Reg 421.1.201 Similar Switchgear Assemblies

[Midwest]

I have read a few posts with regard to Reg 421.1.201 & Similar Switchgear Assemblies, with regard to the definition of such. When 421.1.201 came into being, I was advised at the time about using certain enclosures. This advise, now seems to have changed. I've copied below my questions, and the advise I've now received from Elecsa Technical.

Elecsa Technical, 'Similar switchgear is any switchgear that conforms to the standard BS EN 61439-3 and can be assumed to be assemblies that fulfil the same fundamental application as consumer units. For example, the following would fall within the scope of Regulation 421.1.201:
• One way consumer units supplying such things as showers and the like
• TP&N distribution boards where there is a three phase supply'.

Question;
'On an occasion where a consumer unit is being replaced or relocated, it may be necessary to extend the existing final circuits. There are a few enclosures available, with internal din rail & connectors, to extend the circuits. These enclosures are not made from non-combustible materials, but of plastic. Does the definition of ‘similar switchgear assemblies’ apply to these products used in this fashion?

Reply;
'This will be the decision of the designer but it would suggest based on our guidance in this situation the enclosures and connections do not fall under ‘similar switchgear’.

Question;
'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’?

Reply;
'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.

Whilst some would suggest the answers to the questions are obvious, I sort some clarification.

 

[Nickj]

Very useful, thank you. I had questioned myself whether din rail enclosures need to be and that clears it up.

Maybe the 18th edition will include them, to me it makes no sense that the consumer unit is metal but adaptable boxes to extend wiring are not.

Aren't the regs a wonderful thing

 

[Midwest]

Very useful, thank you. I had questioned myself whether din rail enclosures need to be and that clears it up.

Maybe the 18th edition will include them, to me it makes no sense that the consumer unit is metal but adaptable boxes to extend wiring are not.

Aren't the regs a wonderful thing

The Connexbox enclosure uses Wago Tobjob-S rail mounted terminals, which 'feature direct insertion of solid core cables without the need for use of an insertion tool'. So no naughty electrician, not liable to tighten the terminals securely.

 

[Andy78]

Thanks for the clarification, or at least Elecsa's version of it. I'll add the IET guidance to this thread if that's ok ?

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.’

An example of a similar switchgear assembly is a three phase distribution board that is intended to be operated by ordinary persons. This would have to have isolation that interrupts the three incoming line conductors and the neutral, rather than just double-pole isolation as mentioned in the above definition.


I don't see that this description applies to stand alone RCDs in enclosures, nor isolators with 2 part enclosures such as a Wylex REC2S or a Hager VC02SW, nor an isolator that incorporates a fuse. Metal versions are of course available for those wanting to use them.

 

[Midwest]

Thanks for the clarification, or at least Elecsa's version of it. I'll add the IET guidance to this thread if that's ok ?

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.’

An example of a similar switchgear assembly is a three phase distribution board that is intended to be operated by ordinary persons. This would have to have isolation that interrupts the three incoming line conductors and the neutral, rather than just double-pole isolation as mentioned in the above definition.


I don't see that this description applies to stand alone RCDs in enclosures, nor isolators with 2 part enclosures such as a Wylex REC2S or a Hager VC02SW, nor an isolator that incorporates a fuse. Metal versions are of course available for those wanting to use them.

You don't have to ask my permission to post Andy78 . Where does that IET guidance come from? I note BS7671 has definitions for Switch, Switch (linked), Switch-disconnector, Switchboard, Switchgear but nothing for 'Similar Switchgear Assemblies'.

The rest of the guidance seems similar (no pun intended). I only raised the post, as previously I, and if memories serves me, others were advised differently.

 

[Andy78]

Guidance comes from here. The Elecsa guidance is likely to be taken more or less straight from there.

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

 

[Midwest]

Guidance comes from here. The Elecsa guidance is likely to be taken more or less straight from there.

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

I have read that piece before, which was released soon after A3. But thanks for reminding me of it's existence.

As to why BS7671 never included a clear description of 'similar switchgear assemblies', when it is used in the term in said regulation, is rather strange.

My issue, is Consumer Unit is defined, and Similar Switch Gear Assemblies is explained as 'same fundamental application as a consumer unit', but we ourselves are left to define 'same fundamental application'.

Even BS7671 defines a consumer unit 'principally in domestic premises, incorporating manual means of double pole isolation on the incoming circuits and an assembly of one or more fuses, circuit breakers, residual current operated devices or......etc etc. Switch fuse?

 

[Andy78]

I have read that piece before, which was released soon after A3. But thanks for reminding me of it's existence.

As to why BS7671 never included a clear description of 'similar switchgear assemblies', when it is used in the term in said regulation, is rather strange.

My issue, is Consumer Unit is defined, and Similar Switch Gear Assemblies is explained as 'same fundamental application as a consumer unit', but we ourselves are left to define 'same fundamental application'.

Even BS7671 defines a consumer unit 'principally in domestic premises, incorporating manual means of double pole isolation on the incoming circuits and an assembly of one or more fuses, circuit breakers, residual current operated devices or......etc etc. Switch fuse?

Because BS7671 is like a wife that tells you something but hopes you instinctively know what she actually means, then waits until things kick off until she explains herself fully.

 

[Midwest]

Even BS7671 defines a consumer unit 'principally in domestic premises, incorporating manual means of double pole isolation on the incoming circuits and an assembly of one or more fuses, circuit breakers, residual current operated devices or......etc etc. Switch fuse?

Not trying to make an argument, but what do think about the above, i.e. a switch fuse being a 'similar switchgear assemblies'?

 

[Wilko]

Well it's a double pole switch and a fuse, and if it's within the fabric of the house I think it falls into 421.1.201 - tin hat on

 

[Midwest]

Well it's a double pole switch and a fuse, and if it's within the fabric of the house I think it falls into 421.1.201 - tin hat on

I would, but thousands wouldn't

 

[Pat H]

Well I had my home DNO cutout uprated to 100A a few weeks back and yesterday EON came to upgrade the tails to 25mm I asked if they would add an isolator for me after the meter and before my Henley block. Happy to do that and I now have nice Wylex 100A DP Mains isolator in its plastic enclosure....

 

[Midwest]

Well I had my home DNO cutout uprated to 100A a few weeks back and yesterday EON came to upgrade the tails to 25mm I asked if they would add an isolator for me after the meter and before my Henley block. Happy to do that and I now have nice Wylex 100A DP Mains isolator in its plastic enclosure....

Have a butchers to the reply to my second question #1

 

[Pat H]

Thanks. Knowing the DNO side of things are their responsibility I took it to be ok. The switch is even sealed with their seals. Re risk of fire? Well its not that far from the gas meter and its all wooden under the stairs and coats hang in there. If the head end caught fire it would go up.
But as I've had all that replaced now its far less likely than it has been for the last 26 years we've lived here.

 

[Midwest]

Nope, it just means the DNO does not have to, necessarily comply with BS7671.