MCB tripping and takes out RCD

[scotsguy]

Any help will be greatly appreciated!!
Had house rewired 8 years ago everything fine. 3 Weeks ago down stairs socket ring tripped the MCB but the RCD tripped too and took out everything (on the RCD protected side). Checked the cables for breaks/rodent damage, none. PAT tested all the equipment on the ring all ok. It now does it upto 7 times a day, sometimes at daft o clock in the morning. Sometimes reset is simple, sometimes takes numerous attempts before the MCB will stay put. I'm now at my wit's end, wifey wants a divorce and I want to plug my chair in!!

 

[telectrix]

with nothing plugged in, IR test the circuit.

 

[Paul.M]

IR test the cable.

What outside equipment have you got on that circuit? It's been wet the past 3 weeks.

Is the boiler or any other heating elements on this circuit?

 

[Guitarist]

Hi scotsguy. You say that you had the house rewired. I'm assuming that it wasn't you that did it, so I would suggest getting an electrician in to find the fault. As others have said, IR testing the circuits needs to be done first of all. If it trips several times a day it will be an easy fault to find with the right gear and knowledge. I must admit, PAT testing the equipment would be a long way down on my list.

 

[scotsguy]

Hi scotsguy. You say that you had the house rewired. I'm assuming that it wasn't you that did it, so I would suggest getting an electrician in to find the fault. As others have said, IR testing the circuits needs to be done first of all. If it trips several times a day it will be an easy fault to find with the right gear and knowledge. I must admit, PAT testing the equipment would be a long way down on my list.

Thanks, guitarist (and all the others) You're right I didn't do the rewire, I'm only a mech eng !! The sparky that did the rewire had a go at finding the fault to no avail. His parting comment was " Sometimes these problems can't be found, folk just live with them"? Erm..... no. Nothing else is on the ring, the water heater is independent, outside PIR lights are on the lighting ring, with everything unplugged it still trips, how if nothing is pulling power?
My head is now mince.

 

[mogga]

neutral earth fault if no load As for "living with it" WTF Post your location and there may be a member close by to offer assistance

 

[Des 56]

Thanks, guitarist (and all the others) You're right I didn't do the rewire, I'm only a mech eng !! The sparky that did the rewire had a go at finding the fault to no avail. His parting comment was " Sometimes these problems can't be found, folk just live with them"? Erm..... no. Nothing else is on the ring, the water heater is independent, outside PIR lights are on the lighting ring, with everything unplugged it still trips, how if nothing is pulling power?
My head is now mince.

You dont seem to have for one moment accepted that attitude and rightly so
I and most other sparks would give an almost cast iron guarantee that the fault would be found

You need to make sure the person you employ is competent,perhaps make the job a pay by result contract,it may frighten the chancers off,there are a lot of them saturating our trade in the domestic market unfortunately,scheme members included

Use one of the forum members near to you as advised,there would be a better chance of getting someone decent (they would lose face if they were not up to the job)

 

[telectrix]

spot on des. i don't think any of us would like to admit that we failed to find the fault. TC would have a field day. LOL.

 

[spark 68]

It cannot be just a N-E fault Des, it's taking the MCB out with the RCD.

My thoughts (apart from the usual IR test), are is anything spurred off of it, Alarm panel, aerial amplifier, outside supply, JB under the floor etc..etc.. ?

An IR test and splitting the RFC would almost certainly find this fault or at least narrow it down to one section in fairly short order.

 

[Guitarist]

To suggest you live with an RFC tripping several times a day is ridiculous. Did he actually use any equipment when he "had a go at finding the fault"?
Definitely no fused spurs anywhere off the ring, or maybe something in the loft?

 

[Ponty Massive]

Thanks, guitarist (and all the others) You're right I didn't do the rewire, I'm only a mech eng !! The sparky that did the rewire had a go at finding the fault to no avail. His parting comment was " Sometimes these problems can't be found, folk just live with them"? Erm..... no. Nothing else is on the ring, the water heater is independent, outside PIR lights are on the lighting ring, with everything unplugged it still trips, how if nothing is pulling power?
My head is now mince.

Ha ha, a tradesman who knows his place !!!! Only joking, my Father was a Mechanical Engineer.......He reckons I must have been a Spark on my mothers side

 

[Des 56]

It cannot be just a N-E fault Des, it's taking the MCB out with the RCD.

My thoughts (apart from the usual IR test), are is anything spurred off of it, Alarm panel, aerial amplifier, outside supply, JB under the floor etc..etc.. ?

An IR test and splitting the RFC would almost certainly find this fault or at least narrow it down to one section in fairly short order.

I plead innocent M'lord I never said nowt like that sir (in my best Yorkshire accent) :cowboy:

 

[spark 68]

I suppose you could be really unlucky in that there are two or multiple faults (like I usually seem to get), but an IR test would still find the problem area/s fairly quickly.

 

[robsparky1975]

A sparky that can not fault find is well not a sparky,may only take upto an hour or sooner,but any decent electrician would trace your fault,the one you have used is not doing you a good service at all.

 

[Strima]

His parting comment was " Sometimes these problems can't be found, folk just live with them"

One word, COCK. I am not an experienced sparky by a long shot but I wouldn't leave a customer hanging like that.

 

[ianphilip007]

does the rcd trip when nothing is plugged into the circuit? or only when appliances are attached? This is the first question your electrican should of asked himself, imo I would unplug everything from the ring main and then if rcd still trips you would know you have a circuit problem rather than an appliance with earth leakage. the problem with the fault you describe is that it appears intrtmitent so the rcd will reset suggesting that there is no direct n-e or l-e fault. as has been suggested the ring circuit needs to be broken down or halved and halved again to find the sections with the fault. if i had to guess sounds like a insulation breakdown or maybe a damp section of cable rather than a direct n-e at a socket box

ir test will find just got to perservere

 

[ianphilip007]

to add with the rcd being able to be reset the fault may only be there at certain times so a log of when thr rcd is tripping may help any prospective fault finder just a thought

 

[spark 68]

Hi Ian,

It is taking the MCB with it too.

 

[ianphilip007]

if its taking the mcb out as well then that suggests the fault must be on the live side, live to earth rather than the n-e side on the ring main. but again it appears to be intermitent so something external or external conditions must be causing the fault condition as the op says it occurs under no load conditions. if the ir test results were ok id be looking for possible external causes ( dampness due to wet weather ) that has caused the intermitent tripping. to my mind if it was a damaged cable or a direct fault the rcd would not reset and would make this fault easier to find the fact that it will rest and hold (mcb and rcd) points to insulation breakdown, but it has only been rewired 8 years ago) or external causes

 

[Richard Burns]

Agree with the advice above.
I had a fault a bit like this once tripping for no apparent reason, tested OK, but eventually found an outside cable that was swinging in the wind against a wall and had rubbed through the insulation, if it was wet and windy the cable would short and trip; if the wind was different the cable was away from the wall and would test OK and not trip.