mcb tripping

cherokee · Posted: Mon Oct 10, 2005 5:15 am Post Subject: mcb tripping

I have recently had a new circuit board fitted. Also new sockets in kitchen and bedrooms. Recently the mcb (ring) keeps trippin overnight causing all the mcb`s to trip.If i disconnect everything, and reset the (ring/ sockets) leaving the other mcb off, the main flick switch will reset after about twenty flicks on and off. This will then hold for about 18 hours or so. My electrician can find no earth faults or hot sockets. any ideas??

Lectrician · Posted: Mon Oct 10, 2005 6:15 am Post Subject:

HOT sockets -

RCD main switch I assume??

Do other MCB's trip did you say, or just the socket MCB??

You need another, decent spark, who can use an insulation resistance meter correctly.

cherokee · Posted: Mon Oct 10, 2005 1:25 pm Post Subject:

The (ring/socket) mcb keeps tripping causing the RCCB to trip.
If I turn off all the other mcb`s, and then reset the (ring/socket) mcb, I can then after about twenty flicks of the RCCB, can manage to reset this mcb. Then I can reset the other mcb`s. The problem only seems to occur after about 12 to 18 hours, when I have to go through the same procedure again !!.

Lectrician · Posted: Mon Oct 10, 2005 3:18 pm Post Subject:

The MCB trips aswell??

What sort of loading is on the ring?? Anything unusual??

Any outside sockets, or a feed to a garage/shed from that ring??

Both trips go at the same time??

Do you know your earthing arangements (TN-S, TN-C-S, TT)??

How old is the installation??

What is the rating of the main RCD(I expect 30mA, which isn't ideal, a split load arrangement would have been better)??

What is the rating of the MCB tripping (hopefully 32amp)??

sparxfly · Posted: Mon Oct 10, 2005 8:46 pm Post Subject:

might be a long shot but try unplugging any items in kitchen such as , washer,dishwasher,sometimes these cause problems as components burn out and create an earth leak which would trip your rcd out. also kettles,irons and cookers trip the rcd out as well. if rcd doesnt reset then your electrician needs to take out neutrals one by one until rcd resets.
this is just another path to try.

Rob F · Posted: Mon Oct 10, 2005 9:06 pm Post Subject:

Do you have a washing machine connected via a single pole spur?

There could be a neutral fault on the heating element which could cause the rcd to trip even with the spur fuse removed. Disconnect the neutrals in the spur to prove.

cherokee · Posted: Tue Oct 11, 2005 3:24 pm Post Subject:

Thanks for your replies.
The main rcd is rated at 30ma.
The mcb is rated at32A.
there are 5 sockets on this ring circuit.
circuit impedance is; 0.73(phase) 0.68 (neutral) 0.56(cpc)
insulation resistance; p/n 199.9 p/e 199.9 n/e 199.9 max earth fault loop impedace 0.98
the kitchen sockets are not supplied by this ring.
there is a socket going to the outside garage, but noone can find where this enters the house as the previous owner has concreted a drive over gap between house.
The installation is new. well new kitchen sockets and wiring, new consumer unit. new wiring in bathroom/shower all correctly sized and protected.
new sockets throughout, but aluminium wire/no earth cabling throughout.
the installation was carried out about a month ago, all seemed fine until this last week!!. electrician has been back and double checked everything and has had all face plates off, and can find nothing wrong. Could the new mcb be faulty?. I dont think the aluminium cables can suddenly detiriorate after 30 years, can they?.

Lectrician · Posted: Tue Oct 11, 2005 4:25 pm Post Subject:

Aluminium? Tinned copper, I hope

So no wiring has been renewed.....just the fronts?? False economy!

Those test results do look good. The MCB, if faulty, wouldn't cause the RCD to trip.

Has your spark fitted a new Consumer Unit then?? Why the 30mA trip as the main switch?? What earthing arrangement do you have (any earth cables going into the electricity boards service head)??

Does the trip go day or night in particular??

Does the MCB and RCD ALWAYS trip together??

What do you have plugged into this circuit exactly?? Can you turn that one circuit off, and tell us EVERYTHING that no longer works??

cherokee · Posted: Tue Oct 11, 2005 4:43 pm Post Subject:

Hi,
The mcb and rccb always trip together. The fault happens during the night, never during the day when the sockets are being utilised.
The ring circuit supplies 5 sockets . (lounge)1 x standard lamp, 1 x televisio/dvd. 1 x display cabinet. Bedroom 1 x double socket (alarm clock). bedroom 2 1 x double socket pc/printer.
even when i unplug everything the ring mcb and rcd will trip during the night.
I am unsure of the earthing situation.

Lectrician · Posted: Tue Oct 11, 2005 4:56 pm Post Subject:

Re the earthing system - take a look at your meter, adjacent to the meter will be a 'service head' where the overhead or underground cable terminates. Look for a green/yellow earth wire going INTO this head. Let us know.

Do you have Economy 7 heating, or maybe just Economy 7 for your hot water??

Is it the same sort of time at night, or random??

Any security lights outside??

Garage deffinantly not on this circuit??

How many Consumer Units do you have?? Just one larger one, or maybe a couple??

cherokee · Posted: Tue Oct 11, 2005 6:41 pm Post Subject:

Many Thanks for your reply lectrician. I am at work at the mo so cannot check the service head at the minute. however i do remember a large earth cable bolted to the consumer unit back board. We used to have economy 7 heating but this along with the control unit was dismantled when the consumer unit was replaced. We also have security lights but this does not affect the tripping problem. I will have to investigate the location of the feed for the garage as this is a bit of a grey area at the mo. Im not sure if the fault occurs at a regular time, as it must happen 3 4 5 oclock am. I will set an elec hand clock tonight to ascertain.
There is also only the one consumer unit.
The kitchen was a full rewire along with 9 new sockets and also the addition of a combi boiler unit. I agree the replacement sockets do seem to be a bit of a false economy, but at the time the wiring was checked and was tested perfect, so it wernt broke so i didnt try to fix it. I will post back in a couple of days with the outage times and earthing situation- cheers.

cherokee · Posted: Wed Oct 12, 2005 2:09 pm Post Subject:

I have checked the service head. A large brown earth cable branches off from the incoming cable (service head) onto an earthing block on the consumer unit back board. The earth is then taken from this to the consumer unit. Also an earth is connected to the bathroom water pipes from the unit.
Also the outtage appears to be on a random basis.

Lectrician · Posted: Wed Oct 12, 2005 2:28 pm Post Subject:

It is difficult to advise much further - looks like your sparky who chaged the CU has fitted an inappropriate type of unit for your earthing arrangements. Sounds like you have a TN-S supply, and the sparky has fitted a CU as if it was TT.

This wouldNT cause the fault, and isn't dangerous, but causes problems, as the 30mA RCD is far too sensitive as a main switch for an entire installation. A split load type board would have been better suited.

I think you need a sparky to find out exactly what this circuit feeds, and get some accurate readings. If it is tripping this often, I would expect to find a fault easily with an insualtion test meter.

The only time a fault could be masked from an insualtion test meter is if it was switched off. Check for central heating time clock, immersion timer, outside security photocell or pir. Get the sparky to test PAST these.

cherokee · Posted: Wed Oct 12, 2005 4:35 pm Post Subject:

Thanks again lectrician for your sound and much welcomed advice. I will get the sparky to come out again and advise on the points you raised.
Thanks again, and I will let you know the hopefully sucessful outcome.

Lectrician · Posted: Wed Oct 12, 2005 4:51 pm Post Subject:

No probs....I have corrected my typo above.....