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Ellsa100

DIY
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Hi

Weird problem.

I’m replacing plug sockets. I isolate the circuit for the particular sockets at the fuse board so it is safe to swap out. All good. Suddenly the RCCB for all sockets - not just the circuit of the sockets I have isolated - trips. Why is this happening?

The RCCB doesn’t trip when all the circuits are live. It is as if it won’t let me isolate an individual circuit as it trips the whole consumer unit shortly after I isolate a circuit

Thanks
 
Do you have a socket disconnected when it trips.
 
If by “isolate the circuit” you mean that you turned off the MCB then you have not isolated the circuit fully. The MCB only turn off the line.
To fully isolate a circuit you need to disconnect the neutral as well.

The RCBO/RCD may trip if the neutral is still connected and you touch a neutral conductor to earth.
 
If by “isolate the circuit” you mean that you turned off the MCB then you have not isolated the circuit fully. The MCB only turn off the line.
To fully isolate a circuit you need to disconnect the neutral as well.

The RCBO/RCD may trip if the neutral is still connected and you touch a neutral conductor to earth.
Oh maybe that is it - I flicked the MCB - so you are saying that an earth and the neutral touched? Thanks
 
Finding the correct neutral can be more trouble than it is worth. Usually it would be quicker to simply isolate the rcd and change the sockets.
 
How do I disconnect the neutral after turning off the MCB?
It would be dangerous to try unless you've had plenty of practise. Please don't try and do this.

Just change the sockets under daylight hours, isolate the circuit as you did (or better just use the main switch), and try and avoid touching the wires together. When changing sockets it shouldn't be too hard to keep them separate.

The reason is that the Neutral wire is connected to other Neutral wires and touching it to earth is providing an alternative path back for some current, so the safety device kicks in just in case this current is going through a person.
 
It would be dangerous to try unless you've had plenty of practise. Please don't try and do this.

Just change the sockets under daylight hours, isolate the circuit as you did (or better just use the main switch), and try and avoid touching the wires together. When changing sockets it shouldn't be too hard to keep them separate.

The reason is that the Neutral wire is connected to other Neutral wires and touching it to earth is providing an alternative path back for some current, so the safety device kicks in just in case this current is going through a person.
Thank you - appreciate the advice
 
Just to add that you should be using the main switch to isolate rather than a circuit breaker, as it is not considered isolation for the purposes of a single phase domestic property for an unskilled person unless all live conductors (which includes the neutral conductor) are disconnected.
 
You are most welcome.

Stupid rule.
Just to add that you should be using the main switch to isolate rather than a circuit breaker, as it is not considered isolation for the purposes of a single phase domestic property for an unskilled person unless all live conductors (which includes the neutral conductor) are disconnected.
So is it dangerous to work on a circuit when I use the circuit breaker? I always check with a non-contact voltage tester there is no voltage on the circuit before commencing work on that circuit. Turning off the main switch seems a bit over the top just to work on one circuit? Plus I need lighting. Thanks for your thoughts.
 
So is it dangerous to work on a circuit when I use the circuit breaker? I always check with a non-contact voltage tester there is no voltage on the circuit before commencing work on that circuit. Turning off the main switch seems a bit over the top just to work on one circuit? Plus I need lighting. Thanks for your thoughts.
What you have to realise is that a neutral conductor is classified as a live conductor, because it is intended to carry current in normal use.
 
What you have to realise is that a neutral conductor is classified as a live conductor, because it is intended to carry current in normal use.
Thanks - appreciate that- so should I avoid working on a circuit when I have used a circuit breaker to turn off live for that circuit and tested live and neutral with non voltage contact tester (but not turned off the main switch) and if so why? Thank you
 
Think of it this way Elisa 100. Live current flows out of your meter, via the consumer unit, through all of your circuits and flows back through the neutral wires. This flowing current will be used when you have an appliance or light switched on.

All the neutral circuits are directly connected together in your consumer unit using a metal bar in that consumer unit. Same applies to all of the earth wires (which modern electricians may call a CPC).

Your Circuit Breaker (MCB M being for Miniature) in your case is interrupting the live circuit that it is attached to, but is NOT interrupting the neutral circuit. Current is flowing (returning) through the entire neutral circuit in your house as you will have lights on as you said and maybe appliances in use (eg washing machine) on different circuits.

So even on the circuit you think you have isolated, your neutral remains connected to the rest of the neutrals on live circuits.

If you touch a neutral on your isolated circuit to earth, the residual current circuit breaker (RCCD) in the consumer unit will detect this as a leakage of current. As a leakage could for all it knows be current flowing through you to earth (ie you are getting an electric shock) it plays safe and trips all power off everywhere.

I am a DIYer too and I expect qualified professionals could explain it better than I have. Personally I do not work on circuits without isolating the neutral as well. My consumer unit has a type of switch that does that and I can also isolate the consumer unit totally from the meter if I need to with a simple switch as well. In your case I would turn everything fully off at the main switch and use a battery powered light to assist you if that is needed. Electricity is a killer so don’t take risks.

By the way, non contact voltage protectors are less than ideal for identifying when something is live or not (unreliable and give a false sense of security at times), and will not identify anything that is only potentially live. There are more suitable testers that will be much safer - but obviously that incurs expense and you need to know how to check them and use them.
 
Thanks - appreciate that- so should I avoid working on a circuit when I have used a circuit breaker to turn off live for that circuit and tested live and neutral with non voltage contact tester (but not turned off the main switch) and if so why? Thank you

It's linked to why the RCD tripped. The N conductor is connected to other N conductors inside the consumer unit.
It is possible (should any of a number of things happen upstream, inside or outside your house or with the supply) for the current path of other circuits in your house to go via the socket circuits N wire, via you, to earth.

This reason was why I said "or better use the main switch". @Risteard is spot on that really it should be the only approach in your situation.
You might get away with it 99.9% of the time, but if the supply N happens to break at the wrong moment, it's curtains time!

(This is one of a number of reasons why new consumer units that I fit have double pole isolation on each circuit and separate RCD protection for each circuit. They are much easier to do maintenance on!)

There are other reasons too related to the average experience of DIY people doing this, that would not necessarily apply in your case.
 
Non-contact voltage detectors are NOT to be used to prove a circuit is dead.
I would strongly advise getting a set of two pole voltage detectors, test before isolation to prove working,
isolate, prove dead, then retest detector to prove still working.
 

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