Immersion heater

[ScottishGasMan]

I'm doing first fixing for a cylinder/boiler installation.

The Hot Water Cylinder will have a 3kw immersion heater fitted to it as a backup device should boiler ever pack in.

The cylinder will be in the room next to the CU.

Normally In past properties I've worked in, the cylinders been upstairs, with a standard looking Isolation switch, and a fused spur downstairs.

So Im looking at laying 4mm T+E between CU and a Double pole Isolator (non fused) 4mm flex from isolator to Immersion heater, and ordering a 16A RCBO for the CU.

Total length of cable will be less than 4meters and will be clipped direct, but if the immersion is used it could be drawing 3kw for hours and god knows what insulation etc will go down in future.

I was really wanting only to ask if it would be acceptable to fit with just a DP isolator or whether it would need to be a fused spur ? hear arguments saying one over the other now so got a little unsure what to get.

TAI

 

[EFLImpudence]

So Im looking at laying 4mm T+E between CU and a Double pole Isolator (non fused) 4mm flex from isolator to Immersion heater, and ordering a 16A RCBO for the CU.

1.5mm² is adequate but everyone uses 2.5mm².

Total length of cable will be less than 4meters and will be clipped direct, but if the immersion is used it could be drawing 3kw for hours and god knows what insulation etc will go down in future.

That's not really your problem but the 4mm² will be safe whatever happens.

I was really wanting only to ask if it would be acceptable to fit with just a DP isolator

Yes.

or whether it would need to be a fused spur ?

No need for a fuse with 16A breaker.

 

[ScottishGasMan]

Thanks mate.

I know 2.5mm is the normal way of doing it, but have some 4mm going spare any way so figured the immersion would be the best place for it.

I wasnt sure about needing a Fused spur with that circuit or not but thats that answered for me.

Thanks again

 

[PrenticeBoyofDerry]

*The 3kW element will require 13A supply
*4mm Butyl flex will carry a maximum current of 35A
*If flex is ever surrounded by thermal insulation, then you could consider a 50% de-rating factor, therefore reducing current capacity to 17.5A
*Protective device rated at 16A
*DP isolator rated at 20A

Seems a safe enough design to me.