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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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    I have such an installation I installed a couple of years ago to replace a Fortic tank with a single immersion. I had only a single 2.5mm from the CU and it would have meant major surgery to get a second circuit from the front of the house to the back where the unvented tank is. I opted for the single cable to to terminate in to a 20A switch to use as an on and off switch which supplies a 2 way 20A switch which selects the upper heater or the lower heater. The upper heater  switch position is marked day/ boost and the lower is marked night to benefit from my E7 tarrriff.
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    I have such an installation I installed a couple of years ago to replace a Fortic tank with a single immersion. I had only a single 2.5mm from the CU and it would have meant major surgery to get a second circuit from the front of the house to the back where the unvented tank is. I opted for the single cable to to terminate in to a 20A switch to use as an on and off switch which supplies a 2 way 20A switch which selects the upper heater or the lower heater. The upper heater  switch position is marked day/ boost and the lower is marked night to benefit from my E7 tarrriff.
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