Electrical Shock From Appliances

Thanks Del for you response Actually I did not feel a shock or any of my stuff. But one of the tenants has complaint that he is feeling electrical shock when he touches his electrical appliances. I checked with 3 nos of digital multimeter. All giving the same. And today I have connected the neutral of standby generator to earth, isolated the building from the substation. and still same issue is there. what is confusing me more is same problem in 8 buildings. On your advice I will try analogue meter and come back to you Thanks again

if tenant has complaint that he is getting shock from appliances, then it may be due to that of static charges.

Hi Del, I have used analogue meter, I got 28 volt, on the same test I got 64 volt using the digital multimeter

I'd have expected less than that, but then I'm into electronics rather than electrical... maybe someone else can comment.
Del

Thanks Del,, your answer was useful to me.

It is also very possible that there exist some defective appliances, meaning, appliances that are giving off very high leakage current, being connected to the electrical system using only a non-polarized 2-prong power plug! The above is a very dangerous combination that must be corrected!

It sound like you have a high resistance on the neutral / earth. You must call in the supply company. I have come across this problem before it was traced to a burnt connection on the N/E and as you say it gave a floating neutral.

thanks Tony, but I don't think so because I have completely isolated one of the buildings from the supply company s/s. and run the standby generator and still have the same issue. noting that I have grounded the generator neutral and earth resistance is 0.5 ohm

You say you "grounded the generator neutral" Are your automatic transfer switches 3 pole or 4 pole? If 3 pole you've done wrong. If 4 pole you are ok.

Are the neutral bars and equipment ground bars in distribution panelboards seperated everywhere but at the main service disconnect?

Re-grounding the neutral will divide normal neutral currents between the now parallel neutral and equipment ground conductors.

What is the ground like where the earth rods are? You can have high resistance between the neutral grounding rod and the building earth. Sorry I'm clutching at straws now. Urea around the top of the earth rods will lower the resistance.

I have 2 earth pits 6 meter apart, each contains a 3 meter rod connected to the main panel board, and one pit for generator grounding. all of them around the building. the soil is sandy and its less than 30 meters away from the sea. Thats why I am getting low resistance for building earth. So I don't think that a high resistance between the neutral grounding and the building grounding is there. specially if you know that in soil, if you put any 2 meter rod in the ground you will get less than one ohm resistance with any treatment to the soil Regards

Re: specially if you know that in soil, if you put any 2 meter rod in the ground you will get less than one ohm resistance with any treatment to the soil

Don't count on that. I've been involved with installing ground fields in West Virginia mountains (for coal mines), and we've had a great deal of difficulty (sometimes) getting a low resistance to ground. I think it happens if we're in a very rocky area but find a pocket of soil to drive a ground rod--I suspect the pocket of soil is completely surrounded by rock.

(We've then done various things to get a low ground resistance, including burying lots of steel scrap all bonded together.)

I may be grasping at straws also, but if your neutral/earth connections seem good at the vicinity of the main panel, there might be missing or loose connections elsewhere in the wiring that are causing a floating neutral. Alas, these can be a bear to track down. If you measure phase-to-neutral voltages in various places, you might find some imbalances that may help to track things down. Good luck in resolving this.

You have problems with the power supply, you need a neutral line referenced with the earth terminal at the subestation outside your home, you need in your home joint the earth terminal with the neutral line and measured between phases and neutral line how many volts you get, it will be same in any place of the home.

Just guessing in that I don't really know your power system. However, if the star (or in a single phase 120/240v system the transformer center tap) is not connected to the neutral of the building then plugging in single phase 120 v appliances causes a high impedance corner grounding of the system. You can see some pretty wierd effects with this, including overvoltage on a phase.

There can also be some interesting results if the earth accidently is used as a return or neutral. It can lift the ground wires above the building potential. This effect can also happen with short circuits in the system, and has been known to cause shock when someone touches a "grounded" appliance and building metal such as pipes or other plumbing.

Personally I would try isolating (all) circuits and applying test loads at the incoming panel to make sure you are even controled at that point.

The system we have here is British system, and we have delta- Y three phase transformers , 11,000 volt/400 volt. So the line voltage is 400 and the phase voltage is 230V. All voltages measurements are giving the correct readings, 230 volt each phase to neutral, 400 volt line to neutral. and zero volt between earth to neutral. All phases to earth voltage is 230V. The surprise I got yesterday: I have done the same exercise in other 3 building in the country far away from my project and I found the same issue. One more thing you should consider is that I have linked the earth and neutral in main panel but still getting the same problem. Thank you ALL

In the sentence: "All voltages measurements are giving the correct readings, 230 volt each phase to neutral, 400 volt line to neutral. and zero volt between earth to neutral. All phases to earth voltage is 230V", I think you mean "400 volt line to line" instead of "400 volt line to neutral".

yes, its typing error... thanks for the correction

'A HIGH VOLTAGE CAN BE MEASURED BETWEEN THE EQUIPMENT BODY AND THE EARTH TERMINAL' what do you mean by that? the equipment is not 3-three wire (phase-neutral-earth) connected to the building power socket? If NO, do connect it so, and this apparent voltage disappears . If YES, then you have earth discontinuity somewhere in your wiring, find it and the problem disappears. As to the cause of residual voltage to the body of the equipment (for the No case), it is very simple, leakage from various insulations, leakage current from filter EMI capacitors, all sorts. The matter of 'earthing or not earthing' of Neutral of Main Utility transformer is a totally different issue and irrelevant to the cause of this problem, if i understood well your description of it.

Just for your knowledge, imagine on ships where the neutral MUST be floating for safety purposes. Does this create any problems? Of course NOT.

In any case i agree with all guys stating 'faulse' measurements with DMMs, because of their Hi input impedance (>10MΩ), compared to Analogue meters (usually 10-20KΩ/V AC-DC), so 'loading' the measurement figure. And keep in mind the figures, deadly electric shock when current >20mA, stong shock, but not lethal, >1-5mA (where leakage relays operate usually), and good feeling of it at <1 mA. But beware all of these figure relate to average dry human body, if you are wet, lets say in the bath, and the skin resistance collapses due to humidity, you go 'away' with even 24V.

So along the above lines you can logically locate your 'problem' and deside if its a problem or not. Simple mathematics and calculations.

Good luck an good morning.

Hi, yannissou, Good morning to you too. Dear I have both types of appliances, wired with 2-wires and 3-wires. when I plug them to power socket. The 3-wires appliance have no problem. The problem in the appliances with 2-wires which comes from manufacturer with 2-pin plug. I measure a AC voltage between the body of this appliances and the earth terminal of the socket or even to the gi trunking which is connected to the building earth. the voltage varies from one equipment to another. in the TV receiver I am getting 55 to 60 volt when using DMM and 28 volt if I use analogue meter. I touch these equipments my self and I feel nothing. I even went farther more by connecting a lamp between the body of appliance and the earth terminal and nothing will happen.main lamp will not flash or light up. If I connect the body to earth terminal through external wire, I measure zero volt this mains the earth is healthy.

Ok, so you have no problem, and you cannot realise it !!! What you measured in the first place was totally NORMAL and expectable.

A correct question could be: why some of the equipment come with 2-wire connections while others come in three wire connections.

The answer : equipment with NO exposed metal parts CAN come with only two wire connections, like all plastic covered handtools, etc. Exception : some equipment WITH exposed metal parts do get license for two-wire connection provided they have a grounding connection somewhere on their metal body to be connected to ground 'at will', like HiFi audio equipment, DVD's, etc These equipment you can ground them for FULL SAFETY, because there is always a chance internally an insulated item to short to body.

Now to your remark that you feel no-shock by touching the metal body with one hand and the ground with the other. This I would not usually do, because a/i love the sunshine of my country, Athens, Greece, b/ i love my wife, c/my children, my life...and i prefer to see all that horizontally and not vertically from above Hi-up.... However it confirms that the leakage current normally is very-very low so you cannot feel any electric shock (remember the electric shock comes from the current through your body, not the voltage across it, as you are not an insulator), but if you try to do the same thing (which i strongly dont advise you to do, but only measure it with equipment instead) with wet hands, i am sure you will tell me a different story.

So, to end this matter, ground the equipment whenever possible, instruct other people to do the same, dont mess with grounding the NEUTRAL of the Utility line, especially if you are near sea-side (remember the ship case i mentioned before), if i was in your shoes i would keep it floating, its a lot safer.

Hi Yannissou, good morning. Thanks again and again. and I wish you a happy long life with you beloved ones. " This I would not usually do, because a/i love the sunshine of my country, Athens, Greece, b/ i love my wife, c/my children, my life...and i prefer to see all that horizontally and not vertically from above Hi-up" This was very good,full of fun statement which made me laugh. back to the issue, So you think measuring a 60 volt on the 2-wire equipments is normal. and this voltage is just like spurious voltage. After all tests I have done I think this is it. But how to convince the client of the project who is a billionaire with no electrical back ground.

Hi again, Good evening,

Now then, I read LAALucke made a remark about reversing the 'polarity' of the plug as supposed to the connection of phase and neutral. This could probably work in very old equipment but i doubt it for modern ones. You see the problem is with the extra EMI filtering requested by CE regulations, and as you know a capacitor at AC behaves as 'resistor' in simple words. So we are left with your billionaire...

Ok two ways to go around it,

a/...by connecting to all of them an earth terminal connection at the back of the each equipment to take away this residual current (because its a current, that creates voltage through the 'distributed' resistance-reactance). Alternatively to change the supply cable to a three wire one to all in-question equipment.

b/...take the billionaire for a coffee, explain to him that it is not you, writing the specs of equipment 'circulation' in the market, and plug the same equipment to any power socket he suggests, anywhere in the country (placing a good bet with him in advance, he 'has' enough, or even to any city of your country or of the world, he certainly has a helicopter too, enjoy the ride...) to measure the same voltage from the exposed metal to ground.

And if he opts for b/ tell us to be happy for you.

You are right about old and new equipment regarding the 2 pin polarity.... But I can assure you that there are still some new equipment exhibiting this kind of fault even though it does not always appear to be noticed unless it is checked. The degree of leakage also varies from one to the other, depending on the maker and the origin of the equipment, as well as quality control (batch?). Therefore, better eliminate the case by checking it at the site when the problem seems acute or noticeable.

Thanks

Good morning Yannissou, Thanks again I have sent a report to client in which I quoted some of your posts hoping it will convince him. Unfortunately the client dos not have helicopter, he has 2 private airplanes, but he will not meet a guy in my position and have a cop of coffee with. Regards

On the 2 wire appliances, try re-pluging them with the pins changed (turn the plug to change the pins position).

Some appliances have one of the wires used as neutral (in the mind of the designer) and is used to connect to the body, as ground plane through some filtering circuit.

By changing the pins round, you might get the supposed to be Neutral connected to the actual mains neutral and the problem might disappear. Then Mark the positions for future replugging. (Or correct the internals.... but that is another thing that requires qualified personnel ...).

Hi, LAA Lucke, Thanks for the response. I have tried what you suggested, but it did not work well.

I once had an issue where a faulty circulator pump in a buildings heating system , combined with a "ground" strap that had been tied to a HOT water pipe by a cable TV installer, caused aprox. 90VAC to be introduced onto the SHIELD of the coaxial cable, which THEN fed back through the ground connections of the TV and entered the rest of the electrical system through THAT path.

I turned off ALL the circuit breakers EXCEPT for the heating system , and was STILL able to measure 90VAC on most outlets in the house. Turning off the heater system breaker caused the voltage to go away.

Replaceing the bad pump , and moveing the improperly conected cable ground fixed the problem.

I am NOT saying that this is your problem , I'm just telling you about it as a cautionary story and maybe help you to think outside the box as far as tracking down your problem.

Hope this helps

One thing that could be causing it is spider web wiring,the electrician did not keep the wires together in a bundle and some thing heavy is laying across and crushing one of the strands. Or maybe not.

In the U.S., there are receptacle testers with LEDs that you can plug in to outlets to determine if the wiring is correct. (Ungrounded to ungrounded, grounded neutral to grounded neutral, and frame grounding to frame grounding.) Your local plug layout and terminology may differ from this, but maybe a similar device is available.

Hi guys, Thanks to all of you you for your help and the information you gave to me. I think there is nothing wrong with the installations after all the test i have conducted. I have measured the same voltage in my home. and in other 5 buildings in the country plus the 8 buildings I have in the project. So I dont think that the same mistake have been repeated every where. I think its useful top check in you homes as will to see if this problem is national only or is it international Regards to every body here

Another ongoing (long and guessing) thread that could have been resolved IF the OP had provided from the get-go more information.

Brings me to mind that CR4 to allow anyone for log on should require a country. With arenas like this it makes a difference! The electical differs as we know worldwide. In this thread, the OP seems as not ever provided however asked, for his locale. He provided something inane. He knew what was being requested.

Thanks Bill, No more comments

Salehmelhem

Your supply system is ungrounded system. You link your earth system to your neutral, it is like saying that your earth has a potential difference like that of your neutral. In this connection, there will be no problem on the line to line, line to neutral, and neutral to earth voltages. You will get the correct voltages. However, voltage will be present in the earth wire to equipment body in a 2 wire appliance because you measuring drop of voltage from neutral to body. Not with 3 wire (line-neutral-earth) appliance. If you touch the body, shock will not be felt. One wire in the plug cable is bonded to the appliance body, so if you measure as if you are measuring earth to earth.

To make your system function normally, remove all links connecting the neutral and the earth from your DB, LV panels, and any point in your system.

______________________________

"Iron sharpens Iron"

Dear Salehmelhem,

You may check the following :

1)Ensure that transformer/ Generator neutral is effectively earth ( less than or equal to one Ohm ) and connected effectively and firmly at the neutral bus of the Main Distribution Panel.

2)The Three Phase, Four wire system should be balanced as far as possible

3)Ensure that neutral wire and earth connections are to be continuos, without high resistance joints.

4) You may install ELCB/ RCD to trip the electricity supply in case of high leakage current.

5)All metal enclousure of electrical appliances are to be effectively earth to avoid electrical shock for human safety.

Thanks.