The MCB covering my downstairs sockets keeps tripping at infrequent intervals, maybe about 7- 14 days and when nothing has just been switched on. The mcb can be reset with no problem. I have looked in all the sockets to try to find a loose wire but to no avail and I have changed the mcb. What else can I try?
Tripping MCB
- Thread starter Davidhaigh
- Start date
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what is plugged into the circuit it total at any one time?
What is the rating of the MCB?
Pictures of the board please!
Pictures of the board please!
first are you certain it's an MCB and not an RCBO (an rcbo will have a small test button on it).
does this happen more often when it's been raining?
have you any powerful appliances plugged in?
does this happen more often when it's been raining?
have you any powerful appliances plugged in?
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are you 100% sure? What about things that have been switched on for some time? If it is a genuine ring circuit it will usually be have a 30A or 32A fuse or MCB. Has it?
A 30A circuit will run two 3kW loads indefinitely. However if you also have some other appliance such as a washer, drier, dishwasher or oven on the same circuit at the same time it will be overloaded. A kettle or toaster can do it, but is often not on for long enough.
unplug appliances that are not in use
Examine plugs for signs of scorching e.g. from loose wires inside
If not a faulty appliance, it may be damaged cable.
Common suspects are:
nail or screw into wall or floor has hit a cable (this can be very dangerous)
cables under floor nibbled by rodents
water getting into something, e,g, rain into a garden socket or a leak into a connection under sink/behind washing machine
cable under appliance e.g. washing machine has been crushed when appliance pushed back into position
It can also be a socket that has been damaged by overheating, e.g. two large appliances such as washer and drier in a double socket
3 TVs, 2 DVDs, Sky box, 3 Phone chargers, fridge, microwave, 2 ovens, freezer, 5 standard lamps, jogger, 2 laptop chargers, heated towel rail,dishwasher, washer, 2 recliner chairs, printer, security lights, cd player, ch controls
any 3 of those appliances, if running on a heating cycle, at the same time, will be enough to overload the circuit.
In round terms:
Circuit is rated at 32Amps
3 appliances at 12Amps each = 36Amps
plus whatever else you have running at the same time. The greater the overload the faster it will trip. the other appliances you mention will have lower loads, but they all add up.
From what you say, you do not have a faulty circuit, you have an excessive load.
Do you want advice on how to deal with it?
JohnD";p="1378079 said:
Nothing out of the ordinary and not on at time of tripping
Yes please
If, as you say, it trips when none of those heavy loads are on 
then I would suspect cable damage as described above.
As for spreading the loads so that the circuits will not be overloaded, consult a suitably qualified electrician and say you want a separate kitchen/Utility room circuit so that your heavy appliances like washer, drier, dishwasher will not be on the downstairs ring; and a separate Cooker circuit. If you do not already have separate upstairs and downstairs rings, get that changed.
(this is all modern good practice when houses are being wired. As well as preventing overloads, it also means that in the event of a fault, most appliances that are not on the faulty circuit continue to work. For best results, have the circuits fitted with RCBOs (this will cost about £30 - £50 extra per circuit, but will mean that each has its own RCD so an Earth Leakage fault will not affect the other circuits). This is done on superior quality installations.
If you have any heavy-load appliances that are on a lot, you can have them put on a separate radial circuit, so that they do not put a load on the ring. This includes air-con, a Shed or outbuilding if you use an electric heater in there during the winter, or a garage if you use machine tools or welding equipment or anything out of the ordinary.
then I would suspect cable damage as described above.As for spreading the loads so that the circuits will not be overloaded, consult a suitably qualified electrician and say you want a separate kitchen/Utility room circuit so that your heavy appliances like washer, drier, dishwasher will not be on the downstairs ring; and a separate Cooker circuit. If you do not already have separate upstairs and downstairs rings, get that changed.
(this is all modern good practice when houses are being wired. As well as preventing overloads, it also means that in the event of a fault, most appliances that are not on the faulty circuit continue to work. For best results, have the circuits fitted with RCBOs (this will cost about £30 - £50 extra per circuit, but will mean that each has its own RCD so an Earth Leakage fault will not affect the other circuits). This is done on superior quality installations.
If you have any heavy-load appliances that are on a lot, you can have them put on a separate radial circuit, so that they do not put a load on the ring. This includes air-con, a Shed or outbuilding if you use an electric heater in there during the winter, or a garage if you use machine tools or welding equipment or anything out of the ordinary.
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