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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?
 
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  • Thread Starter Thread Starter
  • #3
  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
 

davesparks

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  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?
 

SparkyChick

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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.
 
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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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SparkyChick

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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.
 

ipf

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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?
 
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 .
 
  • Thread Starter Thread Starter
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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
 
  • Thread Starter Thread Starter
  • #15
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.
 
  • Thread Starter Thread Starter
  • #17
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
 

Baddegg

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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 😁
 

Andy78

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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.
 
Happened to me many years ago changed board ,new board rcd protected tripped on connection , not touched any circuits . Found a socket fixing screw hard caught neutral when originally fitted. Worked fine before rcd fitted.
 

davesparks

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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
Yes it is needed, as it is at the moment it does not comply with the regulations.
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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
As I said that is the normal symptom of a neutral to earth fault which is a very common occurrence.
These faults often go undetected until the CU is replaced and RCD protection added.

This is like getting blood from a stone, >2000 what? Ohms, kilohms or megohms?
And what did you test between, is that the same result L-N L-E and N-E?
 

freddo

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If you had >2000Mohm between live conductors and earth it is unlikely the circuit would cause the RCD to trip!

A good example of why it is important to test an installation before replacing a consumer unit.
 
The OP hasn't replaced the board it is DIY but keeps tripping hence his involvement.
 

littlespark

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I think a photograph of the inside of this board is going to show a complete mess if it’s a diy.

If the board is diy, then I bet there’s other jobs been done in the house... shared neutrals between sockets and another circuit perhaps?
 

123

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I think a photograph of the inside of this board is going to show a complete mess if it’s a diy.

If the board is diy, then I bet there’s other jobs been done in the house... shared neutrals between sockets and another circuit perhaps?
Borrowed neutrals would have no effect in this instance as there is just 1 RCD protecting the whole installation by the sounds of it.
 

littlespark

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Borrowed neutrals would have no effect in this instance as there is just 1 RCD protecting the whole installation by the sounds of it.
Yes. you're right. I misread.
He still could have used a split board, I think they go down to 3+3 with some brands, but for ease of use, RCBO's on every circuit.
 

freddo

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And for the cost of RCBOs now and the convenience they provide it's silly not using them.
 
Could the Neutrals for the socket circuits be mixed up with the socket circuit on the other side of the board? This would mean you are connecting 1 leg of each circuit into the rcd side that's tripping and causing an unbalanced load.
 

Pete999

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Could the Neutrals for the socket circuits be mixed up with the socket circuit on the other side of the board? This would mean you are connecting 1 leg of each circuit into the rcd side that's tripping and causing an unbalanced load.
OP are there 2 lighting circuits if yes could be he has got crossed Ns ie N for up stairs and down stairs crossed, try swapping the Ns over, let us know how you get on.
 

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