AMK said:

How should regulation 537.2.1.7 be interpreted and applied?

There is no such Regulation in BS 7671:2018+A2:2022 or BS 7671:2018, so the short answer is that it is neither interpreted nor applied - there has been no such Regulation for over 5 years!

However, 537.2.6 and 461.2 together effectively replace the requirement.

The parts of BS 7671 regarding isolation and switching were completely revised, and split into Chapter 46 and Chapter 53 (see page 5 of BS 7671:2018+A2:2022).

AMK said:

Regulation 531.2.2 allows the neutral to remain connected if it can be reliably assumed to be at earth potential.

And more fundamentally, Regulation 461.2 ? This also requires equipotential bonding to be in place. Some might argue that if there are no extraneous-conductive-parts, there is no equipotential bonding, so the neutral requires isolation regardless of the supply type and earthing arrangements.

Regardless of all that, in installations where the main switch at the origin is intended for operation by ordinary persons, if the supply is single-phase, the neutral must be disconnected (Regulation 462.1.201).

AMK said:

Some suggest that these methods are sufficient and practical, and that isolating the neutral is unnecessary and impractical.

Further, if you provide a separate neutral disconnecting link and fail to re-instate before re-energizing, that can be very dangerous in a three-phase system (see Regulations 431.3 and 442.3).

AMK said:

The Lead Engineer argues that both supplies, essential and non-essential, need to be isolated to work on the Essential Line side isolator, where the neutral is linked between the line and load. But is this really necessary?

I think that would be down to how one interprets Regulation 461.2 ...

gkenyon said:

years!

However, 537.2.6 and 461.2 together effectively replace the requirement.

Do you understand 462.1? I don’t, neither for that matter do the technical bods at NICEIC. I would love to understand the latter part of that regulation!

gkenyon said:

years!

However, 537.2.6 and 461.2 together effectively replace the requirement.

Do you understand 462.1? I don’t, neither for that matter do the technical bods at NICEIC. I would love to understand the latter part of that regulation!