Immersion heater

If you have an immersion heater 3KW on its own circuit as 3KW is slightly above 13a then I assume you would use a 20a water heater switch ? Or am I being anal as the load would 13.04 amps and a 13a fused spur would be fine. Thoughts ?

Yes. but most immersion heaters are rated at 3kW at 240V and it is quite common to find the real world power is more like 2.8kW

I never use a 13A FCU on a load that is anywhere close to 13A, that is guaranteed to end in early failure.

Three thoughts off the top of my head.

1. Immersions I've seen give a range of power, typically 2.8 - 3.0.  They will only be 3kW at the maximum supply voltage, around 250.

2. Like cooker switches, immersion switches will rarely be used to break the load so would probably be OK.

3. I consider they should be on a dedicated circuit, and so not need a local fuse.

20A DP switch if on a dedicated crcuit. 

13A FCU's are carp these days and will fail - so adding a 2nd fuse is meaningless

Another thought, (prompted by other postings today). If you use a double pole switch you can eliminate the immersion from the RCD random tripping roulette game. 

Geoff1946 said:

Another thought, (prompted by other postings today). If you use a double pole switch you can eliminate the immersion from the RCD random tripping roulette game. 

Click to expand...

Which is precisely why DP isolation switches should always be fitted 

Traineeboy said:

If you have an immersion heater 3KW on its own circuit as 3KW is slightly above 13a then I assume you would use a 20a water heater switch ? Or am I being anal as the load would 13.04 amps and a 13a fused spur would be fine. Thoughts ?

Click to expand...

Roll back time....

and historically immersion heater switches were a 20A DP switch..

(maybe also a variation with a neon)...



A typical modern day equivalent...



If it is on a dedicated 16A 60898 MCB circuit, 

Do the comparisons of the Time - Fault Current graphs for a 13A fuse..

I think you should find that the MCB will operate first..   

So no need to add an extra fuse and an extra joint into the circuit,

(The push-fit connectors of the fuse carrier are prone to failure if used with immersion heaters!) 

Guinness