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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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  • 0

    Thanks for the responses. Specifically Andy this is a 250L direct immersion only unvented tank, there is no other source of heat input. The idea is that both immersions will come on at night using the economy, heat the water and then there will be no method of boosting during the daytime.  Now I can see running two separate cables from 2 breakers would make sense and using 2.5mm but that would also require 2 separate timers as far as I am aware as these are required by Part G of the building regulations. 1 timer would make sense to me however I can see the pro's and cons for any method of wiring. Personnally I do not see why the customer wants this since its about 5-6 hours on one immersion to heat that quanitity of water, so the other immersion could be used as a day time back up, but again its not my choice. And yes Sparkingchip, the electricians are rare here, almost as rare as plumbers. Z, I always carry a coil of 2.5mm flexi in the van and for straight forward swaps use this doing the work myself, that is what caught my eye when this fella used 1.0 and we got the result we did.

Reply
  • 0

    Thanks for the responses. Specifically Andy this is a 250L direct immersion only unvented tank, there is no other source of heat input. The idea is that both immersions will come on at night using the economy, heat the water and then there will be no method of boosting during the daytime.  Now I can see running two separate cables from 2 breakers would make sense and using 2.5mm but that would also require 2 separate timers as far as I am aware as these are required by Part G of the building regulations. 1 timer would make sense to me however I can see the pro's and cons for any method of wiring. Personnally I do not see why the customer wants this since its about 5-6 hours on one immersion to heat that quanitity of water, so the other immersion could be used as a day time back up, but again its not my choice. And yes Sparkingchip, the electricians are rare here, almost as rare as plumbers. Z, I always carry a coil of 2.5mm flexi in the van and for straight forward swaps use this doing the work myself, that is what caught my eye when this fella used 1.0 and we got the result we did.

Children
  • 0 in reply to Rubia30

    I have no issue using 1.25 or 1.5mm2 heat resisting flex for the final short immersion heater connection at the copper cylinder or equivalent.

    Z.

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