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How to supply a 20A Distribution cct?

Farmboy
Sorry if this is too simplistic a question but I'm wondering what you think, given I've had conflicting views from a trade assoc tech dept and Hager tech dept.


A 65m, SP+N, 20A (estimated, but could be subject to some increase) distribution cct, fed from within a commercial setting (an osteopathy/acupuncture service provided in a converted ground floor flat), is to supply a shed/summerhouse with a couple of sockets (for a kettle and TV) and a couple of LED bulkheads (via cb's in the shed CU), sited at the end of the garden. How would you supply the distr. cct at the meter position?

- From a henley block in the existing tails:

              - Its own modular enclosure containing DIN rail mounted main switch and 20A fuse carrier.

              - A rotary handled 20A fused switch disconnector.

- From a 20A cb in the existing CU.


From the trade assoc., one said from the CU, another said it's got to have its own main sw, another said no problem with the modular encl and fuse carrier. While Hager said its got to be the rotary type, not the fuse carrier.


F
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    If consumer unit has space for a 20A MCB or RCBO, and it is of a type readily available, do that.

    If the submain is SWA, and the CU is a bit full,  I'd consider to  change to something less willful (perhaps 2.5mm T and E) for the last foot or 3 , and have a very obvious metal box, either adaptable for large SWA, or just a double socket box and a blanking plate where the outdoor cable glands in and some junction so the cable becomes something easier to work with. It can always be labelled 'supply to outbuilding, isolate at breaker no .4 ' or whatever on the lid.

    IF the CU is full, then a small new one plus henley blocks may be worth considering. Or henley blocks and a switch fuse with a low value fuse in.

    All the stuff about rotary handles seems a bit overkill, was this someone trying to sell you stuff ?  Just needs to be able to be turned off if there is a problem.

    And the place for a thing like a main switch, is in a mini CU at the load end in the new building, as if the fan heater catches light, that is where they need to turn it off from, not running back to the main building, and also if the lights ever need changing, so you can see it is isolated.

    If the supply earth is TT then if it is SWA or not, you need an RCD at the source end, otherwise, I'd suggest non RCD protected cable, like SWA, and then have RCDs at the load end, so the new building is self contained. Take care when drilling holes and siting things in the outbuilding, that rain cannot drive in or run along your cables and into the back of your new kit.


    at 65m have you checked the volt drop considerations, you may need to use either 4mm or 6mm for the bulk of the length, even though it is only 20A,  depending on what you allow for volt drop in the rest of the system. (and more if you think there will be significant load creep in future)


    How is that kettle filled? , do we have a metal water pipe that needs 10mm main bonding, or better, some plastic pipe, that does not.


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  • 0
    If consumer unit has space for a 20A MCB or RCBO, and it is of a type readily available, do that.

    If the submain is SWA, and the CU is a bit full,  I'd consider to  change to something less willful (perhaps 2.5mm T and E) for the last foot or 3 , and have a very obvious metal box, either adaptable for large SWA, or just a double socket box and a blanking plate where the outdoor cable glands in and some junction so the cable becomes something easier to work with. It can always be labelled 'supply to outbuilding, isolate at breaker no .4 ' or whatever on the lid.

    IF the CU is full, then a small new one plus henley blocks may be worth considering. Or henley blocks and a switch fuse with a low value fuse in.

    All the stuff about rotary handles seems a bit overkill, was this someone trying to sell you stuff ?  Just needs to be able to be turned off if there is a problem.

    And the place for a thing like a main switch, is in a mini CU at the load end in the new building, as if the fan heater catches light, that is where they need to turn it off from, not running back to the main building, and also if the lights ever need changing, so you can see it is isolated.

    If the supply earth is TT then if it is SWA or not, you need an RCD at the source end, otherwise, I'd suggest non RCD protected cable, like SWA, and then have RCDs at the load end, so the new building is self contained. Take care when drilling holes and siting things in the outbuilding, that rain cannot drive in or run along your cables and into the back of your new kit.


    at 65m have you checked the volt drop considerations, you may need to use either 4mm or 6mm for the bulk of the length, even though it is only 20A,  depending on what you allow for volt drop in the rest of the system. (and more if you think there will be significant load creep in future)


    How is that kettle filled? , do we have a metal water pipe that needs 10mm main bonding, or better, some plastic pipe, that does not.


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