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Plastic switch in external meter box
aligarjon
112 Posts
Question
Can i fit a plastic switch fuse such as an 800kmf in the external meter box or does it have to be metal.   I am not interested in the dno view, they always seem to be happy with our switch gear in there around here so long as we leave them enough room.


Gary
43 Replies
perspicacious
600 Posts
they always seem to be happy with our switch gear in there 

There's your answer!

Unless you think BS7671 includes DNO meter boxes!

Regards

BOD
Alcomax
312 Posts
Also the KMF  complies with BS EN 60947-3 ; it is not bothered with the dreaded 421.1.201, so can be of a sensible construction.😏 
AJJewsbury
2580 Posts
Unless you think BS7671 includes DNO meter boxes!
Surely BS 7671 covers everything after the supply terminals, whatever it happens to be? I presume the KMF will be after the meter.

I guess the meter box isn't of itself made of non-combustible material. 421.1.201 applies to 'domestic (household) premises' - so I guess it's down to whether you think something within the outside leaf of a wall counts as part of the premises. The normal dictionary definition usually includes all buildings and land - but the usual BS 7671 interpretation generally excludes things fully outside of a habitable building (such a detached outbuildings). So definitely vague to my mind.

If the house is of conventional masonry construction with nothing but another brick wall behind the meter box the risks are probably low, but if it was say timber frame with nothing but breather membrane, softwood and PIR/PUR foam insulation behind the meter box, I might not be quite so confident. So generalizations can be difficult. What about masonry construction but with flammable cavity fill?

   - Andy.
Nikp
34 Posts
Alcomax:
Also the KMF  complies with BS EN 60947-3 ; it is not bothered with the dreaded 421.1.201, so can be of a sensible construction.😏 

Surely 60947-3 is just the standard for the isolator/switch etc and not the enclosure. 

Alcomax
312 Posts
From MEM data sheets.

Single pole & neutral switchfuseThe 800KMF is a fully moulded, compact wall mounted.....

.....dataSpecification

Product standard IEC/EN 60947-3


You cannot interchange or replace the switch or fuse holder base without destroying it.  It is moulded case, there is no enclosure to replace, it is part of the product. If there is a problem you replace the whole unit. It is not manufactured as an assembly to BS EN  61439-3 as it is not a consumer unit and it has not got a separate enclosure that you can re-configure the internals.

Back in 2015, people flapped about and, for a very short period [ short enough so no one noticed the foolishness of it ], there were “metal versions” advertised by those trying to get on the bandwagon. Strangely all vanished now…



 
aligarjon
112 Posts
Cheers guys.   
AJJewsbury
2580 Posts
It is not manufactured as an assembly to BS EN 61439-3 as it is not a consumer unit
Interesting - I thought most would have considered a switchfuse as coming under the heading of 'similar swicthgear' - being pretty much identical in function to a 1-way CU (DP incomer, feeding one OPD, suitable for use at the origin of an installation and so on).

So if it doesn't comply with BS EN 61439-3 isn't that technically another contravention of 421.1.201 - which not only asks for consumer units and similar switchgear in domestic premises to have non-combustible enclosures but for them to comply with BS EN 61439-3 as well.

Steel versions are still readily available - e.g. https://www.screwfix.com/p/wylex-100a-domestic-switched-fused-unit/5290j
that Wylex one for example appears to meet the requirements of  BS EN 61439-3 as well as 60947-3 according to https://www.electrium.co.uk/media/20151123152755_0_Wylex Domestic Switch Fuse Unit.pdf.
   - Andy.
Alcomax
312 Posts
"It is not manufactured as an assembly to BS EN 61439-3 as it is not a consumer unit "


Interesting - I thought most would have considered a switchfuse as coming under the heading of 'similar swicthgear' - being pretty much identical in function to a 1-way CU (DP incomer, feeding one OPD, suitable for use at the origin of an installation and so on).

Like a shark AJ 😀

It , the KMF, is not manufactured as an assembly to BS EN61439-3, as it is not a consumer unit.

However, if there is only a KMF and no consumer unit- unlikely- then the intended use changes and would not be in the spirit of 421 etc.

There are no steel moulded 800KMFs; though there briefly was, though to what BS is lost in time.

Some may chose to manufacture a switch fuse to 61439-3, as opposed to the specific KMF.

In the KMF, you cannot change the fuse holder. It is all in a moulded assembly. You could change the fuse, but that is not resetting a device as you would in a consumer unit. For most intended use the KMF is providing HRC fuse  protection usually upstream of a DBO  in a domestic. It is usually not touched by ordinary persons; they would be accessing the consumer unit. The KMF is just a bigger, beefier device than your 13 amp switch fuse connection unit and we do not usually require those to be steel.
mapj1
3555 Posts

In the way that there is no multitude of thin final circuit wires routed like spaghettii, some pulled violin tight from side to side in front of others, I suggest the risks from one of these are NOT in any way similar to a consumer unit. Let us remind ourselves in the pic below what one a "good" example of a modern post part P (look at the new colours ! ) twin RCD installation can look like. (and remind ourselves that some total shyster charged good money to leave it like that. Funny that word fails the spell check. You  know what I mean. )

And you are not putting your switch indoors. Do it well and do not worry too much.


The risk is simply not similar in any way.
Mike.

 
Nikp
34 Posts
How the hell does someone walk away from a job like that. 
Even that one below the KMF switch if securely covered to IP2x/4x might be serviceable for years. The most important aspect is that all the terminations are tight.  Now the likelihood of that being the case in this instance is debatable.
Legh
Chris Pearson
2574 Posts
Nikp:
How the hell does someone walk away from a job like that. 

If I had done that, I'd run, not walk. 😁

My affliction is being perfectionist. I imagine that there is a middle way.

mapj1
3555 Posts
you cannot fit the lid, as some of the wires come out the front via what should be the gap between body and lid...
I agree if that was not the case, it's probably not actually immediately dangerous, (apart perhaps from the ends of the bus-bar) but it is, to put it as nicely as possible, dog rough, and almost impossible to see what is going on and check with confidence.

I think sometimes a well done DIY job is preferable to a contractor in a hurry to be honest.

My point with that picture is that it is work like that which is the real CU fire risk, and the cause of the updated regs,  and it is being done by folk calling themselves the professionals.
The KMF, or a REC2 or a single RCD in a single plastic box, is a lot less risky, as there are far fewer connections, and the chance of getting it wrong is almost nil.

Mike
UKPN
218 Posts
"I am not interested in the DNO view"
You should be, because without a competency certificate signed by a DNO you are not able to work live on their equipment.
An unauthorised "isolator" is not covered by the suppliers insurance.
The fitting of an unauthorised "isolator" will loosen the meter tails irrespective of a withdrawn fuse so the meter terminals will have to be checked afterwards. This of course requires seals to be broken and replaced, again only persons with a competency certificate are able to do this.
Your best course is to request a suppliers isolator via the customer. The suppliers meter operator will attend, fit, and you being there at the same time can reconnect the tails.
Ascertaining whether a plastic isolator/sw/fuse is allowable under the "wiring regulations" would be futile anyway because that question has been thrown around for years and no one from the "institution has stuck their head above the parapet and given a definitive answer. 

Regards, UKPN.
perspicacious
600 Posts
Your best course is to request a suppliers isolator via the customer. The suppliers meter operator will attend, fit, and you being there at the same time can reconnect the tails.

I didn't read the OP as seeking to install an isolator, there could be one there already. My reading is that the OP wants to use "meter tails" greater than 3 m in length, hence the need for a secondary overcurrent protective device as use of the DNO cut-out fuse is not permitted for meter tails exceeding 3 m.

The OP wants to install this secondary overcurrent protective device in the DNO meter box enclosure for reasons only known to the OP.

It is past my bedtime so may have been typing utter $£%* so, as usual different viewpoints may follow!

Regards

BED
" you cannot fit the lid, as some of the wires come out the front via what should be the gap between body and lid... "
Oh come on..its been set up for the photo. Not even  a 5 day trainee clown would produce artwork as elaborate as that.
Regards....
" The OP wants to install this secondary overcurrent protective device in the DNO meter box enclosure for reasons only known to the OP. "
Lol....It's either a very large meter box or a very small tail extention.
Regards
Chris Pearson
2574 Posts
OK, I have a white plastic box on the wall of my house; or in fact, two of them. One has the DNO's and supplier's tackle and the other has a switch-fuse. I reckon that both are my boxes on my land. My land! So where is the legal basis for the DNO "owning" one of them?
gkenyon
1487 Posts
UKPN:

Ascertaining whether a plastic isolator/sw/fuse is allowable under the "wiring regulations" would be futile anyway because that question has been thrown around for years and no one from the "institution has stuck their head above the parapet and given a definitive answer. 

Regards, UKPN.

That's not true, the words are in BS 7671 itself.

Consumer unit is defined in the standard. It's an assembly with a main switch and protective devices for the control and distribution of electrical energy.

An independent stand-alone isolator, or alternatively an isolating switch/fuse or isolating fuse/switch is not "similar switchgear" ... otherwise we couldn't fit standard shower isolators or cooker control units in domestic premises. 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).


However, in full agreement with you, UKPN, on the position regarding fitting an isolator and loosening meter tails ... bring back 2-screw type terminals, or lugs, for larger CSA cable.

perspicacious
600 Posts
I reckon that both are my boxes on my land. My land! So where is the legal basis for the DNO "owning" one of them?

On that logic, you own the DNO service cable, cut-out and meter Chris!

Regards

BOD

 
AJJewsbury
2580 Posts
An independent stand-alone isolator, or alternatively an isolating switch/fuse or isolating fuse/switch is not "similar switchgear"
I agree that a simple isolator or a single RCD in an enclosure doesn't constitute similar switchgear since neither meet the definition of a distribution board. I'm having difficulty however putting a switchfuse in the same category according to BS 7671's definitions.

What is the essential difference between a switchfuse and a 1-way consumer unit?




   - Andy.
Simon Barker
887 Posts
Chris Pearson:
OK, I have a white plastic box on the wall of my house; or in fact, two of them. One has the DNO's and supplier's tackle and the other has a switch-fuse. I reckon that both are my boxes on my land. My land! So where is the legal basis for the DNO "owning" one of them?

The boxes belong to you.  If a door falls of a box, it's up to you to replace it at your expense.  But if you expect them to supply you with gas or electricity, then you need to provide a box that is acceptable to them.

Alcomax
312 Posts
What is the essential difference between a switchfuse and a 1-way consumer unit?

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.
 
Chris Pearson
2574 Posts
perspicacious:
I reckon that both are my boxes on my land. My land! So where is the legal basis for the DNO "owning" one of them?

On that logic, you own the DNO service cable, cut-out and meter Chris!

As Simon Barker says, the householder (or builder) has to supply (and if necessary, replace) the boxes. It is, of course, a condition of the supply contract that the DNO and supplier may install their tackle in my box, on the garage wall, and in my ground; but that doesn't mean that they own the box or the space within.

gkenyon
1487 Posts
AJJewsbury:

What is the essential difference between a switchfuse and a 1-way consumer unit?

   - Andy.

So an SFCU? Best change all mine for metal-clad types?

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