Since 1993 I spend all my holidays on a small farm in upper Austria. 230/400V 3-ph service, local ground rod, neutral and ground seperate. Panel about 20 years old, completely makeshift. Contains a 100mA 4 pole main GFI.Several single and 3 pole breakers. (btw I don't believe the single poles were allowed back then, but I guess double poles fusing the neutral wouldn't have fitted the already very cramped panel) One of the 3 poles feeding A small gas station, the 2nd feeding the electric range, the 3rd feeding a detached garden house several hundred feet away, fed via UF. Then some 13A breakers feeding lights and receptacles. No neutral busbar, some neutrals put directly under the load terminals of the GFI, most of them together in 2 giant block connectors. Three hot busbars (combs) feeding the various breakers. A complete mess of wires. Blue wires, grey wires, brown wires, black wires, violet wires,... all connected to the breakers. The entire panel has a wooden frame and a grounded metal cover which is only about 1 cm (3/8") away from the hot busbar.
Last year we had some heavy rain and around 11.15 pm the GFI tripped. First guess was lightning, which happens frequently out there. When we tried to reset the GFI it tripped again. So we pulled every plug and tried to reset the GFI. It tripped again. I got furious and threw every breaker. Now the GFI would reset. Then I reset the breakers one by one. When I came to the one for the garden house the GFI tripped. I left it off, reset the breaker and started to put back the plugs. When we hooked up the freezer the GFI tripped again. We didn't want to have the contents of the freezer to decay, so we put some rubber mats from a car under the feet of the freezer to avoid any ground path. Then we told everyone not to touch the freezer. The next day it was sunny and warm. When the electrician came and meggered everything he found... nothing. We pulled the mats out and everything worked. This summer we came back and were told that over the year nothing had happened. I was already a little sceptic, because the kitchen had been remodeled in the meantime. And one day I woke up because one of my brothers and the farmer rushed into my room pulling all plugs. Not hard to guess what had happened. Now there appeared to be two faulty circuits. The one for the garden house and the 1ph circuit feeding lights and receptacles in the kitchen and two bedrooms. After some minutes the Gfi could be reset but would trip again without any apparent reason. Additionally each time we plugged in the freezer it would trip again. When my mom switched on the electric range (2 weeks old) it would also trip the GFI. Hmmmmm. I took off the panel cover and looked around. Sure a mess. Lotsa wires that were stripped too long, two or three wires under one breaker terminal, let alone the ground busbar. But still, no visible reason for the GFI tripping. Now have a nice time.
I've found main GFIs to be a problem precisely because it can be so difficult to track down the fault sometimes.
It sounds as though it could have been a combination of leakage in various places due to the rain getting in. You can find that each circuit turned on individually, or maybe a combination of two or more circuits doesn't cause the GFI to trip, but turn them all on and the combined leakage exceeds the trip threshold.
The part about putting the freezer up on rubber mats stopping the GFI from tripping sounds curious, almost as if the freezer casing wasn't properly grounded.
[This message has been edited by pauluk (edited 08-05-2002).]
This was what we also thought. But when the electrician came he meggered everything at the panel for Hot-ground shorts and found absolutely nothing. Also the freezer was in perfect shape (no hot-ground/neutral-ground/hot-case/neutral-case connections). Also it didn't matter what load we switched on. Was it the freezer, the brand new electric range or anything else, even with the other breakers turned off the GFI tripped. Keep in mind the neutrals weren't fused!
Apparent random tripping of the GFI when different appliances are turned on usually happens when there's a neutral-to-ground fault somewhere. It trips as soon as the load is high enough for the small portion of current that's bypassing the GFI to exceed trip threshold.
But that wouldn't explain how insulating the freezer from the floor stopped the breaker from tripping, unless there was leakage from a cable neutral to the freezer casing when it was standing on the floor.
Pauluk, you got it! When the elctrician came again this summer he didn't fumble around long but took the neutral of the garden hut out of its lug and everything worked perfect since. Each time he tried to reconnect the neutral for determination purposes the GFI tripped immediately. Afterwards we figured out that the resistance of the long neutral run from panel to transformer was high enough to have some power flowing back in the neutral to the garden house. Up there they must've had a neutral to ground and maybe also a hot to ground fault (the tripping reduced when we threw the breaker). Concerning the freezer I can only guess that this was because it had almost stopped raining when we did this and so when we got the mats installed everything had dried up enough to work.
Yes, I have come across problems like this before, normally, with our RCD's (GFCI's),we work on a residual current of 30mA and in hospitals and the like, the residual current is required to be 10mA. But the point is you can have a problem with inter-connected neutrals at the main or sub-switchboard and they take a long time to work out.
Ragnar, I thought I'd bring this oldie up again, since I had a similar thing happen to me last week. And also, because of the fact that I've since learned that it doesn't pay to have a refrigeration unit on an RCD. This is because of the leakage currents caused by the Compressor in the fridge. Fridges and the like are always excluded from RCD protection here.
One of the problems here is that in installations employing the TT earthing system you can't avoid having everything RCD-protected.
It we must use this strange system, it would be helpful if panels were installed with at least two separate RCDs so that the whole house doesn't lose power when one trips. I've seen that done in some newer places, but most TT-system houses in this areas still have just a single RCD feeding everything.