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Thread: Electric in the loft

  1. #71

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    I think I've established that I shouldn't ever be let near electrics! I suppose I may have to bite the bullet and get a friend who knows about electrics.

    Number one rule is preventing me from doing that. Don't tell !

    It's been interesting to see the discussion though and if I do get someone to help me will show them this thread

    Sent from my m8 using Tapatalk

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  3. #72

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    Sorry guys, nodded off last night

    One thing I will say is that we have no test results, and therefore can only make a calculated judgement

    My reason for disagreeing is as follows :

    We do not design circuits capable of carrying potential fault current, we design them based on the lb. If we had to select cables capable of carrying a fault current we would be wiring lighting circuits in 10mm

    If it is the fault current we are worrying about, then reducing the CSA to a 2.5/1.5mm cable, will only reduce the fault current more, this would increase the risk of overheating due to a raise in let-through energy if we compare the resistance of 2.5mm compared to 6mm

    Fault current is inversely proportional to our EFLI, therefore low Zs = higher fault current, high Zs = low fault current. For people looking at this thinking wtf are we going on about, using a larger cable with a larger CPC gives a higher fault current flow which trips the mcb faster

    Regulation 433.1.0 tells us that ' Every circuit shall be designed so that a small overload of long duriation is unlikely to occur '

    Where a protective device is providing protection for fault currents, a check can be made to ensure the rise in temperature of the conductors caused by a fault, does not exceed the limit temperature for the conductor. The time in which a fault current will raise the conductors temperature from its normal temperature to its limit temperature can be caluclated using the adiabatic.

    By using the adiabatic, we can confirm that for faults upto 5s, the amount of heat energy a 6mm can withstand is 476100, the let through energy of a 60898 is either 6kA or 10kA. The let through energy rating of the mcb should not exceed the calculated withstandable energy of the cable, which is doesnt, therefore the OCPD is protecting the cable

    Obviously we should rememebr that if the OCPD has been selected to protect againt overloads, and has a breaking capacity not less than the PSCC at the point of installation, it will also protect against short circuit currents, but we can use the above calculation to confirm

    If the PSSC is too low to trip the OCPD within the required time then the circuit has been poorly designed initially, which then makes no difference on the size of the supply cable

    Sorry ive ranted on enough now, just wanted to try get my point across

    Have a good day everyone !

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  5. #73

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    Admin, feel free to delete my posts if you like, I suppose its getting a bit off topic from the op

    Cheers guys

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  7. #74

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    Quote Originally Posted by Fwank View Post
    In West Yorkshire unfortunately, otherwise I'd happily pay one of you to fit it!
    Might not want my help mate but im also in West yorkshire

    Cheers

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  9. #75

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    Quote Originally Posted by sparky-matt View Post
    Might not want my help mate but im also in West yorkshire

    Cheers
    Would love you help but for safety I'd prefer someone would s few grows under their belt.

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  11. #76

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    Quote Originally Posted by Fwank View Post
    Would love you help but for safety I'd prefer someone would s few grows under their belt.
    Totally understand mate

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  13. #77

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    Quote Originally Posted by hightime2016 View Post
    Sockets are generally wired with 2.5t&e unless something like a cocker socket at 6mm! If you use too big a wire rcds may not trip in time putting house and yourself at risk!

    No one thinks your a twat at all fella we are all just trying to help each other out lol


    Sent from my iPhone using Tapatalk
    Hightime, I know what your saying mate but I think your missing my point, the sockets would be wired in 2.5mm, im talking about the supply cable to a sub mains been 6mm, which would then have different OCPD's protecting the socket circuits, take a garage DB for example, similar setup, fed from the house to a small 2 way DB in the garage, supplying lighting / sockets, protected by their own OCPD's

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  15. #78

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    This is what im talking about, sorry about the cr*p drawing, obviously the spec would change depending on the design, but gives you an idea

    Cheers
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  16. #79

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    Quote Originally Posted by sparky-matt View Post
    Hightime, I know what your saying mate but I think your missing my point, the sockets would be wired in 2.5mm, im talking about the supply cable to a sub mains been 6mm, which would then have different OCPD's protecting the socket circuits, take a garage DB for example, similar setup, fed from the house to a small 2 way DB in the garage, supplying lighting / sockets, protected by their own OCPD's
    I was driving earlier and thinking maybe that was what you ment lol!! In which case yes 6mm board too board haha!


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  18. #80

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    Sorry, probably didnt make it clear enough that there would be a sub DB installed, not just connecting directly to the 6mm

    Anyway, back to the OP....

    Cheers fellas

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