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Main switch short circuit capacity.

wessex
Some guidance please.

Three phase TN-S supply from a private 800 kVA transformer. Distribution via a 240mm2 4 core SWA approx 20m in length from a transformer mounted feed pillar and protected by 315A fuses. At the intake position 100A BS 1361 type II fuses are fitted. I was looking to install a REC 4 main switch down stream from which would be three phase distribution by 10kA rated MCB's. My question is about the suitability of the main switch and its short circuit capacity at it's point of installation with regard to prospective fault current at this point which will be greater than 16kA or do the BS 1361 afford adequate protection for the switch ? Your thoughts please.
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    Although the PSSC is high, the fuses will limit the duration of that fault and therefore the damage, as if the fault current were lower - you need to look at the spec of the REC 4 versus the effective fault current the fuses give you  (so called 'current limiting' with fuses, is really I2t limiting)


    I'd be surprised if protection by the fuses could not be arranged to be enough, as this use of a 'death or glory' last ditch fuse to allow  downstream kit to be more modestly sized is common - and avoids needing a light switch rated for a hundred kA fault in the substation room, and avoids also the cable to be tied to the wall like the book of monstors needs to be tied shut in Harry Potter...

    So some perusal of fuse datasheets and maybe an email or a  call to the maker of the isolator to be sure you are OK , but yes it ought to be possible, or something in that style anyway.
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    Although the PSSC is high, the fuses will limit the duration of that fault and therefore the damage, as if the fault current were lower - you need to look at the spec of the REC 4 versus the effective fault current the fuses give you  (so called 'current limiting' with fuses, is really I2t limiting)


    I'd be surprised if protection by the fuses could not be arranged to be enough, as this use of a 'death or glory' last ditch fuse to allow  downstream kit to be more modestly sized is common - and avoids needing a light switch rated for a hundred kA fault in the substation room, and avoids also the cable to be tied to the wall like the book of monstors needs to be tied shut in Harry Potter...

    So some perusal of fuse datasheets and maybe an email or a  call to the maker of the isolator to be sure you are OK , but yes it ought to be possible, or something in that style anyway.
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