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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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    Chris Pearson:
    Zoomup:
    davezawadi (David Stone):

    What is wrong with the B32 and two 2.5s Sparkingchip? Overload is impossible as I'm sure you realise? Ring connection is not necessary Chris, although it doesn't hurt and satidfies the overload point which worries some people. I expect only 1 heater at a time, but both would work safely. However it would be easier to have a Bath/Sink switch and just use the existing 2.5 cable. Job done. Local isolation/switching on/off is not necessary, although you may find it convenient, along with a timer. Ensure no non-return valves have been fitted anywhere back to the water main.


    If the B32 trips off you have lost all heating. With two B16s and two separate circuits you have a more reliable system.




    I disagree. You have a less reliable system, because the chance of at least one circuit failing is doubled.


    What you have is redundancy so that in the event of failure, only half the heating is lost.




    I don't quite understand your logic Chris. With just one B32 M.C.B. if one element becomes faulty and trips the M.C.B. you have lost both elements for heating. With two separate supplies, via two 16 Amp M.C.B.s and supply circuits there is more inbuilt reliability. If one fails the other can still be used.


    Z.


Reply
  • 0
    Chris Pearson:
    Zoomup:
    davezawadi (David Stone):

    What is wrong with the B32 and two 2.5s Sparkingchip? Overload is impossible as I'm sure you realise? Ring connection is not necessary Chris, although it doesn't hurt and satidfies the overload point which worries some people. I expect only 1 heater at a time, but both would work safely. However it would be easier to have a Bath/Sink switch and just use the existing 2.5 cable. Job done. Local isolation/switching on/off is not necessary, although you may find it convenient, along with a timer. Ensure no non-return valves have been fitted anywhere back to the water main.


    If the B32 trips off you have lost all heating. With two B16s and two separate circuits you have a more reliable system.




    I disagree. You have a less reliable system, because the chance of at least one circuit failing is doubled.


    What you have is redundancy so that in the event of failure, only half the heating is lost.




    I don't quite understand your logic Chris. With just one B32 M.C.B. if one element becomes faulty and trips the M.C.B. you have lost both elements for heating. With two separate supplies, via two 16 Amp M.C.B.s and supply circuits there is more inbuilt reliability. If one fails the other can still be used.


    Z.


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