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55v - 110v centre tap transformer short circuit calculations

Anthony Sullivan

hello

i have been trying to work out how to work short circuit calculations for 110v systems. do i use 55V with c max or do use 110v or even use a 3phase calculation. i am trying to work out if a circuit will trip on 16A c type mcb for short circuit as i am putting a rcbo in to cover the fault current. 

110v 55v 

0.85ohms line to line tested

4mm 2 core cable 

 

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    You could also ask yourself what speed of RCD protection you needed in a system where the sort of live to CPC fault inside equipment that makes the case live, livens it to no more than about 28volts,  I suspect an infinitely slow RCD or none at all would do. You may like to still have an RCD for supplementary protection where one assumes that 2 layers of insulation are damaged but there is no short to CPC, so the full 55v RMS is available to touch, but it is hard to imagine a situation where a single fault to actual danger occurs.

    However BS7671 does not see it that way,

    Mike.

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    You could also ask yourself what speed of RCD protection you needed in a system where the sort of live to CPC fault inside equipment that makes the case live, livens it to no more than about 28volts,  I suspect an infinitely slow RCD or none at all would do. You may like to still have an RCD for supplementary protection where one assumes that 2 layers of insulation are damaged but there is no short to CPC, so the full 55v RMS is available to touch, but it is hard to imagine a situation where a single fault to actual danger occurs.

    However BS7671 does not see it that way,

    Mike.

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