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

 

[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.

 

[mhar]

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

You should have been checking the rating of the meter, not the cu.
A lot of meters only rated at 80A

 

[telectrix]

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?

an isolator does not have auxiliary switching equipment, so is not "similar switchgear".

 

[Midwest]

an isolator does not have auxiliary switching equipment, so is not "similar switchgear".

See now I read that as main (and/or) auxiliary switching.... Reg 421.1.201 refers to 'similar switchgear', which is not defined. The 'grown ups' in the vid I posted seem to suggest (to me) that the REC2 isolators could fall under this reg.

But hey hoe, who am I to say. I keep asking these bodies, but no one appears to want to give a definitive answer. I know some forum members here, are full IET members. Perhaps they could ask them for some guidance on our behalf?

 

[willy fixit]

just getting my post count up

101 posts - congratulations MM!
(Just getting my post count up!)

 

[Spoon]

101 posts - congratulations MM!
(Just getting my post count up!)

Go to the New Members section and welcome them...

 

[Pat H]

I needed tom upgrade my DNO fuse to 100A so needed to increase my tails to 25mm.
Contacted DNO and they agreed to replace tails and increase fuse to 100A
I ordered a 100A isolator (in a plastic enclosure)
When the DNO arrived I asked if they would fit supplied isolator. They were happy to and even added their seals to it. I asked about it needing to be a metal enclosure and they said it was part of their installation so outside the requirement.

 

[Midwest]

I needed tom upgrade my DNO fuse to 100A so needed to increase my tails to 25mm.
Contacted DNO and they agreed to replace tails and increase fuse to 100A
I ordered a 100A isolator (in a plastic enclosure)
When the DNO arrived I asked if they would fit supplied isolator. They were happy to and even added their seals to it. I asked about it needing to be a metal enclosure and they said it was part of their installation so outside the requirement.

Thanks for that (#24), but we are arguing, sorry discussing whether us electricians who have to comply with BS7671, can fit metal or plastic in this situation.

 

[Deleted member 26818]

It’s not a question of whether it’s metal or plastic, the Regulation allows for either.
It can be metal, or it can be plastic inside a metal box.
The question is whether the item (whether it’s a CU or similar) meets the standard of BS EN 61439-3.

Oh and by the way, it’s not similar switchgear, it’s similar switchgear assemblies.

See here: http://electrical.------.org/wiring-matters/55/-files/consumer-units-pdf.cfm?type=pdf

 

[Midwest]

It’s not a question of whether it’s metal or plastic, the Regulation allows for either.
It can be metal, or it can be plastic inside a metal box.
The question is whether the item (whether it’s a CU or similar) meets the standard of BS EN 61439-3.

If we're being picky, its not metal, but an enclosure manufactured from non-combustible material or in enclosed in a cabinet or enclosure constructed of....blar blar.

Ferrous metal is an example of etc. Aren't you a remember of the IET? Ask em for a definitive definition of 'similar switchgear', and we can put this one to bed, forever.

 

[Deleted member 26818]

I repeat, it’s not similar switchgear, it’s similar switchgear assemblies.
Similar items are easily determined, as they are covered by the same standard.