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.

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.

https://www.legislation.gov.uk/uksi/2002/2665/regulation/6

A generator or distributor shall be responsible for the application of such protective devices to his network as will, so far as is reasonably practicable, prevent any current, including any leakage to earth, from flowing in any part of his network for such a period that that part of his network can no longer carry that current without danger.

Now I agree that 5 seconds is used for adiabatic cable assumptions in ' 7671. But for some DNO assets are very massive, 100% overload is fine for several hours. This is only about parts of the Distribution Network, and then only about danger, not damage, so under this rule, transformers blistering paint off are fine, so long as the  hot parts are high and out of reach, and nothing hot drips off where it can cause injury or damage.

so they can get out of that one...

https://www.legislation.gov.uk/uksi/2002/2665/regulation/24

24.—(1) A distributor or meter operator shall ensure that each item of his equipment which is on a consumer’s premises but which is not under the control of the consumer (whether forming part of the consumer’s installation or not) is—

(a)suitable for its purpose;

(b)installed and, so far as is reasonably practicable, maintained so as to prevent danger; and

(c)protected by a suitable fusible cut-out or circuit breaker which is situated as close as is reasonably practicable to the supply terminals.

(2) Every circuit breaker or cut-out fuse forming part of the fusible cut-out mentioned in paragraph (1)(c) shall be enclosed in a locked or sealed container as appropriate.

(3) Where they form part of his equipment which is on a consumer’s premises but which is not under the control of the consumer, a distributor or meter operator (as appropriate) shall mark permanently, so as clearly to identify the polarity of each of them, the separate conductors of low voltage electric lines which are connected to supply terminals and such markings shall be made at a point which is as close as is practicable to the supply terminals in question.

(4) Unless he can reasonably conclude that it is inappropriate for reasons of safety, a distributor shall, when providing a new connection at low voltage, make available his supply neutral conductor or, if appropriate, the protective conductor of his network for connection to the protective conductor of the consumer’s installation.

(5) In this regulation the expression “new connection” means the first electric line, or the replacement of an existing electric line, to one or more consumer’s installations.

1A and 1B are probably applicable, but it's not  a new connection, just a fuse uplift - and while they have given you an earth connection out of the goodness of their hearts, - it's just not low Z enough to blow the fuses :-) .

Which does suggest an RCD or earth fault relay for the site incomer would have been sensible.
I'm sorry to seem so negative, but I fear you will not get much traction - the rules on the other side of the meter  tails are very different to ours.
Mike

mapj1 said:

1A and 1B are probably applicable

What about R.24(1)(c)?

It seems to me that lower-rated fuses could have been used, but that may not have suited the customer's requirements.

mapj1 said:

Now I agree that 5 seconds is used for adiabatic cable assumptions in ' 7671.

But a non-adiabatic approach is also permitted, to protect against thermal effects of overcurrent. There is no maximum time an overcurrent has to be disconnected within ... it's the heat and thermal effects of that overcurrent which might lead to a required time (but this may be hours).

5 s is also (for a 230 V TN system) the required disconnection time for a distribution circuit where ADS is used.

They previously had 100A single phase, even though with not much more than half of that, the voltage had dropped to less than the low limit. They only upgraded because the contract stated 100 amps per phase, thinking that a better quality cables had perhaps been uncovered ( the DNO plan is not very clear, but does show more than 2 cables nearby).

The "heat and thermal effects" led to this ( not much of the 3 phase meter remained):

OldBoy said:

They only upgraded because the contract stated 100 amps per phase

With all due respect, I very much doubt it. There are 100 A fuses in my TP service head, but my contract is for after diversity maximum demand of 30 kVA.

Given that your friend's supply does not seem to be particularly robust, I would be surprised if the DNO permitted the full 69 kVA.