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Adding spurs to immersion heater circuit

About 25 years ago we had a shower fitted and the plumber added a fused spur to the immersion heater circuit for the pump.

I want to upgrade our heating system by fitting an ebus controller in the airing cupboard. This needs a mains supply and there is no accessible ring circuit. Is it permissible to add another fused spur to the immersion circuit?

Mike

  • Depends on the details (amount of spare capacity, consideration of effects of a fault, environment and so on), but there's no fundamental prohibition. It may not be a "conventional" circuit arrangement, but the regs don't demand that it must be.

    Airing cupboard often aren't ideal locations though - typically they're too warm for BS 1363 accessories (I think the limit is of the order of 25 degrees average over 24 h) - you may well get away with it for small loads, but be aware you're probably outside of official specifications.

    Likewise electronics prefer cooler locations for long term reliability.

        - Andy.

  • Thanks Andy. Yes I'm aware that it's not an ideal location for electronics, although the existing controller has been fault free in there since 2009.

    Mike

  • I assume that the controller consumes very little, so you will not overload the circuit.

    The airing cupboard should not be warm 'cos the cylinder should be well lagged.

  • Yes to both (c:

    The controller consumption is 2VA.

    Mike

  • Strictly speaking this is not a "spur", simply part of a radial circuit, which like a tree, may have many branches. Anyway not a problem at 2VA!

  • Presumably you have gas or oil fired central heating as you need to install central heating controls?

    So logically, the immersion heater is only as a backup in case the central heating won’t work, therefore the central heating and immersion heater won’t be used at the same time, so there’s no issue.

    Even if they were used at the same time as well as the shower pump it would not be an issue anyway, as two of the loads are insignificant.

  • I have a gas boiler with conventional CH and HW controls. I recently built an adapter to interface the boiler's ebus to a Raspberry Pi so I could monitor its behaviour and that inspired me to upgrade to controls that use the ebus.

    Mike

  • Regs wise an immersion heater circuit is nothing special, just another  radial circuit for a fixed load, and as such it may as well be extended for fans, pumps,timers lights etc. I would be a little wary of adding a 13a socket as there is a temptation for excessively large  loads like  a heater to be added, but even if that happened, assuming the breaker and cable protected by it are suitably co-ordinated, all that happens is the breaker trips first. Cold bathwater is a nuisance, not a serious danger.

    What you propose is fine, just label it up clearly so any future user knows which breaker isolates what items. If you were putting it in today it  would need RCD protection, but if it is already there and hasn't  I'd not lose too much sleep so long as it is all done in a way that it stays dry and is positioned so it is unlikely  that a wet handed person would have hold if it and something else to complete a fault path at the same time.

    Mike

  • Thank you Mike. I did consult the OSG but was none the wiser which is why I appreciate the advice this forum provides. It will be a 3A fused "spur" not a 13A socket and will be clearly labelled (as all my switches are). The CU has RCD protection.

    Mike

  • Bear in mind that the 3A fuse will make that circuit , by definition, a new circuit therefore Part P notification applies (I do not think anyone would worry about that though in the real world).

    By technical means I do not think your circuit should cause any problems