RCD tripping on circuits after new board change nitemare

[reeves]

just done a board change on a domestic property and i have got faults on 2 32 socket circuits nitemare is there any quick way other than obvious of starting from the first socket then all around the ring, can i measure the fault out with my megger please helppppppppppppppppppppppppppppppp

 

[PC Electrics]

Come on, throw the dog a bone!! We need more info.

What test results did you get on the circuits?
Have you checked you have connected the neutrals up to the correct bars?
Have you checked for cross connection between circuits?
Have you tested the RCD?

 

[Octopus]

What type of "faults" have you got?
How many CU changes have you done before?
Have you tried asking your scheme's technical support?

 

[reeves]

The R1 n R2 are pretty average neutrals are on the correct bars r1 r2 rn all match to there corresponding circuit yeh n then rcd trip out i must say i didnt test insulation 250 or 500

 

[reeves]

yeh i have done plenty just tried to save time rather splitting the ring n then go to each socket individual

 

[Octopus]

The R1 n R2 are pretty average neutrals are on the correct bars r1 r2 rn all match to there corresponding circuit yeh n then rcd trip out i must say i didnt test insulation 250 or 500

May be your lack of proper testing has bitten you on the bottom!

 

[Megavolt]

Try find middle fo ring split it and then test both legs at board then at least you will know which half to consentrate

 

[Octopus]

Try find middle fo ring split it and then test both legs at board then at least you will know which half to consentrate

I think an IR test would be my first step, but I'd have done one as part of the dead tests.

 

[Edd]

reading this, it looks like the IR tester's gota be dug out the bottom of the van.... 2 rings down,, either two seprate faults or the rings have got mixed up.. pretty unlucky ... you gota start with the basics, witch would be as soon as the trip went dig out the tester,, should take a sparks less than an hour to narrow it down to at least an area, and get some power on at worst on radials...

 

[reeves]

May be your lack of proper testing has bitten you on the bottom!

yeh yer rite mad murdock

 

[vernam616]

I suggest calling a electrician mate

 

[Edd]

ok too be more helpfull,,, disconect the neutrals,, leave the earths conected, they give a good refrance point.switch the mcbs off to the faulty circuits. IR test between N-E and L-E if yoo see a reading less than hmmm lets say 5 Mohm then yoo need to start splitting the ring... you really should be looking at greater than 999M ohm or at worst on a normal T and E instalaton at least greater than 100... if you do get greater than 999 then theres a crossed neutral or somthing... but start with one ring and split it. test both legs the one thats good reconect.. see whats working.. mega bad leg. split again.. and keep going..and breath...

 

[spark 68]

As Edd above said,
but I would 'soft test' @ 250V first, in case there is anything spurred off like a central heating boiler or alarm etc.

 

[vernam616]

My reluctant suggestion would have been to check the rings aren't crossed, however ive got a good reckoning that you havnt split the circuits properly on the new dual RCD board, otherwise this easy to rule out method would have been acheived straight away

 

[spark 68]

As you say Vernam,

My first move would have been to make sure the circuit was split properly (ring continuity).
Then do as Edd suggested, but first test across the now disconnected Neutrals to the other sides Neutrals @250V (to rule out any interconnections), before following on with the rest of edds recommendation but again @ 250V first, for the reasons I have already given.

But then again I would have tested for this even before, or at least during the CU change.

 

[Jdsparky]

I think mixed up the two rings might be a good call so try end to ends first as u should have done already but if not that might be the culprit....as its unlikely to be both rings that have faults on but not impossible, especially if u have put one ring on one side and one on another and both rcds trip, u may have them mixed up as I say

 

[Baconhead]

Always a good idea to carry out a few pre tests prior to carrying out a CU change in my opinion,Can save a whole lot of hassle at the end of the change.

 

[tony mc]

I think some more info is required as to what dead tests were performed.

If you say the neutrals are on the correct bars is that because you carried out the 3 step dead tests on the ring finals.

If they are correct and everything is disconnected and both RCD 's are tripping its down to IR testing.

With a 30 mA RCD it should hold above 7666 ohms so once you start IR testing if you get a 0.00 M ohms reading its time to switch over to low ohms and start to work out where the fault /faults are by spliting the ring etc as has already been mentioned!

Is there any quick test with your Megger???

If you get a low ohms reading when testing as a guide to get nearer the fault you can use a bit of maths to give you a rough distance to the fault as you will know the resistance of the cables you are testing.

Once you have completed the dead IR tests let us know the readings !!

 

[Engineer54]

Always a good idea to carry out a few pre tests prior to carrying out a CU change in my opinion,Can save a whole lot of hassle at the end of the change.

Yep!! At the very least it will tell you if any problems are found, it's not from any mistakes that you have made at the CU on completion... I mean how long will it take to carry out a few brief tests prior to changing the CU anyway??

 

[ezzzekiel]

Never understood why after a cu change people start having problems due to existing faults, if you aren't prepared to address them then should you really be changing the board in the first place?

 

[Farmelectrics]

Always do eicr on installation before you change board slow down do the tests properly once there ok you can change board in few hours it's easy knowing in advance your board is not going to trip learnt the hard way myself when I was younger lol

 

[vernam616]

Testing before or afterwards dont suppose really matters does it, its still a fault

A better thing when quoting would be to inform the client of the price and then notify them that you have a hourly charge for finding faults on on completion of the new board

Ironically i changed a board this morning, never tested before hand and powered it up, from experience i had already pre determined that they maybe a borrowed neutral from landing light, and there certainly was, so lighting circuits went onto the same mcb, not conventional maybe but not really breaking any rules

 

[micknew]

Testing before or afterwards dont suppose really matters does it, its still a fault

A better thing when quoting would be to inform the client of the price and then notify them that you have a hourly charge for finding faults on on completion of the new board

Ironically i changed a board this morning, never tested before hand and powered it up, from experience i had already pre determined that they maybe a borrowed neutral from landing light, and there certainly was, so lighting circuits went onto the same mcb, not conventional maybe but not really breaking any rules

The only rule it is breaking is that a potentially dangerous situation exists for any electrician working on the circuits who assumes that the wiring was done correctly in the first place.
Seen an electrician thrown off steps due to a borrowed neutral.

 

[vernam616]

Well whats he doing working live then?

The lighting circuits are on the same MCB, so if anyone needs to work on this circuit they should be isolating

I could understand your point if i had put them on seperate mcbs on the same side

 

[telectrix]

even then, you isolate the circuit, then before anything else, check (at the fitting or whatever you are working on) for dead.

 

[micknew]

Still a wiring which was not carried out correctly due to ignorance of the original installer.
You cannot condone borrowed neutrals left on an installation.

 

[vernam616]

Have a little think about what you post before hitting "post reply" button Mick

 

[micknew]

even then, you isolate the circuit, then before anything else, check (at the fitting or whatever you are working on) for dead.

Agree Tel.

 

[micknew]

Have a little think about what you post before hitting "post reply" button Mick

I did.

 

[vernam616]

Nobody said they condoned it, but if the client doesnt want damage or cannot afford to have the circuit altered the alternative is putting them onto the same mcb, yes not conventional but practical and still safely protected by mcb and rcd. Do you understand that if someone isolates that mcb that the neutral wont be live?

 

[vernam616]

Agree Tel.

You have just agreed with him disagreeing with your post of how its potentially dangerous, yet again this forum never ceases to amuse me with some of the comical members

 

[telectrix]

the problem could arise if you had too many lights on the 2 circuits for the 6A MCB. fair enough if wired in 1.5mm, you could uprate the MCB to 10A ( subject to no serious derating issues ), but if circuits are in 1.0mm, then you'd be in the fertilizer

 

[micknew]

Yes I completely agree with you, and take your point that its down to the client whether they want to pay and have it put right.

 

[micknew]

You have just agreed with him disagreeing with your post of how its potentially dangerous, yet again this forum never ceases to amuse me with some of the comical members

Didn't mean to make you laugh, honest.
Just pointing out the bleeding obvious.

 

[vernam616]

Definatley Tel, but elaborated too much on the original theory

The idea of couple the two circuits into one mcb isnt dangerous, unless like you say about derating etc... But then you could argue an "electrician" would know this

 

[vernam616]

Please tell me Mick what was obvious?

Ill tell you whats obvious and if you are an electrician shame on you as its basic stuff

If i couple them two circuits into one mcb and isolate it means no power is going out which means nothing is coming back on the neutral, thats what made me laugh, as its simple theory, if you cant grasp that you shouldnt be working on equipment or trying to tell an electrician that its "potentially dangerous" as the next electrician could get a belt

 

[T&Earth]

Hi I agree, but sometimes you get an old 4 way BS3036 board with NO extra play on cables with CPC & neutrals twisted together and to carry out these test with old board in is virtually impossible.

T&E

Never understood why after a cu change people start having problems due to existing faults, if you aren't prepared to address them then should you really be changing the board in the first place?

 

[ezzzekiel]

Regardless of anything, if you can't trace and fix faults then your in the wrong job.

Sharing an mcb as stated removes the borrowed neutral as it becomes a single circuit, prefer not to see it done this way but sometimes it's the only option

 

[SirKit Breaker]

Its no good clutching at straws.
It is because of things like this that we test the way we do.

Do all the tests, and in the correct order, you will then know if you have a problem with the fixed wiring, and you will be able to identify the reason for the RCD trip, especially if you have a very low IR result, or some interconnection with your circuit.

I will assume that as you have done this job, you are registered or have notified if not, and so you are competent to Inspect and Test, so i dont need to go in depth with these testing procedures, it is all in your GN3 anyway.

Cheers.............Howard

 

[Farmelectrics]

Vernal what would happen if you didn't test before hand and fitted new board and the ir tests were that poor due to old cables that they wouldn't take rcd board rewire would be needed better to no condition of installation before hand

 

[vernam616]

You use a bit of common sense and have a think of the age when taking board cover off, the surroundings also give a good indication


Of All the boards ive changed now its never bit me in the arse( and trust me its a hell of a lot of boards)

 

[Farmelectrics]

That a a fur shout but isn't it still better to do some per testing work it's only a couple of hours work and can save you a load of hassle

 

[mheyes]

I think you should have done an EICR before swapping the CU. It is a good reference to accompany an electrical installation certificate. It goes a long way to show what you did and what you did NOT do. If something did go wrong with the job six months down the line you will need all the proof you can get, Remember in a court of law ‘HEAR SAY ‘ is not admissible as evidence ! ! ! !

 

[Engineer54]

That a a fur shout but isn't it still better to do some per testing work it's only a couple of hours work and can save you a load of hassle

Shouldn't need a couple of hours, you only need to do some quick confirmation tests on any rings and lighting, (borrowed neutral syndrome..lol!!) That should be sufficient for most homes. The problems come, if you DO find things wrong!! lol!!