Metal enclosure with 3rd amendment.

[JohnW2]

Is it therefore your view that the Standards do define what is regarded as 'non-combustible'? Do they actually use the term 'non-combustible'?

I can't find that term in 61439-1 or -3. I have seen, in other standards, the term "essentially non-combustible" used, which looks like an attempt to address the fact that just about anything would combust if dropped onto the surface of the sun.

That's really what one would expect. BAS has already illustrated the lunacy of taking "non-combustible" completely literally.

If we regard the term as meaning "non-combustible under the expected conditions of use, then yes, I would say that 61439 has addressed that by the tests referred to in my extract.

That sound very reasonable. So, if one takes that view, then what of the second question I asked - what meaning or sense can you make out of "shall comply with BS EN 614393 and shall be constructed out of non-combustible material"???

Kind Regards, John

 

[stillp]

I would say that the words "and shall be constructed out of non-combustible material" are ungrammatical and redundant, since the resistance to abnormal heat and fire is dealt with in the product standard.
This is the sort of thing that happens when committees start to go outside their scope.

 

[JohnW2]

I would say that the words "and shall be constructed out of non-combustible material" are ungrammatical and redundant, since the resistance to abnormal heat and fire is dealt with in the product standard.

Before you say to much about ungrammatical', I should say that I was paraphrasing. What the reg actually says is:

.... shall comply with BS EN 61439-3 and shall:
(i) have their enclosure manufactured from non-combustible material, or
(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material ...

Grammar aside, if you feel that (i) is 'redundant' (which I would agree that it seems to be) then what on earth do you think of (ii)?

Kind Regards, John

 

[ban-all-sheds]

I can't see a single fault increasing the risk. It would require a Live to Case fault and a loss of earth to the case before the case became live.

Not with a TT installation where the live-case fault is upstream of the RCD.

 

[JohnW2]

I can't see a single fault increasing the risk. It would require a Live to Case fault and a loss of earth to the case before the case became live.

Not with a TT installation where the live-case fault is upstream of the RCD.

Indeed (assuming that you intended to type a question mark at the end of what otherwise looks like an {incorrect} statement). Of course, that would be a far worse scenario than simply a 'live metal CU' - all CPCs and exposed-c-ps throughout the installation would then probably also become live.

Kind Regards, John

 

[stillp]

I would say that the words "and shall be constructed out of non-combustible material" are ungrammatical and redundant, since the resistance to abnormal heat and fire is dealt with in the product standard.

Before you say to much about ungrammatical', I should say that I was paraphrasing. What the reg actually says is:

.... shall comply with BS EN 61439-3 and shall:
(i) have their enclosure manufactured from non-combustible material, or
(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material ...

Grammar aside, if you feel that (i) is 'redundant' (which I would agree that it seems to be) then what on earth do you think of (ii)?

Kind Regards, John

Ah, so the bad grammar was yours John! Be ashamed, be very ashamed.
I suspect that (i) only exists so they can give (ii) as an alternative. Both are really redundant though, since the requirements for resistance to abnormal heat and fire are covered by the reference to BS EN 61439-3.
This all calls into question whether the requirements in the product standard are insufficiently stringent, or whether the CUs referred to in the Fire Brigade report as having caused/contributed to fires were compliant with the current requirements of 61439. I don't know how long those requirements have been there, but generally switchgear and controlgear used lower temperatures than are currently given for the glow-wire test. It is therefore possible that the 'guilty' CUs were older ones of good quality, or recent ones that are cheap far-eastern crap made from unsuitable materials. Unfortunately flame-retardant plastics cost more to buy and to use than non-flame-retardant types, particularly since the RoHS Directive restricted ths use of some flame retardants.

 

[JohnW2]

.... shall comply with BS EN 61439-3 and shall:
(i) have their enclosure manufactured from non-combustible material, or
(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material ...

Grammar aside, if you feel that (i) is 'redundant' (which I would agree that it seems to be) then what on earth do you think of (ii)?

I suspect that (i) only exists so they can give (ii) as an alternative. Both are really redundant though, since the requirements for resistance to abnormal heat and fire are covered by the reference to BS EN 61439-3.

I still don't really pretend to understand. If a CU already complied with 61439-3, why would they want to 'offer' ('as an alternative') putting it inside a non-combustible enclosure.

This all calls into question whether the requirements in the product standard are insufficiently stringent, or whether the CUs referred to in the Fire Brigade report as having caused/contributed to fires were compliant with the current requirements of 61439. I don't know how long those requirements have been there, but generally switchgear and controlgear used lower temperatures than are currently given for the glow-wire test. It is therefore possible that the 'guilty' CUs were older ones of good quality, or recent ones that are cheap far-eastern crap made from unsuitable materials.

All possibly true, but if 'they' (JPEL/64) felt that the Standard was insufficiently stringent in this respect, they surely should have said something more specific and understandable about what degree of stringency they did feel appropriate than to simply speak of 'non-combustible materials'?? The Fire Investigator ((click here) wrote:

Plastic Consumer Units in the UK have to be constructed in accordance with BS EN 60439 (replaced in 2011 by BS EN 61438). The plastic enclosures have to withstand 660°C glow wire product tests. The opinion of the author is that this test is not sufficient to ensure the safety of the occupiers in properties where plastic consumer units are installed.

Comments? (has he got that 'replaced in 2011' back-to front?)

Kind Regards, John

 

[stillp]

You mean was it replaced in 1102?
I can't see anything back to front, but he's got the new standard number wrong, as well as the glow-wire temperature. To my mind his inability to get these simple facts right casts doubt on his credibility. He talks a good talk, judging from his CV, so perhaps the mistakes are the journal's rather than the investigator's. I'd like to know why they chose a test from an inappropriate product standard though.
I think perhaps he's trying to say that all plastic parts of the CU should be able to withstand the 960degC glow-wire test, which could probably be achievable if the customers could be persuaded to forgo the nice shiny plastic cover and to pay a couple of quid more. Having seen the garbage that people buy I have little hope of that.

 

[JohnW2]

You mean was it replaced in 1102? I can't see anything back to front, but he's got the new standard number wrong...

Ah - fair enough. I think I may have been getting confused by these (similar sounding) Standard numbers.

... as well as the glow-wire temperature. To my mind his inability to get these simple facts right casts doubt on his credibility. He talks a good talk, judging from his CV, so perhaps the mistakes are the journal's rather than the investigator's. I'd like to know why they chose a test from an inappropriate product standard though.

His CV certainly looks pretty reasonable, so you may be right that the mistakes are not his - but I have to say that, if I were the author, I would want to scrutinise the proofs very careful to make sure that the publisher (or even editor!) had not messed up what I'd written in a manner which might undermine my reputation!

I think perhaps he's trying to say that all plastic parts of the CU should be able to withstand the 960degC glow-wire test, which could probably be achievable if the customers could be persuaded to forgo the nice shiny plastic cover and to pay a couple of quid more.

Yes, he might be trying to say that. Who knows?!

Kind REgards, John

 

[DaftPunk]

I don't understand why such a big deal is being made of all this.

I've been installing nothing but metal clad boards as long as I can remember on commercial and industrial jobs, and a fair few domestic jobs too.

Metal is far better than those flimsy bits of rubbish wylex are churning out and the risks of two faults causing the case to come live are no greater than every other accesory containing ecps in the installation.

 

[JohnW2]

I don't understand why such a big deal is being made of all this. ... I've been installing nothing but metal clad boards as long as I can remember on commercial and industrial jobs, and a fair few domestic jobs too.

Nor do I (understand why such a big deal is being made out of all of this), but not for the same reason as you. No-one is being told that they have to use metal CUs in domestic installations and I strongly suspect that, once the dust of all the misunderstandings and knee jerks has settled, plenty of Amd3-compliant non-metal ones will become available.

Metal is far better than those flimsy bits of rubbish wylex are churning out and the risks of two faults causing the case to come live are no greater than every other accesory containing ecps in the installation.

Opinions will obviously vary. Also, I may be wrong, but I suspect that Amd3-complaint plastic ones will probably be appreciably less flimsy than you have been used to in recent times. There are undoubtedly pros and cons, and I agree that the "two faults causing the case to become live" is a pretty weak argument. One of my greatest fears, particularly give the nature of this forum, relates to those DIYers (and inadequately trained 'electricians') who, even though they shouldn't, will probably always 'dabble', in perhaps very unwise fashions, within a CU. To have their fingers surrounded by earthed metal when they are 'unwisely dabbling' has surely got to increase the risks for them?

Kind Regards, John

 

[333rocky333]

Reminds me of a time on site when I saw a qualified electrician drilling a 20mm hole in a metal board for a new cable, big flash and a bang as he pushed so hard he went through the metal and hit the suply cable shorting it to earth via the drill

 

[DaftPunk]

That's where a bit of wood comes into play

At the risk of sounding cruel / harsh / unconcerned if you're not competent to be fiddling in a cu and you get a shock or it kills you then tough. Lesson learnt. In all reality the risk of shock is not much different at all between a metal cu and an insulated one.

Modern CUs are powder coated and effectively insulated anyway.

 

[JohnW2]

At the risk of sounding cruel / harsh / unconcerned if you're not competent to be fiddling in a cu and you get a shock or it kills you then tough. Lesson learnt.

I realised that someone was bound to say that, but that's not really how safety-related regulations work - at least, not any more! A lot of the regulations and restrictions we have to live with (and some moan about, citing the 'Nanny State') these days are designed to "protect people from themselves" (or "from their own stupidity").

In all reality the risk of shock is not much different at all between a metal cu and an insulated one. ... Modern CUs are powder coated and effectively insulated anyway.

True, although I'm not going to be the person who grasps one whilst touching L with my other hand in order to confirm your point! (and don't forget that it is not deemed safe for me to be allowed to touch a single-insulated live conductor) In fact, I wouldn't even have been surprised if the regs (aka Mr/Ms Nanny State) had actually demanded that metal CUs be 'effectively insulated', and if scratches penetrating the coating therefore resulted in EICR 'fails'!

Kind Regards, John

 

[plugwash]

AIUI electrical safety regulations (for both installations and appliances) are based on the principal that once you use a tool to enter an enclosure you have crossed a line and safety becomes your responsibility.