wiring an immersion heater

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Hi,
I need to install a dedicated circuit to connect my immersion heater. I have a spare 16amp RCD on my Dist unit.
I want to put the 20a DP switch in the lounge, connected to the RCD, and to a dedicated fused spur with a neon outside the cylinder cupboard, to indicate when the heater is in operation. The spur will be connected to the Immersion heater with heat resistant cable. The spur will also prevent accidental switching of the heater on by children, by throwing the switch off, thus isolating the heater from the DP switch.
Do I need to use 1.5mm or 2.5mm HR cable to the heating element?
Is it okay to use ordinary mains cable from the spur to the DP switch in the lounge and from the DP switch to the RCD? Will the 13amp fuse in the spur be okay, or do I need to replace it, (with what rating?)
 
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Hi,
I need to install a dedicated circuit to connect my immersion heater. I have a spare 16amp RCD on my Dist unit.
I think you mean MCB?
I want to put the 20a DP switch in the lounge, connected to the RCD, and to a dedicated fused spur with a neon outside the cylinder cupboard, to indicate when the heater is in operation. The spur will be connected to the Immersion heater with heat resistant cable. The spur will also prevent accidental switching of the heater on by children, by throwing the switch off, thus isolating the heater from the DP switch.
You can do that, if you wish, but why have switch in the lounge at all??. All you need is a 20amp DP switch with a neon outside the immersion cupboard.
You do not need a fused spur anywhere. The 16amp MCB will protect everything.
Do I need to use 1.5mm or 2.5mm HR cable to the heating element?
Yes. 1.5mm cable will be OK provided the run isnt more than a metre or so.
Is it okay to use ordinary mains cable from the spur to the DP switch in the lounge and from the DP switch to the RCD? Will the 13amp fuse in the spur be okay, or do I need to replace it, (with what rating?)
Depends on what you call "ordinary" mains cable. there are many sizes, from 1.0mm to 16mm². For this job you will need 2.5mm² twin and earth.



Also, please note that if you are in England or Wales then this is a new circuit.
To comply with Building Regulations, you must open a new case with the local authority (and pay a wacking fee) or have a registered electrician do the work.
If you are going to DIY it then I guess you a have full set of calibrated test equipment (low ohm, insulation resistance tests, EFLI test etc?)
 
I need to install a dedicated circuit to connect my immersion heater. I have a spare 16amp RCD on my Dist unit.
Do you mean MCB (miniature circuit breaker)?
If the new circuit is not visible or protected by earthed metallic covering then it will also need to be protected by an RCD (residual current device)
You could have an RCBO which combines the functions of an MCB and RCD.

I want to put the 20a DP switch in the lounge, connected to the RCD, and to a dedicated fused spur with a neon outside the cylinder cupboard, to indicate when the heater is in operation.
It's your house but why would you want that?

The spur will be connected to the Immersion heater with heat resistant cable.
Correct.

The spur will also prevent accidental switching of the heater on by children, by throwing the switch off, thus isolating the heater from the DP switch.
They will not 'accidentally' switch it on if it weren't there.

Do I need to use 1.5mm or 2.5mm HR cable to the heating element?
1.5 is adequate but everyone uses (and sells) 2.5.

Is it okay to use ordinary mains cable from the spur to the DP switch in the lounge and from the DP switch to the RCD?
Yes. Twin and earth.

Will the 13amp fuse in the spur be okay, or do I need to replace it, (with what rating?)
No, you should not have a fuse for an immersion.
The 16A MCB in the consumer unit is all you need.
Just use a(nother) 20A DP switch.

This work is legally notifiable to your Local Authority before you start unless you employ a registered electrician.
 
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I know the spur seems unnessessary, but access to the immersion heater cupboard is via a guest bedroom, which might be inconvenient, hence the DP switch in the lounge
 
Thanks for the suggestion about the second DP switch instead of a fused spur, will do.
 
Its called volt drop. Also, the rest of the circuit will be in 2.5mm²
Thanks. It's true that you suggested 2.5mm² for 'the rest of the circuit' - but the reality is that the whole circuit (T&E and flex) could probably be done in 1.5mm² (installation method permitting). It would take about 30 metres of 1.5mm² to hit the limit of permitted VD at 13A, so the drop with the actual run length (quite probably pretty short) would probably be minimal.

Kind Regards, John
 
If I may be permitted once more to harp back to college days on the 15th (mid-eighties) where we had to do an exercise to prove that 1milli was OK to supply an immersion circuit of given length.... thank you!;)

You can't now, but back then, 1 milli was OK for power.

Also, I have never used 2,5 butyl for immersions, always 1,5.
 
The spur will also prevent accidental switching of the heater on by children, by throwing the switch off, thus isolating the heater from the DP switch.
So you are concerned about out-of-control children accidentally operating the switch in the lounge, but not accidentally operating the FCU on the outside of the cupboard?


I know the spur seems unnessessary, but access to the immersion heater cupboard is via a guest bedroom, which might be inconvenient, hence the DP switch in the lounge
But your plan is to use the FCU to stop the switch in the lounge from being used to turn the heater on accidentally. So how would you turn it on on purpose if the FCU in the guest bedroom is off?

Why will there be no out-of-control children around when you have guests staying?


with a neon outside the cylinder cupboard, to indicate when the heater is in operation.
Will the guests be responsible for observing the neon?

When will you want to use the heater? What's wrong with the common system of time switches and thermostats?
 

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