ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades GFI tripping problem

Well, you're so nearly there now that I'll give you another chance to get it. Keep thinking "parallel paths," and don't forget that the GFI in question feeds the whole house.
P.S. Don't let the fact that the kettle was plugged into a ring circuit worry you too much. The fact that the outlets were wired on a ring was of little or no consequence to the fault.


[This message has been edited by pauluk (edited 09-22-2001).]

My next guess would be a crossed or somehow paralelled return or neutral. did some one combine the neutrals of more than one circuit?

You're very close with the parallel neutral idea, but the neutrals of different circuits hadn't been mixed up.

This wouldn't have tripped the main GFI anyway, as it's on the main intake ahead of the fuses and main neutral busbar.

Another hint:

The kitchen re-model hadn't involved the moving of outlets or the rerouting of cables in any way.

Continue to think "parallel paths," and go back to the screw/nail idea.

Is it possible to have nailed a nuetral and have whatever it's nailed to create a parrallel path, achieving the ma needed to trip the GFI under load ??

Did some one hit two dirrerent neutrals when installing a conductive cabinet or mounting an appliance to the wall?

Do you have a neutral to ground fault were the flow to the fault only breaks the 100 milliamp barrier when the neutral is heavily loaded and the voltage drop creates enough of a voltage difference to drive the leakage current beyond the trip point?
--
Tom

Well, between you all, you guys have just about cracked it, so at long last here's the conclusion to tonight's story....

I took the cover off the main panel and shut off the main GFI. Like all our main switches, this is double-pole, so it isolates the neutral from the incoming line. With my meter on the neutral and ground busbars (separate here remember!) I read almost a dead short. Pulling neutrals off the busbar one at time narrowed the short down to the ring circuit feeding the kitchen sockets.

My first thought then was a nail through a cable in one of the kitchen walls, espevcially as this hous belongs to a builder! I left an audible continuity tester connected at the panel and started pulling recepts off the wall, intending to disconnect the neutrals at strategic points to narrow down the location of the short.

At about the 2nd or 3rd outlet I unscrewed, however, the short disappeared as soon as I pulled it forward from the box (these are one piece outlet and faceplate combined - not separate).

Further examination revealed a cut in the insulation of the neutral where the wire was trapped between the side of the metal back box, the screw lug and one of the recept. mounting screws.

It turned out the sockets had been unscrewed and pulled forward to allow for decorating the walls, so it must have happened when someone was rather ham-fisted in screwing them back to their boxes.

Now if this were a PME system with the ground busbar bonded to the neutral, that parallel path would've tripped the GFI as soon as just a 60W light was turned on.

BUT.... The only ground return path here was via the local earth rod, which obviously had a much higher impedance than the solid neutral return.

So with a 3kW load, the parallel ground path was pulling less than 100mA. Any combination of appliances of around 5kW or so total resulted in more than 100mA flowing to the ground rod.

Paul,
great thread !
you had us thinking , mainly because those numbers would be different here..

I could tell you were all giving the old gray matter a good workout.....

I guess it takes some getting used to the different arrangement, especially having a ground system not bonded to neutral and the GFI feeding the whole house.