Plastic switch in external meter box

I'm afraid I'm not following that thinking at all - a swicthfuse does have terminals for the outgoing circuit - that's where you connect the outgoing cable to. There's no need for each terminal to accommodate more than one conductor since it's only a 1-way device. There's no requirement for them to be multi-way bars - just terminals.

So the traditional CU fitted with 5A to 30A BS 1361 ("Specification for cartridge fuses for a.c. circuits in domestic and similar premises") HBC fuses isn't a consumer unit????

No but it might suggest that it should be suitable for operation by ordinary persons - and equipment that doesn't meet BS EN 61439-3 might not be (which is where 421.1.201 starts off).

No. I stand by FUSED SWITCH [ or switch fuse] like a KMF, not being like a DB. There is one neutral connection in, and one neutral connection out. Same for the earth conductor. There is no option for other neutrals or CPCs unless you are particularly rough. You left out a fundamental part of the BS7671 definition of what is a DB. "......together with terminals for the neutral and circuit protective conductors" Consumer Units and the Distribution Boards that are similar switchgear to Consumer Units have neutral and CPC bars. The genuine old style one way distribution boards like wylex/ MEM had a rewirable or HRC fuse or plug in retro MCB, but also had an earth bar and a neutral bar.

Perhaps the point was not clear. Consumer Units are a particular DB for use in Domestics. A KMF has a HRC fuse that is not that consumer friendly to remove unless you are familiar with them. There is no indication that they have blown; same for BS3036, but of course, you can pull this rewireable out and see if the wire is healthy or not.

Even when the KMF is used as an isolator, that does not qualify it as a DB.

So isn't a swithfuse just one example of a 1-way distribution board? They might (or might not) comply with different standards - but BS 7671 doesn't define things in terms of which standards they are constructed to meet, but in terms of their fundamental components and functionality. If it's "an assembly containing switching or protective devices ... associated with one or more outgoing circuits fed from one or more incoming circuits ... " BS 7671 seems to consider it a distribution board.

Now there I've got to differ - Consumer Unit got their name back in the day when rewireable fuses were still king - 'trip switches' (MCBs etc) are just the current fashion. We may well be returning to the situation were consumers may have to pull out and replace bits of their CUs to keep their installation in a serviceable condition if the current fad for SPDs (with replaceable cartridges) continues too.

BS 7671's requirement for a main switch (or main circuit breaker) is that it is as near as practical to the origin of the installation (462.1.201) - which is just what you want if you cut off power to the entire premises for whatever reason - so I still say (unless one is provided by the DNO) the the switch on a switchfuse should be used in preference to one on a downstream CU - especially by ordinary persons who are less likely to understand the distinction and/or be aware exactly where the submain cable runs for example.

AJJewsbury:

BS 7671's requirement for a main switch (or main circuit breaker) is that it is as near as practical to the origin of the installation (462.1.201) - which is just what you want if you cut off power to the entire premises for whatever reason - so I still say (unless one is provided by the DNO) the the switch on a switchfuse should be used in preference to one on a downstream CU - especially by ordinary persons who are less likely to understand the distinction and/or be aware exactly where the submain cable runs for example.

I agree - and if it's the type where the fuse is easily accessible, take out the fuse and put it in your pocket. So is this now the main switch, and are you going to label it as such?

It is raining......

The consumer unit will have things that are in the off position if there is a fault or overload. That is consumer friendly, hence the moniker consumer unit for domestic [household] premises.

Of course, a 1 way SPN distribution board is "similar switchgear"

I do not think we should be condemning the use of KMFs in domestic installations. There are many, many thousands installed, they are compact and manufactured as a switchfuse, usually for a specific purpose where a distribution board is not suitable.

perspicacious:
Can i fit a plastic switch fuse such as an 800kmf in the external meter box or does it have to be metal.


So it wasn't really a question.

The box will be supplied and fitted by myself with switch fuse and tails already fitted for a changeover on the day. As i said in the OP the DNO guys round here are always very obliging and helpful.  The boxes are tight but they don't need to fit their isolator if i have fitted one already.  


Regards


BOD

So how did you come to that conclusion ?  ?

gkenyon:

It could also be argued that an enclosure containing a single RCD, say for a shower, is not "similar switchgear" as it does not include for "distribution", it's a dedicated device (similar, the SRCD).

So is a switch-fuse (+/- RCD) at the supply end of a distribution circuit distributing leccy or not?