Sockets tripping different rccb?

[Adam Paj Paget]

Quick question which I will probably kick my self when I look into the d/b in the morning.
We currently have a house being restored(finishing touches) had western power out this morning to change over to PME, I came home from work popped in the house to catch the first half of the rugby and put the kettle on.
On the split rcd board down stairs ring and upstairs lights on one rcd, with downstairs lights on the other rcd all running fine until I turned the kettle on which tripped out the rcd with only the downstairs lights on any ideas of what I might be missing by the sockets on the other rcd making it trip with the kettle?
All advice welcome (and laughs)

 

[davesparks]

Presumably it was TT with a high Ra previously?
It sounds like the electrician who fitted the CU did not carry out the testing properly before switching it on!
This is the classic symptom of a neutral to earth fault

 

[Leesparkykent]

Neutral-earth fault.

 

[Octopus]

Were any tests done?

 

[Adam Paj Paget]

I understand it's a neutral to earth fault but why would the other rcd trip?

 

[davesparks]

RCD trips due to neutral current diverting via the fault.

 

[Deleted member 26818]

The neutrals are probably incorrectly terminated.
Could be that one leg of the RFC is on one neutral bar, and the other leg in another.

 

[davesparks]

The neutrals are probably incorrectly terminated.
Could be that one leg of the RFC is on one neutral bar, and the other leg in another.

That would result in instant tripping, this is only tripping under load

 

[Deleted member 26818]

How are the neutral currents being diverted then?

 

[davesparks]

How are the neutral currents being diverted then?

Via a N-E fault, the impedance of the fault determines the proportion of the current which diverts and so the amount of load required to cause a trip

 

[Deleted member 26818]

So the current would divert from the neutral to the earth, then from the earth to another neutral and then flow through the other RCD causing that RCD to trip while the first RCD doesn't trip?

 

[Deleted member 26818]

I think it is more likely that the kettle is plugged into a radial protected by the RCD which tripped, due to the kettle having an earth fault.

 

[davesparks]

So the current would divert from the neutral to the earth, then from the earth to another neutral and then flow through the other RCD causing that RCD to trip while the first RCD doesn't trip?

Pretty much, it a common problem

 

[Richard Burns]

I think it has all been said above, however the RCD that trips is protecting the circuit on which the fault is present.
Therefore there is a fault on the downstairs lighting.
because the RCD tripped when using a high load on another circuit this indicates that there is a neutral earth fault on the downstairs lighting.
It does not happen all the time because there is only a small percentage of the current flowing through the fault, however any current in use on the installation can cause this because the current can flow from the main switch common neutral back vie the RCD neutral on the faulty side through the NE fault and to earth.
The current flowing through the neutral does not have a corresponding live current and so the RCD trips.

 

[Adam Paj Paget]

Update
With all circuits isolated on 1rcd, kettle still trips out the rcd with no circuits on.

 

[Lucien Nunes]

Can you confirm that all the outgoing neutrals have been disconnected from the neutral bar on the RCD that trips...

 

[Octopus]

Update
With all circuits isolated on 1rcd, kettle still trips out the rcd with no circuits on.

Any chance you could confirm the tests done on the RCD and circuits?

 

[Adam Paj Paget]

Found the fault gas hob brand new with internal fault

 

[Richard Burns]

Switching off the MCB will not affect the fault as it is on the neutral that is not switched off.
You need to find the fault on the lighting circuit and testing of the circuit will do that for you, to some extent.

Little diagram to clarify (or mess up) your approach


EDIT: Just too late fault is found, typical!!:sick:

 

[MisterE]

But a nice picture anyway :smile5: - Thanks