immersion heater fuse rating?

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just a quick question-a 3kw immersion heater at 240 volts will use 12.5 amps - so will a 13amp fuse be sufficient in the spur socket? i read that a 15amp fuse or 16 amp mcb should be used so i'm not so sure now!!???
 
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you mention "spur socket" which suggests you are thinking of taking it off a ring.

an immersion heater is a fixed appliance which runs for extended periods at max load so it should not be on a ring, it should be on a radial circuit fused as you say at 15A or 16A. It does not need an additional fuse in its switch.
 
sorry i don't know why i wrote that! of course it's taken directly from the CU - I meant a switched unit not a spur switch!!!:) I thought as well as in the CU there was supposed to also be a fuse in the actual unit near the immersion heater? for added protection ? this being my point-why a 15 amp fuse when wouldn't a 13 amp fuse be the closest up from 12.5 amps??!! Is it ok to use a 13 amp or a 15 amp fuse / or a 16 amp MCB??
 
If the butyl sheathed cable leads from your immersion element to a fused outlet, then a 13A fuse must be used in that outlet.
 
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yes it runs from the immersion heater to the outlet in 2.5mm heat resistant flex!! Thanks for your help here-I just wanted to know why it said 15amp fuse when my old one is 13amp and i didn't want anything to go wrong with it and become dangerous!! I take it the 15amp fuse/16 amp mcb is in the consumer unit and the 13amp fuse sufficient for the outlet?
 
yes it runs from the immersion heater to the outlet in 2.5mm heat resistant flex!!
Er, yes, sorry - I meant flex. :oops:

Thanks for your help here-I just wanted to know why it said 15am fuse ...
Please could you be specific about what "it" is in your sentence?

I take it the 15amp fuse/16 amp mcb is in the consumer unit and the 13amp fuse sufficient for the outlet?
I would use the word "correct" in preference to "sufficient", but the answer is 'yes'.
 
sorry i meant i read: a 15amp fuse must be used for an immersion heater, and mine is only 13amp!! I was worried but realise now that the 15amp fuse or 16amp mcb is for the consumer unit and as you have just confirmed to me, the 13amp fuse is for the socket near the heater!

i wonder if you put a 15amp fuse ALSO in the socket instead of 13 it would be ok?
 
you can't

max fuse that will fit is 13A
it is made to the same BS as a plug.
It is also possible to fit a 500Amp slow-blow but I wouldn't recommend it.

You don't need a fuse anyway. A 20A DP switch with neon is ideal.
 

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