Tripping electrics

[deadshort]

Thanks. I would be switching the MCB off

DS

 

[John D v2.0]

If it's RCD or MCB it must be a live/earth fault. Live/neutral would only trip the MCB and neutral/earth would only trip the RCD.
There's a small chance it's a faulty MCB, but an electrician should do an insulation resistance test with no appliances connected to find out more.

 

[mfarrow]

Does leaving the fridge out of the rear socket circuit isolate that circuit from further trips?

It could be a faulty MCB on that circuit (not sure how RCD connected) and also, if you're plugging the fridge into the front via an extension reel these have been known to (somehow) isolate further faults from the appliance.

 

[Kez6670]

Hi just by way of update. Came down this morning and the mcb for kitchen was down but not the rcd. Switched it back on and within 5 mins it went again and tripped rcd. The only way I can get the rcd to stay on now is leaving mcb switched off. The fridge is plugged into front by way of extension lead. Electrician coming tomorrow

 

[securespark]

I bet there is damp involved here. I had exactly this problem in a customer's house, see this thread.

//www.diynot.com/diy/threads/s...eek-with-apologies-to-rf.174273/#post-1186393

 

[JohnW2]

I bet there is damp involved here. I had exactly this problem in a customer's house, see this thread.

Whilst damp (or frank water!) might obviously be the cause of RCD trips, it is surely very unlikley that it could cause an MCB to trip? We've just been told that the OP's "kitchen MCB" tripped about 5 minutes after being reset. If, as is likely, that's a B32 MCB, that would require a current in excess of ~50A - and I don't think one would/could get anything like that current even if one dropped an accessory on that circuit into a bucket of water!

Kind Regards, John

 

[Kez6670]

What do you think could be causing this John I would appreciate any advice

 

[JohnW2]

What do you think could be causing this John I would appreciate any advice

As has been said, if an MCB sometimes trips, that must (unless the MCB is faulty) be due to a 'short circuit' (or something approaching that) - which could be in the wiring, in a wiring accessory (socket, switch etc.) or in some supplied appliance/equipment. As I recently wrote, I don't believe that dampness could be the cause (although it could cause RCD trips).

Are you now saying that it is not always the same MCB that trips, or is it always the "kitchen" one that does?

Kind Regards, John

 

[DetlefSchmitz]

I bet there is damp involved here. I had exactly this problem in a customer's house, see this thread.

Whilst damp (or frank water!) might obviously be the cause of RCD trips, it is surely very unlikley that it could cause an MCB to trip? We've just been told that the OP's "kitchen MCB" tripped about 5 minutes after being reset. If, as is likely, that's a B32 MCB, that would require a current in excess of ~50A - and I don't think one would/could get anything like that current even if one dropped an accessory on that circuit into a bucket of water!

You would have been surprised here yesterday then. We had a lulu of a rainstorm, the road flooded, the water ran down our drive, overwhelmed the drain in front of the garage, poured through the garage and rose high enough to reach the freezer electrics. The first we knew was when a 32 amp MCB tripped. Wouldn't reset till we unplugged the freezer.
It surprised me too. After the water went down, we plugged the freezer in again and everything is ok.

 

[Kez6670]

It's always the same mcb to the back of house

 

[JohnW2]

You would have been surprised here yesterday then. We had a lulu of a rainstorm, the road flooded, the water ran down our drive, overwhelmed the drain in front of the garage, poured through the garage and rose high enough to reach the freezer electrics. The first we knew was when a 32 amp MCB tripped. Wouldn't reset till we unplugged the freezer.
It surprised me too. After the water went down, we plugged the freezer in again and everything is ok.

Yes, it surprises me a lot. You presumably don't know how quickly the 32A MCB tripped after the water hit it, but (assuming it was a B32) it must have been over 36A, and I still would have thought that one would struggle to get that much current through water. However, if it happened, it happened!

No RCD protection, I take it?

Kind Regards, John

 

[DetlefSchmitz]

You would have been surprised here yesterday then. We had a lulu of a rainstorm, the road flooded, the water ran down our drive, overwhelmed the drain in front of the garage, poured through the garage and rose high enough to reach the freezer electrics. The first we knew was when a 32 amp MCB tripped. Wouldn't reset till we unplugged the freezer.
It surprised me too. After the water went down, we plugged the freezer in again and everything is ok.

Yes, it surprises me a lot. You presumably don't know how quickly the 32A MCB tripped after the water hit it, but (assuming it was a B32) it must have been over 36A, and I still would have thought that one would struggle to get that much current through water. However, if it happened, it happened!

No RCD protection, I take it?

As it happens everything here is RCD protected except a couple of indoor fridges/freezers (not the one in the garage). The RCD did not trip. And believe me, if they can find an excuse to trip they will!
I think I knew within seconds as the internet router is powered from the same circuit, and I was tracking the lightning strikes. Guaranteed to get an instant reaction in our house if we lose the circuit powering the internet. So less than 5 minutes to trip the MCB.
Probably need to look for a way the freezer could take a large current when water covered the motor. Maybe the motor wouldn't turn.

 

[bernardgreen]

the 32A MCB tripped after the water hit it

Are we certain this "MCB" is not an RCBO ?

36 amps at 230 volts is over 8 kW That would boil off a lot of water before an MCB tripped.

Dummy loads for generators using highly conductive "water" ( water with sodium salts disolved in it ) require a couple of square feet of electrode area before tens of amps can flow through them.

 

[JohnW2]

As it happens everything here is RCD protected except a couple of indoor fridges/freezers (not the one in the garage). The RCD did not trip.

That's rather amazing. If water was creating an L-N path that was somehow carrying 36A+, it would seem very unlikely that 30mA would not get from L to E!

I think I knew within seconds as the internet router is powered from the same circuit, and I was tracking the lightning strikes. Guaranteed to get an instant reaction in our house if we lose the circuit powering the internet. So less than 5 minutes to trip the MCB.

I'm not sure that you're answering the question I asked - namely how long it was from when the water hit the freezer electrics to when the MCB tripped. You're surely not saying that the water level in the grage got high enough to recah the freezer's electrics within 5 minutes of the rain starting?

Probably need to look for a way the freezer could take a large current when water covered the motor. Maybe the motor wouldn't turn.

I'm not sure what you are suggesting here. IME, the compressors of fridges and freezers are invariably totally enclosed/sealed - so there's no way that external water can get near any moving parts. Are you perhaps suggesting that a short through water reduced the voltage supplied to the compressor to a low enough level that it could not turn, yet with a voltage still high enough that "tens of amps" could flow through the non-turning motor?

Edit: one further thought - are you sure that it was the water, and not lightening, which caused the MCB to trip? (it's not uncommon here for both RCDs and MCBs to trip when there is nearby lightning - presumably due to interference with their electronics)

Kind Regards, John

 

[JohnW2]

Are we certain this "MCB" is not an RCBO ?

I think that we can assume that Detlef knows the difference. He has also indicated that the circuit had an RCD (which did not trip).

36 amps at 230 volts is over 8 kW That would boil off a lot of water before an MCB tripped. Dummy loads for generators using highly conductive "water" ( water with sodium salts disolved in it ) require a couple of square feet of electrode area before tens of amps can flow through them.

Exactly - that's why I find it so difficult to understand how water ingress into an appliance could cause a 32A MCB to trip ... but we can't get away from the fact that we're being told that it happened!

Kind Regards, John