Mystery electrical problem

[RainbowLaura]

The other night I switched on my electric fire, and it made a loud bang and tripped the MCB. The same thing happened 11 or 12 months ago, but at that time a bulb inside it shattered so I simply replaced the bulb and all was fine until now. However this time, when I flipped the MCB back on everything was working perfectly and there was no obvious reason for the trip at all.

Yesterday I got an electrician in to PAT test the fire, which he said is absolutely fine. He then ran some tests on the sockets and has picked up some sort of fault - there is a low current detected even with all appliances unplugged, suggesting that two wires may be too close together and causing a short circuit? The mystery is why it isn't tripping the RCD (which was confirmed to be working) and why the MCB tripping seems to occur as a "one off" before everything works again.

The electrician is coming back in the new year to do the full electrical safety test, as that expired a few months ago. He did suggest it odd that the previous test, done by the previous owners of the house, only lasted 5 years and not the usual 10. He mentioned that perhaps some sort of problem was picked up then.

I am so worried that this will turn into a huge job with replastering and the like

Any ideas much appreciated! The house and electrical system are about 18 years old.

 

[Risteard]

There is no usual length of time for a periodic inspection to be valid. It depends on the condition of the installation.

 

[winston1]

A low current is not a short circuit. RCDs do not trip on low currents or short circuits, they trip on unbalance, typically caused by earth leakage.

How big was this “low current”? Do you have any hard wired appliances, a boiler perhaps or USB ports built into sockets?

 

[winston1]

Going back to the electric fire. Did the electrician open it up and inspect it? If not, why not and get a different electrician. I would suggest that the place where two wires are close together is inside it. They could well have blown apart with the “Big Bang”, so would not show up with a PA test. An internal inspection will show where the Big Bang was with carbon deposits and melted metal.

 

[Risteard]

A low current is not a short circuit. RCDs do not trip on low currents or short circuits, they trip on unbalance, typically caused by earth leakage.

How big was this “low current”? Do you have any hard wired appliances, a boiler perhaps or USB ports built into sockets?

The word is imbalance.

 

[chivers67]

Sounds like you have a low insulation problem somewhere

 

[RainbowLaura]

Thank you for the replies

To be honest a lot of what he said went over my head, and I may have misunderstood about the low current. He definitely mentioned short circuiting though, and said it had been picked up when he tested the socket. He made sure that all appliances on that circuit were fully disconnected, including the heating system and white goods in the kitchen. I don't think he did open up the fire though - perhaps me or my husband could have a look ourselves.

The RCD has never tripped - it was the MCB that went when the bang happened.

Could something like damp be the culprit? It has been very wet here over the last week (though much worse yesterday and we had no problems then).

Would a potential insulation problem be a difficult/costly fix chivers?

 

[chivers67]

Normally If it was a damp issue then it's more likely the RCD would trip, Though a damp issue could cause a low insulation reading and really depends where it is and what's causing it. It maybe something as simple as a piece of cable that's become damp whereby the insulation inside has broken down causing a short. It may have dried out a bit and now instead of a "dead short" causing the MCB to trip out it's now has a low insulation reading which if low enough could produce the scenarion you now have.

This is all guess work though.

 

[RainbowLaura]

I've just thought... I'm pretty certain we didn't switch the electric oven off at the mains while the testing was being done. Could that have made it look as though there was a fault when there wasn't? I so want the fire to be the cause of the problem (though do realise that wishing something won't make it true!!)
Given that he didn't look inside the fire I am still holding out a tiny bit of hope...

 

[sparkwright]

Something left plugged in could certainly give misleading test results.

You were worried about rewiring and plastering - please don't. An 18 year old house should not need rewiring.

 

[RainbowLaura]

Something left plugged in could certainly give misleading test results.

You were worried about rewiring and plastering - please don't. An 18 year old house should not need rewiring.

Thank you, that's reassuring. This is a really bad time for us financially and I have been feeling a bit sick about it all day. Especially if it's a damp problem as well and turns into a double job that runs well into thousands of pounds... I am a bit of a catastrophiser

 

[sparkwright]

There's a danger of getting so wrapped up in testing that so many theories and mistakes mutate into a major problem that doesn't even exist, there may well be nothing at all wrong.

Does the fire work fully? Has an element on it failed?

 

[RainbowLaura]

There's a danger of getting so wrapped up in testing that so many theories and mistakes mutate into a major problem that doesn't even exist, there may well be nothing at all wrong.

Does the fire work fully? Has an element on it failed?

The fire does work fully - as soon as I flipped the MCB back on after the bang and flash it came back on as though nothing had happened... someone else suggested to me that a bit of dust could even have caused it? I have stopped using the fire now though, even though our electrician said it would be fine since it passed the PAT test.

The provisional plan at the moment is to have the electrical safety test done in the new year which should pinpoint the problem, if it's there. Since it's out of date we had been thinking of having it done anyway. Does that sound sensible?

 

[sparkwright]

Yes, wouldn't hurt.

If your house is 18 years old, no doubt you will be recommended to have a new consumer unit.

It's likely to be plastic, not metal. And some circuits such as the lighting may not be RCD protected.

You may get pressurised into having a new consumer unit, when there's little advantage in doing so, other than being a little out of date with the current requirements.

 

[RainbowLaura]

Yes, wouldn't hurt.

If your house is 18 years old, no doubt you will be recommended to have a new consumer unit.

It's likely to be plastic, not metal. And some circuits such as the lighting may not be RCD protected.

You may get pressurised into having a new consumer unit, when there's little advantage in doing so, other than being a little out of date with the current requirements.

Thanks - that is exactly what the electrician said when he was explaining what the test and report would involve. He gave the consumer unit as an example of something that would be flagged up, but also said he personally wouldn't deem it necessary to replace. Will keep our fingers crossed that the results are generally not too troublesome!