Unexplained Tripping...and next door?

[steamboatwilly]

Folks,

Called out to a semi-detatched rental property today...TT, semi-enclosed wired fuse board, 4-way with a 500mA Earth Leakage Voltage main switch (60a). The customer has removed the 5a lighting fuse because the EL switch trips after between 30 seconds and 15-20 minutes. There's a suspicion that when this trips it also takes out next door too (not in so can't check what they have).

Western Power have been out and checked the supply side (so I'm informed). Not sure what they've checked.

- Visually checked, no obvious faults on the lighting circuit
- Checked the usual ceiling roses, etc
- Bonding is good
- Ze is 18.4 Ohms (pretty good eh?)
- A couple of the rooms have mains voltage halogens/LEDs and dining room has a set of LV downlights
- Adding the fuse and switching all circuits on/off does not produce a trip
- Property's earth rod is under an extension floor but measures well. It's probably about 7-8m away from next door's rod (which looks fairly new)

I've suggested we change the EL switch to a proper main switch and 30mA RCD anyway. Would be a completely new 6 way board but budget is restricted. When I go back I'll do the usual IR but I figure this isn't a simple fault...what could cause a delayed action trip?

Ideas appreciated!

 

[Richard Burns]

If you have a voltage operated earth leakage circuit breaker then this is likely to be old and could be faulty so this may be the first port of call.
Delayed faults may be caused by the heating of the light fittings by the lamp causing the earth fault, once the lights are off then the fault clears and depending on how hot the fitting is depends on the repeat time of the fault.
IR the lighting circuit would be the second port of call. However you need to find out why they think it is the lighting circuit if turning the lights on does not cause tripping.
I would not change a 500mA VOELCB to a 30mA RCD unless this is unavoidable because you are maintaining the non segregation of circuits and making it worse in terms of this compliance (whilst making it safer from the electric shock point of view (assuming there are no 30mA RCDs in place already)). A 100mA time delay RCD would be better as a main switch although it may need additional protection on some circuits.

 

[steamboatwilly]

Thanks RB....I did think perhaps heat building up and causing a trip over time...but it tripped today after 15 minutes with no lights turned on anywhere! Customer is sure it *always* trips (eventually) when the fuse is in, and *never* does when it's out. That's the only real evidence, to be fair.

Agree, IR tests would be helpful. There are no RCDs anywhere in the property...a board change is beyond budget alas. I'm beginning to think that the existing EL breaker might be faulty.

 

[Richard Burns]

It would also depend on whether the light switches were on or not to determine the fault location, but if there was a slight fault on the lighting circuit (presumably line to earth or the fuse removal would not work) generating a say 40V potential on the earth, then as current flows through the VOELCB it may itself warm up and / or change its characteristics enough to allow it to trip, or there may be slight surges in the supply enough to just push it over.

 

[steamboatwilly]

It would also depend on whether the light switches were on or not to determine the fault location, but if there was a slight fault on the lighting circuit (presumably line to earth or the fuse removal would not work) generating a say 40V potential on the earth, then as current flows through the VOELCB it may itself warm up and / or change its characteristics enough to allow it to trip, or there may be slight surges in the supply enough to just push it over.

Ermmmm, yes, fair point. Thanks.