Domestic Installs Metal CU's also = Metal PV Isolators

[Worcester]

Interesting webcast yesterday from NICEIC covering the 3rd Ammendment BS7671, we were aware of nearly all of it.

The one thing that made us sit up though was that in accordance with the regs, they specifically mentioned that the two isolators (and any other switchgear) needed for the PV system - CU location and Inverter, they believe falls under clause 421.1.201 (similar switchgear) and so must be enclosed in a non-combustable (usually considered to me ferrous)) material.

Anyone else thought about this ?

(Little metal rotary isolators, double pole mcbs' / main switches in metal enclosures) ...

 

[matthunt]

That looks to me like Napit technical understand the new regulations better than the IET, and as I'm with NAPIT I think I'll go with their answer.

You pay your money you take your choice I suppose mate, no doubt they will all agree to disagree

 

[TedM]

I thought we had already gone through all this sometime earlier.

Whether an item is simply "switchgear" or not seems beside the point to me.

It is a question of does the switchgear perform a function similar to that of a consumer unit - e.g. a garage or shower unit.

For any metal enclosure to conform to Amd 3 then it must comply with BS EN 61439-3 and therefore Amd 3 must apply only to assemblies that are capable of falling under the ambit of that standard.

An assembly that complies with any standard other than BS EN 61439-3 automatically does not fall under the Amd 3 reg and therefore does not need to be metal.

 

[BruceB]

I had thought of that but there did not seem an 100% clear answer. There is no 7671 definition of main or auxilliary switching but would they meet the definition of an accessory or switchgear. I incline to the former if not 'main and auxilliary switching'.

 

[Worcester]

The wording of

421.1.201 Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall:

(i) have their enclosure manufactured from non-combustible material, or

(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material and complying with Regulation 132.12.

NOTE 1: Ferrous metal, e.g. steel, is deemed to be an example of a non-combustible material.

NOTE 2: The implementation date for this regulation is the 1st January 2016, but does not preclude compliance with the regulation prior to that date.

The British Standard; BS EN 61439-3, mentioned in the regulation, is entitled "Low-voltage switchgear and controlgear assemblies; Part 3: Distribution boards intended to be operated by ordinary persons (DBO)"


The key thing is the regulation says that the type of switchgear they are referring to SHALL comply with the above BS, so IF the isolators are covered by the interpretation of: "consumer units and similar switchgear assemblies" then they'll need to be built to comply with the BS, and not the other way round, (if they don't comply with the BS / built to a different BS, then they're not considered "consumer units and similar switchgear assemblies")

So I disagree with WHY napit says it doesn't apply to rotary isolatorsm though do agree with the outcome


From Part 2 definitions of Amd3:

Consumer Units: (See below)

Switchgear: An assembly of main and auxilliary swithcing eqipment for operation, regulation, protectionor other control of electrical installations


According to the IET: Consumer units - IET Electrical

Similar switchgear assemblies

The phrase ‘similar switchgear assemblies’ in Regulation 421.1.201 means those assemblies used for the same fundamental application as a consumer unit. A consumer unit is defined in Part 2 of BS 7671:
‘Consumer unit (may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices or signalling and other devices proven during the type-test of the assembly as suitable for such use.’

An example of a similar switchgear assembly is a three phase distribution board that is intended to be operated by ordinary persons. This would have to have isolation that interrupts the three incoming line conductors and the neutral, rather than just double-pole isolation as mentioned in the above definition

.

The key thing hear is that we are dealing with Part 3 of the BS, which specifically deals with CU's / DB's

Reading the above, I reckon NICEIC have it wrong, and Napit have it right, though for the wrong reason

Qn: Anyone got or seen a copy of BS EN 61439-3:2012 ?

 

[BruceB]

My last comment above was in response to a post that has been deleted, so is looking a bit lonely now, but with no way to edit/delete.

For Ted: Rarely do I disagree with you, but to my mind the function question comes after being switchgear in the first place. I do not see how a single isolator (or even multiple isolators) falls within the definition of switchgear or has the characteristics of a consumer unit. I think isolators if not combined with for example rcds or mcbs etc are just 'accessories'.

In response to Worcester's Qn:
The BSI store says currently not available for some reason.
Here is part of it - go past the Danish front cover.
https://webshop.ds.dk/Files/Files/Products/M249414_attachPV.pdf

 

[TedM]

I don't think we are disagreeing (that might be a first!). What I was trying to say was:

If something isn't a consumer unit/switchgear assembly then it is out of scope. But if an assembly is switchgear then it is not automatically in scope - it must also perform the function of a consumer unit.

Can anything not be switchgear, not be a consumer unit and still perform the function of a consumer unit? I don't think so.

 

[BruceB]

I agree with that! Perhaps I had been reading things out of order - I have posted sometimes without refreshing so others have got in first which messes up the flow.

I see I am not reading closely enough. My response #33 was in response to Sibert's which has not been deleted but is on a different page in my browser.

 

[Gavin A]

so we're all agreed on this other than the IET technical rep, who unfortunately would be among the authors of the stuff being discussed.

tbh he's posted on the IET forums before, I wonder if he'd come and defend his position / discuss it on here.

 

[TedM]

Examining the contraindicative position for a moment - i.e. assume that isolators do fall within the requirement of 421.1.201 - then what unit would you actually use?

I see that Wylex make a dual DC/AC isolator in a metal case and their (old, 2013) technical documentation says:

"Factory Built Assemblies BSEN60439-3 when fully assembled" but it is not clear from the context if this applies to all assemblies listed in the leaflet or only to consumer units.

http://storage.electrika.com/manu/man-0150/pdftech/0150-wylex-13-tech.pdf

So unless Wylex produce updated documentation to say that this unit complies with BS EN 61439-3 then you wouldn't be able to use it to comply with Amd 3 anyway.

Does anyone else know of any metal enclosure isolators that may or may not be approved to BS EN 61439-3?

 

[SibertSolar]

Not for domestic/1ph applications Ted, no

 

[Worcester]

Thanks for the link BruceB

This is the IMPORTANT bit from the BS:

Additional definition
3.1.104 Customer distribution board CDB
An integrated assembly, for the control and distribution of electrical energy, principally in a household or similar premise, incorporating manual means of double-pole isolation on the incoming circuit(s), with polarity observed throughout. They are designed for use exclusively with specific protective devices on the outgoing circuits, and type-tested for use when energized through the specified 100 amp fuse. NOTE Generally known in the UK as a Consumer unit.

So I think that both the IET and NICEIC guys according to the LETTER of the regulations are WRONG when relating to rotary isolators (the important words from above are "and distribution" ); if putting in a 'garage' / 'shower' or similar small unit with a main switch and at least one MCB, then it needs to be in a non-combustible enclosure.

If we consider the SPIRIT of the regulations, then see here for the reason for the introduction of non-combustible CU's: (Consumer units - IET Electrical)

Reason for the new regulation

Regulation 421.1.201 was introduced because of reports from fire investigators of a recent trend of increasing numbers of fires involving consumer units having a moulded thermoplastic enclosure

The cause of the fires investigated was almost invariably found to be resistance heating as a result of poor electrical connections due to poor workmanship or lack of maintenance. Examples of such poor workmanship are thought to include:

- failure to tighten neutral conductor connections to the same torque as line conductor connections due to a misconception that neutral conductors carry less current;
-inadvertently taking cable insulation inside the terminal at a connection, resulting in the securing screw or the clamp of the terminal not making proper contact with the conductor;
- failure to check factory installed connections for tightness where required to do so by the manufacturer; and
- tightening connections to an incorrect torque and/or with inappropriate tools.

The crucial importance of checking that all electrical connections are properly made, and of taking remedial action where necessary, should never be forgotten.

Whilst the main cause of fire within plastic consumer unit enclosures is without doubt poor workmanship, other potential causes of fire within plastic consumer unit enclosures are thought to include:

- the type of internal components, such as where terminations have only one securing screw or are of the 'cage clamp' type); and
-where increased heat transfer to the enclosure is caused by the close proximity to an internal item, such as a neutral bar or a conductor terminated at the neutral bar and protruding above it.

Intent of the new regulation

The intent of Regulation 421.1.201 is considered to be, as far as is reasonably practicable, to contain any fire within the enclosure or cabinet and to minimise the escape of flames.

Then on the basis that the same poor workmanship could occur on a a rotary isolator, double pole MCB or incoming RCD you can see why IET / NICEIC will send out the message that they wish it to be in a non-combustible enclosure

If you've never seen it, then you should seee the sparks and flames you can get when a short circuited DC cable (for Isc testing) on a small domestic installation is pulled apart - it's just like an arc welder.

HOWEVER, (and this is where the argument falls down) I would hope that MCS registered solar PV installers, the installation being of a specialist nature are particularly aware of the dangers of the above poor workmanship issues and so take particular care to ensure those errors don't occur. Unfortunately we have took often come across badly installed isolators.

 

[TedM]

Gordon, I think the BEAMA document I linked to earlier confirms the "and distribution" point you make and with which I agree, when it lists (albeit non-exhaustively) the "similar assemblies" that it says the new reg applies to.

But even if you want to comply with the spirit of the new regs and install a metal enclosed isolator then where are you going to get one from that is also stated to comply with BS EN 61439-3 by the manufacturer?

 

[TedM]

Now I have had time to read through the copy of EN 61439-3 that Bruce linked to, I would say that it is logically impossible for a simple isolator to pass all the tests specified in the standard for the simple reason that some tests (10.11.5.7.2 and 10.11.5.7.4) require testing of 'final circuit protective device(s)' which, of course, a simple isolator doesn't have.

Any manufacturer who states that their isolator complies with BS EN 61439-3 is not going to be telling the whole truth.

 

[Gavin A]

Maybe someone could draft a letter to IET on this that we can all sign, and invite them to respond and be questioned on here?

 

[SibertSolar]

Good idea