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Electrical Power off in Outbuilding After Tripping Circuit Breaker

Postby Davidgrg » Sat Mar 21, 2015 6:47 pm

My outbuilding was power supplied through a power cable from the kitchen.
Recently the mail circuit breaker tripped. After checking all the electrical switches, I found that this outbuilding power switch in the kitchen caused the breaker tripped.
So I have disconnected this cable to keep the elctricity running in other rooms.

I'm not sure what is the problem with the cable or switch of the outbuilding. I changed the fuse of the switch but still problem exists.
Any idea what is the best way to check this and what could be the possible reason ?

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Postby ericmark » Mon Mar 23, 2015 12:42 am

At a quick guess I suspect water ingress somewhere.

We have a number of protective devices.
1) Fuse this melts with over current automatic disconnecting supply.
2) MCB this is two devices in one it has a magnetic part which works very fast and a thermal part which works a lot slower and it replaces the fuse but unlike the fuse a slight decrease in the prospective short circuit current can cause a huge change in tripping times.
3) RCD this device measure current in and current out if nothing goes to earth these should match but if current goes to earth then these will auto disconnect. They come in many flavours 10mA, 30mA (for personal protection) 100mA, 300mA, 500mA (for fire protection and where a TT earth system is used) also active (auto trips with power loss) and passive (stays on with power loss).
4) RCBO which is a MCB and RCD combined.

In the main RCD and RCBO have trip buttons to test them but also some MCB's had two buttons also.

So information you have given is not enough to work out what has happened. My daughter had a problem and my son an electrician could not find the problem with a simple multi-meter his expensive meters had failed. I needed to go with my insulation tester to find the fault.

Some times one is lucky and can guess at the fault but also you can go round and round in circles looking for it. The first thing is to work out what has changed. Be it digging garden or heavy rain some times one can guess at cause and find it.
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Postby collectors » Mon Mar 23, 2015 6:03 am

It’s a bit of eliminating things one by one.
Is it an RCD safety switch that is tripping or a normal circuit breaker?
If it’s an RCD it is quite likely damp, if a breaker a short.
1st make sure everything in the shed is unplugged. (Try fuse again)
2nd Check cable if visible that goes to shed to see if it’s been damaged by a shovel or even rats & squirrels.
If nothing is visibly found you will need to disconnect & strip down to start testing cables from the kitchen switch to the shed.
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