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ChickenGeorge65

Help needed in trying to diagnose a fault please

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ChickenGeorge65

Hi all, from my house I have a cable running to my garage in which I have a consumer unit with 4 x MCB's. 2 MCB's are for lighting (one circuit in my garage and the other in an adjacent outbuilding). The other 2 MCB's are for sockets (one circuit in my garage and the other in the adjacent outbuilding). Yesterday all was working fine and no electrical work has been done since. Tonight I flicked a light switch in the outbuilding and the whole feed to the garage from my house (running of 32Amp MCB) tripped. I've tried all lights and sockets in the garage and outbuilding turned off - but the 32Amp MCB in the house feeding the garage won't turn back on. I then tried turning all 4 x MCB's in the garage consumer unit off and then I CAN reset the house MCB. But as soon as I try any one of the 4 MCB's in the garage it trips the house MCB again.

 

It's made me suspect that the fault lies in either the garage consumer unit or the U/G cable fed from house to garage - BUT yet the house MCB doesn't trip with the garage one on and all MCB switches off.

 

Does anyone have any ideas please? Many thanks.

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Evans Electric

It sounds like  your supply cable is OK  .

 

Is it definitely an MCB  that trips or is it an RCD  .    If its an MCB it sounds like a dead short .

The consumer unit is full of water .

The consumer unit has a dead mouse across the terminals . 

There is rodent damage somewhere  (  Squirrel , mice or rats gnawing cables) 

Are you sure it is ANY of the MCBs that trip the circuit or just one in particular ...  I'm thinking fluorescent fitting with a melted ballast in it .     A light bulb with a short in it .   Something faulty plugged in to a socket . 

 

Another thought is ...there was a dead short  which has beggered  up the 32A MCB .

 

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MDJ
15 hours ago, ChickenGeorge65 said:

Hi all, from my house I have a cable running to my garage in which I have a consumer unit with 4 x MCB's. 2 MCB's are for lighting (one circuit in my garage and the other in an adjacent outbuilding). The other 2 MCB's are for sockets (one circuit in my garage and the other in the adjacent outbuilding). Yesterday all was working fine and no electrical work has been done since. Tonight I flicked a light switch in the outbuilding and the whole feed to the garage from my house (running of 32Amp MCB) tripped. I've tried all lights and sockets in the garage and outbuilding turned off - but the 32Amp MCB in the house feeding the garage won't turn back on. I then tried turning all 4 x MCB's in the garage consumer unit off and then I CAN reset the house MCB. But as soon as I try any one of the 4 MCB's in the garage it trips the house MCB again.

 

It's made me suspect that the fault lies in either the garage consumer unit or the U/G cable fed from house to garage - BUT yet the house MCB doesn't trip with the garage one on and all MCB switches off.

 

Does anyone have any ideas please? Many thanks.

My advice is to ring an Electrician, it wouldn't take long to find out what is amiss.

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ChickenGeorge65

Evans Electric...thank you for your advice and suggestions.

 

MDJ... the point of me asking here was to save the cost of an electrician diagnosing what I wanted to find myself!

 

Interestingly, I checked all of Evans Electric's suggestions and found nothing amiss. Today I have turned everything off - and gradually switched things back on - and mysteriously everything working fine again?? Problem has just gone away?? Very bizarre,, but glad I didn't ring a sparky immediately and incur whatever they'd have charged :) 

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Murdoch

^^ nice to see you have such little faith in trades people.

 

We are mainly self employed, have business overheads, homes and families .... So work has to pay, as full time charity work isn't an option. 

 

 

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Hefferl

I think you're just postponing the inevitable .....

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Sharpend

Moisture anybody?, I’ll bet it comes back again!! 

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Sidney
47 minutes ago, Sharpend said:

Moisture anybody?, I’ll bet it comes back again!! 

I have to agree.

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Doc Hudson
6 hours ago, ChickenGeorge65 said:

Evans Electric...thank you for your advice and suggestions.

 

MDJ... the point of me asking here was to save the cost of an electrician diagnosing what I wanted to find myself!

 

Interestingly, I checked all of Evans Electric's suggestions and found nothing amiss. Today I have turned everything off - and gradually switched things back on - and mysteriously everything working fine again?? Problem has just gone away?? Very bizarre,, but glad I didn't ring a sparky immediately and incur whatever they'd have charged :) 

 

Not very bizarre and I doubt you have saved anything, merely postponed finding the true cause that a DIY person who has no access to test equipment, such as an Insulation resistance tester, cannot diagnose via forums or you tube. I (and I guess the majority of qualified electricians on here), have seen numerous instances of intermittent problems on various types of circuit that an unskilled person had previous diagnosed as cured because it had started working fine again for a few weeks. I would be cautious of leaving any circuit that has tripped a 32a MCB for very long without having the standard dead tests carried out to verify the cable integrity. There are a lot of dangers with your current diagnosis approach, rather like choosing to drive a car with bald tyres, it could work fine for a long period, but should you need to stop quickly it could be fatal. 

 

Doc H.

 

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ChickenGeorge65

Thanks to everyone for their advice... which I WILL be taking.

The underground cable feed from my house to the garage is NOT currently an armoured cable (don't ask...it's a situation I've inherited).

In the very near future I will be replacing the whole lot using a qualified electrician - new u/g armoured cable feed, new consumer unit and update on all the circuits in my out-building. I just needed an answer to get the power back on temporarily.

As advised, would seem moisture (somewhere?) could've been the issue.

Many thanks.

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Doc Hudson

It may help your understanding if you keep in mind a few key principals: Electricity always generates heat whilst travelling through a circuit. greater current, (greater power / bigger loads), will generate greater heat. Electricity can bridge or jump a gap where live parts are exposed or have damaged insulation. Bigger currents can jump bigger gaps (that's basically what thunder & lighting are). Damp and moisture in contact with damaged insulation can create an easier path for electricity to bridge between conductors causing high fault currents and rapid rise in temperature in the circuit before the fuse(s) trip.

 

Continuity and insulation resistance tests on your underground cable will probably take less than 30 mins. It would identify if the cable is seriously defective and should be disconnected immediately, Or if it has signs of ageing but still has a bit of life left in it, Or if it tests out all safe and functional and should be good for many years. Even at a standard 1 hour call out charge I guess this would only be £30 +/- £5. and would leave you much wiser about the condition of the underground supply.

 

Doc H. 

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Rob.
10 hours ago, Doc Hudson said:

It may help your understanding if you keep in mind a few key principals: Electricity always generates heat whilst travelling through a circuit. greater current, (greater power / bigger loads), will generate greater heat. Electricity can bridge or jump a gap where live parts are exposed or have damaged insulation. Bigger currents can jump bigger gaps (that's basically what thunder & lighting are). Damp and moisture in contact with damaged insulation can create an easier path for electricity to bridge between conductors causing high fault currents and rapid rise in temperature in the circuit before the fuse(s) trip.

 

Continuity and insulation resistance tests on your underground cable will probably take less than 30 mins. It would identify if the cable is seriously defective and should be disconnected immediately, Or if it has signs of ageing but still has a bit of life left in it, Or if it tests out all safe and functional and should be good for many years. Even at a standard 1 hour call out charge I guess this would only be £30 +/- £5. and would leave you much wiser about the condition of the underground supply.

 

Doc H. 

 

Is that so.... 

 

Slight typo on Docs part there, the higher the potential difference increases the distance in which the electricity can jump. The more current involved, the bigger and hotter the arc produced is. Also once an arc is struck, higher current will keep the arc 'flowing' over a greater distance due to it being able to ionise its surroundings. 

 

Agree with everything else, for what it's going to cost. Get someone with suitable test equipment to diagnose the issue. 

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Doc Hudson

*NOTE*

Please also see new split thread for further discussion on what are reasonable hourly rates;

and keep further discussion on this thread related to helping the OP solve his problem.

 

Doc H.

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