On 25/07/2019 08:52, Jeff Layman wrote:
On 25/07/19 07:45, wrote:
On Thursday, 25 July 2019 07:29:51 UTC+1, MMÂ* wrote:

A relative lives in a 300-year-old house. Yesterday he called to warn
that when I visit tomorrow (Friday) it's likely that roughly half the
house will still be without power. The other, smaller, half is
unaffected.

The electrician he called has so far not been able to diagnose the
cause of the problem. The half that is out is on a separate "fuse"
box. The other half of the house is unaffected. I write "fuse" in
quotes, but I understand that it does at least have the switches, not
old-fashioned fuse-wire fuses, although the equipment seems to be very
old.

The electrician, who is fully booked up today, tried for several hours
yesterday to pinpoint the cause and thought he had found it. But then
the "fuse" (i.e. switch) popped out again later in the afternoon.

Does anyone have any comments as to the cause? And how would an
electrician go about narrowing down the problem area? According to my
relative, the electrician knows what he's doing, i.e. isn't an
amateur.

How does one trace through all the wiring in the affected side,
especially given the age of the property?

Thanks.

MM

Half the house without power means a whole CU dead, not one final
circuit. They're called MCBs btw. If any one MCB tripped you'd only
lose one circuit. You're presumably losing the whole CU, so it sounds
like it has an RCD that's tripping. If that's the case, there are 2
tests to do. Insulation test each final circuit, then PAT test or
insulation test all your appliances. Usually that will pinpoint the
culprit.

Sometimes you can find the bad appliance by just insulation testing
with a multimeter, one probe on L&N & the other on E plug pin - with
the appliance unplugged of course. There should be no conduction
there. So you may solve it with a £10 multimeter and an hour.
Sometimes the fault is only picked up with high voltage testing.

A clear pic of the 'fusebox' would help


NT

If an RCD is tripping then the simplest thing to do is switch off all
the MCBs, reset the RCD, then switch on each MCB in turn until the RCD
trips again. Then you know which circuit is faulty. It can be turned off
and left off until the electrician appears. The other MCBs can be left
on so at least some of the house had power of some sort.

However, if it's an intermittent fault, and the faulty MCB is already
known ("But then the "fuse" (i.e. switch) popped out again later in the
afternoon."), why wasn't that just left off and the RCD reset until the
electrician was able to do further testing?


Bugger. I was hoping that the OP had passed away.

--
Adam