Immersion wiring

Discussion in 'Electricians' Talk' started by breezy, Oct 21, 2017.

  1. breezy

    breezy New Member

    What size wire should I used to add a timer switch to my existing on/off immersion switch please?
     
  2. retiredsparks

    retiredsparks Super Member

    2.5 mm heat resistant flex.
    RS
     
  3. JP.

    JP. Screwfix Select

    It cant be that easy surely RS?..:)
     
  4. retiredsparks

    retiredsparks Super Member


    I doubt it, someone sure to say different....
    :cool:
    Rs
     
  5. Lectrician

    Lectrician Screwfix Select

    1.5mm heat resist would be fine, assuming this is going DP Switch > Timer > Element.
     
    leesparkykent likes this.
  6. seneca

    seneca Screwfix Select

    Yes i'd say 1.5mm too, provided it's not going half way around the house of course!
     
  7. Coloumb

    Coloumb Screwfix Select

    Woh betide anyone wiring it off a ring final too. The whole SF sparky communities will be round to fry your balls.
     
    seneca likes this.
  8. JP.

    JP. Screwfix Select

    Not being funny or owt - but say your imm heater elly is 2 to say 2.5kW then if this was wired into the ring main would it be non compliant?

    I can only liken the imm element to say a dish washer or washing machine element - and we know that these elements are allowed to be run orfffffff the Ring Final via fcu or whatever - in other words most of the time they are hard wired into the ring final..:D:D

    Most imm elements are 3kW though
     
  9. Bob Rathbone

    Bob Rathbone Screwfix Select

    The immersion heater current draw is within that permitted for connection to a domestic ring final circuit, BUT, if you are heating 60 to 80 litres of water with a 3 kW element, it's going to take some time. The regulations recognise this and have placed a restriction on connecting water heaters to domestic rings, they limit the water capacity which means that the water heats quickly and the thermostat cuts the heater off. The supply is only loaded for about 10 minutes rather than half an hour or more as would be the case with the 60 or 80 litre tank. The capacity of the ring final circuit is not taken up by water heating duties.
     
    Bazza likes this.
  10. JP.

    JP. Screwfix Select

    Many thanks for your elucidation Bob - all points noted m8.
     
  11. breezy

    breezy New Member

    Thank you all! Would this setup be ok?

    DP switch (master)

    >SP Switch (2 way + off)

    > 1 - timer + neon
    > 2 - off
    > 3 - on + neon

    Existing wiring looks to be 2.5mm which might not fit in the 2G space, 1.5mm would probably be flexible enough to if that would suit.
     
  12. MGW

    MGW Screwfix Select

    Is this some thing new? I only have the original BS7671:2008 which in the appendix says any non portable appliance over 2 kW should have a dedicated supply to avoid cable overload, this could be a problem where the consumer unit is close to the appliance as one leg of the ring could take most of the load.

    If we use some common sense ovens, and the like only use max power when first switched on, once warm they cycle on/off so not really a problem, the two items which draw power over an extended time is the immersion heater and the drier, the latter may be stand alone or could be part of a washing machine. But tumble driers typically run for 1.5 hours so around 4.5 kWh and an cold immersion heater can take 10 kWh to heat 150 litres 60 degrees C so the immersion could take twice the power running for 4 hours plus where the tumble drier is only 1.5 hours.

    If a cable is over loaded there is a time factor, however how much hotter a cable will get in 4 hours compared with 1.5 hours I am not sure? I can see where the electric kettle at 5 minutes is not a problem as so fast, but the appendix actually lists ovens which will normally reach running temperature within 20 minutes, so the tumble drier is three times that so we would clearly need a dedicated supply to a tumble drier.

    The regulation 433.1.5 said the load current in any part of the circuit is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable. This is down to where on the ring the load is drawn, so in my house where the kitchen is other end of house to consumer unit, all kitchen loads will be reasonably central so no problem, in my mothers house where the consumer unit is in the kitchen you could well end up with a overload on one leg of the ring.

    I can find nothing which actually states the water heating capacity of the tank the heater is in, and I think this would be a problem as with the Willis system the immersion heater is only in a 5 litre tank, but it heats the 30 gallon cistern from the top down, seems only the Irish have worked out how to do this!
     
  13. Bob Rathbone

    Bob Rathbone Screwfix Select

    This is something old, been around for years and it is the reason that over and undersink water heaters only have a 15 litre capacity. Yes, common sense on ovens works as they only heat air which does not absorb as much heat energy as water. Have you noticed that the heaters in washing machines and dryers are normally below 3 kW at around 2.8 kW, why would that be? Thanks for your reply, your points are valid.
     

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