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Electric Immersion Heater Wiring

Postby Clunk77 » Wed Feb 13, 2008 9:11 pm

Had a bit of an issue tonight with an electric immersion heater. It appears the element has split (due to hard water??) and has backed the electric to the timer shorting out and more or less catching fire and melting the unit.

I'm about to replace the element and timer but have serious doubts over the way it's currently wired plus it's in my little girls room which is even more of a worry.

It starts with a non fused isolation switch which draws in the power. Another cable then goes to the timer with the element power cable then coming out and feeding the heater. Their appears to be no protection in the loop.

I don't believe the timers purchased for immersion heaters have any protection or the element itself. I've read that you can power the heater direct from a 13amp plug.

Wish I done a sparky course at college!! :?

Anyone have any ideas on this. Is this currenty wired in the wrong way?

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Postby sparx » Wed Feb 13, 2008 10:22 pm

Hi Andy,
Immersion heaters should be on seperate circuit from consumer unit which should be protected by either a 16Amp MCB or a 15A fuse, therefore as long as cable is rated higher ie 2.5mm2 at 18.5-27A depending on installation method, or even 1.5mm2 at between 14-19.5A the flex between isolator switch, timer and heater should be 2.5mm2 if so no overload can occur.
The most likely cause of 'burn outs' is loose connections. When purchasing a replacement heater ensure the thermostat has an overheat cut out as well as normal setting dial, it is illegal to fit one without but 2 local large plumbers merchants & 2 local hardware stores recently tried to sell me ones without O/H cutouts!!!
One said "funny you don't want one without, Simon B. (a good plumber) said the same only the other day"!
Check if rewireable fuse that correct size wire in place, if in doubt I would suggest replacing switch with fused connection unit (switched-fused spur),
or better still get a leckie in to replace wiring for you.
regards SPARX
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Postby Clunk77 » Thu Feb 14, 2008 7:31 am

Thanks a lot. Appriciate your help.
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