does absence of a mains Earth lead affect the performance of scopes, AND HOW? - Page 1
Forum section: electronics / beginners

author: ali6x944
author_rank: Frequent Contributor
timestamp: February 27, 2016, 02:46:14 pm
content: hi guys,I live in an old area in Saudi, and in the old days they didn't add a earth lead to the plug...i didn't consider this a problem, until the ground alligator lead start zapping me... i went and saw a couple of videos and saw Dave's video "-How To Track Down Common Mode Noise", in it he state that you shouldn't remove the earthing...so,does absence of a mains Earth lead affect the performance of scopes, AND HOW?

author: Ian.M
author_rank: Super Contributor
timestamp: February 27, 2016, 03:01:26 pm
content: As a modern scope will have a switched mode PSU that relies on the Earth connection being present as a ground for the inlet filtering and for the filter cap that shunts any switching noise capacitively coupled across the transformer, use of an un-Earthed outlet to power it is likely to seriously compromise its small signal performance due to excessive noise.If you are in a building without an effective mains earth, and you are interested in RF or low level analog signals, you will need to arrange effective earthing for the outlets on your workbench. Unfortunately introducing earthing in a an otherwise earth-free system has safety implications, and at a minimum all other outlets in the same room should have RCD protection and you may need to add equi-potential bonding.

author: ali6x944
author_rank: Frequent Contributor
timestamp: February 27, 2016, 03:30:09 pm
content: that explain a lot, but is it the reason for the painful shocks from ground alligator lead ?does PVC pipes in the sink give effective earthing?

author: AF6LJ
author_rank: Unknown
timestamp: February 27, 2016, 03:35:36 pm
content: Quote from: ali6x944 on February 27, 2016, 03:30:09 pmThat is not an effective Earth connection.As for noise filtering effectiveness changing on a 2 wire VS a 3 wire system; I have a two wire system here (very old house in the US) and the lack of an Earth ground has no effect on the EMI radiated from the numerous SMPSs here in the ham shack.

author: Ian.M
author_rank: Super Contributor
timestamp: February 27, 2016, 04:06:29 pm
content: It does to a large extent depend on the EMI filter configuration. Many PSUs simply have a bifilar choke with class X caps across line and Neutral either side of it and from a filtering viewpoint, don't care whether or not an Earth is present.However its common to have additional class Y caps from Line and Neutral to Earth and if the supposed Earth is floating, this arrangement capacitively couples half the AC supply voltage (but with a high source impedance) onto the instrument chassis. Its also usual to have a class Y cap between the PSU 0V rail and the -ve side of the PSU primary side reservoir cap, as a return path for HF switching noise capacitively coupled from the transformer primary to its secondary. If the 0V rail isn't grounded, this also tends to introduce lower harmonics of the supply frequency.If the device under test isn't grounded, its 0V rail will be at the same potential as the scope chassis and capacitive coupling between your hand holding the probe and the board can be enough to swamp any low level LF signals and modulate RF signals due to disturbance of the bias point of active devices.

author: ali6x944
author_rank: Frequent Contributor
timestamp: February 27, 2016, 04:09:48 pm
content: Quote from: Ian.M on February 27, 2016, 03:01:26 pmI'm using my DS1054Z to probe AM signals that is detected by a crystal radio, so as Ian.M said, i need an effective mains earth .the problem is I'm living in the second flour, and i have no effective way to do it without drilling a hole in the wall or stretching a ridiculously long wire to earth, due to the fact that no pipes in the system is metal, i have no central heating or gas pipe going from earth to me, except the A/C copper pipes going up to the roof...not sure if it is useful

author: Ian.M
author_rank: Super Contributor
timestamp: February 27, 2016, 04:21:31 pm
content: I wouldn't assume the aircon pipework is properly grounded. If it isn't you *really* don't want to connect it as your bench 'ground' as it could introduce dangerous voltages and will certainly introduce electrical noise. There is unfortunately no substitute for a proper ground, so that means something like a 10 sq mm copper lead down an exterior wall to a properly installed and tested earth roddriven deep enough for the soil to remain moist all year. That's possible to get done if the building is owned or long-term leased by someone in your household, but if its a rental property and national law doesn't require grounding, you are unlikely to get permission.What *NOT* to do:http://www.thaivisa.com/forum/topic/542931-quick-and-dirty-groundingearthing-installation/

author: ali6x944
author_rank: Frequent Contributor
timestamp: February 27, 2016, 04:23:47 pm
content: Quote from: Ian.M on February 27, 2016, 04:06:29 pmthanks for clearing that out of the waynow searched for DS1054Z PSU:

author: Aodhan145
author_rank: Frequent Contributor
timestamp: February 27, 2016, 04:25:36 pm
content: Worst case scenario, Whats to stop you walking outside ramming a big earth spike into the ground and wiring it to the socket your scope is plugged in to? Would this work?

author: ali6x944
author_rank: Frequent Contributor
timestamp: February 27, 2016, 04:55:11 pm
content: Quote from: Aodhan145 on February 27, 2016, 04:25:36 pmbudget, to buy 14 Gage wire is expensive, for one meter of this cost 34.65 USD and i roughly need 50m if i will go from the stairs to the free space beside the apartment building that will equal around 1732 USD, now u r thinking go vertically from the window, Security Bars are in the way, they are not the problem the thick metal mesh between the bars is so I'm just lost!if u know any method of grounding or if i could use smaller Gage...thanks anyway that really kinda helped

author: retrolefty
author_rank: Super Contributor
timestamp: February 27, 2016, 05:02:03 pm
content: Quote from: Aodhan145 on February 27, 2016, 04:25:36 pmBecause the earth ground resistance between the newly spiked ground rod might well have high (as in unsafe) resistance from ground rod resistance/reference at the source of building power service entry. Ground rods and interconnected grounding systems can be very expensive and detailed. I measured open circuit between two ground rods, 10 feet a part, as they were pounded into a rocky substrate.

author: Ian.M
author_rank: Super Contributor
timestamp: February 27, 2016, 05:37:32 pm
content: Quote from: ali6x944 on February 27, 2016, 04:55:11 pmThat seems grossly excessive. They certainly aren't paying that for the wiring in every new sky scraper being built. Also 14 gauge wire would be a very poor choice for an earthing conducter, I wouldn't use less than 6 sq mm.4mm dia bare Aluminum wire would do the job and should be a lot cheaper than copper wire. The only problem with Aluminium is terminating it reliably where moisture may be present, However with the right technique it can be soldered reliably to a copper terminal. If its hard drawn Aluminum wire it can also be crimped, but that needs Noalox anti-corrosive jointing compound or similar. The joint must NOT be buried, the wire must turn upwards towards the joint to provide a drip loop and it should be covered against rainfall.You would of course need an adequate ground rod. Unless there is an irrigated garden area, soil moisture levels may be so low that a very deeply driven rod would be needed. The other problem is rubble around the building foundations - this can make it very difficult to drive an rod in far enough.

author: ez24
author_rank: Super Contributor
timestamp: February 27, 2016, 06:17:23 pm
content: Quote from: ali6x944 on February 27, 2016, 02:46:14 pmI also have a 2-wire system (110v). Those that have 3-wires cannot believe people can live with 2. I have had no problems with my Rigol. But assuming your 2-wire system is normal (for 2 wires), what are you measuring? I just work with low DC stuff so that might make a difference.I believe man got to the moon on 2 wires, so 2-wire systems are not the end of the world.Do you have 220v?

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2016, 06:18:39 pm
content: You could try runing the oscilloscope from an isolation transformer. That would help to get rid of the painful shocks when touching the crocodile clip. The Rigol DS1054Z will run off much lower voltages than 100VAC. I've managed to get mine to run off 30VAC but I'd recommend higher so a transformer with two 24V secondary windings in series to give 48V would do.

author: nour
author_rank: Frequent Contributor
timestamp: February 27, 2016, 06:20:12 pm
content: I also live in saudi arabia, in a modern area and there is no ground at allI have tried using water pipes and after connecting the wires to the pipes I discovered the fact that the pipes are not metaldon't know the material and actually the place which I live in has the lowest moisture level on earthat the summer I feel like I am going to crackso to dig and try to place a ground rod I think I will have to dig very deep may be 1k or so(the ground around here literally rocks and nothing but rocks, oh and lots of sand of course )When touching my scope's probe and the ground with bare foots I have like 150 volts sine wave on the screen, it's of course the poor's man rigol 1054

author: nour
author_rank: Frequent Contributor
timestamp: February 27, 2016, 06:22:28 pm
content: Quote from: Hero999 on February 27, 2016, 06:18:39 pmthat's a very new piece of information for me, didn't know it can run with less than 100 voltsI have a couple of isolated transformers, I will try this, seems good idea to try, at least I wouldn't have 150 volts on my screen when touching the probe

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2016, 06:55:59 pm
content: Quote from: nour on February 27, 2016, 06:22:28 pmYes, the Rigol DS1054Z will work from voltages as low as 36VDC and 30VAC. Awhile ago I looked at building a battery pack for my DS1054Z but I didn't pursue it because I already have an Owon with a built-in battery.https://www.eevblog.com/forum/testgear/battery-pack-for-rigol-ds1054z/msg717702/#msg717702

author: SeanB
author_rank: Super Contributor
timestamp: February 27, 2016, 07:10:43 pm
content: Saudi, so not much chance of there being rain, and you probably will need to go down 20m or more to get a low impedance ground though, unless you are living near the sea. Aluminium wire, or even galvanised steel strap ( around 30mm wide and 1.2mm thick, sold in rolls as roof strapping) will work well here, and is easier to attach to the building exterior. If the building is a steel frame structure then the steel structure will provide an adequate earth through the concrete foundation it is bolted to.

author: poorchava
author_rank: Super Contributor
timestamp: February 27, 2016, 08:07:27 pm
content: I have my scope connected through an isolation transformer 99% of the time. I hook it up to earthed mains only when I'm doing some high precision probing.Sent from my HTC One M8s using Tapatalk.

author: Keyrick
author_rank: Contributor
timestamp: February 28, 2016, 01:31:02 am
content: If the transformer feed that provides service to the building is not grounded, a ground rod will do nothing (Except provide a path for lightning should that lightning hit your scope!). If the feed to the building is truly 2 wire, there are no options for an Equipment Ground Conductor (EGC) : Ground/Earth.The EGC in 3 wire installations a there to protect EQUIPMENT, as it provides a low impedance path to ground during a fault condition, enabling a CB to operate or a Fuse to open. GFIs & RDIs protect people.If you are getting a shock from touching the alligator clip, somewhere else on your body is touching a conductor. Bare feet is never a good idea, my friend, when working on Mains powered equipment.My guess is that your building power feed is grounded somewhere in the building, maybe to the ufer connection in the concrete foundation, and you are somehow in contact with that concrete. Is that possible?

author: nour
author_rank: Frequent Contributor
timestamp: February 28, 2016, 03:42:36 am
content: Quote from: Keyrick on February 28, 2016, 01:31:02 amare you sure about the transformer part, if so thats mean people can't just dig a hole in the ground and make their own ground rod if the main transformer is not groundedcan you point us to illustration for general details about this point!

author: Keyrick
author_rank: Contributor
timestamp: February 28, 2016, 05:11:55 am
content: Quote from: nour on February 28, 2016, 03:42:36 amhttp://www.electrical-installation.org/enwiki/File:FigC01a.jpgIf the transformer isn't grounded at some point, where is the path for your ground rod to get back to the source? With no path back to the source, there can be no protection provided to the equipment in the event of a fault. We are not only talking about a path, but also about a reference. If the transformer is not referenced to ground, a ground rod can't see it (electrically) and it will provide no protection. (It will be good for your x-tal radio as the AM transmitter typically is referenced to ground.)The link above shows that power distribution in SA is 3 phase Wye with the transformer grounded at its center tap. So in this case, the ground rod would have a path back to the transformer. In the US the requirement is to have that path to have an impedance of 25 ohms or less between the rod and the transformer. While that is really hard to measure, most contractors just install two rods, or connect the building ground conductor to a ufer in the concrete. I do not know the impedance requirements in SA so I can't answer that.

author: MarkF
author_rank: Super Contributor
timestamp: February 28, 2016, 07:20:06 am
content: This video on grounding myths maybe be helpful for you:

author: Aodhan145
author_rank: Frequent Contributor
timestamp: February 28, 2016, 11:13:58 am
content: Quote from: retrolefty on February 27, 2016, 05:02:03 pmA couple of ground rods in good ground should provide a low enough resistance path though.

author: Ian.M
author_rank: Super Contributor
timestamp: February 28, 2016, 12:52:01 pm
content: Of course it is desirable to get a low earth loop impedance (as long as the maximum possible fault current will be within the capabilities of the breaker), but since the introduction of the RCBO it is no longer so actively critical, as the breaker can be tripped by a few tens of mA of current imbalance between live and neutral, rather than by the fault current exceeding its load current rating.This does of course suppose that the incoming supply is intentionally earth referenced rather than fully floating. However it would be exceptional for it not to be. As I mentioned earlier, *ALL* outlets in the room must be RCD protected, so some sockets may need to be replaced by ones with an integral RCD.Seehttps://www.tlc-direct.co.uk/Book/8.6.1.htmfor how to measure earth electrode resistance.The only remaining safety issue is lighting. Any room with an electronics workbench needs some lighting that wont shut off if the RCD protected circuit supplying the bench trips. If there is whole house RCD protection, this may mean you need to fit at least one self-contained maintained emergency light over the bench (maintained because the physical hazards if you trip the RCD are immediate, and the startup time of a non-maintained CCFL fitting is undesirable. A non-maintained LED fitting would be acceptable if its turn-on delay is low enough)If you are going to be doing any significant quantity of mains powered appliance repair work, if possible, it helps to have a minimum of two separate RCD protected circuits supplying the bench. You *WILL* get nuisance breaker tripping due to switch on surges in toroidal transformers etc. and occasionally may get a fault to earth, that wasn't spotted by your initial inspection and safety tests on the incoming item. Its a lot less stressful if your bench lighting, bench PC, and any other test equipment that should not be subjected to an uncontrolled shutdown are on a separate circuit to the device under test so they stay on.

author: retrolefty
author_rank: Super Contributor
timestamp: February 28, 2016, 05:58:35 pm
content: Quote from: Aodhan145 on February 28, 2016, 11:13:58 amNo it won't. Watch that video a few posts below. Ground resistance from a single point ground rod is non-linear with distance through 'earth'.The main point in their 'myth busting' is that round rods must never to be used INSTEAD of a real 'return ground' conductor (copper or alum.) to the voltage source (transformer on pole) or else service panel breakers will never trip on faults but still allow enough current to kill.

author: Ian.M
author_rank: Super Contributor
timestamp: February 28, 2016, 06:44:00 pm
content: Wrong. A TT earthing system is exactly that: Separate earth rods at the supply source and at the consumer with no earth conductor provided by the utility company. For safety, the earth loop resistance must always be low enough for the breaker to trip reliably and the maximum voltage rise at the consumer earth rod musn't be excessive if there is a fault current less than the tripping current.It is difficult and usually uneconomic to get the earth loop resistance low enough to reliably trip ordinary over-current breakers, so a TT system almost invariably requires RCD protection.Seehttp://electrical.theiet.org/wiring-matters/16/earthing-questions.cfm?type=pdf

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: February 28, 2016, 08:07:49 pm
content: There are other videos by Mike that go much more into depth.Basically, the distribution system is earthed to protect their (and your) equipment from transients that naturally occur where these transients want to get to the Earth.So we have two different meanings for "earth": protective earth (to trip RCD/GFCI for your safety) andsystemsearth (to protect your/their equipment as much as possible).Lightning hitting a telephone system outside your home will induce that high voltage into your phone line and it'll look for the lowest impedance and straightest path to the soil. That's what the ground rod is for - to get lightning to the earth with a little damage to you and your equipment.The entire earthing system is bonded to Neutral so that the current will travel through it and get back onto the Neutral and head back to the utility's transformer/generator.You only need as many ground rods to conform to local law; and these rod(s) should only connect to ONE point as demonstrated in other videos. Typically, this will be 25 Ohms contact resistance to the soil.Adding ground rods though can make your electrical supply DANGEROUS if your utility's system ISNOTgrounded because if there was a fault in your system where the electricity went to Earth and then the utility suffered the same fault, then the Earth would not be floating, it'd be in circuit. So check with your utility before even thinking about adding ground rods to the property.