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) ...

 

[Gavin A]

I weren't volunteering btw, up to my eyeballs

 

[SibertSolar]

Haha...I nominate Gavin!

 

[TedM]

I'll stick a post on the IET forum.

 

[TedM]

IET Forums - PV and BS7671 Amd 3

I understand that PV installers have been receiving conflicting advice from different bodies (IET, NICEIC, NAPIT) regarding the applicability of BS7671 Amd 3 421.1.201 and metal enclosures for AC and DC DP isolation switches, which are a standard part of any domestic PV system.

Some are being told that they must install isolation switches with only metal enclosures and others that it is OK to continue to use the normal plastic housed ones.

The BEAMA guidance document does not specifically list PV DP isolation switches as being 'in scope' in their (non-exhaustive) list of "similar assemblies".

As the new regulation has two parts - namely compliance with BS EN 61439-3 and the requirement for a metal enclosure - I have briefly looked at BS EN 61439-3 and it appears that some of the tests required for manufacturers to complete in order to show compliance with this standard can only be applied to assemblies that contain "final circuit protective device(s)" which are obviously absent from a simple DP switch.

There is also a definition in the standard that assemblies have a rated voltage no higher than 300V AC, which would appear to preclude 1000V DC units.

It would therefore appear to be logically impossible for any manufacturer to state that their isolator switch assemblies are BS EN 61439-3 compliant.

And it would then appear that it would be impossible for any PV installer to obtain any isolation switches that can comply with 421.1.201 - whether they have metal enclosures or not.

My interpretation is therefore that DP isolation switches as used in PV installations are, in fact, outside the scope of 421.1.201 and that metal enclosures are not required.

Can anyone provide any clarification on this matter?

Thanks,

Ted

 

[BruceB]

I have had a reply from the IET moderators saying they have drawn Richard Townsend's attention to the thread on the IET website so hopefully we willl soon understand his thinking.

 

[Gavin A]

cheers ted. I'd also post up the NAPIT response as well, to give IET something to chew on.

 

[Gavin A]

ps as this only takes effect from January, it's looking likely to be a bit of a moot point unfortunately

 

[TedM]

IET Response:

The new clause 421.1.201 in BS 7671:2008 (2015) is still being bottomed out by industry, before the caveat requirement takes effect in January 2016. Having spoken to national committee members/Panel chairman, I feel, at this time, that a rotary isolator could be enclosed in a plastic housing, taking account of any external influences. This will be confirmed with formal guidance in due course.

-------------------------
Richard Townsend
Senior Engineer
Standards and Compliance
THE IET

 

[Gavin A]

nice one. Occasionally sense does prevail.