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Sub-Board - Second Consumer Unit

Discussion in 'Electrics UK' started by FRAN1870, 7 Nov 2018.

  1. JohnW2

    JohnW2

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    True, and the current-carrying of the cable is that current deemed to raise the conductor temperature to that "temperature rating" of 70°C (for given installation method and environmental factors). The CCC 'correction factors' ("Ca") for ambient temps above 30°C (table 4B1 in BS7671) indicates that, for a 70°C thermoplastic cable) the tabulated CCC has to be halved at an ambient temp of 60°C. The table goes no further than that but, at least in theory, the CCC should fall to zero if the ambient temp is 70°C.

    Having said that ...
    I have certainly experienced T+E cable that he been 'wound around' CH pipes for decades without apparently having come to any harm.

    Kind Regards, John
     
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  2. Taylortwocities

    Taylortwocities

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    He can certify that the work complies with the Wiring Regulations (BS7671). In addition (If needed) he/she can notify that the work he/she has done complies with Building Regulations.
     
  3. FRAN1870

    FRAN1870

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    I'm sure in this old lump there are many instances of lighting and socket cables crossing CH pipes ... I think my main concern is that the sub board could be pulling some amps.
    (2 x ovens plus kitchen & utility ring main etc) which I assume would raise the temperature of the cable anyway?
     
  4. JohnW2

    JohnW2

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    AS you've been told, it's pretty common - CH pipes and cables going through the same small notches in the top of floor joists used to be very common..
    In terms of cable heating, it's the average current over a significant period of time that really matters - and you'd probably be very surprised by how low, in practice, that average would be, even with the loads you mention.

    Kind Regards, John
     
  5. winston1

    winston1

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    Yes, but not many amps as not everything will be on at once. You also have a very much oversized cable so its temperature won't rise much.
     
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  6. FRAN1870

    FRAN1870

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    OK fellas thanks for your help ... I'll try and whack a bit of insulation between the cable and pipe and rest easy in my bed tonight.
    (the cable runs under my bed).
     
  7. FRAN1870

    FRAN1870

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    Ok one more question ... sorry for all the anxieties.

    The hot / cold feed water pipes run very close to the subboard. I’m not so fussed about it leaking as it’s a continuous length. However the pipe runs pretty much over the top of the top cable feed into the board. I was thinking that condensation might form and drip into the box?

    Maybe some lagging is in order?

    Your thoughts?
     

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  8. SimonH2

    SimonH2

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    I doubt if that's unusual. The hot pipe will not be a problem, in theory the cold pipe could form condensation and drip. For insulation to stop the condensation, it needs to be impervious to water vapour and be sealed all the way along and at it's ends - otherwise water vapour gets in, saturates the insulation, and eventually starts dripping.
    We had that latter problem at a previous job because the contractors didn't install the (quite expensive) Armaflex on the chilled water pipes for the office air conditioning properly (basically never even looked at the instructions). They had to come and take some of it off and replace it - the stuff that came off was well saturated from the inside out.

    But one thing that really surprises me is that the new board is installed on a wall which I assume is still the be skimmed. It's more normal to skim the wall before putting stuff on it - you'll have plaster all over the board, and if you ever have to change it, there'll be a hole in the skim with a non-flat border round it.
     
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  9. FRAN1870

    FRAN1870

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    Thanks for the info ... I looked at some insulation today in B&Q but it said resitsance to fire was euro E which I understand isn’t very resistance at all so im not sure what to buy. I know fire resistance isn’t the intent but I didn’t want to solve one risk with another.

    The sparky did say that he could take it off before plaster but I’ll tape it up if not, I’m not fussed about it being changed as I can skim it over if needed.

    It’s the first risks I’m concerned about
     
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