Central Heating Mains Electrical Supply Isolation Question

[TheNamek]

Finally getting around to tidying up the yeehaw dog's dinner wiring of the central heating system left by installer some twenty four years ago! My question is whether each item/device/appliance is required to have its own independent isolation.

CU has 16A MCB for the heating system. An FCU on the kitchen wall switches the supply to all the gubbins in the airing cupboard, including the programmer, immersion heater, valves, pump, and also the boiler (which s in the kitchen). The immersion is switched by a double pole switch, and the heating/HW control system (and boiler) is fed via another FCU in line after the one in the kitchen.

Any regs say that I need the second FCU for the controls and boiler since there is an FCU in the kitchen that switches the whole lot off anyways?

 

[Newboy]

No each device isn't required to have it's own isolation.

It's very unusual to find the immersion on the same circuit and it would suggest that the over-current protection for the central heating components is very over-rated.

It would make sense (and be a lot safer) if you provide a separate circuit for the immersion heater.

Do not have multiple isolation for the central heating components - single switched fused spur with fuse as required by the system. If you have multiple feeds and isolation to various components then you risk parts of the system being live when other parts of isolated.

Single live feed via a wiring centre would be best bet

 

[TheNamek]

Thanks for reply.

Additional sole circuit for immersion not podsible without major flooring disruption. I'm going to have to split supplying 4mm cable into two FCUs - 13A for immersion and 5A for heating components.

 

[EFLImpudence]

It's very unusual to find the immersion on the same circuit

It may be unusual but there is nothing wrong with it electrically.
It will be inconvenient in the event of a fault as both central heating and immersion will be off.

and it would suggest that the over-current protection for the central heating components is very over-rated.

The over current protection for the central heating system is the 3A fuse in the FCU.
The rest of the supply circuit is protected by the 16A device in the CU.

It would make sense (and be a lot safer) if you provide a separate circuit for the immersion heater.

There is no need. It would not be 'safer'.
Anyway, the 'separate' circuit, if installed, would be for the central heating.

Do not have multiple isolation for the central heating components - single switched fused spur with fuse as required by the system. If you have multiple feeds and isolation to various components then you risk parts of the system being live when other parts of isolated.

Single live feed via a wiring centre would be best bet

Correct.