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Topic Title: main linked switch for an installation
Topic Summary: how do 'you' interpret 537.1.3 with regard to DNO provided isolators
Created On: 03 July 2018 10:39 AM
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 03 July 2018 10:39 AM
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psychicwarrior

Posts: 633
Joined: 18 October 2010

good morning - perhaps being pedant:

A DNO provides one of those isolator switches (REC types?) after the meter to allow the supply to be isolated etc.

Reading 537.1.3 would imply that the REC switch should not be assumed to act as the main linked switch required and a separate main linked switch or linked circuit breaker is required *in addition* ?



Of course if a single consumer unit is connected then there is no issue, but if there are a few boards supplied from some supply terminal blocks (aka 'henley'), the REC switch may not satisfy 537.1.4. (only if 'we' agree that an installation requires one main switch that isolates everything of course); is an additional main switch required (not withstanding DNO distances protected etc) if a REC switch is present - I think not.
 03 July 2018 11:20 AM
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gkenyon

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In 18th Ed, 462.1 (replaces 537.1.3 in 17th AMD3) doesn't seem to have the statement about the distributor's switch.

However, worth considering that distributor's equipment is excluded from the scope of BS 7671, and therefore it could be argued that the means of isolation described by 462.1 would still have to be provided ?

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 03 July 2018 11:28 AM
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AJJewsbury

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The second paragraph of 537.1.3 is a bit odd - OK you can rely on the supplier's isolator if there is one - but what if there isn't? Are they suggesting that where BS 7671 starts at non isolatable meter terminals you can't comply with BS 7671's isolation requirements? And while it says it may be used to isolate between the origin and the main switch, it doesn't actually say anything, yea or nay, about using it to isolate further downstream. You might assume that it's implying that it can only be used to isolate the first section, but it doesn't actually say that.

If the supplier's switch is acceptable for isolating the first bit of the BS 7671 installation, then I'd consider invoking the spirit of last paragraph of 537.2.1.1 - as long as service conditions permit then it can be used as a common means of isolating sections further downstream as well.
(I say 'spirit of' as 537.2.1.1 talks about circuits as as we don't (normally) have overcurrent protective devices between the meter nearby CU's main switches, it's strictly speaking all one circuit.)

Failing that, deem each CU to be supplying a separate installation, so each CU has its own 'main switch'.

Certainly I can see no value in having an additional REC2 before the Henleys.

- Andy.
 03 July 2018 12:04 PM
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chrispearson

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462.1 Each electrical installation shall have provisions for isolation from each supply.
462.1.201 A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation.


It all rather depends upon how you interpret "installation". If it is anything from (and including the service head) to the very last LED then if there is only one DB, the main switch of the DB satisfies; but if there are more than one DB, it could be said that there must be a common means of isolation before the Henley block. However, if each DB and its circuits is regarded as an installation in its own right, then each one's main switch satisfies the requirement. The problem with the latter approach is that the various tails between the meter and main switches are no longer regarded as part of the installation.

Originally posted by: psychicwarrior

... is an additional main switch required (not withstanding DNO distances protected etc) if a REC switch is present - I think not.


Strictly, I would tend to agree, but when did you last see a DB with no main switch?
 03 July 2018 10:37 PM
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Weirdbeard2

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Is a suppliers cutout fuse that is sealed, an alledged offecnce to remove, and you have to book an appointment for a disconnection, a BS7671 compliant method of isolation? At least where there is a DNO supplied isolator, their side is usually sealed,
 08 July 2018 04:34 PM
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Weirdbeard2

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Bump?
 08 July 2018 04:46 PM
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aligarjon

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Originally posted by: gkenyon

In 18th Ed, 462.1 (replaces 537.1.3 in 17th AMD3) doesn't seem to have the statement about the distributor's switch.



However, worth considering that distributor's equipment is excluded from the scope of BS 7671, and therefore it could be argued that the means of isolation described by 462.1 would still have to be provided ?



Would you like to mention that to who ever compiles the condition reports where we are expected to inspect the supply equipment and sign to say that it is safe.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 08 July 2018 07:07 PM
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chrispearson

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Originally posted by: Weirdbeard2

Is a suppliers cutout fuse that is sealed, an alledged offecnce to remove, and you have to book an appointment for a disconnection, a BS7671 compliant method of isolation? At least where there is a DNO supplied isolator, their side is usually sealed,


Yes and no!

17th Edn Table 53.4 = yes for a TN earthing arrangement; no for TT (and IT).
 09 July 2018 02:55 PM
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AJJewsbury

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17th Edn Table 53.4 = yes for a TN earthing arrangement; no for TT (and IT).

Ah, but for TT systems you can still isolate at the cutout after unsealing - isolate L by pulling the fuse, then isolate N by disconnecting N using a screwdriver (as per reg 537.2.1.7 etc).
- Andy.
 09 July 2018 11:25 PM
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UKPN

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gkenyon is correct. The "Wiring regulations" has no effect on the DNO/Supplier system/network. Different regulations. (ESQCR. Mandatory). BS7671 is a code of practice. On a consumers premises a transformer, if applicable, the service cable, the cut-outs are the DNO responsibility under ESQCR. The neutral terminal if used for PME earthing is the DNOs responsibility and consequently the bonding requirements.The tails to meter, meter and tails to isolator (and isolator) are Suppliers equipment. I understand that in the code of practice BS7671 there is a section under testing/inspection whereby inspection of the DNO service is required. Obviously an error as the equipment is out of the scope of the standard.

Regards, UKPN

Edited: 09 July 2018 at 11:40 PM by UKPN
 10 July 2018 09:05 AM
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Zoomup

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"A DNO provides one of those isolator switches (REC types?) after the meter to allow the supply to be isolated etc.

Reading 537.1.3 would imply that the REC switch should not be assumed to act as the main linked switch required and a separate main linked switch or linked circuit breaker is required *in addition* ? "

Regulation Z1: Use common sense. Does the REC2 switch off the supply to the whole installation? Then in practice it is a main switch. Forget the legalities. I rest my case.

Z.
 10 July 2018 01:32 PM
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ectophile

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Originally posted by: UKPN
I understand that in the code of practice BS7671 there is a section under testing/inspection whereby inspection of the DNO service is required. Obviously an error as the equipment is out of the scope of the standard.


Since the DNO never inspects the DNO's equipment to check that it is safe for continued operation, it would be helpful if someone does. Even if that's only to warn the customer that they should report a problem to the DNO.

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S P Barker BSc PhD IEng MIET
 10 July 2018 02:51 PM
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Zoomup

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Originally posted by: ectophile

Originally posted by: UKPN

I understand that in the code of practice BS7671 there is a section under testing/inspection whereby inspection of the DNO service is required. Obviously an error as the equipment is out of the scope of the standard.





Since the DNO never inspects the DNO's equipment to check that it is safe for continued operation, it would be helpful if someone does. Even if that's only to warn the customer that they should report a problem to the DNO.


That is a very good observation. Similar to the metering people not maintaining the time switches used with economy 7. Some are hours out of synch. with the real time and have deep layers of dust on them.

Z.
 10 July 2018 05:20 PM
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Weirdbeard2

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Originally posted by: AJJewsbury

The second paragraph of 537.1.3 is a bit odd - OK you can rely on the supplier's isolator if there is one - but what if there isn't? Are they suggesting that where BS 7671 starts at non isolatable meter terminals you can't comply with BS 7671's isolation requirements?


It appears so
 10 July 2018 05:44 PM
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Weirdbeard2

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Originally posted by: UKPN

gkenyon is correct. The "Wiring regulations" has no effect on the DNO/Supplier system/network. Different regulations. (ESQCR. Mandatory). BS7671 is a code of practice. On a consumers premises a transformer, if applicable, the service cable, the cut-outs are the DNO responsibility under ESQCR. The neutral terminal if used for PME earthing is the DNOs responsibility and consequently the bonding requirements.The tails to meter, meter and tails to isolator (and isolator) are Suppliers equipment. I understand that in the code of practice BS7671 there is a section under testing/inspection whereby inspection of the DNO service is required. Obviously an error as the equipment is out of the scope of the standard.



Hi UKPN, thanks for the insight presuming you are an official spokesman. It would seem that in order for any installation to comply with BS7671 there should be an isolator owned, installed and sealed by the suppliers, leaving BS7671 compliant terminals from there on. Have a word and get them to fit a sticker that shows the earth arrangement and perhaps main fuse size if it's not too much trouble
 11 July 2018 12:40 AM
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gkenyon

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Originally posted by: UKPN

gkenyon is correct. The "Wiring regulations" has no effect on the DNO/Supplier system/network. Different regulations. (ESQCR. Mandatory). BS7671 is a code of practice. On a consumers premises a transformer, if applicable, the service cable, the cut-outs are the DNO responsibility under ESQCR. The neutral terminal if used for PME earthing is the DNOs responsibility and consequently the bonding requirements.The tails to meter, meter and tails to isolator (and isolator) are Suppliers equipment. I understand that in the code of practice BS7671 there is a section under testing/inspection whereby inspection of the DNO service is required. Obviously an error as the equipment is out of the scope of the standard.



Regards, UKPN
My opinion on a few points

(a) Need to be a little careful here. The OP was regarding whether the DNO switch could be that required by BS 7671. Clearly not for BS 7671:2018, but possibly for BS 7671:2008+A3:2015 ... If BS 7671:2018 requires one, and there's no mention of other equipment meeting the requirement, it can't be the DNO-provided one because that's outside the scope of BS 7671 and can be removed by the DNO at any time, thereby leaving a non-conformant installation. (This could therefore be used as an excuse to disconnect the installation by the DNO for safety under ESQCR by virtue of Regulation 26, specifically with BS 7671 being quoted in Regulations 21, 22 and 25). (See BS 7671 Appendix 2, item 2.)

(b) The ESQCR mentions BS 7671 directly, and for the specific purposes of:
(i) Consent for connection or altering connection with the DNO supply (Regulation 25)
(ii) Operating switched alternative or parallel sources of energy under Regulations 21 and 22

Further, BS 7671 is the preferred method of demonstrating compliance with the Building Regulations and Building (Scotland) Regulations.

So, I think it's true to say BS 7671 a little more than a Code of Practice ... it's the British Standard for the safety of electrical installations (as defined in its scope).

(c) It is not an error that BS 7671 includes on the model EICR form for someone to report any issues they may see with the distributor's equipment (although I don't believe it's a specific "requirement" in Chapter 62 of 17th+A3 or Chapter 64 of 18th). Whilst DNO equipment is outside the scope of BS 7671 (in terms of design, selection and erection), as by definition, it's outside the electrical installation, any issues with the DNO equipment may have a direct impact on the safety of the installation, and therefore surely during periodic verification, it's right and proper for the inspector to report anything they see that is or might become unsafe?

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com

Edited: 11 July 2018 at 08:23 AM by gkenyon
 11 July 2018 08:20 AM
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Jaymack

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I carried out an EICR on a flat yesterday, it had a 100A "isolator" of ETN make fitted and engraved "Property of Southern Electric". This was actually 2 SP isolators in a DP slot, i.e. not linked. Testing the "DP switch" as you do, I trapped a finger beneath the SP isolator that did initially operate to "OFF" .......... painful and needs a warning label for PPE (Gloves).
Another problem was that the screw holding the clamp for the main fuse in place, was damaged resembling one of those security screws for gate hinges etc., I had already cut the seal and then couldn't get the fuse details for the report! (I am authorised for SSE paper seals).

I will report this to their distribution centre, not that I expect a result, but to CMA and record the fact that I have not damaged their screw.

Regards
 11 July 2018 11:31 AM
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chrispearson

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Originally posted by: gkenyon

c) It is not an error that BS 7671 includes on the model EICR form for someone to report any issues they may see with the distributor's equipment (although I don't believe it's a specific "requirement" in Chapter 62 of 17th+A3 or Chapter 64 of 18th). Whilst DNO equipment is outside the scope of BS 7671 (in terms of design, selection and erection), as by definition, it's outside the electrical installation, any issues with the DNO equipment may have a direct impact on the safety of the installation, and therefore surely during periodic verification, it's right and proper for the inspector to report anything they see that is or might become unsafe?


Interesting that the 18th Edn makes the inspection of the DNO's and supplier's tackle explicitly external and visual - so no need to open anything or even pull the tails and give them a good wiggle.

App 6: "EXTERNAL CONDITION OF INTAKE EQUIPMENT
(VISUAL INSPECTION ONLY)"
 12 July 2018 10:09 AM
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AJJewsbury

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However, worth considering that distributor's equipment is excluded from the scope of BS 7671, and therefore it could be argued that the means of isolation described by 462.1 would still have to be provided ?

I don't don't see why the means of isolation has to be 'owned' by the BS 7671 installation in order to be effective as a means of isolating (part of) the supplied BS 7671 installation. Before the days of REC2 style isolators, ringing up the Electricity Board and getting them to pull the fuse was the only way of isolating the installation before the CU's main switch - and I've yet to read anything official to explicitly say that's no longer acceptable.

There is a means of isolation - needing to involve a third party to operate it might be inconvenient, but isn't really much different to when a BS 7671 means of isolation is sealed or locked off in the on-position and someone else controls the key - as might happen in a BNO or Landlord/tenant situation.

- Andy.
 12 July 2018 04:53 PM
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Zoomup

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18th. 462.1.201 "A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation."

That covers the REC2 nicely, whoever owns it or installs it.

Z.
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