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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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    Scanning the thread (sorry it's late)... I'd be saying whoever said separate tails into a block is talking out of the back of their head. The main isolator in the CU provides isolation and is lockable with the correct lockoff kit. It may be more CONVENIENT to have a separate isolator, and that would be a sensible option if total isolation of all live conductors may be required routinely (however slowly the routine rolls round). But REQUIRED, No.


    With everyone else on the 'definitely upsize the cable'. Unless you know the load isn't going to grow (single fixed load)... never let volt drop be your guiding rule. It's a last ditch 'this cable's too small' rule.


    As to discrimination (sorry, selectivity). Cartridge fuse units for domestic CU's are available on Ebay, from commercial sellers. Just because it's ebay doesn't mean you can't trust it, it just means the level of trust is lower.  Ditto numerous other online marketplaces.


    But nobody yet seems to have mentioned (APOLOGIES if someone has, again, scanned it fast) the idea of a C or even D curve breaker to protect the distribution SWA...  and normal B curve in the distant board.


    On a short, they'd trip in order of their rating, unless the fault was catastrophic, in which case who cares which one trips provided one of them does, on an overload, the B's will trip faster.  Its possible if you're dedicated enough to feed the curves into software and superimpose them and find out where they cross, but who cares if a BS3036 with 2  strands of 5A wire trips before a C16. I want whatever that is dead <grin>
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  • 0
    Scanning the thread (sorry it's late)... I'd be saying whoever said separate tails into a block is talking out of the back of their head. The main isolator in the CU provides isolation and is lockable with the correct lockoff kit. It may be more CONVENIENT to have a separate isolator, and that would be a sensible option if total isolation of all live conductors may be required routinely (however slowly the routine rolls round). But REQUIRED, No.


    With everyone else on the 'definitely upsize the cable'. Unless you know the load isn't going to grow (single fixed load)... never let volt drop be your guiding rule. It's a last ditch 'this cable's too small' rule.


    As to discrimination (sorry, selectivity). Cartridge fuse units for domestic CU's are available on Ebay, from commercial sellers. Just because it's ebay doesn't mean you can't trust it, it just means the level of trust is lower.  Ditto numerous other online marketplaces.


    But nobody yet seems to have mentioned (APOLOGIES if someone has, again, scanned it fast) the idea of a C or even D curve breaker to protect the distribution SWA...  and normal B curve in the distant board.


    On a short, they'd trip in order of their rating, unless the fault was catastrophic, in which case who cares which one trips provided one of them does, on an overload, the B's will trip faster.  Its possible if you're dedicated enough to feed the curves into software and superimpose them and find out where they cross, but who cares if a BS3036 with 2  strands of 5A wire trips before a C16. I want whatever that is dead <grin>
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