and designers (in worst case the previous handyman owner).

author: SeanB
author_rank: Super Contributor
timestamp: January 26, 2017, 06:29:59 pm
content: Being an old building, and with the grounding likely being a much later addition an inspection by a qualified electrician will be in order. If the building is that old and has been lax in maintenance there is a high chance any grounding rods, bondings and such might well have rotted away, been disconnected for various reasons or otherwise are missing. Thus a check and rectification is in order.

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2017, 07:48:23 pm
content: Quote from: Vtile on January 26, 2017, 05:36:45 pmI had some shoes once where the fabric between my feet and the rubber came loose so it was rubbing when I walked, I was getting the most powerful static zaps I've ever had from that, I started to dread getting near metal objects.I'm also reminded here of an incident I had at work about 15 years ago. I had one of those halogen torchier lamps in my office and I had noticed a small tingle a few times when I touched it but hadn't thought too much of it. One day I pulled the VGA cable off a PC which was still connected to the monitor on the other end and it swung and brushed the lamp. There was a flash and a loud bang and the breaker tripped. Turns out the wiring in the lamp had chafed and the metal body of the lamp had been live all that time. It blew a chunk out of the D-sub shell on the VGA cable, I'm glad I never touched it while I was well grounded.

author: AzzyAsi
author_rank: Newbie
timestamp: January 26, 2017, 10:21:35 pm
content: Wow, thanks for all info.I think as long as the potential difference is the same between live-null, and live-ground, I can conclude the ground is properly ground being the same potential to null. Right?So I guess the most probable scenario is that radiator and the pipes were kind of live by unknown reason. But keep in mind the building is from the 60's 10 floors tall, 12 flats per floor and all radiator are interconnected. So who knows what happened over the years to become live.The tingle was not static.. it would not go away. Anyway for many years I had this cable from the radiator to computer case. Since the tingle was obvious while resting my feet on that radiator and touching any metal part of PC (and having a metal keyboard it was hard to avoid). So this solution worked OK.Now I can't do any testing because the problem is gone or isolated from me. I know for sure that few years back I have measured the voltage and read 220V AC from case to radiator, and that the radiator would light up a pen-tester-thingy, barely. I don't know what sort of amps were running there but no breakers tripped. (and about the breakers.. we have ceramic fusible fuse cartridges, and not automatic breakers)But here there are unfortunately many improvisations of all sorts that kind of worked, but still shoddy and unsafe. And sometimes true incompetence. (I remember a big one made by the electrical company: they routed to homes two phases and no neutral.. that was fun but nothing was damaged in my house but my neighbor's TV did not survive.)Safety is not tight as in other places like UK (120V, polarized plugs, child finger safety, fuse inside plug.. etc), but I guess makes people a bit more aware as there are not many incidents regarding electricity.Other odd practices. When you don't have an outlet nearby, but you have the junction box at hand, just make an extension from there and twist the wires bare hand ONLY one at a time. - this practice was common for cable-internet providers to power a corded drill to fix various switch boxes on the hallway where are no outlets.You all know it's not recommended to touch the live wire, but if you are insulated from ground it's quite safe actually. (Don't try it though)I do have decent knowledge about electricity, but nothing fancy in electronics, yet I am a mechanical engineer, and transformers, motors, generator, batteries, etc were thoroughly studied. General wiring of a building was not.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 27, 2017, 12:17:53 am
content: Quote from: dimkasta on January 26, 2017, 03:36:36 pmEvery country has its own procedures, and here in the US we are more lax than many others about our "professionals" qualifications.Which can lead to an interesting situation. I once purchased a house as a rental unit. The HVAC system was on the roof, and when it acted up I went up on the roof to see what was up. The wiring to the unit was in metal conduit, but there was an indoor outlet in a box laying on the roof. I got a tingle when I touched the box, decided I didn't have the time or energy to mess with it and called a "professional". He went up, looked at the obviously not to code work, heard my story about a tingle and refused to work on it until that was resolved.The bottom line, I had to fix it myself. Whoever had done the work didn't care about color coding so it was a long day adventure to track down all the problems and correct them. After all that the HVAC was still dodgy, so called a different professional. Same story, second chapter. Didn't have a clue, wanted to sell a new unit. So back to me, the non-professional, who found the bad starting capacitor and bad internal neutral connection in the HVAC. A two element problem was too much for the "professional".Conclusion: It is wise to be cautious about mains (and high pressure gases and fluids and volatile liquids and cryogenic fluids and caustic substances and .....). But if you think before acting and research what you are doing there is no reason you can't do it, possibly better than the pros.

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 12:34:27 am
content: My experience with HVAC guys is they all want to sell you a brand new system for all but the most trivial of problems and sometimes even then. They will also go on about heat load calculations and equipment sizing as if it's rocket science when systems are only made in a handful of sizes and looking at what's installed on similar places in your area is as effective as calculating it.I got my HVAC certification a number of years ago so I could purchase refrigerant. It was easy, just had to read a pamphlet and pass an exam, most of which was common sense stuff or dealt with the legal handling and disposal of used refrigerant.

author: Brumby
author_rank: Unknown
timestamp: January 27, 2017, 12:58:55 am
content: Quote from: AzzyAsi on January 26, 2017, 10:21:35 pmNot necessarily.Just because two points are at the same potential does not mean they are connected.I would go for a separate testing scenario to categorically ascertain the grounding status.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 27, 2017, 01:09:22 am
content: Quote from: Brumby on January 27, 2017, 12:58:55 amHaving ascertained that they are at the same potential I would feel safe enough to trying to measure the resistance. Carefully. If the resistance measures the same with the wires connected both ways I would feel somewhat confident that they are connected. At that point in time. You still won't know if the connection is intentional or permanent, and you won't know the magnitude of the currents which might flow. The value of the resistance would be a factor in how I felt.