How to isolate an earth leakage problem

[AndyD]

I did make an information thread about earth leakage tripping faults, it was aimed more at DIY'ers but it might be worth a read for ideas.

What actual tests have you done on the circuits and what were the results ie insulation (megger) tests of the final circuits and Ze (or Zdb) etc. Did you try an actual proper ramp test of the earth leakage? What loads is the earth leakage supplying?

[MullerR]

Hi Andy.

I Read your article about the Earth leakage tripping faults and I think I still have a lot to learn. The Information is of much help to me. Unfortunately I have not done any tests like the Insulation resistance and ramp test as I did not have my testers with me, We were visiting the people and the only tester I had was my multimeter and ELCB/polarity tester. Thanx for the info on the testers as well, when I did my trade, testers like the Ramp tester and earth leakage clamp tester were not mentioned to us as important to have testers, but thanx to you I will have to buy me.

The house is quite old and there is not much electronics in the house, or shall I Say not more than there were in the past, just the normal, freezers(2), deep freeze, Microwave, TV, Decoder, PC... The installation also is old and the earth leakage feeds all the circuits (Plugs, Lights, Stove and geyser). I believe I will be visiting again during this month, but the main thing that buggers me is the fact that it dont even want to trip when tested with a ELCB tester, but the RCD in the Kitchen that is in the ready board trips when tested as well as the one in the garage.

[Dave A]

but the main thing that buggers me is the fact that it dont even want to trip when tested with a ELCB tester

Assuming you've used a plug socket tester which didn't show any faults on the socket outlet, I've heard of loose terminal connections causing this sort of problem.

[Sparks]

Being an old installation there is possibly bad earth continuity in the house, quite probably a floating earth which will still light the lamp of the polarity tester. Also confirm that the socket outlet you are testing actually has ELCB protection. It could be a new circuit added in with the neutral connected to the top of the ELCB.

[AndyD]

L-N reversal through the earth leakage could cause it possibly not to trip if there was no load current through it during testing plus it could make it not trip on the test button. Also I've come across weird intermittent ''not tripping'' issues with RCD's which have the supply and the load side of them wired the wrong way around.

My favorite one is that in theory a small low insulation fault N-E on one of the circuits being supplied could also cause the test button not to work but the earth leakage unit itself could still be fine. I've yet to come across this in real life but it could certainly cause some headscratching if it ever did occur .

It's all guesswork until you do the usual tests when you next visit.

[MullerR]

Thanx guys. With my next visit i will be doing some tests and make sure to get behind this problem.

[ACEsterhuizen]

When would a fault before, (upstream) of the E/L device cause the E/L to trip? Meaning there is no fault under the E/L (L & N disconnected at E/L terminals load side). Ramp test clear on E/L 27Ma @40Ms. TN-C-S supply.

[AndyD]

When would a fault before, (upstream) of the E/L device cause the E/L to trip? Meaning there is no fault under the E/L (L & N disconnected at E/L terminals load side). Ramp test clear on E/L 27Ma @40Ms. TN-C-S supply.

I see you treated yourself to a ramp tester, I'm jealous, I haven't bought any new testers for several months now .

How often is it tripping? Is it regular as clockwork or is it random?

It's not one of the old types of RCD as per pic below that has an earth reference wire on it by any chance? If it is there could be a slim chance that an earthing fault on the supply side could present parallel paths that could cause a fault in a neighboring property to cause the RCD to trip.



I've only ever once experienced an external problem causing RCD nuisance tripping and it was an RCD that tripped almost every evening when the streetlight outside the house switched on. I can't for the life of me remember what make it was but I replaced the RCD with an identical new one and it also did the same. After another replacement of a different make it stopped happening. I did some power quality monitoring at the supply and couldn't see any evidence of transients that would point to arcing when the streetlight switched on so eventually decided it was a harmonics issue with that particular brand of RCD but I could never prove it.

I've heard hearsay of poor connections/arcing on the council supply side causing RCD's to trip as well so maybe check the Ze and the neutral-earth voltage of the supply.

[ACEsterhuizen]

Thanks Andy. New SABS approved Schenker SP E/L with L N only no earth. (tried 2 new ones). Total random intermittent tripping. Ze (external impedance all ok when tested (0.17Ω).

You were spot on. Poor connection & arcing N/E on council supply in street feeding to house. Municipality came out open their street box and the N/E was arcing, burning, loose connection, hanging on a thread. Fixed it, all OK, 8 hrs no tripping.

But why? i don't understand why a fault before the E/L would cause it to trip.


Yes i am

[AndyD]

TBH I'm not sure why it would cause an RCD to trip, there's no current imbalance on the load side which is the criteria for tripping. I'd guess it's an anomaly with the internal electronics maybe.

How's the tripping fault, is it still holding?

[Justloadit]

TBH I'm not sure why it would cause an RCD to trip, there's no current imbalance on the load side which is the criteria for tripping. I'd guess it's an anomaly with the internal electronics maybe.

I think it has to do with reflected current flows in the E/N wires. All circuits connected to the council point on the E/N circuits are connected in parallel to all the different loads, however when there is a break on the council side supply line, as is the case described by ACEsterhuizen, and because of high current flows and inductance in these circuits, a pulse is injected into the neutral line towards the load side. THE RCD , by nature of its design, is to trip when there is an imbalance in the currents in the L and N circuits. When this pulse comes down the line, there is a mismatch between the L and N, and the RCD can not differentiate where the imbalance is coming from, source or load, and the mechanism then trips.

[ACEsterhuizen]

Hi Andy yes all is ok now thanks. and thank Justloadit I almost understand that.

[Justloadit]

The pulse I am referring to is called EMF.
Its the shock you get when you touch the coil contacts of a 12V relay, and disconnect the power to the coil, you feel a jolt. What happens is the inductance of the coil, because of the turns, causes a reverse voltage of several magnitudes greater then the supply in the opposite direction of the supply for a short duration of time. This is better seen when a relay contact breaks the current connection in a loaded circuit, and you see the spark across the contact points. This pulse is generated by the decaying magnetic field due to the loss of power, and depending on the current can be several hundreds of volts, in the case of a high voltage electrical system. The pulse in your application is propagated down the line through the ELB and discharges in the load Neutral to the earth of the equipment. The reason there is a flow of electricity is due to a capacitance between any 2 metals, the dielectric could be air, PVC or some other insulator.

This capacitance effect is noted when running long wires side by side, and one wire is connected to N and the other is through a switch to L. When you place the multi-meter across the open switch wire, you get a reading of 100+ volts. This voltage is flowing between your meter high impedance input, and the capacitance caused by the wire PVC. This is also known as floating voltage.

[LloydJ]

I've tried all this but ALL my plug circuits aren't working even though ALL breakers are up. Please help??

[AndyD]

If all your circuit breakers are in the up position and there's no power at your sockets then it's not an earth leakage tripping problem. Possible a poor connection somewhere or even a faulty breaker but either way you'll need to get a sparky in woh has the test equipment to find the problem.