Trip switch gets hot and won't engage until cool

[macadonald]

Hi Guys,

Just curious, but the tenants in my flat said that they had no lights and the fuse had gone, but they couldn't switch it back on. It's not an old wire fuse, but a 6amp trip switch. They then said that after a while it would switch back on. They claim this was once it had 'cooled'.

Will pop over tonight, but out of interest do the trip units get old over time and need replacing?

Thanks

 

[ban-all-sheds]

Sounds like a loose connection is causing the MCB to get hot enough for the thermal trip to operate.

I expect it'll need replacing, and be on the lookout for damage to the cable(s).

 

[Taylortwocities]

Could be loose connection at the top of the MCB. Also, look to make sure the busbar at the bottom is properly engaged and the screw is tight.

And per above, get a new MCB once you have found the problem.

 

[ricicle]

BUT - please DO NOT attempt any work in your consumer unit unless you feel you are confident/competant to do so.

 

[macadonald]

Thanks for the advice guys. I would not attempt anything more than pulling out the old MCB and pushing in a new one, which I have done before

 

[ban-all-sheds]

Better get your electrician in then, because there's checking to do, not just replacing a plug-in MCB...

 

[Spark123]

How many watts of lighting is there on the lighting circuit? Is there anything else on the said lighting circuit i.e. sockets?

 

[macadonald]

Hi guys,

Well I'm still alive to give you an update. It was a 6amp circuiot breaker that had just 4 single bulbs running on it in a 1 bedroom flat. It fortunately was just a push in circuit breaker and I replaced it. Will keep an eye on it and if it trips again, I will call in a sparky.

Thanks

Kyle

 

[JohnD]

apart from a loose connection, which can cause overheating, a very common cause of an MCB tripping and being hot is that it is overloaded. This happens when excessive loads have been put on the circuit, either from damage, or incompetent electrical work, or where numerous or large appliances have been connected. The excessive load is not so high that the MCB trips immediately, but will trip in a time which is dependent on the size of the overload. It would be pretty well impossible for four single bulbs to cause a 6A MCB to trip.

You say you have plug-in MCBs, which suggests a Wylex Standard CU. This could be anything up to fifty years old and does not suggest an up to date installation.

 

[ban-all-sheds]

Hi guys,

Well I'm still alive to give you an update.

Let's hope your tenants remain in the same state.

It fortunately was just a push in circuit breaker and I replaced it.

Did you read nothing that was said about loose connections?

Will keep an eye on it and if it trips again, I will call in a sparky.

It has overheated several times.

You have not found, or done a single thing to find, the cause of that overheating.

You have failed in your duty of care to your tenants. Get an electrician in NOW you cheapskate.

 

[macadonald]

Thanks JohnD,

I've asked a builder doing some work on the bathroom to get his electrician over to take a look and give me a quote on a new circuit board and as you suggest it is a 'Wylex Standard CU', so needs replacing. He pointed out that there is a chance that an extractor fan is wired into the lighting, but we'll see what the sparky says.

 

[Taylortwocities]

Thanks JohnD,

I've asked a builder doing some work on the bathroom to get his electrician over to take a look and give me a quote on a new circuit board and as you suggest it is a 'Wylex Standard CU', so needs replacing. He pointed out that there is a chance that an extractor fan is wired into the lighting, but we'll see what the sparky says.

Super. The fan is probably wired into the lighting circuit but the load will be no more than a standard light bulb so wouldn't have much of an effect on the total load.

Good plan to get the board changed!

 

[JohnD]

...and the fault, wherever it is, traced and repaired.

the electrician must be a member of a Competent Persons Scheme. Ask him which one and look at the evidence.

 

[ban-all-sheds]

as you suggest it is a 'Wylex Standard CU', so needs replacing.

That would be a good thing to do, but it doesn't "need" replacing, unless it's been damaged by overheating. The biggest problem is lack of RCD protection, and that's not easy to retro-fit to an installation like yours in a way which complies with the Wiring Regulations except by replacing the CU, but in and of itself it is perfectly OK as long as it's in working order. There is no requirement to upgrade old installations to current standards.

Were it mine I'd want it replaced, but be wary of anybody who tells you it must be replaced if it's undamaged.

And be wary of anybody who proposes to replace it without doing testing first, in case you have faults which will become real problems with a new CU.