Downstairs lighting circuit MCB randomly tripping since electrician's visit last week.

[ban-all-sheds]

The lighting circuit is still drawing a large amount of current at random intervals even though everything apparently attached to it is switched off..

You really, really, really have to find out why

 

[ceecjc1]

You really, really, really have to find out why

I'm glad you said that, since the electrician didn't seem particularly interested. He actually called his friend up and asked if the red flashing LED went faster under greater load, which surprised me.

Any suggestions on how to identify where this load is coming from?

 

[John D v2.0]

I think you need to call an actual electrician and not this joker. He's left you with a dangerous situation, he hadn't a clue what was going on so he just did something random so he could get paid. If you haven't paid him, don't.

The actual electrician should ir test the whole circuit with all bulbs out, then whichever bit fails, keep subdividing until they find the fault.
If the fault really is intermittent, this will be time consuming, hence why the original electrician didn't bother (plus it was beyond his ability)

Another option would be a heat thermal camera.

 

[garyo]

If your meter LED is the usual 1000 imp/kwh then that's about 2KW being drawn. That's a fair amount of heat. Have you checked your cycling appliances like fridges/freezers/etc? Maybe someone did a lazy wiring job on a socket.

 

[John D v2.0]

Fridge seems unlikely due to the high current. However Immersion heater would be a good shout, only a few minutes but infrequently. Sounds like a thermostatically controlled thing. Maybe the electrician either flicked it on by mistake or even wired it into the lights where it was disconnected before or connected elsewhere!

Op do you have an immersion heater in your cupboard? Or another heater for water or anything.

 

[garyo]

Or what about an outside PIR activated light?

 

[ban-all-sheds]

Ah - a 2kW light on the outside of his house that he has never noticed.

Good thinking.

 

[John D v2.0]

Or what about an outside PIR activated light?

Pir activated patio heater?

 

[JohnW2]

If your meter LED is the usual 1000 imp/kwh then that's about 2KW being drawn. That's a fair amount of heat.

Indeed so - and, as I said before, that's the sort of amount of current that would be needed to trip a B6 in around 5 minutes. If it's some genuine load which has somehow been wired into the lighting circuit then fair enough (although it needs to be found and sorted out) but, as I also said before, if that amount of power is being dissipated in some 'fault', then there would be a very real fire risk.

Kind Regards, John

 

[ceecjc1]

UPDATE: It's not fixed.

I've been away with work for a couple of days and the lights haven't tripped at all while I've been gone. However the first thing I did when I got back just now was check the meter cupboard and, again, the MCB for the lighting circuit is buzzing quietly and the red LED is flashing quickly. Turning off the MCB stops the buzzing and the LED goes back to flashing very infrequently. It's daytime, all of the lights are off, something is gobbling up a bunch of power.

This time, this particular MCB is noticeably warm to the touch and did not let me reset it for a few minutes. I assume the previous fix by the electrician (of removing a slightly melted transformer) had improved the situation just enough to stop the MCB tripping but the main problem is still not diagnosed.

Thanks for all your suggestions. I don't have an external 2kW PIR light I do have an external dawn-dusk light but this was switched off. I just now pulled out the sensor as well as the transformer for the 5W LED light attached to it and both are stone cold so I doubt either had been sinking 2kW. In any case, I had previously (physically) removed the outdoor sensor from the circuit and it hadn't stopped the MCB from tripping, so I don't think this is faulty.

Again, every light attached to the circuit (including the external dusk-dawn sensor and light) is working.

I'm going to call back the electrician and get him to do a proper test of the circuits. In the meantime the MCB is staying switched off.

 

[garyo]

PM me your location in berks. I have a thermal imaging camera that I'd be happy to point at your ceiling if you're close by...

 

[John D v2.0]

In the meantime the MCB is staying switched off.

Honestly you need to keep it off, especially when you're out or in bed! Especially away.
In its current state it's an unknown fire risk!

 

[Alec_t]

I'm going to call back the electrician

It's been suggested you call a different electrician.

 

[ceecjc1]

It's been suggested you call a different electrician.

Yes you are right and a different guy is coming next week, I will report back on the mystery...

 

[Alec_t]

If the problem has only arisen since the downlighters were installed, my money would be on the feed wiring to the downlighters having been damaged, or badly routed such that insulation has melted at some point, causing an intermittent short of an unswitched wire.