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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

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    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.

    I wonder if the cause of the fire might have been something other than just undersized conductor - 1.0mm² should be good for 15A or 16A if clipped direct at ambients up to 30 degrees - and even if conditions were less than ideal (e.g. in a building void or ambient a bit warmer) I'd only expect it to run a little over warm, soften a bit perhaps, and maybe eventually break down in a decade or two instead of closer to a century. Bursting into flames requires quite a substantial temperature - so perhaps more likely a loose connection?

       - Andy.

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  • 0

    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.

    I wonder if the cause of the fire might have been something other than just undersized conductor - 1.0mm² should be good for 15A or 16A if clipped direct at ambients up to 30 degrees - and even if conditions were less than ideal (e.g. in a building void or ambient a bit warmer) I'd only expect it to run a little over warm, soften a bit perhaps, and maybe eventually break down in a decade or two instead of closer to a century. Bursting into flames requires quite a substantial temperature - so perhaps more likely a loose connection?

       - Andy.

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