Odd RCD behaviour

[securespark]

Had RCD trouble today, having swapped what read as a healthy circuit onto the RCD side of a SL board.

The RCD didn't trip on switching on, only when certain things were plugged in. The fridge was OK, the freezer on a different circuit (still through the RCD) tripped.
Table lamps tripped the RCD too.

In my experience, a dead neutral/earth short will trip the unit as soon as the circuit is energised. This is obviously not the case!

I finally tracked it down to what appears to be an intermittent NE fault on the GF ring final.

I auto-tested the RCD with the faulty ring in circuit. It failed the 1x test, but passed the others.

However, when I removed the faulty ring from the RCD side, the RCD tested fine.

Can you explain all of this???

 

[cozycats]

I had a similar setup a while back, the rcd was fine until something was plugged in to the ring The n-e fault was on the lighting circuit in the end, although that had not caused any tripping problem.
hope it helps!

 

[plugwash]

afaict NE faults that aren't dead shorts are generally the cause of strange RCD behaviour.

As the load increases the potential difference between N and E at the fault increases (especially on TN-S and TT systems but it will also happen to a lesser extent on TN-C-S systems). Therefore the current through the fault increases until the RCD trips.

 

[securespark]

Tis PME.

The IR reading between N & E is 0.00

 

[Jim2287]

Tis PME.

The IR reading between N & E is 0.00

take the cables out of the terminals to test them or do you have PEN conductors in your installation ?

 

[securespark]

Tis PME.

The IR reading between N & E is 0.00

So you have no CPCs in your circuits ? You dont do IR on live side

Hey?

I have CPC's, hence the IR reading between N & E.

You do do IR on the live side, but with the power off, OC...

You can even do IR between L & N, providing you dissasociate all loads beforehand.

Don't understand what you are saying.

 

[Jim2287]

Tis PME.

The IR reading between N & E is 0.00

So you have no CPCs in your circuits ? You dont do IR on live side

Don't understand what you are saying.

me neither, was thinking neutral was switched

take the cables out of the terminals to test them then they are seperated as they dont go to the service side

 

[securespark]

I did.

 

[Jim2287]

Ok i read wrong then

U said its PME and u had 0.00 omhs on PE-N so ....