100A DP Isolator Installation Between Meter and CU

[jaydub]

Hi guys,

When installing a new CU does anyone ever install a 100A double pole isolator switch between the meter and the consumer unit?

Very often I come across 16mm tails which need to be upgraded to 25mm so I join the old tails to new in a Henley block and get the DNO to come and upgrade their side at their convenience.

Instead of using a henley block could I use an isolator instead?

In anyones opinion would there be any disadvantages to this?

I wouldhave thought having an isolator would be very handy but the meter guys hardly ever bother putting one in, even now.

They're also relatively inexpensive. Another thing, I cannot seem to finda 2-module metal enclosure so would this would be okay in a plastic enclosure? That to me seems like a bit of grey area.

Any help appreciated. Thanks

 

[Andy78]

I haven't, can you share?

Similar switchgear assemblies
The phrase ‘similar switchgear assemblies’ in Regulation 421.1.201 means those assemblies used for the same fundamental application as a consumer unit. A consumer unit is defined in Part 2 of BS 7671:

‘Consumer unit (may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices or signalling and other devices proven during the type-test of the assembly as suitable for such use.’

Consumer units - IET Electrical - http://electrical.------.org/wiring-matters/55/consumer-units/index.cfm

 

[Highresdis]

Wylex seem to take a different view point;
https://www.electrium.co.uk/media/20151123152755_0_Wylex Domestic Switch Fuse Unit.pdf

Whilst their drive might be financial, they must of received guidance from somewhere.​

Whenever Western Power install one at my request or on behalf of the energy company, they never fit a metal enclosure.

 

[jaydub]

Surely you would only install one of those metal wylex switch fuse units when installing tails longer than 3m?

 

[Midwest]

Whenever Western Power install one at my request or on behalf of the energy company, they never fit a metal enclosure.

They don't have to comply with BS7671, as far as I'm aware.

 

[Midwest]

Similar switchgear assemblies
The phrase ‘similar switchgear assemblies’ in Regulation 421.1.201 means those assemblies used for the same fundamental application as a consumer unit. A consumer unit is defined in Part 2 of BS 7671:

‘Consumer unit (may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices or signalling and other devices proven during the type-test of the assembly as suitable for such use.’

Consumer units - IET Electrical - http://electrical.------.org/wiring-matters/55/consumer-units/index.cfm

421.1.201 refers to consumer units and similar switchgear. In BS7671 Switchgear is defined as 'an assembly of main & auxiliary switching equipment for operation, regulation, protection or other control of an electrical installation'. That's sounds like an isolator to me?

 

[jaydub]

Forgetting about whoever installs it then, IF an isolator can be fitted that is of a plastic nature, surely then, that answers all of our questions?

 

[Andy78]

Wylex seem to take a different view point;
https://www.electrium.co.uk/media/20151123152755_0_Wylex Domestic Switch Fuse Unit.pdf

Whilst their drive might be financial, they must of received guidance from somewhere.​

I think that is because that article is about switch fuses which provide circuit protection and therefore provide a similar function. They are also tested to the same product standard as CUs.
Fair play to them for upping standards of products.

 

[Andy78]

421.1.201 refers to consumer units and similar switchgear. In BS7671 Switchgear is defined as 'an assembly of main & auxiliary switching equipment for operation, regulation, protection or other control of an electrical installation'. That's sounds like an isolator to me?

Yep an isolator would fall under the definition of switchgear, but the IET guidance on the matter clearly says that similar switchgear refers to switchgear similar to a CU in function. It's poorly written in my opinion though.

 

[Midwest]

Forgetting about whoever installs it then, IF an isolator can be fitted that is of a plastic nature, surely then, that answers all of our questions?

Systems for the distribution of electricity to the public, is excluded from the scope of BS7671, reg 110.2 (i). So if the DNO/Supply fit an isolator, it does not need to comply with BS7671, as far as I'm aware.

 

[Midwest]

Just to show I'm not trying to be argumentative, here's my question and answer I received from Certsure technical (I've even left in the spelling mistake);

1. Sometimes the installation of meter tails to a new consumer have to protected by a switch fuse. Would the use of Wylex plastic switch fuse, REC 2 or similar plastic isolators, being installed in an external plastic meter box on an external wall, be defined as being installed ‘within domestic premises’?


'The Suppliers and meter equipment would fall outside the scope of BS7671.
As a designer installing any equipment in external meter enclosures we would suggest a risk assessment is carried out to make a judgment of the likelihood that fire originating inside the enclosure or similar switchgear might lead to the outbreak of fire in the household building. We trust this answers your questions'.

 

[Strima]

'The Suppliers and meter equipment would fall outside the scope of BS7671.
As a designer installing any equipment in external meter enclosures we would suggest a risk assessment is carried out to make a judgment of the likelihood that fire originating inside the enclosure or similar switchgear might lead to the outbreak of fire in the household building. We trust this answers your questions'.

So basically they haven't got a clue and just pass the blame onto you...

 

[jaydub]

So what they are saying is, if you choose to install an isolator you should carry out a risk assessment to cover your own --- in case it catches on fire through fault or negligence. That is what it sounds like to me...?

 

[Midwest]

Some might recall the Elexshow Harrogate 2015 vid, this subject is touched on at 25:45mins;

Side step

 

[multimick]

that wylex unit has a 16mm earth terminal why does it not have a 25mm terminal,when normally you would be using 25mm swa in it ?.fitted one last week real pain for the earth

 

[Ian1981]

that wylex unit has a 16mm earth terminal why does it not have a 25mm terminal,when normally you would be using 25mm swa in it ?.fitted one last week real pain for the earth

Why would you use a 25mm earthing conductor in domestic?
25mm 2 core swa or 16mm for the line and neutral and a separate 16mm earthing conductor ran in parallel surely?