MCB Keeps Triping

[the_parkster]

I've recently extended my socket ring by two double sockets. All seemed OK for a few days, but now, every couple of hours the MCB trips and the socket ring go's down.

I am right in thinking this is an overload issue as opposed to a short circuit, as if it was a short circuit the MCB wouldn't let me reset?

If so, can I increase the fuse/MCB for the socket ring main, or do I just need to watch how many appliances I have on at any one time?

Any advice would be greatly appreciated.

Many thanks, Andrew

 

[ban-all-sheds]

You can't just blindly fit a bigger MCB - it's job is to protect the cables from being overloaded and prevent fires etc.

What rating is the MCB?

What size cable has been used for the ring main (original and your extension)?

What appliances were already used on the ring?

What new ones have you added with this extension?

 

[totty]

Have you extended the ring or are the double sockets spurs ?
You can only have 1 double socket per spur !

not that this would cause the MCB to trip.

Does it still trip every couple of hours if you have nothing or very little running on the ring ?

 

[the_parkster]

Thanks for the advice guys. I'll check the MCP rating tonight and drop a note back on.

The new double sockets are on the ring, as I extended the ring rather than take spurs.

Appliances on the ring are, frigde/freezer, washing machine, microwave, dishwasher, portable TV, electric heater, kettle, small radio.

Cheers, Andrew

 

[Kimba]

Also, a quick test would be to unplug everything from the ring that is currenty off due to trip MCB, then see if the MCB will re engage with zero load. This isn't a perfect test, but would certainly indicate if a fault condition or an overload condition is most likely.

Bare in mind, if the electric heater, kettle, dishwasher and washing machine where all on at the same time, you could be very close to the maximum rating of the MCB if it is a standard 32Amp.

 

[ban-all-sheds]

That looks like too much. Obviously it depends what is on simultaneously, and at what stages in their cycles (have you noticed any patterns?), but look at the potential:

F/F 500W? 1kW?
W/M up to 2.5 - 3kW
microwave 1kW?
D/W up to 2.5 - 3kW
TV 200W
electric heater 1 - 3kW
kettle 2-3kW
small radio. negligible

Total 7-11.5kW? 30 - 50A?

You can read about assumptions, and diversity with regard to kitchen appliances here .

My best guess is that you are going to have to split the load across two circuits. Which are the appliances that you introduced onto the ring via these new sockets?

 

[Kimba]

My thought exactally, and if the washing machine is heating water, plus turning the drum, you have the initial stall current of the motor + heating elements, in addition to kettle which could even be a 4kw disc one, a 2kw heater day, and a d/w (again heating water).

Either way you will be sailing close to the wind, and even change the MCB for the same rated C curve model, you are likely to trip it from overloading. The fact it worked for a while before would also indicate that it is perhaps the fact you recent tried to do too much at the same time?

 

[the_parkster]

Guys,

It's actually the RCD on the fuse board that's tripping out, not either of the MCB's on the socket rings! Does this mean I defo. have an earth fault?

If so, how come the RCD let's me re-set it and then it intermittently trips, sometimes it will be 30mins before it trips and sometimes it 2 - 3 hrs?

All advice appreciated.

Many thanks, Andrew

 

[breezer]

there is an intermitant earth fault, your freezer / fridge is doing it, faulty new wiring.

has freezer always been on this ring?

i would suspect faulty wiring, take all new sockets off and check you havent "nicked!" a cable MAINS OFF FIRST

 

[the_parkster]

Cheers for that. I'll check all the new sockets, plus the existing ones I've had the front plates off tomorrow - in the light, with the MAINS OFF!

The fridge/freezer has always been on this ring. Also, I did notice that a few of the back boxes were not earther, can I just run some earth cable from the back box earth screw to the face plate earth screw (obviously using the green/yellow sheaving for identification?

Many thanks, Andrew

 

[ban-all-sheds]

Not only can you run an earth wire as described, you should do it...

 

[securespark]

Ban

The IEE says you no longer need to link the earth from the accessory to the box if it has a fixed lug (as opposed to older boxes that had two adjustable lugs).

To posters reading this - please if you are in any doubt, fit an earth link between box & socket anyway.

 

[ban-all-sheds]

I said "should", not "must".

The IEE may say it's not needed any more, but I think it's good practice. The threads on the screws or the lugs can get damaged, and not work very well. Corrosion could reduce the efficacy of the contact. People sometimes lose the screws, and use a replacement which "almost" tightens up properly.

I know it's extremely unlikely, but your life might depend on a good electrical connection across the small surface area of contact between the threads on the screw and the box lug. I shall carry on using an earth wire.

 

[securespark]

Ban

Wasn't having a go, just repeating info gleaned from IEE over the years.

 

[the_parkster]

Guys,

I've sorted it!!!

The RCD tripped last night and would not re-set, two of the circuits protected by the RCD would come back on, but the downstairs sockets would not.

I took off all the face plates for the sockets that I'd put in or had taken off to decorate, etc., put them all back on ensuring the connections were sound and it still tripped out!

Right I thought, lets take them all off and stick on terminal blocks to see if the ring circuitry itself was OK. I took of the first face plate, stuck on a terminal block and thought well lets just see if it's OK now (as the face plate looked a bit old and tired) and hey presto everything came back on.

It was a fault in the bl@@dy face plate!

Replaced the face plate and everything is now all OK - put all the appliances on at the same time and not a sniff of a trip in sight!

I would like to thank all who replied, as I could not of done it without the advice/guidance of you guys.

Many thanks, Andrew