failed mcb?
- Thread starter barraclc
- Start date
Sponsored Links
B
Big_Spark
barraclc said:
Yes. Try turning the MCB off, wait a few seconds and then turn it back on.
You should feel a resistance to turning it on. If you don't it may be that the magnetic trip inside the MCB has failed.
B
Big_Spark
It is not "common" for MCB's to fail, but like any component they can and do, so it is not unusual.
The best method to check is with a multimeter. Check the output side of the MCB to see if you have power flowing out of it, and what voltage it is.
If the voltage is significantly lower than mains or you have no output, then bin the MCB and replace with a new one.
However if you have power from the MCB, you will need to start looking for a fault.
What type of circuit doe this MCB protect?
The best method to check is with a multimeter. Check the output side of the MCB to see if you have power flowing out of it, and what voltage it is.
If the voltage is significantly lower than mains or you have no output, then bin the MCB and replace with a new one.
However if you have power from the MCB, you will need to start looking for a fault.
What type of circuit doe this MCB protect?
Sponsored Links
it's a lighting circuit with 8 60W bulbs and 3 switches on it. I turned on the lights the other day and a bulb appeared to blow, except this time all the bulbs went out. I checked the trip switches but as I've said already all were in the on position. I've reset the whole RCD as well as the mcbs and still no joy. All other circuits are working fine. So by deduction it's either:
1. mcb
2. light switch
3. break (although no idea how it would occur) in the wiring
The switch wiring appears ok, and my wiring in the circuit is not particularly old. I can't see how a break in the wiring would've occurred so i'm thinking that the mcb is the main suspect. My next step was to do what you've suggested and work my way around the circuit with a meter.
1. mcb
2. light switch
3. break (although no idea how it would occur) in the wiring
The switch wiring appears ok, and my wiring in the circuit is not particularly old. I can't see how a break in the wiring would've occurred so i'm thinking that the mcb is the main suspect. My next step was to do what you've suggested and work my way around the circuit with a meter.
- Joined
- 11 Jan 2004
- Messages
- 42,733
- Reaction score
- 2,633
- Country
You could temporarily disconnect another lighting circuit, and attach the "faulty" circuit live conductor to a 5/6A mcb you know works and see what happens when you switch on. BUT TURN OFF FIRST!!
M
Millennium_Boy
That's why I keep a few spare MCB's to hand, in case of a failure etc, I just swop out the dud MCB for a good one, and its solved (provided the wiring of fine!!!)
The switch on the front of an MCB is called the 'dolly' and although it stays up the inner workings of the MCB protection can remain protecting the circuit. Fire Alarm dollys are locked in the ON position by means of a dolly lock but the circuit is still protected. It sounds like the dolly is mechanically seizing so you could try switching it on and off a few times to free it up. For safetys sake I'd replace the MCB.
And of course it could be that you are unable to reset the MCB due to the fact that the lighting circuit still has a fault on it!
take out all the lamps and then try resetting the MCB if that fails then you may need to check out the whole circuit for faults possibly an earth fault ie lampholders, flexes, switches, light fittings etc.
take out all the lamps and then try resetting the MCB if that fails then you may need to check out the whole circuit for faults possibly an earth fault ie lampholders, flexes, switches, light fittings etc.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
