Upstairs lighting MCB not working?

[Paul Smith]

Hi Guys

I went to change an extractor fan in the bathroom today which runs off the light switch. I thought I'd isolate the power upstairs using the upstairs lighting MCB. I always double check there is no power there by switching on the lights and using my fluke to test for voltage and all the light still work? Would you say I have a defective MCB on the main board?

Cheers

Paul

 

[telectrix]

might be the bathroom lighting is on a different MCB. try the other 6A MCBs.

 

[Octopus]

Is everything else in the house working? Have you tripped a rcd?

 

[ChrisElectrical88]

Are you a DIYer or somewhat qualified?

 

[Paul Smith]

I did the electricians course about 5 years ago but never followed it through to a proper job. I've forgotten most of the stuff now :-( Just by chance that I've found a fault I think when I went to Isolate the upstairs lighting. The MCB is labelled upstairs lighting but it all still works when I tripped it?? I'm an Avionics engineer by trade so I'm fully competent with continuity, voltage, insulation resistance etc..

I tried the other MCB's but nothing is switching off the upstairs ring main....

There is only one RCB on the board. This has not tripped. The board is a 16th edition.

Thanks for the replies.

Paul

 

[telectrix]

unless there is a cross connection between circuits, 1 of the MCBs must turn off the power to the lights. does turning off the main switch kill them?

 

[Des 56]

Are the mcbs that you are switching 6amp mcbs
Labels are only an indication and have been known to be not what they may seem

 

[Paul Smith]

unless there is a cross connection between circuits, 1 of the MCBs must turn off the power to the lights. does turning off the main switch kill them?

Hi Telectrix

I haven't flicked the main switch yet (Mrs Smith is watching TV.) However I have 240v at the upstairs lighting MCB and 0V when you trip that switch so that would confirm the MCB is working. I'll have to wait till she goes to bed or I'll be in trouble :-(

 

[telectrix]

if you have 0V, how come the lights still work , as your previous post?

 

[Paul Smith]

if you have 0V, how come the lights still work , as your previous post?

OK I have figured it out sort of. The upstairs lights run of the smoke alarm MCB and vice versa. Someone can't label properly :-( That's easily remedied. You're right Des 56..

The bathroom lights and fan must run off a different MCB.

The only RCD I have on the board appears to protect the socket ring mains..

 

[SJD]

Even in new builds, it is not uncommon to find circuits mis-labelled, e.g. a couple of circuits with the labels swapped. Obviously whoever signs the work off doesn't check!

 

[Paul Smith]

Figured all the circuits out now. Need to do a spot of re-labelling then at least I'm back to square one.