Metering enclosures - is plastic OK?

As far as BS 7671 is concerned the "non-combisible material" for consumer units and similar switchgear assemblies (421.201) only directly applies to domestic (household) premises.

  - Andy.

AJJewsbury said:

As far as BS 7671 is concerned the "non-combisible material" for consumer units and similar switchgear assemblies (421.201) only directly applies to domestic (household) premises.

  - Andy.

Agreed, but it is not unreasonable to extrapolate that there must be a general concern about fire propagation when plastic enclosures are used. Where there is a sleeping risk or a significant difficulty in evacuating a building, it might be reasonable for a fire risk assessment to acknowledge the concern and require mitigation. 

jbrameld said:

We had a challenge on one project (in a hospital) where the client (after installation) declared these to be switchgear and non-compliant with the regulations as they were not metal. 

Is a hospital 'residential premises' ?

I do know that some 'safety and compliance audit' companies cover themselves by advising that, whilst BS 7671 only requires metal consumer units (and similar assemblies) to be metal, if there is a risk, there is a risk ... If it wasn't in the specification, though ...

It's definitely not a 'consumer unit' as BS 7671 has a very specific definition of this (top of page 32 in BS 7671:2018+A2:2022) ... to be a 'consumer unit' and come under 421.201, it would have to contain a multipole isolator and at least one other type-tested device.

However,  it could be argued that metering equipment in an enclosure like this could be considered 'controlgear' and therefore 'switchgear or controlgear assembly' would apply, because it's not one item of equipment in a box, but an assembly of meter and CTs and wiring. In other words, you can't just assemble this on-site according to BS 7671 (see Regulations 113.1 and 133.1.1) ... the assembly should have been 'manufactured' to an appropriate assembly standard (such as BS EN 61439 series) and there should be a DofC, or, alternatively, Regulations 133.1.2 and 133.1.3 applied, including agreement from the Client ?

gkenyon said:

Is a hospital 'residential premises' ?

They were in the days when the on-call house officer had a bedroom on the ward.

And, of course, there were the doctors' and nurses' residences, although they got a bit jumbled up at times. ;-)

More seriously, if the risk is that sleeping people may not be aware of a developing fire, even if the patients are asleep, the staff are not.

In answer to the original question, IMHO the description is not of something which switches or controls anything.

Chris Pearson said:

In answer to the original question, IMHO the description is not of something which switches or controls anything.

It's still an 'assembly' though.

gkenyon said:

, you can't just assemble this on-site according to BS 7671 (see Regulations 113.1 and 133.1.1) ... the assembly should have been 'manufactured' to an appropriate assembly standard (such as BS EN 61439 series) and there should be a DofC, or, alternatively, Regulations 133.1.2 and 133.1.3 applied, including agreement from the Client ?

hence, the above still applies. I'm open to BS EN IEC 61010 series ... or another alternative.

but it is not unreasonable to extrapolate that there must be a general concern about fire propagation when plastic enclosures are used.

Agreed but the CU situation isn't just about plastic enclosures - it's (allegedly) also about the factors that contribute to the fire starting in the first place - e.g. trying to push 100A through terminals that were never designed to to take stiff 7-strand conductors or withstand wiggling when meters etc were replaced.

   - Andy.

jbrameld said:

There will be an associated supply for the meters, usually as a dedicated final circuit from a local distribution board with the circuit protection fitted in that board.

So you could have a plug and socket-outlet and side-step BS 7671 altogether.

Just a thought!

Chris Pearson said:

So you could have a plug and socket-outlet and side-step BS 7671 altogether.

Although the Electrical Equipment (Safety) Regulations will apply, and you will have to demonstrate how you met the essential requirements of the legislation - that could be by the use of a designated product standard, although a technical file route is acceptable.

gkenyon said:

However,  it could be argued that metering equipment in an enclosure like this could be considered 'controlgear' and therefore 'switchgear or controlgear assembly' would apply, because it's not one item of equipment in a box, but an assembly of meter and CTs and wiring. In other words, you can't just assemble this on-site according to BS 7671 (see Regulations 113.1 and 133.1.1) ... the assembly should have been 'manufactured' to an appropriate assembly standard (such as BS EN 61439 series) and there should be a DofC, or, alternatively, Regulations 133.1.2 and 133.1.3 applied, including agreement from the Client ?

And this is where I start to struggle with what constitutes what and where an installer starts to assume a 'manufacturer' role with associated complexities, testing, approvals and costs that customers likely are not interested in entertaining.

If we expand this thought process a bit - consider a smart home installer/system integrator: They buy a large DIN rail enclosure 'product' and then several other control and monitoring 'products' such as ELV power supplies, lighting controllers, blind controllers, central control processors, meters etc. - there are thousands of such DIN rail products to choose from. Each product is likely made to it's own relevant standard.  By the act of taking a number of devices and building them into the enclosure to make an 'integrated system'/'assembly' what would be expected of that integrator?  Would each project with a slightly different assembled combination of 'products' need to be tested to ensure compliance with 61439?  That doesn't seem remotely practical.

At the other end of the scale - an electrician takes a DIN-Rail doorbell transformer and puts it on it's own into a DIN-rail box.  Are they now a manufacturer, and need to submit that assembly for testing and/or issue a DofC for it?  That doesn't seem practical either.

Is there a pragmatic solution to this conundrum?

jbrameld said:

If we expand this thought process a bit - consider a smart home installer/system integrator: They buy a large DIN rail enclosure 'product' and then several other control and monitoring 'products' such as ELV power supplies, lighting controllers, blind controllers, central control processors, meters etc. - there are thousands of such DIN rail products to choose from. Each product is likely made to it's own relevant standard.  By the act of taking a number of devices and building them into the enclosure to make an 'integrated system'/'assembly' what would be expected of that integrator?  Would each project with a slightly different assembled combination of 'products' need to be tested to ensure compliance with 61439?  That doesn't seem remotely practical

Practical or otherwise, BS 7671 is quite clear that such assemblies ought to conform to relevant standards.

One basic issue is dealing with ambient temperature inside the enclosure, and how that affects the operation of protective devices.

Another issue can be EMC.

The basic premise of "two or more conformant products must lead to a conformant product" isn't necessarily true. This is often abbreviated to:

CE+CE≠CE

Can you put 'assemblies' together and 'self-declare'? ... yes, that's entirely possible, as it's not a product that's placed on the open-market, but keeping a technical file of the design and build is important to demonstrate either:

(a) how you think you've met the requirements of standards; or

(b) how you otherwise claim you have met the 'essential requirements' of the Electrical Equipment (Safety) Regulations.