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

 

[Strima]

The meter installers will never put one in as this will increase cost.

And yes it does make sense to fit an isolator, especially as a lot of smart meters will detect when the fuse has been pulled and may not allow the power to come back on.

Plenty of switches out there to choose from: Wylex 100A DP Supply Isolator - https://www.tlc-direct.co.uk/Products/WYREC2S.html?source=adwords&ad_position=1o1&ad_id=45425533757&placement=&kw=&network=g&matchtype=&ad_type=pla&product_id=WYREC2S&product_partition_id=174057653827&test=finalurl_v2&gclid=CjwKCAiA-KzSBRAnEiwAkmQ157Kt_x523muqnFlf4y4TXEAW-EshYmwvjADqoV6nxokuHPGgm8Vz1hoCdV0QAvD_BwE

 

[Taylortwocities]

When the initial spec for the smart meters came out there was an isolator as part of the requirement. Subsequent cost-cutting saw it removed as a requirement. How dumb is that?

 

[Octopus]

Why are you changing the tails?

Countless homes have 60A fuses and some 80A so 16mm are OK.

 

[jaydub]

Thanks for your reply Strima, I've just ordered one in to my local wholesaler, so will give that a go!

 

[jaydub]

Murdoch, does it not specify in BS7671 that all supplies must now be 25mm regardless? Maybe I have misinterpreted this.

 

[Andy78]

Murdoch, does it not specify in BS7671 that all supplies must now be 25mm regardless? Maybe I have misinterpreted this.

No it doesn't.


I use these when I put them in.

Hager - Meter Box Switch - http://www.hager.co.uk/product-catalogue/energy-distribution/enclosures/meter-box/features/38347.htm

Very good little unit with strain relief and seal-able 2 part case.

 

[Ian1981]

Generally the only time 25mm tails are a must In domestic are new builds where the local DNO requests 25mm tails and a 16mm earthing conductor as standard ,usually because a 100amp fuse has been fitted.

 

[jaydub]

Fair enough guys, thanks.

That hager one looks smart. Any idea on price?

 

[Midwest]

Metal or plastic. I've asked for my scheme technical a few times now as to whether such an isolator needs to comply with reg 421.1.201, and the response has been somewhat vague.

In fairness it would perhaps be more clear cut, where such an isolator would be installed in a domestic property. Not perhaps in an outside mounted meter box, but they would not give definitive answer. It would be down to 'the designer to risk access'. When the 18th draft was up for comment, I did suggest a better definition than 'similar switchgear'. Something to consider perhaps?

 

[Andy78]

Fair enough guys, thanks.

That hager one looks smart. Any idea on price?

I pay about £20 inc from my wholesaler.

 

[Andy78]

Metal or plastic. I've asked for my scheme technical a few times now as to whether such an isolator needs to comply with reg 421.1.201, and the response has been somewhat vague.

In fairness it would perhaps be more clear cut, where such an isolator would be installed in a domestic property. Not perhaps in an outside mounted meter box, but they would not give definitive answer. It would be down to 'the designer to risk access'. When the 18th draft was up for comment, I did suggest a better definition than 'similar switchgear'. Something to consider perhaps?

I've seen enough official guidance to convince me that a DP isolator does not fall under the wording or intent of that reg.

 

[Midwest]

I've seen enough official guidance to convince me that a DP isolator does not fall under the wording or intent of that reg.

I haven't, can you share?

 

[Taylortwocities]

£24 on eBay.
The Wylex REC2 is nearly half that price.
Wylex 100A DP Supply Isolator - https://www.tlc-direct.co.uk/Products/WYREC2S.html

 

[Midwest]

I've seen enough official guidance to convince me that a DP isolator does not fall under the wording or intent of that reg.

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.​

 

[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?

 

[Midwest]

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...?

IMO I can rarely see the time when 'I' would install an isolator. I can see the occasion when I would install a switch fuse isolator, in which case I would install a metal one.

However, the other consideration is, would the DNO/Supplier allow you to fit a metal enclosure in 'their' meter cabinet?

 

[Midwest]

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?

I probably go for a 25mm 3c myself, mostly if it weren't too long. Installing one thing instead of two things. But then I'm lazy.

 

[Ian1981]

IMO I can rarely see the time when 'I' would install an isolator. I can see the occasion when I would install a switch fuse isolator, in which case I would install a metal one.

However, the other consideration is, would the DNO/Supplier allow you to fit a metal enclosure in 'their' meter cabinet?

To be honest I can’t see you fitting one in their meter box as you just don’t have the room.
It’s hard work trying to convince a builder to fit a 2nd meter box to house the fused isolator

 

[multimick]

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?

yeah i ran 25mm 3 core it was only 10 meteres

 

[jaydub]

Crikey this really is minefield of what if's isn't it...

Maybe I will not bother with it...

 

[Ian1981]

yeah i ran 25mm 3 core it was only 10 meteres

You can get a reducer pin for the 25mm so you can terminate into the terminal easier.

 

[multimick]

Crikey this really is minefield of what if's isn't it...

Maybe I will not bother with it...

just getting my post count up

 

[Midwest]

To be honest I can’t see you fitting one in their meter box as you just don’t have the room.
It’s hard work trying to convince a builder to fit a 2nd meter box to house the fused isolator

I did come close to fitting one in a cabinet on one job. Was room just. Got to the point of enquiring with the DNO, but when I measured my tails run, it was 3m.

 

[Midwest]

just getting my post count up

Ask that Chinese chick to add you to her spybot list, that will ramp things up for you.

 

[Ian1981]

I did come close to fitting one in a cabinet on one job. Was room just. Got to the point of enquiring with the DNO, but when I measured my tails run, it was 3m.

My experience regarding the length of the ‘tails’ with the DNO is basically “we don’t care”

 

[Midwest]

My experience regarding the length of the ‘tails’ with the DNO is basically “we don’t care”

I'm shocked. I'm always very careful measuring the run of the tails. Fingertip to opposite --- (1metre).

 

[Octopus]

Murdoch, does it not specify in BS7671 that all supplies must now be 25mm regardless?

No - but the "pretty" pictures in the OSG do suggest this is the case.

When I do a CU change I carry 25mm tails, 16mm GY and 10mm GY and the appropriate Henley blocks and MET's - then I can cover each eventuality....

If its a new build I certainly would fit 25mm tails.

 

[mhar]

The alternative to 'upgrading' the tails to 25mm is to ensure that the fuse does not exceed 80A.
What supply do people think they get these days? Halfway down this page Western Power Distribution - Information for electrical installers - https://www.westernpower.co.uk/Connections/Information-for-Electrical-Installers.aspx is the specification for a standard WPD supply (albeit one that needs one letter inserting).
Does the size of the supply vary accross dnos?

 

[Percyprod]

Working for dno, meter tails governed by rating of cu, NOT supply fuse. 100amp cu=25mm tails.

 

[static zap]

.......careful measuring the run of the tails. Fingertip to opposite --- (1metre).

May have to re-calibrate for "Moob-droop" !

 

[Ian1981]

Working for dno, meter tails governed by rating of cu, NOT supply fuse. 100amp cu=25mm tails.

Domestic consumer unit Main switches are rated upto a maximum rating of 100amp , does not mean you have to be using 100amp as your maximum demand.

 

[Ian1981]

Working for dno, meter tails governed by rating of cu, NOT supply fuse. 100amp cu=25mm tails.

Domestic consumer unit main switches are rated upto a maximum rating of 100amp , does not mean you have to be using 100amp as your maximum demand.

 

[Deleted member 26818]

421.1.201 as everyone knows requires the enclosures of CUs and similar switchgear to be made from a non-flammable material (essentially metal).
However 421.1.201 also requires that they comply with BS EN 61439-3, which most everyone seems to forget.

So if your DP 100A isolator or switchfuse does not comply with BS EN 61439-3, you cannot install it irrespective of whether the enclosure is metal or even if you enclose it within a metal cabinate or enclosure.

Unfortunately, BS EN 61439-3 only applies to CUs, so you won’t be able to install either a DP 100A isolator or switchfuse.

 

[Deleted member 26818]

Should point out, that the previous post only applies if you believe DP 100A isolators and switchfuses are similar to CUs.
If you don’t believe they are similar, then you can still install them and they can be plastic, metal or whatever.

 

[Midwest]

Should point out, that the previous post only applies if you believe DP 100A isolators and switchfuses are similar to CUs.
If you don’t believe they are similar, then you can still install them and they can be plastic, metal or whatever.

I believe I'm paying too much tax to HRMC. I'm arguing, they are not believing.