462.2; Is an external main isolator required prior to the integral switch disconnector in main MCCB panel board?

Question

Hello, 
 We have a main MCCB panelboard on a client's site in a new building, that has the incoming cable from their nearby substation (not DNO) terminating into the switch disconnector within the MCCB panelboard. 
 There is no adjacent external/separate switch next to the panelboard. 
 To isolate the whole MCCB panelboard, the fuses need to be pulled from the nearby upstream substation, which belongs to the client, so organising such is not a big issue. 
 To isolate all the outgoing circuits from the panelboard and all the downstream MCB DBs that are within the building, the integral switch disconnector inside the panelboard will provide. 
 The proposed building maintainer has intimated that they think this contravenes 462.2. 
 They say that the busbars within the panelboard would fall under 462.2 that requires 'isolation for all live conductors'. 
 However our take on it is that the integral switch disconnector does isolate all the busbars and outgoing circuits inside/on the MCCB panelboard. Only the live side terminals on the switch disconnector will remain live.

Question is; 
 Is the above setup compliant with 462.2? Or, is a separate/adjacent main intake switch needed upstream of the MCCB panelboard to comply?

Thanks.

broadgage · Accepted Answer

In my view, the practice as described is compliant, simply because it is the norm and is generally accepted. In smaller installations it is common practice to take the meter tails directly in to the main switch of a D/B without any means of isolation except by removing the DNO fuse, which is firstly prohibited and secondly does not isolate the neutral. 
 At least in the situation described, the D/B can be isolated by removing the fuses in a nearby substation.

AJJewsbury · Answer

I'd tend to agree with broadgage - 462.2 talks about every circuit ... and as circuits are defined by the position overcurrent protective devices (rather than say isolators) so sticking in an extra isolator just before the panelboard would still leave the majority of the supply circuit in the same situation as it was before - so if it was thought not to comply without an extra isolator, it would still not comply even with one. Or to put it another way, introducing an extra isolator just moves (the perceived) problem back a few inches - it doesn't solve it. 
 That said, I can see a point of view that in some situations (say where the panelboard has to be replaced), it might be very convenient to have some local isolation available - but that's more an issue of convenience and customer requirements rather than safety or isolation - so a matter or contract rather than BS 7671. 
 - Andy.

mapj1 · Answer

Agree its not breaking a reg, but it may be worth looking at, especially if a lot of 'going in' to the panel board is anticipated and fuse pulling to do so would disrupt other operations on site. 
 Equally in a well designed board it may be the bits before the built in isolator that remain live are small and/or shielded from accidental contact, such that any necessary work on the outbound wiring can be done using the internal isolator but without isolating the incoming supply. This would be much as on a smaller scale consumer units may be opened while the meter tails remain energized.. Mike.

462.2; Is an external main isolator required prior to the integral switch disconnector in main MCCB panel board?

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