Plastic switch in external meter box

A few.


One is called a consumer unit as it is done to a standard where it is intended for use by ordinary persons, but it's also the application; is that the only consumers equipment?


DBOs [ consumer units] to BSEN 61439-3 are limited to 63 amp per way; note your example is 45 amp, also it is pre 61439-3, but I get the gist. KMFs and switch fuses can have HRC up to 80 amp /100 amp respectively. The KMF/switchfuse devices usually serve a full blown consumer unit to BSEN 61439-3, in that instance it is clear the consumer unit is the thing intended for use by an ordinary person.


Those are the essential differences, but there are other things beyond BS7671 and the clumsy wording of 421.1.201,

like the Building regs and particular requirements for dwellings.

421.1.201  is only “what shall comply with 61439-3”. Firstly it is "consumer units". In my opinion the "similar switchgear" was to cover the potential use of TPN DBs for a 3 phase domestic or converted to single phase for lots of ways; it becomes a DBO when used in a domestic, most are now 61439-3 anyhow, but when the reg was published, some TPN distribution boards were not manufactured as DBOs. The Consumer Unit is specifically intended for use by ordinary persons, a DBO. Also the similar bit is for self assembled consumer units where you purchase an enclosure separately and the devices separately. I will go with a consumer unit like enclosure with a main switch with one or more ways/MCB’s that you can re-arrange yourself to not escape being 61439-3. But we have to be careful what we attribute “similar switchgear” to. It could lead to a bit of a conflict with notification requirements for building regs.

Replacing a 800KMF with a new one is not notifiable works because it is not a consumer unit.

I'm not sure I'm following the 'use by ordinary persons' thinking. As I read it, 421.1.201 isn't saying that the requirement for non-combustibility applies to BS EN 61439-3 equipment - rather it's saying that where ordinary persons are about (domestics) then it must both comply with BS EN 61439 as well as having an non-combustible enclosure - the BS EN 61439-3 is part of the requirement rather than part of the condition. I agree that the 'similar switchgear' was (at least in part) intended to cover TPN DBs in domestic situations - but the requirement is still that these need to comply with BS EN 61439-3 too. TPN boards, even where they do comply with BS EN 61439-3 can't be described in BS 7671 as consumer unit simply because BS 7671's definition of a consumer unit only applies to single phase equipment (i.e. having DP incomer).


Likewise, in my mind if the fuse blows in a switchfuse in a domestic, the first thing the householder is going to do is to try to replace it (especially if they're of the generation that was taught to wire a plug) - and such a fuse can plausibly blow even if there's not a fault on the submain itself - either due overloading or poor discrimination with downstream MCBs on a fault after the downstream CU.  If a householder is following instructions to 'turn off at the main switch' surely the switchfuse is exactly the place they should be doing it. So really I don't buy that the existence of a downstream CU means that the householder wouldn't have any cause to operate the switchfuse.


I didn't know about the 63A limit for outgoing ways for CUs - and am a little surprised about that - since the BSI site in the overview of BS EN 61439-3 https://shop.bsigroup.com/ProductDetail?pid=000000000030393941 says " rated current (Inc) of the outgoing circuits does not exceed 125 A and the rated current (InA) of the DBO does not exceed 250 A" - and some examples of 80A/100A switchfuses (e.g.  https://www.tlc-direct.co.uk/Products/WYDSF100M.html) appear to claim some sort of compliance with BS EN 61439-3 as well as 60947-3.


I'm still struggling to see why a 3x12 way TPN DB with 125A incomer and perhaps several 63A outgoing MCB is considered to be similar to a CU, but a 1-way SP distribution board with a 100A incomer and a 63A outgoing fuse isn't.


Fortunately building regs have their own definitions of things (and often didn't align with BS 7671 ones anyway) - as far as I can tell the notification requirement applies only to consumer units (not similar switchgear) - so perhaps there's no need to notify a TPN board replacement in a domestic?

 

So an SFCU?

Ah yes, fair point. Actually there are times when I do want to regard a FCU as a distribution board (e.g. when reading 314.4). It's perhaps a little easier to claim it's not similar to a CU though - if only in size - it's won't be employed to handle the sort of currents a CU could, or have a similar breaking capacity (6kA rather than 16kA) so less suitable for use at the origin of an installation and so on.


Simple switches or RCDs in a box are easier to dismiss - since they don't even meet the definition of a distribution board (which is central to BS 7671's the definition of a CU).



Seeing that apparently compliant solutions exist (e.g. that metal-clad Wylex switchfuse which meets BS EN 61439-3 as well as 60947-3) for domestic use, should we really be recommending the use of apparently non-conforming alternatives?


   - Andy.

A few.


One is called a consumer unit as it is done to a standard where it is intended for use by ordinary persons, but it's also the application; is that the only consumers equipment?


DBOs [ consumer units] to BSEN 61439-3 are limited to 63 amp per way; note your example is 45 amp, also it is pre 61439-3, but I get the gist. KMFs and switch fuses can have HRC up to 80 amp /100 amp respectively. The KMF/switchfuse devices usually serve a full blown consumer unit to BSEN 61439-3, in that instance it is clear the consumer unit is the thing intended for use by an ordinary person.


Those are the essential differences, but there are other things beyond BS7671 and the clumsy wording of 421.1.201,

like the Building regs and particular requirements for dwellings.

421.1.201  is only “what shall comply with 61439-3”. Firstly it is "consumer units". In my opinion the "similar switchgear" was to cover the potential use of TPN DBs for a 3 phase domestic or converted to single phase for lots of ways; it becomes a DBO when used in a domestic, most are now 61439-3 anyhow, but when the reg was published, some TPN distribution boards were not manufactured as DBOs. The Consumer Unit is specifically intended for use by ordinary persons, a DBO. Also the similar bit is for self assembled consumer units where you purchase an enclosure separately and the devices separately. I will go with a consumer unit like enclosure with a main switch with one or more ways/MCB’s that you can re-arrange yourself to not escape being 61439-3. But we have to be careful what we attribute “similar switchgear” to. It could lead to a bit of a conflict with notification requirements for building regs.

Replacing a 800KMF with a new one is not notifiable works because it is not a consumer unit.

I'm not sure I'm following the 'use by ordinary persons' thinking. As I read it, 421.1.201 isn't saying that the requirement for non-combustibility applies to BS EN 61439-3 equipment - rather it's saying that where ordinary persons are about (domestics) then it must both comply with BS EN 61439 as well as having an non-combustible enclosure - the BS EN 61439-3 is part of the requirement rather than part of the condition. I agree that the 'similar switchgear' was (at least in part) intended to cover TPN DBs in domestic situations - but the requirement is still that these need to comply with BS EN 61439-3 too. TPN boards, even where they do comply with BS EN 61439-3 can't be described in BS 7671 as consumer unit simply because BS 7671's definition of a consumer unit only applies to single phase equipment (i.e. having DP incomer).


Likewise, in my mind if the fuse blows in a switchfuse in a domestic, the first thing the householder is going to do is to try to replace it (especially if they're of the generation that was taught to wire a plug) - and such a fuse can plausibly blow even if there's not a fault on the submain itself - either due overloading or poor discrimination with downstream MCBs on a fault after the downstream CU.  If a householder is following instructions to 'turn off at the main switch' surely the switchfuse is exactly the place they should be doing it. So really I don't buy that the existence of a downstream CU means that the householder wouldn't have any cause to operate the switchfuse.


I didn't know about the 63A limit for outgoing ways for CUs - and am a little surprised about that - since the BSI site in the overview of BS EN 61439-3 https://shop.bsigroup.com/ProductDetail?pid=000000000030393941 says " rated current (Inc) of the outgoing circuits does not exceed 125 A and the rated current (InA) of the DBO does not exceed 250 A" - and some examples of 80A/100A switchfuses (e.g.  https://www.tlc-direct.co.uk/Products/WYDSF100M.html) appear to claim some sort of compliance with BS EN 61439-3 as well as 60947-3.


I'm still struggling to see why a 3x12 way TPN DB with 125A incomer and perhaps several 63A outgoing MCB is considered to be similar to a CU, but a 1-way SP distribution board with a 100A incomer and a 63A outgoing fuse isn't.


Fortunately building regs have their own definitions of things (and often didn't align with BS 7671 ones anyway) - as far as I can tell the notification requirement applies only to consumer units (not similar switchgear) - so perhaps there's no need to notify a TPN board replacement in a domestic?

 

So an SFCU?

Ah yes, fair point. Actually there are times when I do want to regard a FCU as a distribution board (e.g. when reading 314.4). It's perhaps a little easier to claim it's not similar to a CU though - if only in size - it's won't be employed to handle the sort of currents a CU could, or have a similar breaking capacity (6kA rather than 16kA) so less suitable for use at the origin of an installation and so on.


Simple switches or RCDs in a box are easier to dismiss - since they don't even meet the definition of a distribution board (which is central to BS 7671's the definition of a CU).



Seeing that apparently compliant solutions exist (e.g. that metal-clad Wylex switchfuse which meets BS EN 61439-3 as well as 60947-3) for domestic use, should we really be recommending the use of apparently non-conforming alternatives?


   - Andy.