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Correct wiring for twin 3Kw Immersion heaters

Rubia30

Morning folks,

I have a simple question presumably for an electrician that I could do with the answer to having just witnessed some poor installation practise. As a plumber I recently changed a 3.0Kw immersion for a 3.6Kw immersion. It was then left for the electrician to wire in whilst doing other work in the house. He used a 1.0mm conductor with that size immersion. 16amp Mcb on the consumer unit and the wire got a little warm, melted the insulation and caught fire. Very luckily the customer was in the room at the time and caught it in time to go and isolate the power and put out the smoldering wire.

Now this fella is going to go and wire in dual immersions both 3Kw to a single economy 10 unit. How should this be done safely? I'm presuming a single cable radial from the consumer unit 32amp MCB with either a 4mm or 6mm cable so 37amp or 47amp clipped direct with a junction box with two separate again 4 or 6mm cables and not anything less from the junction box? I'm asking since this is work that is taking place on an Island off the west coast of Scotland where building control or any CPS is totally absent. 

Thanks

Parents
  • 0

    1.0mm is almost certainly too small, some might judge it "just about OK but right on the edge." I would expect it to get warm but not to the extent of catching fire. Some other factor must be involved for it to catch fire.

    For a 3 kw immersion heater I would have used a 16 amp MCB and 2.5mm cable, unless derating for grouping and/or thermal insulation required a larger size.

    For a 3.6 kw immersion heater I would have enquired a bit more since that is not a common size. If it was an imported unit and rated at 220 volt, 3.6 kw then for use on our mains which is still about 240 volts most of the time in most places, then a 20 amp MCB might be better. If it was truly designed to use 3.6 kw at 240 volts, then 16 amps should suffice.

Reply
  • 0

    1.0mm is almost certainly too small, some might judge it "just about OK but right on the edge." I would expect it to get warm but not to the extent of catching fire. Some other factor must be involved for it to catch fire.

    For a 3 kw immersion heater I would have used a 16 amp MCB and 2.5mm cable, unless derating for grouping and/or thermal insulation required a larger size.

    For a 3.6 kw immersion heater I would have enquired a bit more since that is not a common size. If it was an imported unit and rated at 220 volt, 3.6 kw then for use on our mains which is still about 240 volts most of the time in most places, then a 20 amp MCB might be better. If it was truly designed to use 3.6 kw at 240 volts, then 16 amps should suffice.

Children
  • 0 in reply to broadgage

    Most definitely practically 1.0mm2 T&E is far too small for a load of 3kW that will be running for a considerable time.

    Z.

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