Taking up on some earlier comments, using RCD as a solution, raises a few other issues I.e. by doing so you are making the system, particular when maintaining essential supplies less secure.

as an example on one project, a UPS was used to maintain lighting on mains failure. The lighting design had a number of distribution boards housing 5amp fuses for final sub-circuits. the UPS manufacturer was asked to prove that during FAT, under an fault condition would the 5amp fuse disconnect, L-N and Zs impedances for the circuits were given for simulation, they could not provide evidence.

i guess has anyone got any empirical evidence on how these issues were overcome.

Anthony Smith said:

as an example on one project, a UPS was used to maintain lighting on mains failure. The lighting design had a number of distribution boards housing 5amp fuses for final sub-circuits. the UPS manufacturer was asked to prove that during FAT, under an fault condition would the 5amp fuse disconnect, L-N and Zs impedances for the circuits were given for simulation, they could not provide evidence.

This is a supply to safety services, and should comply with the relevant standards. It's a specific case. See Regulation 560.5.3, which leads to a design decision to perhaps consider IT system for those circuits? Where BS 7671 applies to this type of installation, Regulation 560.7.4 effectively tells us to provide an appropriate number of circuits so that OCPD operation does not impair other circuits.

BUT

See earlier post - this isn't simply a UPS, but a CPS - and the requirements of BS EN 50171 and Regulation 560.6.10 of BS 7671 apply to the "UPS" itself - but the whole system ought to comply with the BS 5266 and BS EN 1838.

Anthony Smith said:

as an example on one project, a UPS was used to maintain lighting on mains failure. The lighting design had a number of distribution boards housing 5amp fuses for final sub-circuits. the UPS manufacturer was asked to prove that during FAT, under an fault condition would the 5amp fuse disconnect, L-N and Zs impedances for the circuits were given for simulation, they could not provide evidence.

This is a supply to safety services, and should comply with the relevant standards. It's a specific case. See Regulation 560.5.3, which leads to a design decision to perhaps consider IT system for those circuits? Where BS 7671 applies to this type of installation, Regulation 560.7.4 effectively tells us to provide an appropriate number of circuits so that OCPD operation does not impair other circuits.

BUT

See earlier post - this isn't simply a UPS, but a CPS - and the requirements of BS EN 50171 and Regulation 560.6.10 of BS 7671 apply to the "UPS" itself - but the whole system ought to comply with the BS 5266 and BS EN 1838.