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Procedure for tracking down RCD faults


smart51

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So the hall light is switched from 2 different locations in the hall and the landing light is switched from ONE location in the hall and one switch upstairs?

 

The issue I am sure will be in that switch with all the wires and tape.  I am certain you will find it is taking L from the downstairs light and sending the 2 "strappers" (the 2 alternate switched L's) upstairs on a t&e.  and upstairs, the landing light is getting it's N somewhere from the upstairs light circuit.

 

That is the normal borrowed neutral scenario.  And the solution is usually to take an extra N from the downstairs lighting circuit up to the landing light. 

 

 

BUT the fly in the ointment is you say it is a SOCKET circuit that trips when you put the landing light bulb in.  Can you confirm that is really the case?

 

Anyway if you want to test this theory, disconnect the N from the landing light and insulate the removed cable, then connect a temporary cable from the landing light N to the downstairs light N at the consumer unit.

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Yep.  Switch off the landing light.  Remove the bulb.  Reset all the trips.  Refit the bulb without switching it on - the front sockets circuit trips.  Switch on the landing light, the downstairs light circuit trips.

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25 minutes ago, Onoff said:

Double check he hasn't put a ring neutral in a lighting circuit RCBO and vice versa. 

This is what annoys me about the attitude if this "electrician".

 

HE should be checking things like that and he should have done so at least at the time of the board change if not before.  His attitude of wanting to charge the customer £90 per hour to sort this out is making my blood boil.

 

A quick check would be look at all the cables going into each rcbo, and if you see two of different thicknesses going into the same terminal, that would ring alarm bells. Lighting cables would normally be 1mm and socket cables 2.5mm, clearly visible as different sizes.

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From an EE perspective:

 

How long before house installs need a proper circuit diagram and cable labelling like industrial set-ups do? It's a bit nonsense have to guess/figure out what cable end corresponds to what other cable end and draw the circuit out on a scrap of paper/in your head. The situation is quickly getting more and more complex with PV, diverters, batteries, Loxone, wifi controls, car chargers, 'high integrity' backup circuits/CUs, earth relays etc etc - the chances of having the correct picture in your head just by observation are getting less and less. While EEs and industrial sparks sometimes have to debug an undocumented PCB or control cabinet, it's quite the exception.

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I cut through the boards and insulation in the loft this morning to look at the wiring to the landing light pendant.  There is a ring that goes in and out with the light bulb connected to the neutral.  There's a third twin and earth with both red and black going to the light bulb live.  This appears to go to the landing light switch common.  The landing light switch S1 and S2 are wired to the stairs light switch S1 and S2.

 

Would I be right to separate the ring from the landing light, then take a neutral from the hall pendant up into the loft and connect that to the landing light?

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42 minutes ago, smart51 said:

Would I be right to separate the ring from the landing light, then take a neutral from the hall pendant up into the loft and connect that to the landing light?

Definitely separate the ring N from the landing light and make that connection safe in some form of junction box.  Do that first and confirm the socket circuit no longer trips when you put the bulb in.

 

then you have to find a N from the downstairs light circuit.  A downstairs light fitting may be an easier place to find that if, it really depends on the house layout and construction and where is the easiest place to get a new cable down to from the landing light.  It could even go back directly to the CU if that is easier.

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29 minutes ago, Alan Ambrose said:

From an EE perspective:

 

How long before house installs need a proper circuit diagram and cable labelling like industrial set-ups do? It's a bit nonsense have to guess/figure out what cable end corresponds to what other cable end and draw the circuit out on a scrap of paper/in your head. The situation is quickly getting more and more complex with PV, diverters, batteries, Loxone, wifi controls, car chargers, 'high integrity' backup circuits/CUs, earth relays etc etc - the chances of having the correct picture in your head just by observation are getting less and less. While EEs and industrial sparks sometimes have to debug an undocumented PCB or control cabinet, it's quite the exception.

+1

 

I have wired ours as full radial lighting so every light fitting and switch has a wire back to the panel with a number. Appreciate that this cannot be done in this situation but we should move to it, or something equally simple for future builds. The only thing the old approach has going for it is that is probably uses less cable.

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Some success.  The landing light now works without tripping the lighting circuits.  Well done everyone who said borrowed neutral, and thanks.

 

I'm 6 hours in today, lifting floor boards on the landing and in the loft, drilling through joists, a floor and a ceiling to get a neutral wire from the hall pendant to the landing pendant and it all works.  I've just got to clip the wires to the inside architrave of the boiler cupboard and put back all the boards.  Luckily, the carpets are all up and the fitters are coming tomorrow to lay new carpet.

 

We've not moved in yet, so I don't know when the sockets circuit tripped.  But when I got there this morning, the front sockets circuit had gone.  I think it has a problem of its own which is perhaps marginal, so sometimes it will work and sometimes not.  Somehow the lighting circuit tripping tipped it over the edge yesterday.

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