Circuit Isolation

[Pbbjolly]

Hi, I need to isolate an electrical appliance from the mains supply before doing a bit of fault -finding. There is a live wire in the mains cable feeding the appliance. I obviously need to disconnect this live wire from the appliance's terminal box. But there is a switched live also. Does this need to be disconnected also? Many thanks for reading.

 

[ricicle]

What sort of appliance are we talking about ?

 

[Pbbjolly]

Hi, it's a boiler.

 

[EFLImpudence]

A boiler/heating system should have a double pole switch (somewhere) which will isolate the whole system.
This would include any switched live conductors as well.
You must 'test for dead' using an appropriate two-pole voltage indicator.

Obviously we cannot tell from here whether it has been installed correctly so, if you cannot tell, you should isolate by turning off the main switch at the consumer unit.

 

[Spark123]

There is ususally a fused spur feeding the whole heating system which is the point of isolation.
What sort of fault finding are you doing? What is the issue? If it is something on the gas side then you really need to contact a registered gas engineer - DIY gas work isn't a good idea.

 

[PrenticeBoyofDerry]

Identify the circuit, then isolate the circuit, before removing covers, then test for dead using an approved voltage indicator, that was been proved prior to testing and proved afterwards.
Then you can start disconnecting stuff.

 

[bernardgreen]

If this boiler is part of a heating system with thermostats and/or timers then you must ensure that the switched live is isolated. The hazard is that you test it and find it dead before you start and then will you are working the timer or thermostat operates and the switched live becomes live.