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Twin immersion heaters

Former Community Member
Former Community Member
I am in the process of going unvented.  I have to use immersion heaters, and the new cylinder has two.  I have one feed to the existing immersion.  It is on 2.5mm2 T&E and connects to a 32A MCB on the CU.  I'm adding a DP isolating switch in the cylinder cupboard.  Will that be complaint for one of the immersion heaters?

To fully install the cylinder (ie the second immersion), I plan ask an electrician to either
(1) run an additional 2.5mm2 T&E cable back to the CU, connect it to the existing 32A immersion heater MCB at the CU. So the MCB protects two separate cables and the 2.5 T&E is within its capacities. 

Or
(2) run a new 6mm2 T&E cable back to the CU, connect to the existing MCB and in the cylinder cupboard, split the feed to two DP isolators, one for each immersion and its timer.


I'd be grateful for advice - are both approaches compliant?  Is one better than the other?  The amount of work will be similar.
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  • 0
    DC:

    Thanks - just saw another thread on 13A capacity of today's kit versus 1960s and 1970s - the consensus seemed to be to keep 3kW rated appliances off ring mains, despite the nominal rating.  I suppose an domestic electric fire or fan heater at that rating would have a room to cool, immersions are normally in cupboards and the wiring cannot dissipate heat so well.


    We normally use a heat resisting flex for the final connection to an immersion heater. 2.5mm2 T&E cable is fine for a 3kW immersion heater supply up to the local switch. . A 20 Amp switch with a neon indicator is better for the final connection rather than a fused connection unit or 13 Amp plug. Modern switched fused connection units can vary in quality. Some will be o.k. for a 12.5 Amp load, other will burn out quickly. P.S. previous post edited.


    Z.


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  • 0
    DC:

    Thanks - just saw another thread on 13A capacity of today's kit versus 1960s and 1970s - the consensus seemed to be to keep 3kW rated appliances off ring mains, despite the nominal rating.  I suppose an domestic electric fire or fan heater at that rating would have a room to cool, immersions are normally in cupboards and the wiring cannot dissipate heat so well.


    We normally use a heat resisting flex for the final connection to an immersion heater. 2.5mm2 T&E cable is fine for a 3kW immersion heater supply up to the local switch. . A 20 Amp switch with a neon indicator is better for the final connection rather than a fused connection unit or 13 Amp plug. Modern switched fused connection units can vary in quality. Some will be o.k. for a 12.5 Amp load, other will burn out quickly. P.S. previous post edited.


    Z.


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