Isolate circuit but trips fuse board

[Ellsa100]

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

 

[cireland]

Were you removing a socket at the time it tripped?

 

[westward10]

Do you have a socket disconnected when it trips.

 

[westward10]

Touché.

 

[Taylortwocities]

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.

 

[Ellsa100]

Were you removing a socket at the time it tripped?

Possibly. But the circuit was isolated (as in I had flicked the switch at the fuse board for that circuit)

 

[Ellsa100]

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

 

[Ellsa100]

Oh maybe that is it - I flicked the MCB - so you are saying that an earth and the neutral touched? Thanks

How do I disconnect the neutral after turning off the MCB?

 

[cireland]

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.

 

[timhoward]

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.

 

[Ellsa100]

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

 

[Ellsa100]

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.

Thank you

 

[cireland]

You are most welcome.

Stupid rule.

 

[Risteard]

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.

 

[Ellsa100]

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.