Discuss Main RCD Tripping & Not MCB in the Electrical Forum area at ElectriciansForums.net

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DIY expert tried changing his own Consumer unit from an old 3036 re-wireable CU to a 18th Edition (100A main switch / 63A 30mA RCD / 7x MCBs) I was called out because he couldn't get his sockets (ring main) back on - NEITHER CAN I, I HAVE TRIED EVERYTHING I THINK...
The Lines are terminated into the MCB (off position), the Earths terminated and the Neutrals left out - just touching the neutral bar with the conductors trips the main RCD even though the MCB is off - Any suggestions?
 
  1. IR Clear
  2. End to End Resistance - R1 0.26 / Rn 0.28 / R2 0.44
Thank you for replying / not come across this fault before

What does IR clear mean?
What value of IR have you measured L-N, L-E and N-E?

Is there someone you could ask to help with this as I assume you are pretty new/inexperienced you've not come across a N - E fault before?
 
If your MFT allows you to press and hold the test button when doing an IR test to keep the test voltage applied, I would encourage you to hold the button for at least 30 seconds and keep an eye on the reading/virtual analog needle if you have one and see if there are any sudden drops that return to a high value before dropping again and then returning.

This can be indicative of a pin ----- in the insulation with say a conductor pressed up against an earthed metallic back box or another conductor with damage or the CPC.

Also remember... if it is a neutral-earth fault, it may not be on the circuit you initially think.

Is the single RCD protecting all 7 MCBs? If not, then I'm guessing the lighting circuit isn't on the RCD and if that's the case, IMHO, it's non-compliant. That aside from the fact they should be split up to minimise disruption/inconvenience in the event of a fault.
 
The fault I haven't come across before is the RCD tripping when touching the neutral conductors (for the ring main) to the neutral bar when all MCBs are off (the only equip. turned on is the 100A Main sw & 63A Main RCD)

IR Clear - >2000
 
Can you explain the configuration of the consumer unit. Seems odd to have a 100A main switch then a 63A rcd main switch. Is it dual rcd, split load with some on the rcd and others not.
 
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Polarity OK? Has he made a right royal cock up and got it backwards? If so, then it could be indicative of a fault on another circuit.
 
It seems like a bad set up, but who knows. There could well to be more than one problem. As above, is it a split CU?
Are the other circuits OK, that is, is the RCD operating if the RFC is totally disconnected?
 
Can you explain the configuration of the consumer unit. Seems odd to have a 100A main switch then a 63A rcd main switch. Is is dual rcd, split load with some on the rcd and others not.
I think it's a Screwfix special (MK Sentry) - 100A Main sw suppyling 63A RCD which then supplies the 7x MCBs
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It seems like a bad set up, but who knows. There could well to be more than one problem. As above, is it a split CU?
Are the other circuits OK, that is, is the RCD operating if the RFC is totally disconnected?
Yes RCD fully working without the neutral conductors terminated, basically no RFC everything working fine
 
Earth neutral fault . Does not need to be turned on .like when working on a circuit and you accidentally touch neutral earth will trip RCD. Protecting all circuits .
When you put it like that - that's exactly what it is, simple but effective
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How many neutral bars. Is the rcd right next to the main switch.
Yes
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Well then, get everything unplugged and start a RFC inspection.
I think that is definitely needed - just didn't have the time today to test all sockets on the RFC - was looking for a quick fix really or if anyone has come across this type of fault before
 
Sounds like that consumer unit is not correctly configured. If the rcd is next to the main switch you would expect another rcd further along making it dual rcd. Have you tried completely disconnecting all other circuits and just connect the ring final.
Wouldn't mind seeing a pic of the consumer unit inside.
 
Sounds like that consumer unit is not correctly configured. If the rcd is next to the main switch you would expect another rcd further along making it dual rcd. Have you tried completely disconnecting all other circuits and just connect the ring final.
Wouldn't mind seeing a pic of the consumer unit inside.
It looks correctly configured for me - all 7 circuits supplied from RCD - correct I would expect another RCD aswel, but is it really needed with only 7 circuits - not tried disconnecting all other circuits - sorry not got a pic
 
It looks correctly configured for me - all 7 circuits supplied from RCD - correct I would expect another RCD aswel, but is it really needed with only 7 circuits - not tried disconnecting all other circuits - sorry not got a pic
On 7 circuits I’d have gone full rcbo.....1 rcd covering them all is a PITA as your customer is finding out...incorrectly wired somewhere? Fault was probably there on the old setup but never picked it up
I’d start with @westward10 advice and disconnect the other circuits and start on the rfc from there..good luck though ?
 
It looks correctly configured for me - all 7 circuits supplied from RCD - correct I would expect another RCD aswel, but is it really needed with only 7 circuits - not tried disconnecting all other circuits - sorry not got a pic
If the single RCD is for the whole installation then it would not really be suitable for purpose nor compliant with regs.
 

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