Immersion Wiring

Discussion in 'Electricians' Talk' started by RDowson, Aug 10, 2022.

  1. RDowson

    RDowson New Member

    Hello,

    Just been looking at the wiring for my mum’s immersion water heater.

    It’s a 3kW immersion with what I assume is a 20A switch in the kitchen.
    What I’m confused about is that there is a 13A fused spur in the airing cupboard.
    I can’t tell if there is a dedicated 16A breaker in the consumer unit or not.

    I’ve attached some pictures of the setup.
    Does this seem right?


    B8EFBA2C-FD00-40E1-AC57-FEE6391F5420.jpeg 3EFE9333-138E-46E1-A5A7-EE75D7CE1F56.jpeg BCA4D717-AF97-4295-A808-F950DE579F15.jpeg F814E448-E016-4B5B-9D14-B55D8287F41C.jpeg
     
  2. Alan sherriff

    Alan sherriff Active Member

    Looking at the white flex normally for immersion heaters which is fed from fused spur unit can lead to little overheating of the switch if anything just if possible to switch of the 16 amp breaker and ascertain the circuit is fed from there it may be the case
    To replace with a double pole 20 amp switch would elevate any overheating ,but the fused spur may be fed of the ring circuit in which case the switched fuse has to stay to give protection of cable ,would need more investigation before
    moving forward have seen lots of immersion heaters on 13 amp spurs and overheat ,
    correct way 16 amp circuit breaker for the circuit wired in 2.5 m\m twin and earth normal set up terminated via junction box or double pole switch and flex connected to the circuit . The circuit is for the immersion only nothing else the switch with neon on will suffice for isolation. box below looks like a wiring centre for central heating
     
  3. MGW

    MGW Screwfix Select

    I know the regulations in the appendix say items like immersion heaters should be on a dedicated circuit, and back in 1954 although rest of house had the new 13 amp sockets, the immersion heater had a 15 amp plug and socket fed from a dedicated fuse in the fuse box.

    Even in the 70's and 80's we still used a dedicated fuse or MCB for the immersion, but demarcation between trades was not as strict, so no real need for a 15 amp plug and socket to allow the plumber to change the immersion without wiring it in.

    But at some point one needed a unit to change from twin and earth installation wiring to heat resistance flex into the immersion heater, a 13 amp plug should be in free air, so we have two devices we could use, the fused connection unit, or the cooker outlet unit, the latter is normally only used for cookers, so the unit typically used is the FCU, does not really need a fuse when fed from a 15 or 16 amp dedicated supply, but units to change from twin and earth to flex may be made, but are not readily available, and with a FCU we have a lot of material to dissipate the heat from the fuse, the 13 amp plug should always be in free air, and this might not be the case with an airing cupboard.

    MCB's should have labels, but last house never did, we assume 5/6 amp is lights, 15/16 amp immersion, and 30/32 amp ring final or cooker, and 40/45 amp shower or cooker. When my fuse box here was replaced with a consumer unit we had one circuit unidentified, but to work out if ring finals split upper/lower, or side to side is some thing which should be done. Even if side to side is better, not much you can do if up/down, but need to know how to isolate if some thing goes wrong.

    I thing I turned on the immersion heater to see if it worked, but never been on since. But only way to find out is switch MCB's off and see what stops working, with a neon in the switch it should be easy enough.
     
  4. The Happy Builder

    The Happy Builder Screwfix Select

    If it’s working leave it alone.

    Presumably the immersion heater is only for backup if there’s a problem with the central heating?
     
  5. RDowson

    RDowson New Member

    It’s not really been used until now. It’s now cheaper to heat the water with the immersion than gas so I’m going to fit a timer so it can heat overnight on the 5p/kWh rate.
     
  6. RDowson

    RDowson New Member

    I’ll try turning off breakers and see if I can work out if the immersion is on one of its own.
    I assume if it’s not then the spur is fine, and needed?
    If it’s on its own breaker I assume the spur should be replaced with a 20A switch?
     
  7. The Happy Builder

    The Happy Builder Screwfix Select

    Has she got electric night storage heaters to heat her home?
     
  8. RDowson

    RDowson New Member

    No
     
  9. The Happy Builder

    The Happy Builder Screwfix Select

    I’m not getting this, I assume that she has gas central heating to heat her home and hot water, but is on an Economy Seven electricity tariff with an almost unbelievably low off-peak rate of 5 pence per KWh?

    But that would mean she is currently paying a premium rate for daytime electricity without gaining any benefit from the low overnight rate at all, plus any tariffs she is on now will sky rocket over the Winter unless she on an extremely good fixed tariff.
     
  10. RDowson

    RDowson New Member

    It’s not an economy 7 tariff.
    It’s Octopus Go which is an EV tariff. 14p/kWh peak and 5p/kWh off peak. It’s fixed for a good while. Even then, the off peak rate shouldn’t go much above 7.5p.
     
  11. The Happy Builder

    The Happy Builder Screwfix Select

    In that case you need to remove the 20 amp switch in the kitchen and replace it with a timer that can be set to mirror the EV charging periods.

    Then the 13 amp Switched Fused Connection Unit in the airing cupboard can be replaced with a 20 amp switch with a flex outlet.
     
  12. RDowson

    RDowson New Member

    That’s what I planned to do. Just want to know if the fuses spur should stay or be replaced by a 20A switch.
    I’ll do some testing with the breakers to see if the immersion is on its own breaker.
     
  13. The Happy Builder

    The Happy Builder Screwfix Select

    It needs a 20 amp with a flex outlet, they are made without them.
     
  14. RDowson

    RDowson New Member

    Assuming it’s not on a shared breaker.
     

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