Replacing an RCD in a MK Consumer Unit

[mbuckhurst]

I've got an MCB in my consumer unit which I think is faulty, mainly due to the fact I turned it off along with all the others trying to identify which circuit my garage sockets were connected to, from then onwards it simply refuses to turn back on, even though there is nothing plugged into the sockets and it has not been changed.

I'm having difficulty getting an electrician to turn up so thought this really should be a job I can tackle with ease. But as I've never done it before I just wanted to check a few things:

1) How do I open the consumer unit to get access to the MCBs.

2) All the photos I've seen suggest a busbar provides the connection on the lower side of the MCB, but how on earth is a circuit made? Would I expect to screw a cable into the top connection?

thanks

mike

 

[Dippy]

Yes it is easy, BUT unless you are prepared to cut the power to the CU it is also potentially very dangerous because the current limit from a shock could be as high as 100A.

CUs do vary so I suggest you post a photo first.

As I'm sure you've guessed - if the replacement trips too then you have a circuit fault and not an RCD fault.

 

[aptsys]

Is your consumer unit a split load board? Try turning off the main switch and then trying to turn on the RCD. If it turns on fine then there's an earth leakage somewhere, if not, the RCD could be damaged.

As a sidenote, MK Sentry RCD's have a pretty stiff mechanism when trying to turn the RCD back on. Are you giving it a good hard push right to the top? If the RCD is tripping, the mechanism should release the switch from the actual contacts so you'll feel it trip part way through it's travel.

 

[DESL]

Which is MCB or RCD?

Your subject title quotes RCD

but post mentions MCB

Assuming it is the MCB you are it is relatively simple BUT a little more info would be usefull before you can proceed safely

1. Have you ever done anything with electrics before

2. Do you know any body that has done electrics

3. Removing the cover on a CU can be hazardous for the unwary and the fact that you are asking how to remove cover is a cause of concern.

4. Does the CU have a red part marked 'main switched circuits' and a green part marked 'RCD circuits' in other words split load.

 

[mbuckhurst]

The unit is split load. I've tried resetting the whole unit from the main switch and still no joy.

When I reset the MCB that seems to be duff, it simply doesn't hold, there's no force, it just fails to grip the switch in the on position. You certainly can't feel any tripping going on. I've switched MCBs at work that keep tripping in the past, this one doesn't feel like that's happening at all.

In answer to your questions DESL:

I've got the replacement MCB which is the same model number as the original failing one.

1) Yes, I've rewired a couple of bedrooms before the house was then fully rewired a couple of years ago.

2) No.

3) The reason I ask is because I realise its dangerous and therefore would like to know what I'm tackling before I start. Unfortunately the electricians never left any manuals.

4) Yes it's split load.

 

[DESL]

Ok

Will the MCB reset with the power off?

 

[mbuckhurst]

Ok

Will the MCB reset with the power off?

I'm at work at the moment, but I'm sure I tried it and it felt exactly the same whether power or no power, basically as though nothing was catching when pushing it into the on position.

mike

 

[DESL]

was MCB in off or tripped postion

MK Breaker switches sit in a mid point if they have tripped and need to be switched to off position before they can be reset

 

[mbuckhurst]

thanks for your help, I finally got round to replacing the unit and everything works fine again, however I did find the MCB was clearly used, so I'm starting a new thread about that...

cheers

mike