OldBoy said:

persisted in the fault mode (apparently faulty meter or loose meter connection) for perhaps in excess of 15 minutes, further aiding the developing fire. Currently, their loads are all single phase and shared across the 3 phases, with ample capacity for future load additions.

This is not usually in the scope of BS 7671, being distributor's equipment ?

OldBoy said:

Both the calculated pfc and measured value indicate around half the pfc required to operate the cutout fuses in the prescribed time, and in the event, persisted in the fault mode (apparently faulty meter or loose meter connection) for perhaps in excess of 15 minutes, further aiding the developing fire. Currently, their loads are all single phase and shared across the 3 phases, with ample capacity for future load additions.

Operate in the required time for what? The DNO will not guarantee operation of their protective device for protection against electric shock, or thermal effects, in accordance with BS 7671.

A poor meter connection, or damaged meter, is not really the type of fault that BS 7671 is intended to address, as it's not really 'overcurrent' (fault or overload) or 'fault protection'.

By the "prescribed time," I meant the 5 seconds stipulated in the ESQC regulations (and BS7671).

OldBoy said:

By the "prescribed time," I meant the 5 seconds stipulated in the ESQC regulations

Does ESQCR require 5 seconds disconnection time?

OldBoy said:

(and BS7671).

The distributor's cutout is outside the installation, and therefore can't be used for protection against electric shock ? In a TT system, it definitely won't provide that function.

Just because it is outwith BS7671, it does not mean that the DNO installation is not required to be safe and to disconnect in the event of overloads and short circuits, at least up to the point of connection of the consumer equipment.  It would be reckless of a DNO to fit fuses that failed to blow before the meter tails (or street supply cable for that matter)   connected to it reached a dangerous temperature in the event of an L-N fault. (*)

Agree that the earth may or  may not be a contractual obligation on the DNO - though then there should be an earth fault relay or a large RCD somewhere if it isn't and they should be able to clarify.

(*)That time may be more than 5 seconds, but I'd be surprised if it was much more, as otherwise there will be problems of exceeding the volt drop permitted by 230V +/- 10% at full load.
Mike.

I’d seen it somewhere, but it was in an SP Networks Document:

SP Energy Networks refer to the 5sec limit in their document

LOW VOLTAGE EARTHING POLICY AND APPLICATION GUIDE

Though it is implied in  the ESQD regs part 2, sec 6. Part 7 sec 24 generally and more specially perhaps 24 (c), and 28 (c) too perhaps.

Interestingly too, 23 (4) refers to the supplier making their neutral or protective conductor available at the customer installation.

I found the SP Energy 36 page document, found by chance on the web, particularly interesting, here’s a link here: https://www.spenergynetworks.co.uk/userfiles/file/EART-01-002.pdf , and wondering if other DNO's have a similar document available.

OldBoy said:

I’d seen it somewhere, but it was in an SP Networks Document:

SP Energy Networks refer to the 5sec limit in their document

LOW VOLTAGE EARTHING POLICY AND APPLICATION GUIDE

But if the earthing arrangements are TT, I don't see how a fuse would provide 5 s disconnection ... it would only make sense for TN-C-S and TN-S.

OldBoy said:

I’d seen it somewhere, but it was in an SP Networks Document:

SP Energy Networks refer to the 5sec limit in their document

LOW VOLTAGE EARTHING POLICY AND APPLICATION GUIDE

But if the earthing arrangements are TT, I don't see how a fuse would provide 5 s disconnection ... it would only make sense for TN-C-S and TN-S.