Basic Question.

Discussion in 'Electrics UK' started by liftman, 23 Feb 2009.

  1. liftman

    liftman

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    A friend of mine recently moved my vailant combi boiler for me, i wired the 240v supply, i used .75mm cable as that was all i had at the time, i would appreciate any thoughts from pro's that this is o.k, just a bit concerned now that i should of used a bigger cable.
     
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  3. seco services

    seco services

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    0.75mm is ok.
    was it heat resistant ?
     
  4. gas4you

    gas4you

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    .75mm is fine, but it should be heat resistant to 85C.
     
  5. liftman

    liftman

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    Thanks for speedy reply, it was'nt heat rated, which does concern me as the cabling is in the same run as the hot pipes under the floor.
     
  6. dodginess

    dodginess

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    My experience is electrical and not plumbing but here goes:

    Do you know what the boiler's rated at? As a rough guide, a 3kW device (drawing just under 13A) should really have a heat-resistant 2.5mm cable to be safe. I don't know whether this is standard practice but it's usually recommended to have devices like this on their own radial circuit as well, though this is less critical.

    From experience, if it's not too much hassle for you to fix it's always better to get something like this sorted - if it does actually need sorting - otherwise you'll just end up worrying about it :) Start as you mean to go on, etc.

    Neil
     
  7. JohnD

    JohnD

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    it is also a good idea to insulate the pipes with Climaflex or similar. Then, as well as saving energy on heat loss from pipes, and with a gap between pipes and cable, the temperature will be reasonably low.

    If the cable is in contact with hot pipes, the service life of the insulation will be greatly shortened.

    I have seen this on PVC T&E which becomes hard and brittle, and gets surface cracks even when it has not been moved.

    There is a table of temperature and service life somewhere, but I have not got it.

    p.s. Boilers are supposed to be on a 3A fuse in the FCU (I was told last week on the plumbing forum)
     
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  9. londonboy

    londonboy

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    Most gas boilers only need a 3amp fuse (actually drawing little more than 1amp).
    0.75 flex will be fine, most flexes now are rated at 85 degrees, sometimes its actually written on the side of the cable.
    .... But I would never run a cable beside hot pipes under the floor! If possible lift the floorboard next to the pipes and drill them out (50mm below top) to prevent nails/heat damage![/quote]
     
  10. londonboy

    londonboy

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    ... Almost every heating job I do (as an electrician) I see that! Keep twin and earth well away, flex's withstand heat slightly better. Still go hard and crack with age etc. What do people in here think of running flex's under floors? For fixed wiring? It's a common debate at work, NIC man says its ok, although we all prefer to use t+e and 3 core+e
     
  11. JohnD

    JohnD

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    You mean drill the joists, right?
     
  12. liftman

    liftman

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    Thanks for the information, the boiler supply is on a 3 amp spur from the kitchen ring main, as i am currently in the process of fitting a new kitchen it is no problem to lift the boards and re-run it separately with the correct cable, which is what i will do now that i have the right advice. Thanks again.
     
  13. londonboy

    londonboy

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    Yeh thats it... Still seeing too many roomstats etc laid across the tops of flow and return!
     
  14. JohnD

    JohnD

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    don't forget to insulate as well.
     
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