Calling all electricians.

[whiskywill]

Is it possible for an MCB to die without tripping a circuit?
The story - When I woke up yesterday morning my radio alarm clock was dead as was my bedside light. I assumed that the MCB for that circuit had tripped. I check the distribution board and everything appeared normal.
Later, after our young twins had been for an early afternoon nap, I mentioned the power problem to my wife because the baby monitor cameras are mains powered. She replied that they worked OK.
At their bedtime, just after 7.00 p.m. every bedroom power point was again dead.
At 11.32 p.m., just as I was dropping off to sleep, my bedside light lit up. It was still OK this morning.
Any ideas?

 

[porker]

Hi, I'm not an electrician (but am a qualified electrical engineer). I have had an MCB go faulty before i.e. it failed in the 'ON' position so it is possible. Could also be a faulty connection somewhere in the circuit. Can you swap the MCB over for a spare and see if the fault transfers or goes away? Intermittent faults are always a pain to find. You really need to investigate when it is dead.
As always, safety first. Isolate power before working on it and if you don't know what you are doing get someone who does.

 

[Monkey Mark]

Mcb's can indeed become faulty.

You could try swapping it with one from another circuit to see if the problem also swaps to another circuit. But at the very least check the connections to ensure no loose wires.

Depending on brand they are cheap to replace.

Edit; beaten to it.

P.s. have you had any testing done revently? It's fairly common for them to fail after insulation resistance testing.

 

[whiskywill]

Deleted due to duplication.

 

[whiskywill]

P.s. have you had any testing done revently? It's fairly common for them to fail after insulation resistance testing.

No testing done. Because the fault is intermittent, changing the MCB might not identify the problem. I will check the connections in all 16 double sockets on the circuit first.

Thanks both for your quick responses.

 

[Phil Pascoe]

If you disconnect the first socket on the ring, it should show whether there is continuity on all the others (if they're all live)? Just a thought, I'm not a sparky.

 

[Monkey Mark]

If its a ring main, disconnect the feed out to first socket and return from last and check resistance. A loose connection at any socket should with this "ring final". Much quicket than opening each socket.

 

[mind_the_goat]

Of course with a ring main, a loose connection on a socket is likely to go unnoticed as there are 2 routes for the current to take. If this is just in your bedroom, and the mcb covers a whole floor, then it suggests you have a spur in the bedroom. Check all the sockets in the bedroom first and see if you can find where the spur is connected to, usually a socket but could be a junction box hidden away somewhere. I would suggest it's quite important to find the fault, if it's a loose connection it could cause arcing and overheating.

 

[whiskywill]

If this is just in your bedroom, and the mcb covers a whole floor, then it suggests you have a spur in the bedroom.

It's not just the one bedroom. It's the whole of the first floor that is affected.

As a last resort I could drag in the electrician who installed the system to take a look. It's a 24 year old self build house so will be a real test of his memory. I did most of the cable pulling, under instructions, and chasing into cement render but I didn't do the final connections.

 

[HOJ]

After 24 years you are well overdue a "Periodic Inspection" the recommended interval is every 10 years, for domestic installations.

 

[whiskywill]

It seems to be a loose connection problem. Two sockets in the bedroom nearest to the distribution board are live, so it's a case of working around the first floor from there.

HOJ, does anybody actually have "Periodic Inspections"?

 

[Monkey Mark]

It seems to be a loose connection problem. Two sockets in the bedroom nearest to the distribution board are live, so it's a case of working around the first floor from there.

HOJ, does anybody actually have "Periodic Inspections"?

They have to if it's a rented property.

 

[HOJ]

HOJ, does anybody actually have "Periodic Inspections"?

Yes they do, some insurance companies (in the small print,) in the event of an incident will ask for the last report.

Invariably, properties are inspected and tested when things start to go wrong.

I am only advising as a cautionary note that 24 years is a long time for things to degrade, age related & Mice.

Like my wood burner, I have to get a HEATAS registered chimney sweep to give me a certificate every YEAR............