RCCB tripping when under load problems

[Shurbunkin]

Hello

I am new to the forum and was hoping I could pick your collective brains.
I am an electrician with 7 years experiance. I have mainly worked for the MOD and on commercial and industrial builds throughout my time.
I now do the odd bit of domestic work and need some help on a kitchen ring main I have installed.

The circuit is wired in 2.5mm twin and earth. The circuit is protected by a 32b MCB and a 63amp RCCB covers this and a bank of 5 other circuits.
I have tested the ciruit with a fluke tester and the readings have all come back perfect. Low continuity values. Insulation resistance tests clear. Fault loop impedance test came back at 0.54 ohms. (Max 1.16 ohms)
When I turn the circuit on the MCB and RCCB holds fine but as soon as I plug something in the RCCB trips. I thought this was strange as the circuit tested out fine and all the other circuits on the RCCB work fine aswell. I disconnected all the neutrals from the other circuits and left all circuits off but the kitchen circuit, but still when load is applied the RCCB trips.

I don't have a lot of experience with testing but know enough to get by, I thought. I have asked fellow electricians and they suggested the RCCB or MCB was faulty so I have changed them both. Still the probem persists.

Any ideas what the issue may be?

Thank you for your help in advance

Fellow sparky

 

[Midwest]

IR fault on an adjacent RCD controlled circuit?

 

[Octopus]

Have you got an earth leakage clamp metre?

 

[Toneyz]

If you have not got your neutrals mixed up then I would say a neutral to earth fault based on it trips out when plugging something in.

 

[Dave OCD]

Check that the circuit neutrals are connected to the same neutral bar as the other circuits on that RCD.

 

[Octopus]

When you did the IR tests did you leave all the cpc's connected to the cu?

 

[buzzlightyear]

I don't have a lot of experience with testing but know enough to get by

The circuit is protected by a 32b MCB and a 63amp RCCB covers this and a bank of 5 other circuits

what ,ring a ring of roses !

 

[buzzlightyear]

 

[marconi]

Some further easy things to check:

1. Test RFC IR L-E and N-E.

2. The IR of load you are using to test the RFC.

3. Polarity L-N at each socket. Modern sockets switch the N first and L second on closing and L first and N second on opening.

4. Undo but do not completely remove the securing screws on each socket. Then carefully pull back on the socket and look inside to check whether the RFC live conductors, N especially, are touching the securing screws. Then remove the screws completely and examine the state of the insulation of the live conductors for damage due to screws, or nipping or sharp edges.

5. Tightness and solidity of all RFC connections. Make sure the insulation of the live conductors ends before entering the terminal holes.

6. Check tightness and solidity of 32A MCB and RCD in/out connections including to busbar.

7. Where cable sheath has been cut back to check the condition of insulation on L and N. Any small nicks?

 

[Deleted account]

Post pic of internals of cu. might help.

 

[mhar]

3. Polarity L-N at each socket. Modern sockets switch the N first and L second on closing and L first and N second on opening.

Isn't late break, early make the other way round? The source of energy (the L) is disconnected first then the 'escape route' for the energy (the N) is disconnected a fraction of a second later?

 

[SparkyChick]

Isn't late break, early make the other way round? The source of energy (the L) is disconnected first then the 'escape route' for the energy (the N) is disconnected a fraction of a second later?

That's how @marconi described it. Neutral is closed first and opened last.

 

[static zap]

Isn't late break, early make the other way round? The source of energy (the L) is disconnected first then the 'escape route' for the energy (the N) is disconnected a fraction of a second later?

Switch - vs - Make / break ..English ...

 

[elsparko]

are there any appliances plugged into the circuit? you mention it is under load?

 

[Shurbunkin]

Thank you all for you suggestions

are there any appliances plugged into the circuit? you mention it is under load?

I only had my 110v transformer plugged in so thought maybe there was a fault with it but took it apart and looks fine. Plugged into another socket circuit and worked fine. So I then plugged the site hover into the troublesome cicuit and it tripped so it a circuit issue, not an appliance

I will thoroughly test the other circuits again and see what I can find. Strange thing is they are all on and under load. The kitchen ring main is the only one that has problems, and that tested out fine as well.

The next thing will be to take all socket fronts off to see if theres a socket screw in a cable as suggested. Although would insulation resistance test find this?

I will take a picture of the CU when im next on site and post it. Need to make sure it looks pretty

Thanks again

 

[Shurbunkin]

When you did the IR tests did you leave all the cpc's connected to the cu?

No I didnt. I turned all MCBs off. Will try that

 

[Shurbunkin]

Have you got an earth leakage clamp metre?

No I dont

 

[Deleted account]

Check any hard wired appliances like boilers, extractor hoods etc are disconnected as well. Not just switched off.

 

[marconi]

Thank you for the progress report. It satisfies our interest.

 

[Shurbunkin]

IR fault on an adjacent RCD controlled circuit?

I think this may be the case as well. Will need to head over there again and spend a couple of hours testing the rest of the circuits one last time