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Metering enclosures - is plastic OK?

jbrameld

We have a bit of our business that installs additional submetering into non-domestic premises.  This typically involves fitting CTs to sub-main/distribution circuit cables and connecting those to a meter in a DIN rail enclosure that we provide.  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.

We use plastic DIN rail enclosures generally, as we do not regard these as 'switchgear'.

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.  All arguments relating to definitions to BS7671 fell on deaf ears, and the hospital-specific guidance which he cited made no mention of such a requirement.  Pointing this out was similarly futile.  

Eventually we replaced them for metal enclosures - and charged the customer for the replacement.

It got me wondering though - is there anything from a regulatory perspective that would mandate use of steel enclosures for (just) metering?  Would that change if there was an MCB/RCBO in the same box providing protection for the meter (s)(and nothing else)?

Thanks,

Jason.

  • 0

    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.

  • 0 in reply to AJJewsbury
    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. 

  • 0
    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 ?

  • 0 in reply to gkenyon
    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.

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