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How to supply a 20A Distribution cct?

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.


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Parents

  • will need 10.0 or 16.0mm2 for Volt drop limitation at 20 Amps over 65 metres.






    No it won't - 16mmsq is more than you need to supply a small house or flat !!

    It's not a lighting-only circuit, so the larger volt drop figure applies. You may need 6mmsq, not more.


    Selectivity between 20A and 16A is not guaranteed, and wont be for fuses either,  though if you accept the overload case being limited by the breakers at the load end, then the source end protection only needs to handle short circuits in the cable, and disconnect in 5 seconds or less for a short at the far end just before the load end breakers, so the source end MCB  could be 32A.


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  • will need 10.0 or 16.0mm2 for Volt drop limitation at 20 Amps over 65 metres.






    No it won't - 16mmsq is more than you need to supply a small house or flat !!

    It's not a lighting-only circuit, so the larger volt drop figure applies. You may need 6mmsq, not more.


    Selectivity between 20A and 16A is not guaranteed, and wont be for fuses either,  though if you accept the overload case being limited by the breakers at the load end, then the source end protection only needs to handle short circuits in the cable, and disconnect in 5 seconds or less for a short at the far end just before the load end breakers, so the source end MCB  could be 32A.


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