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Topic Title: Switch fuses and isolators - domestic
Topic Summary: Do they all have to be constructed of non-combustible material?
Created On: 15 June 2017 08:06 PM
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 15 June 2017 08:06 PM
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nElectric

Posts: 7
Joined: 08 November 2010

Since Amendment 3 it is clear that in the domestic environment fuseboards (consumer units) have be constructed of non-combustible material - for simplicity's sake, lets just say metal for now. Does this also apply to isolators such as Wylex Rec2 or switch fuses such as Skolmore DB700? Do they come under 'similar switchgear assemblies' in 421.1.201? Or are they still allowed to be of plastic construction?
 15 June 2017 08:13 PM
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alancapon

Posts: 6838
Joined: 27 December 2005

At the risk of restarting this discussion, my belief is a switchfuse yes, but an isolator in its own enclosure, no.

Regards,

Alan.
 15 June 2017 08:18 PM
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gkenyon

Posts: 4905
Joined: 06 May 2002

Originally posted by: nElectric

Since Amendment 3 it is clear that in the domestic environment fuseboards (consumer units) have be constructed of non-combustible material - for simplicity's sake, lets just say metal for now. Does this also apply to isolators such as Wylex Rec2 or switch fuses such as Skolmore DB700? Do they come under 'similar switchgear assemblies' in 421.1.201? Or are they still allowed to be of plastic construction?
In my opinion, yes. DBOs (distribution boards and consumer units for operation by ordinary persons) should comply with BS EN 61439-3, and therefore in dwellings, they would come under "similar switchgear" element of the relevant regulation.

REC2 is an interesting discussion, because if they are part of distributors' equipment, they are exempt from BS 7671, but if not ... and also is a stand-alone isolator "similar switchgear" ???

I can't really see the difference between a REC2 being plastic, and a consumer unit being plastic, so arguing semantics on this point is really an issue for me regardless of whether it has to comply with BS 7671 ... if the consumer unit has to be "non-combustible", why not the supplier's equipment (or consumer's by virtue of it being an isolator, it may not be considered "similar switchgear")?

And if there are conflicting requirement in BS 7671, which has precedence?

For instance, a particular DBO has to be located somewhere it may be subject to corrosion ... but it has to be "metal" because that's the only option ... both corrosion and fire protection make it "unsafe" ... so which requirement takes precedence?

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

Web-Site: www.gkenyontech.com
 15 June 2017 09:54 PM
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alancapon

Posts: 6838
Joined: 27 December 2005

Originally posted by: gkenyon
. . . And if there are conflicting requirement in BS 7671, which has precedence? . . .

I am currently sat in Belfast International airport waiting for a delayed flight, so BS7671 is not to hand.

The key to this is BS7671s definition of "switchgear". I don't believe it can apply to a single isolator on its own. I think the definition is something about an assembly of protective devices, but an isolator on its own is not a protective device as it needs to be operated by hand.

Regards,

Alan.
 15 June 2017 09:54 PM
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WiredScience

Posts: 312
Joined: 25 January 2012

Originally posted by: gkenyon

I can't really see the difference between a REC2 being plastic, and a consumer unit being plastic, so arguing semantics on this point is really an issue for me regardless of whether it has to comply with BS 7671 ... if the consumer unit has to be "non-combustible", why not the supplier's equipment (or consumer's by virtue of it being an isolator, it may not be considered "similar switchgear")?



The subtle difference is the REC2 as fitted by the DNO usually has twin allen screws rather than the useless cage clamps mere mortals have to contend with, so is far less likely to cause problems. In other news, I've never seen a DNO operator using a torque screwdriver...
 15 June 2017 10:07 PM
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alancapon

Posts: 6838
Joined: 27 December 2005

Originally posted by: WiredScience
. . . In other news, I've never seen a DNO operator using a torque screwdriver...

Our electricians who fit meters do.

Regards,

Alan.
 16 June 2017 05:14 PM
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WiredScience

Posts: 312
Joined: 25 January 2012

Alan, I think your DNO is probably an exception as it's still run properly by the sounds of it. Anyway, it could be argued that you don't need to comply with the non-combustible consumer unit and switch-gear regulation as it's UK specific
 16 June 2017 05:33 PM
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AJJewsbury

Posts: 15632
Joined: 13 August 2003

Plus the DNOs seem to have kept their heads when it comes to maintaining shock protection (especially on TT supplies and TN-S ones where Zs > 0.38 Ohms) - how many metal CUs have you seen with a class II / double insulation symbol?
- Andy.
 16 June 2017 05:34 PM
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weirdbeard

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A related recent topic:

http://www.theiet.org/forums/f...AR_FORUMVIEWTMP=Linear

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:beer)
 18 June 2017 12:10 AM
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spinlondon

Posts: 5484
Joined: 10 December 2004

Simple answer is no.
They are separate and dissimilar items covered by different standards.
Of course, some will disagree, despite the evidence and will start enclosing FCUs in metal boxes.
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