RCD tripping and MCB has 3 rings coming out of it

armbase · 14 Apr 2008

Hi All.

IN my CU I have an RCD controlling 2 MCB's. One MCB is causing the RCD trip.

The offending MCB is used for my livingroom and 2 bedrooms. Now it has 3 live (red) wired coming out of the top if it.

I intend checking the area that each of these wires cover by disconnecting one at a time and finding if the RCD doesn't trip. If it doesn't then I can light test the sockets to see wher ethe power is isolated on the defective ring.

Is it normal to have 3 wires coming out of a MCB?

If there is one room that is causing a problem then is it more likely to be
A) a wire
B) a socket (I can check by using blocks to see if the problem is alleviated) or
C) All of the above

Cheers
Bob

333rocky333 · 14 Apr 2008

I would say more likely something plugged in or connected to a FCU.
It may be the wiring, but I would unplug everything on the circuits first and switch off the FCU,s if any.
Socket unlikely,to cause a fault, unless damaged or wet

armbase · 14 Apr 2008

333rocky333 said:
I would say more likely something plugged in or connected to a FCU.
It may be the wiring, but I would unplug everything on the circuits first and switch off the FCU,s if any.
Socket unlikely,to cause a fault, unless damaged or wet

Oooops Sorry I forgot to say that everything is unplugged from the circuit.
And it happened when were were doing nothing.

AND I have to say that this is a great site. A reply in about 10 mins.

Thanks for the help

Best regards
Bob

PS I can help with Computer/software stuff So I'll do my bit to become "part" of the community.

JohnD · 14 Apr 2008

(d) a nail through a cable

(e) water leak esp near boiler or pump

(f) mouse gnawing cable

Chri5 · 14 Apr 2008

The 3 x reds is likely to suggest ring in / out (that's 2) and a spur direct from the MCB

333rocky333 · 14 Apr 2008

There are 3 reds
2 of them might be one ring , it starts there goes whereever and returns,
The other third wire ?

It could be 3 radials ,one per room , what size is the mcb

If it is a ring
if you disconnected them as you say one at a time, two of the reds when connected one at a time , would do the same sockets
So be carefull as with one connected , one of the disconnected reds might return and become live.
Is it tripped now and wont reset, because if it is only tripping once a day, you are unlikely to find the cause the way you say.

JohnD · 14 Apr 2008

If you have a meter you can do a continuity test on the reds to see if there seems to be a ring and if the other is a spur. However lack of continuity can be a broken ring. Continuity test on the associated blacks, and at a socket, will give more clues. resistance tests on the reds and the blacks and the associated G&Y will give ring confirmation (but G&Y may have parallel paths esp from Supplementary Bonding).

You can disconnect the spur red (if it is one) and see what stops working.

Taylortwocities · 14 Apr 2008

And while we are talking about "blacks". Your fault could be on the live or the neutral conductor.
So when you are disconnecting the reds from the MCB - to localise your fault - you must also remove the associated neutral (black) from the neutral busbar otherwise your RCD will still trip!

armbase · 14 Apr 2008

333rocky333 said:
Is it tripped now and wont reset, because if it is only tripping once a day, you are unlikely to find the cause the way you say.

Yesterday it wouldn't stay on and was tripping continuously.

It has never tripped before but now it is okay (just home from work). Just before the trip I'd washed the floor but didn't use much water. And certainly not as much as previously. I can only assume water got in somewhere.

Should I get an electrician out to check things properly or just wait to see if it reoccurs?

All the best
Bob

JohnD · 14 Apr 2008

you need to find the fault

if it is a damaged cable it might seem to disappear

if it is water penetration it will come back at an inconvenient time.

It will not magically repair itself.

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RCD tripping and MCB has 3 rings coming out of it

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