Replacing circuit breakers in a domestic fuse box.

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Hi

One of my circuit breakers has blown and when I re-set it, it trips the whole system. Do I just need to replace that CB? It seems wider than the MCB I have seen pictures of on the web - is this normal? ALso, I tried to pull the old one out to get the rating and I couldn't - are they usually touch to pull out?

All help gratefully received (asap)!
 
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MCBs do not normally pull out, unless they are the ones to replace rewireable fuses in ancient fuseboards.

If resetting it is tripping the whole system, this suggests a fault with the wiring or an appliance somewhere. A faulty MCB on its own won't cause other devices to trip.

What circuit is this MCB for?
Pictures of the fusebox will help.
 
I hate to admit but I had a bit of a leak with the boiler, and water sprayed onto the boiler plug, which not surprisingly short-circuited the whole system and tripped all the CBs in the consumer unit. I managed to reset all the other CBs, but the one for the boiler circuit will not re-set.

I have opened up the plug sockets (fixed) for it to dry and I am hoping that once it has the CB will work.

What do you think?
 
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the fault will not be with the MCB so no point trying to change it. If the thing you are talking about is wider than the other MCBs and has a test button on it, it is an RCD not an MCB. A photo will indeed help, as flameport says. //www.diynot.com/forums/viewtopic.php?t=129539

The fault will be in the wiring, most likely a switch or outlet near or under the water leak. if the water was very clean it will dry out OK in time. If the water was black you may need to remove and clean or replace the accessory.

I hope you do not have any junction boxes hidden under the floor.
 
So do I! The boiler is in the loft, so I think that apart from the sockets that got sprayed up there, everything else has excaped. There wasn't enough water to drip down through onto the top floor.

Do you think maybe it is just the 3A fuse that would have blown in the fixed socket?

Is ther anything else I can do apart from wait for it to dry out and then screw the covers back on and try the CB again?

Thanks for your help so far... ;)
 
No.

But you could TURN OFF THE POWER and test for dead then undo the fixing screws of any suspect accessories and gently loosen them to help them dry out.
 
It's def not the RCB as I reset that to see what it would do when I was trying to get the other CBs to work (and there is a little yellow button on it). My CBs just seem chunkier, but the little switch on the front is the same size.

Unfortunately it is at my tenants house so I have not got a photo to hand.
 
Hi,

It's hard to visualise from your description what is actually tripping so could you either upload a photo or describe in detail what the consumer unit looks like.

What actually tripped when you turned the boiler circuit back on? What is written on the switches you can't reset? Is there anything which trips with a 'test' button next to it?
 
Consumer unit is of the newer type, with both the normal mains elec off switch and an RCB (mid way through the CBs), which seems to control the sockets and other circuits in the house (not the lights though).

Basically the whole system tripped off when I wetted the boiler socket by accident (when my boiler spurted water everywhere), but I managed to get all (except the ring with the boiler power on it) back on. I've opened up the boiler socket to dry (it is a fixed one with a 3A fuse but no light) and I am hoping that when it drys out it will work again. I am not sure if it blew the fuse, but I will take a new one with me to try tomorrow.

Thanks, jmh
 
WD40SmartStraw_310x310.jpg


;)
 
Looks like I replied as you posted the one above mine.

So correct me if I've got it wrong. It's a split load board with an RCD covering half the board with the socket circuits. Initially the MCB for the circuit the boiler is on tripped, and turning it back on now trips the RCD.

If so I would guess the boiler fuse hasn't gone. Sounds to me like you had/have a short circuit which initially tripped the individual circuit MCB, but are now left with a short circuit to earth which is taking out the RCD.

Could be just damp still but if it's dried out tomorrow and still tripping the RCD start checking if any wiring in the fused spur you removed has come loose, or if you have nipped a wire when screwing it back on.
 
Are you suggesting I use WD 40 insde a plug socket?

It depends how far the water has penetrated.

If you purge the accesory with Water Displacement - 40 ;) and dry as much off as you can with kitchen paper, it usually works a treat.

Obviously, make sure the power is off first.
 

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