Rcd issue head scratcher

[Matesrates]

Hi all. Ive been testing a flat with a main switch consumer unit and a mixture of mcbs and rcbos.

All test perfect until rcd test for kitchen ring rcbo its a wylex b32a rcbo.

With cables connected to rcbo but nothing plugged in it gives readings of >300 for x1 and >40 for x5
Then when cables disconnected the readings are fine. 2 other rcbos in board and they are fine. Tried two other rcbos and same problem occurs. Has anyone came accross this before?
Thanks

 

[Andy78]

Yes, what are the IR readings for the circuit ?

 

[Matesrates]

All >500mohms on 500v

 

[Jamie']

Edit

 

[telectrix]

Tn when cables disconnected the readings are fine.

that's the correct way to test, without any circuit/equipment affecting the trippin gtimes. if readings are good, then that's it. end of.

 

[Matesrates]

Thanks, its the first time ive seen it. Theres only 3 points on the circuit 2x double sockets and a 20a dp for a fridge. Its an empty flat so nothing plugged in atall. Thanks again

 

[Lucien Nunes]

Possible crossed rings / bridged circuits. The IR might test fine on its own but there's a parallel path back to the board when one of the other circuits is also energised.

 

[Midwest]

I would agree something is affecting the RCBO. I've left an appliance mistakenly connected, and had a neutral- earth fault also, that stopped my MFT testing an RCD.

 

[Andy78]

Likewise, I have had faults on connected circuits preventing RCDs from operating when tested with circuits connected.

 

[littlespark]

Its measuring the workings of the RCBO unit. disconnect the cables and test again.

 

[Midwest]

Its measuring the workings of the RCBO unit. disconnect the cables and test again.

But it is also possible the install has an undiscovered fault. RCD's should able to be tested, with final circuits connected.

 

[Matesrates]

My boss passed it onto the housing association. They said just rewire the circuit, easy enough with gyproc walls. All tested with circuit connected.

 

[westward10]

That's the idea, rewire the circuit.

 

[Pete999]

Hi all. Ive been testing a flat with a main switch consumer unit and a mixture of mcbs and rcbos.

All test perfect until rcd test for kitchen ring rcbo its a wylex b32a rcbo.

With cables connected to rcbo but nothing plugged in it gives readings of >300 for x1 and >40 for x5
Then when cables disconnected the readings are fine. 2 other rcbos in board and they are fine. Tried two other rcbos and same problem occurs. Has anyone came accross this before?
Thanks

Guess there is something wrong with the circuit connected to the RCBO then, answer the circuit needs a complete electrical test.

 

[Matesrates]

It was a small rfc with only 3 points. I had tested end to ends, R1+R2 IR then zs and all had no adverse readings until i got to the rcd test. It was a kitchen circuit in a care home all points were fed via conduit drops

 

[Dillb]

My boss passed it onto the housing association. They said just rewire the circuit, easy enough with gyproc walls. All tested with circuit connected.

I never realised fault rectification was so simple to resolve.

 

[westward10]

Been doing it wrong for years, learn something new everyday. Rcd don't trip, rewire a fault free circuit to resolve.

 

[Dave OCD]

@Matesrates - When you rewired the circuit did you find anything that could have caused the issue?

 

[Matesrates]

There was a socket that had been moved during a kitchen refurb connections in block buried in tile adhesive.
All other circuits tested ok

 

[Dave OCD]

You wouldn't think a bodge like that would happen in a Council property eh ? But I still don't see what was bypassing the RCD tripping coil when all tests on the circuit were spot on.