immersion heater cable size

[nikon70]

ok i have done my calcs and this is what i have come up with.

a) 25m from CU to Immersion heater (50m ring not radial)
b) Immersion heater is 3kw
c) Cable is going next to central heating and hot water pipes approx temp 60-80 deg C, approx 200mm from the pipes, boxed in together
d) Going thru 250mm loft insulation then in the loft clipped to wall

so according to this i would need a 13Amp fuse and a 10mm cable

are my calc correct?

 

[Spark123]

I think you need to re-consider your run - if the most onerous ambient temp is going to be 80deg then it is going to cause a lot of issues, especially where the operating temp of a normal PVC cable is 70deg. The max of XPLE is 90deg however still only allows a 10deg rise.
Immersions are normally connected as radial. 10mm as a ring? Good luck getting those into an accessory!
New ciruit = notifiable to LABC under part p too

 

[nikon70]

thanks for the reply.

thats my thinking...

i will run the cable a different route... i was not 100% happy with this idea anyway.

i will run a radial clipped direct under plaster in conduit with 3 other cables

13amp breaker 2.5mm cable

happy with that!

basically the boiler engineer that is there installing the doodah things wanted it up with his pipes.

i will route it differently )

 

[Spark123]

It can be clipped direct or it can be in conduit but not both at the same time!
Never seen a 13A breaker, usually a 16A is the next size up.
2.5 is what is normally used for a 16A radial, however it may still be too small if it is going to be run in through thermal insulation.
The work is still notifiable under part p.

 

[JohnD]

the pipes need insulating as well.

 

[nikon70]

sorry i meant in conduit up the wall and clipped in the loft im trying to do too many things at the same time

no insulation where im going to take the cable up.

yeah 16amp again thinking of other things...

 

[nikon70]

the pipes need insulating as well.

pipes are lagged

 

[skenk]

How do lagged hot water pipes make an ambient temperature of 80degC 200mm away, boxed in together or not???