Bg consumer unit swap issue

[Duane B]

So a job today involved swapping over a domestic consumer unit due to shower swap and bathroom lights being altered and no rcd present. And previous spark fitting a dreadful cheap plastic c/u. & taking the customers money and run. 

1 x final ring only for up and downstairs sockets Inc kitchen. 

1 x converted cooker circuit into a single socket outlet on fridge.

1 x 1.5 mm radial that's supplying an immersion heater hmmmmm yes looks a bit heated. But bells out OK.  Advised replace. 

1x 10mm shower circuit 

Up and down light circuits with borrowed neutrals. 

House 45 year old since last rewire. All cables in pvc/pvc T/E

major issues with rcd nuisance tripping. Broken down circuits to problem ones by placing lights and shower on one rcd side leaving.  Ring. Radial and immersion on the other rcd.  Put immersion on high integrity for testing purpose on its own out the way. 

Immersion in 1.5mm and found immersion element down. Problem sorted. No no no. Still tripping rcd.

Final ring main on one 32A passes insulation resistance tests on all cross interconnected cables.  Nothing reading down. Inc converted radial to a single socket. 

As soon as a fridge. Kettle. TV extension lead plugged in or switched on or plug pUlley out or placed in. Trip trip trip on the rcd rcd won't turn back on until you have waited 30 50 seconds for it to discharge.  Ramp tested rcd trips out at 33 milli amp.  So not to sensitive.  Then it stays on. But then it will trip seconds or 60 min later. Grrrrrrrrrrrrrrrrr to it. 

I'm thinking sockets all knackered . Old type held in with 4 pins 2 top 2 bottom. Didn't wanna remove incase further problems start. 

Plus. After having a nightmare all day and having to put a bypass in to keep the socket power on for the couple. 

Customer advised they had some sort of a surge. Lightening strike  Blew anything connected in the sockets. Even blew plug's out. So why is ir tests all coming back good. 

there was no bonding at all either. As previous spark never fitted it. It's now fitted with the new board gas and water. 

Sooo what we thinking guys n gals. Because I have had a day from he'll on this.  Advised it needs rewire. But why the tripping. Could try new rcd and remove some socket fronts when I go back. 

What a nightmare. 

 

[ProDave]

IR testing of circuits and BETWEEN circuits will sort all of this. Did you do any testing before CU swap?

An RCD trip under load on a circuit that tests ok will most likely be a N-E fault on a different circuit connected to the same rcd.

It won't be the old socket fronts of IR and continuity are okay.

 

[Barx]

Could be a number of things from neutrals being in wrong neutral bar, to shared neutrals, to leakage, to cream crackered appliances to poor connections (missing neutral connection).

Thorough testing of the circuit conductors is usually the easiest way to find such issues. Make sure you haven't mixed the RCD neutral fly leads up in the CU leading to you thinking you have circuit neutrals connected right, but it actaully being wrong.

 

[Murdoch]

This is why I won't fit dual RCD boards anymore ...

Are you 100% sure that all the cables are in the right neutral bars? and that with everything disconnected the IR is over 2 meg ohms?

Why did you recommend rewiring the immersion - 1.5 should be good for 17A, depending on the installation method.

You've done well to do a comprehensive CU change, install bonding and all this fault finding in 1 day!

Sounds like you only have 5 circuits, so I would add the radial to the "good" RCD which should leave you with just the sockets - them just be very methodical with your testing.

Do you have a clamp meter? Its possible that leakage from 1 circuit can affect another on the other RCD.

 

[Sharpend]

Didn't I read that when everything is plugged back in it was trip trip trip? Is there a clue there????? 

Or was it tripping with nothing plugged in??? 

 

[Duane B]

1st thing I did was check and double check fly leads I.e on netral bars etc. Been caught out before on that. All 100% . Ring intact on end to end testing. Insulation resistance >500 Meg 500vdc

Even tested as a double check on a 1000vdc result   greater >1000

i.r done between. L to E and L,N to E & N to E. Etc all OK.  

Lights at 18 M ohm  but there on 2nd rcd holding. Which ramp tests at 27 milli amps. 

Still think sockets as low ohm test all over the show on shutters being worn. But never had troppo g on worn shutters before. 

Everything unplugged. It trips. Thought at 1st fault on appliances. I.e fridge etc. Even with something of mine it trips. And it's all pat tested. Lol.  Gonna make up an earth leakage test lead. Immersion cable melted in parts hence rewire that signs of overload. Plus I've always done them in 2.5mm

One ring on a whole house Inc kitchen not the best really is it on 50 year old pvc pvc

 

[binky]

sounds like a 'knicked cable' ie socket front plate screw touching neutral, not enough to cuse dead short, but will develope over time into proper short .

 

[Duane B]

Thought a 1000 vdc would of shown something. Yes I no guys I'm a butcher. Lol but when your up against it I like to get fullness out the meter. Lol. Still didn't read down.  Was hoping my mate was holding the other end. Lol

 

[M107]

Best one I had like this & it took an age to track down....

Turn any big appliance on in the house on any socket circuit (6 to choose from) off went the RCD. Pump in a garden pool was at fault.

Doesn't help I know, apart from dont always assume it is as simple as a trapped cable.

 

[Duane B]

Lol. Yeah no what ya mean. Went to kitchen switched kettle on. Yes Trip. 

Got kettle in living room switch on. Tes Trip. 

Go to fridge of radial unplug switch off etc trip. 

TV on 4 way ext. Switchbtv on trip. Reset. Unplug ext. Trip. 

Had to bypass rcd. At least lights and shower on rcd. But sockets oh joy. Nuisance tripping unreal. When it plays up they do test your patience don't they. 

And ramp test shows 33 milli Amps. Biatch Ring.  Lol

Still rekon surge that blown socket plugs out wall have done something. Lol apparently 

 

[binky]

forgot to state the obvious - you've probably got in a tiswas trying to rectify ****e electrics. Go back to basics, 1 cct at a time, split ring in middle and test 1 leg etc etc.

I worked on a house that had suffered a lighting strike on the overhead pole many years ago. Board was foobarred but cables were OK, so rushed 16th edition bord change later I had  a fault on the lighting. After much firkin about in the attic (it was chocker with collected family stuff) it tuned out to be the shaver light at the very end of the cct that as been 'repaired' by owner.

 

[Murdoch]

If it's a high integrity board, can't you just put the sockets on a MCB until you locate and fix the fault.

when you do your ir tests, the cpc was connected to the cu Earth bar?

 

[Sharpend]

Is there an outside light with a dodgy lamp fed either via socket cct or separate circuit on same RCD? 

 

[M107]

Binks is right, divide & conquer........ Split the ring as the first task.

Do that & post the readings as you dont say what they were when you tested.

 

[Duane B]

If it's a high integrity board, can't you just put the sockets on a MCB until you locate and fix the fault.

when you do your ir tests, the cpc was connected to the cu Earth bar?

Dropped another isolator in replace of the rcd. So no integrity now. And circuits being tested was completely  dropped off all bars no connections.  End to ends were all around 0.35. And 0.55 cpc

Is there an outside light with a dodgy lamp fed either via socket cct or separate circuit on same RCD? 

There was. But double pole spurs was switched off

 

[Duane B]

forgot to state the obvious - you've probably got in a tiswas trying to rectify ****e electrics. Go back to basics, 1 cct at a time, split ring in middle and test 1 leg etc etc.

I worked on a house that had suffered a lighting strike on the overhead pole many years ago. Board was foobarred but cables were OK, so rushed 16th edition bord change later I had  a fault on the lighting. After much firkin about in the attic (it was chocker with collected family stuff) it tuned out to be the shaver light at the very end of the cct that as been 'repaired' by owner.

Even choc blocked one leg out of the c/u to see if any difference. Trip trip.  Gotta go back so I'll retest fresh eyes N all as they say at least they got power and it's a better state than found. 

 

[Sharpend]

When you're doing IR do the figures creep in any way? 

 

[Doc Hudson]

. And circuits being tested was completely  dropped off all bars no connections. 

Did you keep the CPC's connected to main suppliers earth during IR tests?

Did you test RCD's with all circuits disconnected?

(For what its worth, if only five circuits I would have fitted a full RCBO's board not a dual RCD CU)

Doc H 

 

[Duane B]

Did you keep the CPC's connected to main suppliers earth during IR tests?

Did you test RCD's with all circuits disconnected?

(For what its worth, if only five circuits I would have fitted a full RCBO's board not a dual RCD CU)

Doc H 

I understand. But when you got a 10 way on the van spare. Thought I'd fit it.  Ramp test was with all circs disconnected and then rcd tested at outlets. Plus I always test ir with cpc disconnected.  Full dead tests nowt connected to board. Ensuring safe to do so of course  I.e customers clients out the way.  Plus 5 way rcbo board extra cost to customer. Due to rcbo prices

 

[Murdoch]

 Plus I always test ir with cpc disconnected.  

Thats the wrong way of doing it  - all CPC's and earthing must be connected to the CU when conducting IR tests....