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Discuss 100A DP Isolator Installation Between Meter and CU in the Electrical Forum area at ElectriciansForums.net

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jaydub

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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
 
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
 
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.
 
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?
 
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.
 
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
 
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?
 

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