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Meter Tail Size on long run.

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  • 07-08-2012 11:05am
    #1
    223vmax
    Registered Users Posts: 475 ✭✭


    I'm currently building an extension and have the existing ESB supply coming to the front gable. Since the extension now joins into this gable I want to move the ESB supply entry point. The current meter is situated in the main hall of the house.
    I have decided to install an exterior meter box at the front of the house in the extension and now need the meter relocating along with the ESB supply entry point moving from the gable to the meter box via an undergraound cable. I have trenched out and installed the red ESB duct from pole and up a hockey stick into the new meter enclosure. The ESB pole is approx 10M from the house.
    The distance between the new meter box location and the existing CU is approx 23M. Part of the run of this cable is through some attic space which often in summer gets quite warm above 35C. The supply is a domestic 80A supply. Would 25mm2 cable be sufficient for the consumer tails to the new meter considering the conditions? Any help or pointers appreciated.


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    #2
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    when you say 80amp do you have an enhanced 16kva supply or do you mean the esb fuse is 80amp?


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    #3
    223vmax
    Registered Users Posts: 475 ✭✭223vmax


    Sorry M cebee, the main ESB fuse is 80A and the CU RCD is 63A.


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    #4
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    A 25 sq. will be able to safley and indefinitley carry that load.

    What you have to do now is ensure that the maximum permissable volt drop is not exceeded on the far end of any final circuit.

    As far as I can remember the maximum allowable volt drop is 4%.
    I would be normal to allow 1 to 1.5 % volt drop to the distribution board and no more than 2.5 to 3% on the final circuit.

    For this you will need to know the design current and mV per amp meter for each of the cables.


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    #5
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    yes it's 4% max installation volt drop from esb meter to socket or light etc.
    and obviously cable needs to be sized correctly according to main ocpd
    (63amp mcb in cabinet in this case)

    what design current would you use for the tails on a 12kva supply to calculate volt drop?
    would you put in 63amp to be on the safe side?



    he definitely won't have any issue with 25's anyway

    and 16's may even do


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    #6
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    Yes, I would use 63A as the design current.
    It would not be possible to use anything else unless you can provide a very good reason.


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    #7
    223vmax
    Registered Users Posts: 475 ✭✭223vmax


    Thanks for the replies. Anyone know where I can source some 25mm2 cable. All my local suppliers dont go any bigger than 16mm....I'm in East county Galway.


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    #8
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    It may be cheaper for you to buy 3 x 25 sq. mm SWA than drive around the country or pay for delivery. Just a thought.


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    #9
    223vmax
    Registered Users Posts: 475 ✭✭223vmax


    M cebee wrote: »

    and 16's may even do

    Would 16mm2 do on this job? Im being quoted high prices for this cable.:(


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    #10
    .G.
    Registered Users Posts: 5,415 ✭✭✭.G.


    It depends on the method of installation,the ambient temp,the length of run and the design load.

    On the info you've given even at temps of 40c in your attic the CCC of 16sq is still 81amps.

    Volt drop won't be an issue on a run of 23m at a design load of 63amps either as its well within the 4% allowed.

    If the cable is mounted in free air, ie not run through or under any thermal insulation then I think your fine with 16sq.


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    #11
    223vmax
    Registered Users Posts: 475 ✭✭223vmax


    thanks, what Ci value would you use for a 10M length of this cable running through duct in the cavity of a wall filled with pumped bead insultaion? The insulation does not come into contact with the beads at any point.


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    #12
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    superg wrote: »
    It depends on the method of installation,the ambient temp,the length of run and the design load.

    On the info you've given even at temps of 40c in your attic the CCC of 16sq is still 81amps.

    Volt drop won't be an issue on a run of 23m at a design load of 63amps either as its well within the 4% allowed.

    If the cable is mounted in free air, ie not run through or under any thermal insulation then I think your fine with 16sq.

    4% volt drop is for the tails and the 'final circuit'

    when i checked it i think it was just over the 1.5% figure that 2011 quoted

    i think 16's might just do anyhow

    the other option besides swa is 25mm pvc/pvc singles and a 16sq pvc earth

    they can be got online from meteor


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    #13
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    M cebee wrote: »
    4% volt drop is for the tails and the 'final circuit'
    Correct.
    when i checked it i think it was just over the 1.5% figure that 2011 quoted
    1.5% is a guide only. That figure is set by the designer. Once you do not exceed the 4% mentioned above you comply with ET101.
    A 3% would be permissable, but then you may have to increase the size of cable for final ciruits to keep the overall volt drop < or = 4%.
    i think 16's might just do anyhow
    Yes, but see above.

    I would simply work out the VD on 16sq. cables at 63A and take it form there.

    the other option besides swa is 25mm pvc/pvc singles and a 16sq pvc earth

    they can be got online from meteor
    That would work.


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    #14
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    2011 wrote: »
    Correct.


    1.5% is a guide only. That figure is set by the designer. Once you do not exceed the 4% mentioned above you comply with ET101.
    A 3% would be permissable, but then you may have to increase the size of cable for final ciruits to keep the overall volt drop < or = 4%.


    Yes, but see above.

    I would simply work out the VD on 16sq. cables at 63A and take it form there.



    That would work.

    i doubt it would be practical to have 3% for domestic tails


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    #15
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,593 Mod ✭✭✭✭2011


    M cebee wrote: »
    i doubt it would be practical to have 3% for domestic tails
    Probebly not, but my point is it is permitted. This is why 1 to 1.5% is generally accepted as a good guide.


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    #16
    223vmax
    Registered Users Posts: 475 ✭✭223vmax


    M cebee wrote: »

    the other option besides swa is 25mm pvc/pvc singles and a 16sq pvc earth

    they can be got online from meteor

    Thanks M cebee. I looked on their website and I can't find 25mm they have the 16mm pvc/pvc alright but I must be looking in the wrong place.Can you send me the link please?


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    #17
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    Doesn't seem to be in Stock
    I've always bought 25 pvc./pvc off them before for 80amp domestic enhanced supplies

    I don't know if 3*25 swa is stocked here at all
    You may get by with 16t&e


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    #18
    .G.
    Registered Users Posts: 5,415 ✭✭✭.G.


    M cebee wrote: »
    4% volt drop is for the tails and the 'final circuit'

    Fair enough, not what we were told in college but there you go.

    He'll have to do a few calculations then,one for the 16sq and then one for each of his final circuits and add them up.

    Only way to be sure or go with 25's to be certain


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    #19
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    ya

    i don't recall anything much from college-mostly checking up rules

    getting 25's for single phase is a hassle if i recall-i always used meteor for the singles

    is 3*25 swa with single phase colours available?doubt it


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    #20
    223vmax
    Registered Users Posts: 475 ✭✭223vmax


    Ok I managed to source some SWA 3 core for my job. Next question "Do I need to put ferrels on the ends of the L,N & E for connection into the ESB meter?


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    #21
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    no

    the swa will gland into the enclosure containing the 63amp main ocpd
    not the meter
    assuming you're fitting one


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    #22
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    I think he was more asking about using ferules on the ends of the conductors.

    In answer to that, if that was being asked, they are not needed for swa cores, and would not be a good idea.

    Ferules would be used on flexible cores which would be in silflex cables as an example, or single core flex used for linking different busbars and terminals in DB`s.

    As these flex cores have lots of very thin strands, lots of the strands tend to go around the sides of terminal screws if ferules are not used, and so the connection would not be great.


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