Neutral leaking 220V to Earth

[Etienne Swanepoel]

Hi

I've recently been doing contracting work for a factory, mostly upgrading and alterations to the electrical system of the factory, in order to meet with compliance for the COC's. While I'm busy doing that the customer requested from me to go and check a problem they're experiencing in their packaging area (which I was still yet to start fixing in the near future).

They've reported to me that when they use their single phase 220V vacuum sealing and normal sealing machines, that the power lights dim out on their machine, as soon as they start using the sealing elements. I took the machines to a different location, in the factory, and they work 100%.

I've started looking at the plug socket's and the DB itself for loose connections etc. And find nothing wrong, when doing standard voltage + resistance tests. I've also went and fetched anything that could use (eg a heat gun with different heat settings), started plugging it in a different socket outlets. The heat gun works fine under normal circumstances (as tested at the workshop). I plug it in and use the different heat settings. The first two only blows the fan, but you cant feel any heat coming out. The third and fourth settings plainly doesn't go on at all.

Ive plugged in my tester, and asked somebody just to operate the heat gun, I've found that the single phase live 220V to ground goes dead (0V) and the neutral to ground 220V. Switching off the heat gun shows again the normal readings live to neutral is 220V, live to ground 220V, and the neutral to ground (earth) 19V.

I got two questions, does the elevated neutral to earth voltage seem too high (I tested the upstream DB, found that the Neutral - Earth is 110mV)? And then did anybody experience this as yet?

[AndyD]

Yes, the N-E voltage is too high, it's 220v under load which is way too high, even 19v is too high!!!

Just be careful with what tester you use though, many digital testers can give confusing readings because of their high input resistance makng them super-sensitive to 'ghost', 'stray' or coupled voltages but this is often more of an issue with dead tests so it could go some way to explaining the 19v you see with no load connected. See here for more info.

If the neutral voltage with respect to earth is rising when the circuit is under load it's almost certain the neutral is high resistance somewhere in the circuit. Most likely cause is a poor or burned connection or termination. The other possibility is the the CPC is rising in voltage WRT true earth and the neutral is staying at 0V, this is an even worse case scenario and could injure or even kill someone who comes into contact with the chassis or anything connected to the earth wire. Either way this is a fault you're going to have to localise and repair and the circuit in question is hazardous and should be isolated and locked out until remedial work is complete. A loop impedance tester would be the weapon of choice rather than a heat gun and a volt meter.

[ians]

The fact that live to earth goes to 0 volts indicates the earth is broken or disconnected in the circuit or incorrectly wired. Take an earth leakage plug tester and plug it into the socket and check if all 3 lights come on then try trip the earth leakage unit. Chances are the plug tester will show you were in the circuit the problem is.

[Etienne Swanepoel]

Ok I've located the problems (and quite a lot of them). I've located a connection box, on top a cable racking system on the way from the sub station, to the particular DB in question. The neutral connection done there was crimped, but not properly. Rectified the problem.

I've took out all the connected loads, out of all the plugs located in the area, switched off all the breakers, EL's and the main breaker, done a insulation test, found a few dead shorts, some by incorrect cable cleaning methods, and some by poor connections on top on the rooftop. I've even had to remove an entire circuit (cable and all), of all the damage done, because of people used that are not even qualified electricians. I have to replace the entire cable, plugs etc on that line, but that is a story for another day.

I've even found one Earth Leakge by itself, getting a reading of 0,3 meg ohm tested on 500V, between live and neutral, without cables on it, and in switched off position. Replaced that one.

When done with all that, I've checked the system again, everything tested now was correct. Also that loose main neutral, test now correctly to earth, as from the main sub station.

Strange how incorrectly done bonding of cables, can make a electrician's life so difficult. Especially on a neutral line.

It is as AndyD stated, this could have been a hazardous situation, which no one was even aware off, but as with most of normal production factories in South Africa, companies tend to place safety dead last, and production first. Using correct and qualified electricians instead of normal assistants working in the factory, would make all our lives a lot easier.

Thanks for the info.

[AndyD]

Glad you got it sorted out, the circuit was undoubtedly a hazard. Most of the time with these types of faults you just need to follow the entire circuit and a visual inspection of all terminations will reveal the problem although it's sometimes logistically easier said than done though in a working factory environment.

[Reginald]

The fact that live to earth goes to 0 volts indicates the earth is broken or disconnected in the circuit or incorrectly wired. Take an earth leakage plug tester and plug it into the socket and check if all 3 lights come on then try trip the earth leakage unit. Chances are the plug tester will show you were in the circuit the problem is.

I think that's what I would have done first before resorting to earth loop impedance tester. Either way both should lead to an idea of what seems to be F*** Up.

[BlueArc]

Needing some help with a very strange problem. Using a 220V single phase spinning disc KWH meter I measure 220V N-E with the load on (NOT A GOOD THING).
Load Off 0V N-E. Change KWH meter to a DIGITAL KWH meter and measure 0V N-E with load - Fixed! However when I change back to a NEW spinning disc KWH meter the problem re-occurrs. Can anyone explain why the spinning disc "creates" this problem. I have done an insulation resistance test which comes up clean. All the connections are tight and free of debris. No joints in the SWA cable. Really confusing...

[Justloadit]

Maybe I am going to ask a few stupid questions.
Where did you do the voltage measurement, before or after the meter?
What was the reading between Live and Earth, with reference to the Neutral earth measurement?
It could be the instrument is incorrectly labelled on the output side or the input side (take your pick), so Neutral is where live is and Live is where Neutral is.

[DieterT]

Possibly the star point on transformer that is not properly earth or earth been stolen that supplies the factory.
Do an earth loop impedance test at your main DB and see if he earth resistance is above 1.92ohm
If you find the resistance to be to high, then bridge out the neutral and earth at the supplier meter box.
Should elevated voltage on neutral exceed 25v then inform the supplier, should it exceed 50v then disconnect the installation and inform the supplier

[Dave A]

If you find the resistance to be to high, then bridge out the neutral and earth at the supplier meter box.

I get the distinct sense that is advice that needs some rather long "subject to" clauses.

[DieterT]

I get the distinct sense that is advice that needs some rather long "subject to" clauses.

Subject to SANS10142-1
Can only be done on the supplier side and not on the consumer side.
Remember,depending what tipe supply (TNC/TNC-S) your neutral & earth point is connected on the star point of the transformer.

So either the neutral is split into a neutral and earth at meter box feeding consumer board or it is split from the star point of the transformer.

When such a bridging of your neutral to earth has been done it has to be clearly indicated (labeled)
It can be easly tested with a loop tester which in turn will show a high resistance (above 1.92ohm)

If this does not rectify the high resistance then an annexture K form should be filled in and handed to supplier to notify them of potential danger

This information supplied was aimed at the post from Ettiene Swanepoel about the 220v on neutral. Also another reason why a neutral will have 220v on is due to a loose live connection.

Voltage on between incomming neutral and earth is allowed up to 25v touch voltage.

NB : All this information on rectifications are only allowed to be done by an regristered electrician or a person being supervised by an regristered electrician.

[BlueArc]

thanks for the advice chaps. After speaking to the client he informed me that they had a burnt neutral a while back that the council repaired. Unfortunately they didn't do a very good job and did not tighten the connections. All is fixed up and working just great. What still bugs me is the difference between the digital and "old school" spinning disc KWH meters. Anyway like my mom used to say "if it ain't broke don't try and fix it" thanks again for the advice it is greatly appreciated.

[DieterT]

thanks for the advice chaps. After speaking to the client he informed me that they had a burnt neutral a while back that the council repaired. Unfortunately they didn't do a very good job and did not tighten the connections. All is fixed up and working just great. What still bugs me is the difference between the digital and "old school" spinning disc KWH meters. Anyway like my mom used to say "if it ain't broke don't try and fix it" thanks again for the advice it is greatly appreciated.

BlueArc, it is possible that the mechanical meter is doing this as the meter itself has a coil inside and therefor partially a resistance and not like the electronic meter that uses CTs or in the case where it carries the load it uses a contactor inside. I stand under correction thou.

PS : As per council inspector "always after the council have connected and re-energized the supply,check and make sure it is done right"
Reason he said this to me, is because we where ahead on a project and I said to him that everything is already connected and ready for power to be switched on. He informed me that the guys they use to connect and switch on has only been "trained" to do just that and that they aren't electricians. It is possible that they could switch L & N around... Much sadness...