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) ...

 

[BruceB]

re: Domestic Installs Meta CU's also = Metal PV Isolators

Look at the definition of switchgear in section 2 of 7671. It includes the words 'main and auxiliary switching equipment'. A single isolator (or for that matter a single upfront rcd) does not meet that definition and so can continue to be in a plastic enclosure. Arguably.

 

[solarsavings]

re: Domestic Installs Meta CU's also = Metal PV Isolators

But that's not what they said yesterday morning Bruce.

 

[Leesparkykent]

re: Domestic Installs Meta CU's also = Metal PV Isolators

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 above is written by the IET (wiring matters)^ . If the NICEIC say they "believe" that is falls under 421.1.201 I would say I "believe" it doesn't and carry on as I am.

 

[BruceB]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

I was out working and did not listen to it.

There has been some discussion on the IET site in recent weeks, but not conclusive. It really does annoy me that this is another example of where the rules get changed but the people changing them issue little guidance that explains their thinking and intentions so the minutiae of the regulations get debated for months.

Personally I think I am a fan of plastic enclosures in a domestic situation for isolators. Metal enclosures means they must be earthed. That is one more point of failure. I currrently do not run an earth to a dc isolator unless I am running swa to it.

 

[Gavin A]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

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) ...

it doesn't say 'similar switchgear' it says 'similar switchgear assemblies'

A consumer unit is an assembly of multiple switch gear units, an individual isolator is a single unit of switch gear, not an assembly of multiple units.

therefore NIC are wrong.

 

[Leesparkykent]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

it doesn't say 'similar switchgear' it says 'similar switchgear assemblies'

A consumer unit is an assembly of multiple switch gear units, an individual isolator is a single unit of switch gear, not an assembly of multiple units.

therefore NIC are wrong again.

edited post for you Lol.

 

[Worcester]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

A consumer unit is an assembly of multiple switch gear units, an individual isolator is a single unit of switch gear, not an assembly of multiple units.

Hi Gavin, they are also insistent it applies to an RCD protected TT system, where the RCD is on the main incoming as a stand alone unit. By your logic, it shouldn't apply to that either..

I think the PV scenario it's a misinterpretation, however we have fixed 3rd party installs with molten internals of rotary isolators because the connection wasn't properly tightened, which is precisely the reason for the non-combustible CU requirement.

 

[Leesparkykent]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

Hi Gavin, they are also insistent it applies to an RCD protected TT system, where the RCD is on the main incoming as a stand alone unit. By your logic, it shouldn't apply to that either..

I think the PV scenario it's a misinterpretation, however we have fixed 3rd party installs with molten internals of rotary isolators because the connection wasn't properly tightened, which is precisely the reason for the non-combustible CU requirement.

If you take that logic on the rotary isolator then the same would apply to a double pole switch for an immersion heater....

 

[davesparks]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

it doesn't say 'similar switchgear' it says 'similar switchgear assemblies'

A consumer unit is an assembly of multiple switch gear units, an individual isolator is a single unit of switch gear, not an assembly of multiple units.

therefore NIC are wrong.

It says switchgear assemblies, not assemblies of switchgear. They're different things.

 

[davesparks]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

If you take that logic on the rotary isolator then the same would apply to a double pole switch for an immersion heater....

No, a 20A DP plate-switch is a wiring accessory.

 

[Worcester]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

If you take that logic on the rotary isolator then the same would apply to a double pole switch for an immersion heater....

That was my argument too.

 

[Worcester]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

So...
Anyone a member of the IET and care to get some guidance in writing that we can all use?

 

[Leesparkykent]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

"Similar switchgear assemblies" are assemblies that are used for the same fundamental application as consumer units.

 

[Leesparkykent]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

No, a 20A DP plate-switch is a wiring accessory.

So....

 

[TedM]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

As I read it the new regulation applies to "distribution boards" only as, apart from the non-combustible enclosure part, it also requires compliance with BS EN 61439-3.

So if an "assembly" meets a BS EN other that 61439-3 then it is not relevant to the new regulation.

See http://www.beama.org.uk/asset/7DF1EEE0-F314-452B-81E276BC561F4B89/ for the BEAMA report that is intended to clarify the amendment.

Item 4 in that report says exactly what Lee has been saying and follows that with a list of what they consider to be in and out of scope of the regulation but with the caveat "The above table provides general guidance and is not intended to be an exhaustive list of inclusions and exclusions."

"Photo-Voltaic combiner boxes" are in scope so, in future, these are going to have to be both BS EN 61439-3 compliant and non-combustible.

 

[Gavin A]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

but where would you use pv combiner boxes in a domestic situation?

 

[Gavin A]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

It says switchgear assemblies, not assemblies of switchgear. They're different things.

hmmm it'd seem you're right.

In accordance with EN 60 439-1, Subparagraph2.1.1., a low-voltage switchgear and controlgearassembly is“A combination of one or more low-voltageswitching devices together with associated control,measuring, signalling, protective, regulatingequipment, etc., completely assembled under theresponsibility of the manufacturer with all theinternal electrical and mechanical interconnectionsand structural parts (…).”

http://www.nema7.com/PDF/allen_bradley_guide_switchgear-controlgear_assembly.pdf

Still not convinced that an individual isolator is really classed as being similar switch gear to a consumer unit. It's more similar to a dual pole switch than to a consumer unit - a dual pole fused switch would be more similar to a Consumer Unit due to having the fused protection within it.

 

[TedM]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

but where would you use pv combiner boxes in a domestic situation?

Possibly in a large domestic system, such as those Worcester has some experience of, perhaps?

 

[Gavin A]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

Possibly in a large domestic system, such as those Worcester has some experience of, perhaps?

you'd need more than 2 inputs into the same MPPT on the inverter, which usually only happens on 20kW+ 3 phase inverters assuming dual trackers.

As earthing the metal enclosure would do bugger all for the safety of it on the DC side, I'd be inclined to stick with insulated enclosures anyway - citing regulation 712.412 as evidence to support that... "protection by the use of class 2 or equivalent insulation shall preferably be adopted on the dc side."

 

[matthunt]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

Hi folks, had it in writing from the IET themselves that Rotary isolators will need to be housed in metal enclosure!!

 

[Darkwood]

Re: Domestic Installs Meta CU's also = Metal PV Isolators

Hi folks, had it in writing from the IET themselves that Rotary isolators will need to be housed in metal enclosure!!

Can you forward a copy of your correspondence if possible and post it up, wording and interpretation can be key to such an important point.

 

[TedM]

And how many rotary isolators also comply with BS EN 61439-3?

 

[matthunt]

E-Mail as follows:

Dear Matt,

Thakyou for your query. Richard Townsend, Senior Engineer with the Technical Regulations team has provided the below response

From me: "Would this mean that Rotary Isolators for a PV System,both on the AC and the DC side need to be metal or completely enclosed in a metal Enclosure?"

Richards response: "Yes a rotary isolator is classed as switchgear and therefore would need a metal enclosure, or an alternative isolator would need to used"

 

[Gavin A]

Hi Matt, could you please pm me the email address as I'd really like to nail them down on that for the DC side at least, as I don't think they've thought that through at all and it contradicts regulation 712.412

 

[BruceB]

Interestingly, Napit technical on their forum have taken a different view a few days ago. At least they give a reason for their view. I hope they will not mind if I quote it:

"Regulation 421.1.201 Non-combustible Consumer Units and Similar Assemblies
Q. Would solar PV dedicated consumer units need to be metal?
A. Yes, if fitted in a domestic (household) premises. Regulation 421.1.201 applies to both consumer units and similar switchgear.
Q. Do solar PV rotary isolators have to meet Regulation 421.1.201?
A. Regulation 421.1.201 refers to similar switchgear assemblies complying with BS EN 61439-3, this standard is for low voltage switchgear and control assemblies. Distribution boards intended to be operated by ordinary persons.
The standard isolators used in PV systems fall under a different standard: BS EN 60947-3 Switches, disconnectors and switch-disconnectors. Therefore these isolators are exempt from this regulation."

 

[Gavin A]

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.

 

[TedM]

The standard isolators used in PV systems fall under a different standard: BS EN 60947-3 Switches, disconnectors and switch-disconnectors. Therefore these isolators are exempt from this regulation."

Exactly the point I was making.

 

[BruceB]

In my view there is some ambiguity in the answers from both the IET and Napit. Here’s my 2p’s worth.

Let us start with definitions:

Accessory. A device, other than current-using equipment, associated with such equipment or with the wiring of an installation.

Switchgear. An assembly of main and auxiliary switching equipment for operation, regulation, protection or other control of an electrical installation.

And the regulation:
421.1.201. Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS 61439-3 and shall etc………..

The IET asserts ‘a rotary isolator is classed as switchgear’. Why? It meets the definition of accessory above to my mind. To be switchgear it has to have ‘main and auxiliary switching equipment’. A single isolator is not switchgear by definition. Therefore in my view it falls outside ‘similar switchgear assemblies’ phrase in 421.1.201.


Napit I think comes to the right answer, although there is a slight misquote. It is wrong to say, ‘Regulation 421.1.201 refers to similar switchgear assemblies complying with BS EN 61439-3’; it actually says ‘……… shall comply with BS EN 61439-3’. So if it is a ‘similar switchgear assembly’ then it must comply with that BS. Isolators comply with BS EN 60947-3, but if in a consumer unit or forming part of a switchgear assembly then their enclosure must meet BS EN 61439-3, but a single isolator appears to fall outside the 421.1.201 requirement to meet that enclosure BS.

Personally I think I am happy to keep single isolators in plastic enclosures, as well as a REC2s or upfront rcd.

 

[SibertSolar]

What if you have multiple switch disconnectors housed within the same enclosure?...