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Topic Title: Enclosures.
Topic Summary: Fire.
Created On: 09 July 2018 01:45 PM
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 09 July 2018 07:14 PM
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sparkingchip

Posts: 11373
Joined: 18 January 2003

Originally posted by: AJJewsbury

Where can I buy an Amendment 3 all insulated enclosure for an R.C.D. or one already made up that complies, for TT use please?


Wylex also seem to have an S-type RCD in a REC2 enclosure in their 2018 catalogue - http://www.wylexreasons.co.uk/...logue%20Feb%202018.pdf - their page 18 (physical page 20). Oddly it doesn't have a product code, but as neither do many of the new AFDD products, I suspect it's just due to it being new rather than anything untoward.

- Andy.


The Wylex Type B RCD on the previous page is in what looks like a dedicated plastic enclosure that cannot be swapped for a different enclosure, that is the problem with specifying equipment not made for the UK market.

Andy B
 10 July 2018 10:45 AM
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Alcomax

Posts: 368
Joined: 12 November 2009

Unfortunately some have not had the new 18th delivered yet. Mine has just arrived and so looked at the new group of regs mentioned by Mr Kenyon below:



421.1.201 might ... if it's in a dwelling ... because it's switchgear as defined in Part 2. For those wanting to revive the "it's not switchgear" argument, see 536.4.201 in BS 7671:2018, the first para of which answers this question once and for all on what this assembly could be ... and the rest of the Reg effectively states "got to be the right box for the RCD, as tested by the manufacturer, or you're responsible for the assembly" ... including ratings to meet 536.4.201. 536.4.201-536.4.203 may be new to BS 7671, but they are just stating the product situation that's been in place for a long time re- whether the assembly is the installer's responsibility or the manufacturer's.


Agreed the new regs quoted above are more specific on what bit of kit is acceptable in what type of box and, importantly, what your responsibilities are if you decide to "adapt" a BS EN61439 series assembly such as a consumer unit.

Semantics of switchgear and subsequent deliberations were more to do with establishing a logical path to what is the least "unsafe" arrangement, the more unsafe being the unearthed class 1 consumer unit.

I would say that 536.4.203 note 2 will be a bit of a downer for all those persuaded it was a good idea to adapt a class 1 metal consumer unit into a pseudo "class 2" by adding an "insulating" gland kit.

Reg 536.4.203 Integration of devices and components

Briefly " The relevant part of the BS EN 61439 series shall be applied to the mechanical and electrical devices..........eg circuit breakers, control devices, busbars into an enclosure or existing low voltage assembly....................shall only be declared suitable according to the assembly manufacturer's instruction or literature...."

...and note 2

If an assembly deviates from its original manufacturer's instructions, or includes includes components not included in the initial verification, the person introducing the deviation becomes the original manufacturer with the corresponding obligations.

Originally posted by: chrispearson Wylex will sell you a two-pole S type RCD in a REC2 enclosure, which seems to address the OP and subsequent discussion above.


The above is what I have been doing for the last three years in respect of TT and metal CU's, where appropriate.
 10 July 2018 11:17 AM
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AJJewsbury

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"For Class I enclosures in TT systems where RCD protection is used on outgoing circuits, double or reinforced insulation of all live conductors (incoming cables, extension terminals, etc.) on the supply side of the incoming device, e.g. main switch, shall be used. Insulated and non-metallic sheathed cables are deemed to meet the requirements of double or reinforced insulation".

Normally there's a lot more to meeting 412 than just sheathing incoming cabling. One very important part of 412 is the requirement that protective conductors, if they're present inside the enclosure, must be insulated as if they were live conductors. That makes a lot of sense in the CU on a TT system as if a stray c.p.c. did touch any pre-RCD line conductor not only would the CU itself become live, but so might earthed parts throughout the entire installation. Insulated & sheathed is OK as far as it goes, but what stops a c.p.c. touching either the incoming cable's conductor where the sheath & insulation are stripped to enter the incomer's terminal (with the best will in the world it would be difficult to guarantee less than a 1 or 2mm gap from all directions), or indeed touching the terminal screw or entering any of the other apertures that modular devices usually have (e.g. for fork bus-bars). To my mind bare c.p.c.s from T&E and the like with a bit of loose G/Y sleeving over them would never count as adequate insulation for a live conductor.

So what alternatives might there be to achieve a similar degree of safety? I think most of us would dress the internal wiring of the CU so the c.p.c. were nowhere near the incomer - but given the rat's nest that most older CUs seem to contain after a decade or three of additions and alterations - that doesn't feel like a reliable long term approach.

If you want to stop wires touching the live terminals etc on the incomer then some physical barrier might do around/over the terminals and the area where the cable sheath/insulation stops - but to be effective it presumably would have to be IP4X or IPXXD.

Or move over to Irish style T&E with fully insulated c.p.c.s (and insulated earth bars in CUs).

- Andy.
 10 July 2018 12:53 PM
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psychicwarrior

Posts: 633
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Were things really that unsafe before all this. I suppose someone/somegroup has to decide at what point enough has been done to improve matters...and this, for now, is what we are seeing. oh well.
 10 July 2018 06:57 PM
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Zoomup

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A Wylex reply regarding obtaining an Amendment 3 compliant insulated R.C.D enclosure.


"You can use the ESE2 but it wouldn't be Amendent 3 compliant, we don't do any insulated enclosures that are AM3 compliant."

Z.
 10 July 2018 08:11 PM
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gkenyon

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Originally posted by: Zoomup

A Wylex reply regarding obtaining an Amendment 3 compliant insulated R.C.D enclosure.





"You can use the ESE2 but it wouldn't be Amendent 3 compliant, we don't do any insulated enclosures that are AM3 compliant."



Z.
Or 18th Ed compliant for dwellings ...

Don't forget, if this is "Distributor's Equipment", it's out of scope for BS 7671 in any case.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 10 July 2018 08:25 PM
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Weirdbeard2

Posts: 564
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Originally posted by: gkenyon

Don't forget, if this is "Distributor's Equipment", it's out of scope for BS 7671 in any case.


As is the 'isolating' fuse in the DNOs cut out, it would appear that it is impossible for any installation to comply with BS7671!
 10 July 2018 09:05 PM
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sparkingchip

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Joined: 18 January 2003

What about surge protection devices, are they okay in plastic enclosures?
 11 July 2018 08:08 AM
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sparkingchip

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Originally posted by: sparkingchip

What about surge protection devices, are they okay in plastic enclosures?


The presumably outdated Wylex sales brochure for their surge protection devices shows a main switch and the SPD mounted side by side in a plastic REC4 enclosure for installation upfront of an electrical installation.

So what is an alternative to that, an alternative that will easily allow an electrical installation to be upgraded with retrofitted SPD?

Andy B
 11 July 2018 09:20 AM
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sparkingchip

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 11 July 2018 10:16 AM
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Zoomup

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Joined: 20 February 2014

Blow the cost of the enclosure and type, just look at the price of S.P.Ds.

e.g. A Wylex combined unit such as NHSPD4421T12 is over £400.00 trade plus VAT.

I think that I will just unplug the computer and telly during a storm and listen to the battery radio.

Z.
 11 July 2018 10:21 AM
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sparkingchip

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I'm not questioning the cost, I just want to know what is a safe enclosure for a SPD in a TT installation mounted externally to the consumer unit.
 12 July 2018 10:42 AM
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AJJewsbury

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Joined: 13 August 2003

I'm not questioning the cost, I just want to know what is a safe enclosure for a SPD in a TT installation mounted externally to the consumer unit.

I can't see anything in the regs (17th at least) that says that a normal plastic enclosure wouldn't be allowable (it's no kind of distribution board).

I do have some reservations personally though - I'm not entirely convinced about how SPDs behave when subjected to a sustained overvoltage - perhaps as the result of a broken supply N (resulting in 440V-iish L-N on a single phase installation) or HV fault imposed on the LV network (1430V for <=5s or 480V indefinitely if I read section 442 correctly). It seems that the SPDs might start to conduct, so dissipating power, but unlike a lightning strike or single pulse of noise from switching, they'd keep heating up for a significant length of time. I can't help feeling there's a new fire risk there.

For SPDs in TT installations you probably can't think in terms of a simple Class II arrangement as the SPDs themselves inherently need a PE connection. If the SPD itself ever fail to short (as they are liable to do I understand) the result could be similar to L-earthed metal case situation (complete with exporting the touch voltage to the rest of the installation). I gather the usual approach is either to put the SPD downstream of the first RCD (so arrangement can be Class I), or to have the main SPD connected L-N (rather than L-PE) and then another N-PE.

- Andy.
IET » Wiring and the regulations » Enclosures.

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