Weird electrical problem

[Sam Inglis]

I work from a studio space in a converted industrial building. It's a single room that has its own metered electrical supply and consumer unit. There are two rings running from the consumer unit, one for the lights and one for the sockets.

I've been having intermittent but frustrating problems with the latter. As there's no other source of heating, I often need to run a heater from one of the sockets. I use a low powered heater which is rated at 2kW maximum, and I never have it on full power. This often works fine for weeks on end, but then on other days when I'm doing nothing different, the circuit breaker for the socket ring will trip apparently at random, often several times within a day. I've tried three different heaters, running from different sockets. It happens regardless of what's going on elsewhere in the building, and has happened when I'm the only person in.

My landlord got an electrician to visit yesterday. He couldn't find any faults in the consumer unit or the sockets, and the supply should be capable of delivering something like 45A, so a small heater shouldn't be anywhere near overloading it. He replaced the MCB in the consumer unit and so far the problem hasn't recurred, but we still don't understand why it happened in the first place. His best guess was that dust or other material falling onto the element in the heater might sometimes be producing short circuits -- but one of the heaters I've been using is an oil filled radiator which is completely sealed.

Any thoughts?

[Kwackman]

Silly question maybe, but are you sure it’s the heater?
Have you spent a long time in the studio without the heater plugged in? (Not likely in the winter!)
If not, then it’s possible the ring might trip without the heater, and the problem could be somewhere else?

[Wonks]

How old is the basic electrical installation? MCBs can start to fail and trip sooner as they get old. If so, the new MCB should sort it.

Not knowing the building layout, any chance rain is getting in somewhere there are electrical connections?

With all of your loads on the circuit off, does the meter show any residual current draw that could indicate the circuit doesn't just serve you?

[Hugh Robjohns]

What kind of trips are fitted to the consumer unit?

Rather than tripping on over-current (which seems unlikely, as you say), it could be tripping due to eath leakage.

I had that problem here, and ended up having to split the downstairs ring feeding my studio off onto a separate earth leakage trip, separate to the original one for the rings for the rest of the house.

In my case the combined leakage to ground from all the various bits of technology around the house occasionally became just enough to upset the trip. But it happened so randomly and seemingly without being related to doing anything specific that it was months before I figured it out and got my tame electrician to do a bit of rewiring.

[Wonks]

A standard MCB doesn't trip on earth leakage, just current.

[Sam Inglis]

Silly question maybe, but are you sure it’s the heater?
Have you spent a long time in the studio without the heater plugged in? (Not likely in the winter!)
If not, then it’s possible the ring might trip without the heater, and the problem could be somewhere else?

I'm pretty certain it has only happened with the heater plugged in. And yes I have spent some very cold days in the studio for fear of turning it on!

[Hugh Robjohns]

A standard MCB doesn't trip on earth leakage, just current.

That might be why I asked what kind of trips were fitted....

[Wonks]

But it's only the socket ring that trips.

[Sam Inglis]

How old is the basic electrical installation? MCBs can start to fail and trip sooner as they get old. If so, the new MCB should sort it.

Not sure. Maybe ten to fifteen years?

Not knowing the building layout, any chance rain is getting in somewhere there are electrical connections?

The building is a crumbling Victorian warehouse which has its share of problems with water coming in. But the electrical wiring in my room is well away from anywhere that seems vulnerable, and the problem hasn't been associated with wet weather.

With all of your loads on the circuit off, does the meter show any residual current draw that could indicate the circuit doesn't just serve you?

No.

[Sam Inglis]

But it's only the socket ring that trips.

Yes. The main RCB has never tripped. AFAIK the socket ring trip is a standard MCB.

[Wonks]

So at least another unit isn't being used a cannabis-growing factory using your electricity.

Other options if the MCB doesn't fix it are a loose/poor wire connection somewhere, or rat-chewed wires.

I doubt if you know whether the sparky looked at the wiring in all the socket outlets to check for poor wiring?

[Sam Inglis]

He used a socket tester and took a couple of them apart.

[Drew Stephenson]

I didn't spend much time in that room when I visited so I can't really remember a lot about it, but I do remember some big solid walls; do you have any condensation issues?
We had an issue in the kitchen here with condensation trickling down the walls and getting behind the socket plate.

[Sam Inglis]

It's not impossible, but I haven't noticed condensation on the walls. I got it to trip once yesterday while the electrician was there, and I doubt it was a cold enough day for condensation to form.

[ef37a]

Not seen a value for the mains voltage?
When Blackstar moved into their first proper workplace we found a 500VA Variac would trip the breaker often enough to be a B nuisance. Eventually found the sub had been left tapped at about 258V IIRC, certainly well over 230 volts!

Also found that when the KT88s went "purple death" in a 200W amp they took out the amp fuses as they should and the 10A in the plug but also the breaker and that last is not right.

Decades before when on the tellies we had problems with a VCR in a village and a UV recorder on the mains found spikes over 1kV, so external pulses can trip your breakers. And yes, breakers do wear out, or more properly they get "trippy" after a lot of operations. Had that in the factory and that was a VERY serious problem because that breaker fed the cafe!

Dave.

[Sam Inglis]

I've just dug out my trusty digital multimeter and measured 244V at one of the sockets.

[James Perrett]

Show us a picture of the circuit breaker that trips...

Older systems used breakers that just detected over current but some newer systems also measure residual current.

[Wonks]

As it's a standard MCB (from all accounts) in a consumer unit, it will only have the live circuit passing through it, so it can't measure any residual current. The consumer unit will have an overall residual current protective device and that's not tripping.

[Hugh Robjohns]

This seems to be very presumptive attitude for the sake of a quick check on the actual breakers installed in the box....

[Sam Inglis]

Show us a picture of the circuit breaker that trips...

Older systems used breakers that just detected over current but some newer systems also measure residual current.

The MCB that was replaced was one of these.

[Wonks]

This seems to be very presumptive attitude for the sake of a quick check on the actual breakers installed in the box....

Presuming anything else would be silly on a landlord's fit-out. Anything beyond a standard consumer unit with overall RCD and standard MCBs would be in the realm of a specialised extra-cost work. I've worked on hundreds of fit-outs in my time and though it's not my direct area (except in some specialist instances), I'll work alongside the electrical engineer and use/review their drawings.

Plus Mike had already said it was a standard MCB.

[James Perrett]

I wondered if it was one of these

https://www.bgelectrical.uk/uk/circuit- ... vices/rcbo

A photo of the actual item would answer the question. There is obviously a slightly obscure issue so as many accurate details as possible are needed if we are to solve the mystery.

[N i g e l]

is the new one the same value as the old one or bigger ?

I've just dug out my trusty digital multimeter and measured 244V at one of the sockets.

The mains voltage and frequency will vary throughout the day.
That will also cause the drawn current to vary, even with the same load.

[Sam Inglis]

I wondered if it was one of these

https://www.bgelectrical.uk/uk/circuit- ... vices/rcbo

A photo of the actual item would answer the question. There is obviously a slightly obscure issue so as many accurate details as possible are needed if we are to solve the mystery.

Here's a photo of the one that was removed. I assume the replacement is like for like.



EDIT: for some reason the inline image link isn't working,

You were linking to the page containing the image rather than the image itself - for ImageBB you have to right click on the image and then chose "Copy Image Address" while for Imgur you have to choose the PHPBB option from the link menu -JP

[James Perrett]

OK - so that is a standard MCB. If the replacement fails then you almost certainly have a problem. Could something have chewed through a cable hidden away somewhere? Does it fail when you are switching things on or does it fail when nothing changes?

Switch mode power supplies can cause huge current spikes when switched on but those spikes shouldn't be long enough to trigger a B type MCB.