Extremely vague, and doesn't really seem to preclude a brick-built enclosure (as has been implied, probably closer to 'non-combustible' than metal!).
Kind Regards, John
New cable crossing existing gas pipe - pg18 of on site guide unhelpful
- Thread starter mrstitt
- Start date
Kind Regards, John
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How does a house provide basic protection? Or don't you know what that means either?
It provides double and/or reinforced protection if you close the doors and windows (except that the front door lock bridges that protection, but then these fittings are isolated from hazardous parts by the appropriate clearance and creep-age). I'm quite confident that a double cavity brick wall, a double glased window would for each element meet the requirements for single insulation, and that a UPVC window frame or door would also provide reinforced insulation if tested.
Medium and High voltage substations are often built within a masonry structure, Concrete is often used to provide firewalls with ballistic protection in transformer yards. You can't have a transformer fire causing significant damage to adjacent transformers as this would threaten the security of the grid.
A house could also be an enclosure, as long as you didn't let non-competent people in it. But then I know a few competent people who are't very sociable - perhaps they would consider it an advantage to be prohibited from allowing non-competent people into their house. They would of course have to risk assess everything that they propose do within their enclosure - including eating and sleeping.
Medium and High voltage substations are often built within a masonry structure, Concrete is often used to provide firewalls with ballistic protection in transformer yards. You can't have a transformer fire causing significant damage to adjacent transformers as this would threaten the security of the grid.
A house could also be an enclosure, as long as you didn't let non-competent people in it. But then I know a few competent people who are't very sociable - perhaps they would consider it an advantage to be prohibited from allowing non-competent people into their house. They would of course have to risk assess everything that they propose do within their enclosure - including eating and sleeping.
Probably would. Know anyone who has performed the tests?
I think you're confusing 'enclosure' with 'enclosed electrical operating area'.
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It was mrstitt, not me, who talked about houses. I was merely talking about a brick-built enclosure (one assumes with some sort of access door!) - which I would think could provide basic protection.
In any event, in context, despite the BS7671 definition of an "enclosure", I'm not sure that such a 'secondary enclosure' would necessarily have to provide basic protection, would it (if the enclosure of the plastic CU within were already providing basic protection)?
Kind Regards, John
Well, if you're going to claim compliance with BS7671, then the enclosure would have to meet that definition, so it would have to provide basic protection, although I agree that would then be two layers of basic protection.
I think I probably am. But I'm obviously being pedantic also.
But a ceramic enclosure would tend to be preferable to metal for combustibility purposes. But then some ceramics have a reasonable moisture content and aren't as good an electrical insulator as they first appear - but normally far less conductive than steel..
Yes, so all we need is a non-porous, non-brittle ceramic material and we can make compliant consumer units! I wonder if NASA have any left of those tiles they used on the space shuttle?
The additional requirement in amendment 3 requires an enclosure that is non combustible. No mention of electrical safety whatsoever. We earth the enclosure because we are obliged to do that, but not as a result of this amendment.
If the enclosure was ceramic, and had an internal and separate means of providing electrical insulation, then we would be okay.
Its worth noting that the non-combustible enclosure can contain combustible parts - such as protective equipment and cable sheaths made from plastics.
Indeed whilst case of the metallic enclosure is provided with basic insulation (although in reality it is reinforced), all plastic enclosures provide reinforced insulation.
Since we're getting fairly pedantic .... I've just noticed something we've overlooked. We've been talking as if 421.1.201 just says that a plastic CU may be enclosed in "an enclosure constructed of non-combustible material..." (thereby theoretically invoking the BS7671 definition of "enclosure", which requires that it affords basic protection). However, what it actually says is "a cabinet or enclosure", so that (in the absence of a BS7671 definition of "cabinet") a brick-built cabinet with a 'non-combustible door" (whatever that might be) would presumably not be required to afford basic protection (although it would).
Kind Regards, John
Eh?
Having previously done impact testing to ensure compliance of an electrical product with electrical safety standards, its not actually that difficult to meet the mechanical requirements. Hence if you give a mains socket a good kicking you will often expose hazardous parts.
I've not got the standard to hand - but from memory you allow a 50mm ball bearing to fall from a 750mm height onto each surface - something like that anyway.
you would hardly need a NASA designed ceramic.
That sounds like UL508?
Indeed - but it was stillp, not me, who (I would say rather pedantically) raised the point that any mention of "enclosure" within BS7671 must be taken to imply the definition of that word as given in Part 2 of BS7671 - which definition requires that the (secondary) enclosure provides basic protection.
In any event, as I've just written to stillp, we are apparently allowed to put our plastic CU in a cabinet, rather than an enclosure, if we so wish - and that does not invoke any BS7671 definition
Kind Regards, John
Good point! There is an IEC definition though:In any event, as I've just written to stillp, we are apparently allowed to put our plastic CU in a cabinet, rather than an enclosure, if we so wish - and that does not invoke any BS7671 definition
581-25-02
Note – A cabinet is usually fitted with doors and/or side panels, which may or may not be removable.
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