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principles of selectivity between upstream fuses protecting a parallel conductor distrib circuit and the downstream fuses

psychicwarrior

Goodly morrow

Academic scenario:   a final circuit is protected by a 32A fuse/mcb and it is supplied by a distrib circuit that uses two parallel line conductors each protected by two 32A fuses

For selectivity,  if there is an overcurrent (overload or fault) on the final circuit near to the fuse,  can one 'simply' consider the distrib circuit fuses as one fuse (each summed as such)  ?

As there might not be 'selectivity' graphs for a 'summed' fuse/mcb arrangement,  what would one do ...  best ask the manufacturer ?

Thanks for any help in understanding, for my lacking brain.

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    AJJewsbury said:
    With 2 conductors in parallel, they're each likely to be at least half the fuse rating

    I was thinking that if you want two circuit protective devices both legs would match the fuse/MCB rating and be doubled to add integrity, circuits for essential services, so each leg can work independently. 

    Would not they also be full size if doubling up to half the volt drop?

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  • 0
    AJJewsbury said:
    With 2 conductors in parallel, they're each likely to be at least half the fuse rating

    I was thinking that if you want two circuit protective devices both legs would match the fuse/MCB rating and be doubled to add integrity, circuits for essential services, so each leg can work independently. 

    Would not they also be full size if doubling up to half the volt drop?

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