I have a Client that will not provide a Risk Assessment to omit an RCD Commando Socket for a Data Cabinet. He wishes to employ a local isolator for the Cabinet, however he is concerned that the PDU Strip that arrived on site from the factory and pre-fitted within the data cabinet would still need an RCD. It is my opinion that the Factory built Data Rack is classed as a piece of equipment and as such does not form part of the Contractor's installation. If the Rack had arrived on site without the PDU strip fitted and it was installed by the Contractor then this would form part of the installation and therefore would require an RCD. Any advice/assistance would be appreciated.
Well, except for the potentially significant convenience of not having to turn the power off and verify exposed terminals are dead before unbolting things - as with signal cables, bonding can be removed and re-fitted, as soon as the jumbo mains plug is removed from the supply... Yes you can have local isolation switches one per rack, but these in the heat of battle such things can be another source of accidentally switching off the wrong thing.
and the supplementary bonding must be in place and tested (notice) before the equipment is energised.
I feel the need to reinforce the fact that, for the assumption that risks are controlled to be true, ALL of the supplementary bonding must be in place, including the connection between the rack earth bar and the PE of the power distribution strips, though. Whilst this is now clearly stated in the latest version of BS EN 50310, I can't tell you how many racks I've seen, and continue to see see without these connections made.
It's also worth noting the following:
if you go back to BS EN 61140, there should be no reason RCDs can't be used for individual socket-outlets (except the discussion we've had in the Forums already about the 18th Edition that SRCD standards aren't listed in the relevant Regs in Chapter 5 of BS 7671 ?)
the design decision to connect a "rack" using plug and socket-outlet rather than a fixed wiring connection point is really a preference. The often-used statement that "it makes it easier to install and remove racks as we need them" doesn't hold water, as to comply with BS EN 50310, you need to make fixed wiring connections for the CBN bonding to each rack, and execute relevant electrical tests stated in that standard.
This does bring out a point from BS7671, which is the blanket requirement for RCDs for sockets up to 32A. In an installation such as this with supplementary bonding to earth, the RCD has exactly zero use! There is no shock risk unless the equipment is opened and live terminals accessed, whatever earth fault occurs. This point needs revision, because it simply doesn't make any kind of safety sense. From your point of view I suggest fitting 63A BS4343 connectors to the installation. If they choose an RA, it is fairly straightforward, the environment is controlled and nothing else may be plugged into the socket, and the supplementary bonding must be in place and tested (notice) before the equipment is energised.
Given BS EN 50310 (which is referred to from BS 7671), at least some of the rack power distribution is covered by BS 7671, as to the latest version of BS EN 50310 it requires local bonding to the rack earth bar, and the rack earth bar bonding to the room earthing etc.
This does indeed ask the question whether RCD protection is required for the socket-outlets if no risk assessment is provided.
The only other option open to you is to use rack power distribution units that employ couplers (to BS EN 60320) rather than socket-outlets to BS 1363 or BS EN 60309 - BS 7671 does not (at present) require RCD protection for couplers. So provided the power distribution strips comply with relevant standards ...
