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Electric boiler wiring

KMA1987

Hoping someone can help me with a question on the wiring requirements for a 12kw electric boiler.

For context, I’m attempting to have a botched installation rectified after the manufacturer said the warranty had been invalidated by an incorrect installation (both plumbing and wiring aspects). I’m not an electrician and I’ve had a couple of electricians look at it now and received different answers.

The boiler in question is a Trianco Aztec Classic 12kw (installation manual here: https://heatingpartswarehouse.co.uk/wp-content/uploads/2023/06/Aztec-Classic.pdf). The relevant page for the wiring instructions is 16.

My specific question is whether the boiler and the external wiring controls (we have a Reliance 8 zone wiring centre) should be on separate circuits? The wiring requirements state: “Miniature circuit breakers (MCB) MUST be fitted between RCD unit and boiler and RCD and any external controls….An additional MCB rated 6A will be required to supply the external controls.”

The current setup is the boiler and controls are on a 63A type B RCBO, with a switched fused spur on the same circuit for the controls. Whether this was ever correct/appropriate for the previous boiler I can’t say, but the installer has obviously just tried reuse what was already there on a like-for-like basis with the new boiler (different manufacturer/model).

One electrician has said the external controls should have been installed on a separate circuit with its own MCB, and the other that it can be on the same circuit and just replace the fused spur with a 6A MCB.

Happy to provide more information and grateful if there’s anyone with experience with electric boilers that may be able to help.

Parents
  • 0

    I wonder if what the Manufacturer is trying to say is that he would like the power & control supplies to come from separate OCPDs so that, in the event of failure of the main heater supply, the control system remains alive?

    This could be for similar reasons as to why a gas boiler utilises a 'pump run-on' facility to allow heat to be removed after the flame has been extinguished. Ensuring the control system remains alive could allow a circulating pump to strip any remaining heat from the boiler in the event of sudden disconnection of the heater supply.

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  • 0

    I wonder if what the Manufacturer is trying to say is that he would like the power & control supplies to come from separate OCPDs so that, in the event of failure of the main heater supply, the control system remains alive?

    This could be for similar reasons as to why a gas boiler utilises a 'pump run-on' facility to allow heat to be removed after the flame has been extinguished. Ensuring the control system remains alive could allow a circulating pump to strip any remaining heat from the boiler in the event of sudden disconnection of the heater supply.

Children
  • 0 in reply to AdrianWint

    To rely on that always happening is not safe in a power cut, so may be desirable, but should not be designed in as essential. I'd not really  expect the 63A supply to trip, or at least not with much greater risk than total loss of the mains fuse ,when it would all go at once. It all depends what else is on the supply, and its capacity.

    If you had in effect a 63 A sub-main, and the main boiler load  of 53A or so  with no further fusing down, and the control fused down to say 5A derived from it, how often will the over-run not happen in practice ?  
    Mike.

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