Interesting Fault

[andyb]

Had a call out yesterday to a house where the rcd on a board supplying storage heaters would trip intermittently. When I arrived the rcd would not reset at all. The rcd was also the main switch for the board.
Obviously an earth/neutral fault I thought, so with all the mcbs off and the the rcd off I did an IR test between n+e, result >999.
So a faulty rcd then, contemplating a 20 mile round trip to Electrifix I did what I thought was a pointless thing and disconnected the earth from the earth bar and reset the rcd. It stayed up. Touched the earth on the earth bar and the rcd immediately tripped.
Retested at the board and again got good results.

Any thoughts? I did solve it but it had me going for a while.

 

[Leesparkykent]

You left the earth out

 

[malcolmsanford]

Moisture?
Element breaking down?

my starteds for 10

 

[HappyHippyDad]

Anything to do with an appliance?

Without the earth connected, if there was a fault to earth then the RCD may not trip if its just relying on an earth path through the bonding which may be >1667. But you have tested to see if there was a neutral/earth fault!

I'll keep thinking.

 

[andyb]

Moisture?
Element breaking down?

my starteds for 10

All circuits were off Malcolm and the board was dead.

 

[andyb]

Anything to do with an appliance?

Without the earth connected, if there was a fault to earth then the RCD may not trip if its just relying on an earth path through the bonding which may be >1667. But you have tested to see if there was a neutral/earth fault!

I'll keep thinking.

No, as I said there were no faults on the circuits.

 

[telectrix]

fault on neighbouring property?

 

[andyb]

My next test was also a silly test,

I tested between earth and the outgoing neutral on the rcd and got a fault.
Then tested again at the neutral bar and there was no fault.
They were connected by a solid copper conductor.

 

[andyb]

fault on neighbouring property?

No Tel, it was fault on the board.

 

[HappyHippyDad]

So the solid conductor had a break?

 

[andyb]

I think I'm going mad by now, I removed the solid link and the fault had disappeared from the rcd completely. Still no fault on the neutral bar.
Replaced it and the fault returned.

 

[andyb]

So the solid conductor had a break?

No still solid.

 

[HappyHippyDad]

This is getting intriguing...

 

[andyb]

It was a Crabtree board with the earth and neutral bars extremely close together. Just 1 or 2mm apart.
The neutral bar had become loose and was intermittently touching the earth bar, When I tested the neutral bar to earth my probe was pushing it away from the earth bar so no fault.
When I took the probe away they were making contact again so I got a N/E fault just a few inches away on the switch.
Easily sorted once discovered, glad I never shot off to Electrifix.