Plug-in immersion heater?

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I have a socket just outside my airing cupboard. I want to fit an immersion heater in the cylinder in the cupboard but I'd rather avoid paying for a new separate circuit (it's only going to be used as a backup in case of boiler failure.) Would it be permissible to simply attach a 13 amp plug to a heat resistant cable, feed the cable under the floorboard and out to the plug, and plug in when needed?
 
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Why not run some 2.5mm TE from the socket and have a f/spur in the cupboard. Add a neon to make sure no one switches on accidently.

Most work at 3000w, which is 13A.
 
Why not ......Most work at 3000w, which is 13A.

isnt there something in the 17th edition of the regs saying that fixed appliances of more than 2kw should have a dedicated circuit? (not sure of the wording so it may not apply)

it would be something to be aware of whether you abide or not.
 
:oops:

Well if there is, I've not found it. Anyone wish to comment ?

My caveat would be that it is highly unlikely that any of the existing work will be to 17th, which sort of makes it ok since it's a DIY allowable (as in no Part P or notification) required :D
 
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If it holds more than 15 litres then it should be on it's own dedicated circuit.
 
You're both right, I think.

I say I think, as I have not seen the OSG:2008.

However, the the 16th OSG advises as baz does.

And 7671:2008 does indeed advise appliances larger than 2kW having their own circuit.

This is to avoid overloading our old mate the ring final.
 
Yep, appendix of of the 17th ed OSG does advise water heaters in excess of 15L to be on their own circuit.
The 2kw thing possibly comes from appendix 15 in BS7671:2008
 
That sounds right..too lazy as always to get my red book out of the van... ;)
 
And 7671:2008 does indeed advise appliances larger than 2kW having their own circuit.
That's virtually every washing machine and tumble drier in the land....

i think it may say something like 'constant load' so a washing machine is ok, but i guess a >2kW drier (or immersion heater) still wouldnt be, although in the case of the op where it is just a backup so intermittent use would you fit it?. i seem to remember people discussing whether an oven counted or not, I've not got a copy of the regs.
 
Yeah - I've only got the draft - I'll have to gird my wallet and get the red jobbies. Suspect I'll make do with the 16th GNs for a while though, except maybe 1 & 7.

I know a few people who are MIETs, so I'll get them to buy them for me and cop the 20% discount..... :D
 
As with many of the recommendations in the OSG, they are based on presumptions and general experience. Ideally, for an immersion heater in regular use 13A taken from a ring would seriously reduce the current available for other appliances. However where the immersion heater is only used as a backup it is no different from plugging in a 3KW fan heater during cold weather. As a "backup" system I would not hesitate in connecting it to a ring. BUT...

We know there is a socket nearby, but is it a ring? It may be a spur or radial in its own right, it may be wired with 3/036 or 7/029, we should not assume its 2.5mm. So we need to know more about the circuit before giving advice.

Now plugging in an appliance is not a Part-P affair true, but adding a spur is. Its a modification of the system design. If the socket is already a spur then it would also be contrary to BS7671.

Using a plug and heat resistant cable would technically be legal but running the cable under the floorboard may (would probably) involve a mechanical risk to the cable (at its point of entry to the floor) and be highly undesirable.

The user should also be advised that the socket should be of the switched type and the heater plugged in while the switch is off to avoid contact sparking.

(We may assume that since the immersion heater is a new fitting the thermostat will be of the type having a manually reset overheat device).

Having said all that, if the hot water tank has no immersion heater then a new tank may be necessary. The cost of this may well exceed by many times the cost of having the circuit checked out!
 

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