Metal enclosure with 3rd amendment.

[securespark]

I broached this in the "What's new in the 18th Ed.?" thread.

AFAICT, some manufacturers have developed non-ferrous CU's that comply.

Big debate over on the IET about it:

http://www.theiet.org/forums/forum/...d=59402&STARTPAGE=1&FTVAR_FORUMVIEWTMP=Linear

 

[JohnW2]

AFAICT, some manufacturers have developed non-ferrous CU's that comply.

There clearly are some mixed messages - so I guess the answer will be that "some will and some won't". However, from what flameport said, it sounds as if at least two of the major players probably "won't".

I may be totally wrong but I would have thought that if a suitable non-metal material can be found, fabricating a CU out of it would be cheaper than making a metal one.

Kind Regards, John

 

[AndyPRK]

Dunno who this bloke is……..

I expect he is lurking somewhere

With 20000+ posts, our JW wouldnt have time to do a 10min video, would he

JohnW2 wouldn't no.

 

[ban-all-sheds]

I have not bought the book but am told for fire prevention consumer units now have to be metal in domestic premises.

This raises two questions:-
What about with TT supplies?
What when consumer unit is in the garage which itself is suppose to be fire resistant?

Actually, IMO it raises a 3rd.

"Where is the evidence which shows that there was a problem with non-metallic CUs of sufficient significance to justify this new regulation, bearing in mind that the people writing the regulations are supposed to be scientists and engineers, and that if they create new regulations which cannot be justified by formal cost-benefit analyses then that makes them superstitious charlatans who deserve nothing but contempt and ridicule."

 

[ban-all-sheds]

I know it does eventually burn, but AFAIK Bakelite is pretty hard to ignite.

 

[JohnW2]

Actually, IMO it raises a 3rd: "Where is the evidence which shows that there was a problem with non-metallic CUs of sufficient significance to justify this new regulation .... "

I have to say that I'm very much inclined to agree.

Kind Regards, John

 

[JohnW2]

I know it does eventually burn, but AFAIK Bakelite is pretty hard to ignite.

.. and the same for whatever it is that they make plastic accessories etc. out of (some sort of urea-formaldehyde resin, or suchlike, I think). Indeed, I think much the same is true of many thermosetting plastics.

Kind Regards, John

 

[ericmark]

I watched the video and the first thing which come to mind is if a plastic lid on a metal consumer unit does not comply how can a plastic stuffing gland in a metal consumer unit comply?

As to non combustible enclosure my garage should be non combustible the room is designed to hold a car and to inhibit the fire of a car to an extent where users of the rest of the house have enough time to exist before the fire spreads to the living quarters.

OK it's a large enclosure but never the less it is an enclosure. There is nothing which says items inside the enclosure must not burn it only refers to the enclosure itself.

So I suppose plastic meter boxes are also out now?

So in real terms fit the consumer unit inside a metal biscuit tin and all is OK?

This is where I see the problem there is nothing about ho much heat the metal enclosure must be able to sink so it does not set fire to items outside the enclosure.

So what we are looking at is getting rid of 100A x 230 V = 23kW of power without the unit getting hot enough to set on fire anything around the metal box.

At 250°C wood starts to produce ignitable gases this of course also refers to wood products so in real terms the metal box must be able to dissipate enough heat so it will not reach 250°C.

Now it would depend on the size of the enclosure but I just can't see how such a small box with no cooling fins could ever dissipate 23kW of heat into the air and wall without it's temperature raising above 250°C.

So in real terms it's all rather pointless.

 

[JohnW2]

I watched the video and the first thing which come to mind is if a plastic lid on a metal consumer unit does not comply how can a plastic stuffing gland in a metal consumer unit comply?

Good question.

So I suppose plastic meter boxes are also out now?

Only if they contain a CU.

So in real terms fit the consumer unit inside a metal biscuit tin and all is OK?

In concept, yes, although a biscuit tin might be too small - the reg allowing a plastic CU to be within a non-combustible enclosure does refer one to the reg about 'adequate access' etc.

This is where I see the problem there is nothing about ho much heat the metal enclosure must be able to sink so it does not set fire to items outside the enclosure.

Quite so - it's not as if a fire is going to originate in the plastic casing - something has to be burning or, at last, getting very hot, inside it,and that will remain the case regardless of the material of the casing. What happens with cable exits - intumescent seals?

So in real terms it's all rather pointless.

As I wrote in response to BAS's comment, I certainly do wonder - particularly about the point that BAS raised - as to whether there is evidence of enough problems due to non-combustible CUs to warrant/justify such a relatively major change. However, we are, of course, stuck with it!

Kind Regards, John

 

[eveares]

What does the 3rd amendment say about TT earthing systems. I guess nothing as they termed it "non combustible" and not "metal clad".

Also what Is the practical solution for TT earthing systems? Non conductive metal, some other non metal non combustible material.

Will there be any exceptions or further alterations to the regs in regards of the 3rd amendment?

 

[Taylortwocities]

Oh yes, and my meter is made of plastic. I know its not covered by BS7671 but wondered if the non-combustible requirement will seep into the supply regulations. Or maybe a meter has never caught fire…?

Oh yes, and the DNO-supplied REC2 isolator is made of plastic…….

I must set up a company making hole cutters/chassis punches and grommets of many different sizes to fit

 

[ban-all-sheds]

http://www.eponthenet.net/article/48882/Fired-up-over-consumer-units.aspx

 

[ericmark]

I can see that where consumer units are fitted in or around escape routes then they should be metal. Really it is a no no to fit a consumer unit under the stairs. The 422.2 in the original BS7671:2008 covers this already.

The problem of cause with existing buildings is the DNO head is already existing and often there is little an electrician can do as far as where the consumer unit will be located.

From BAS link it would seem the existing consumer units often don't comply with existing regulations so to alter the regulations seems similar to reducing the speed limit from 50 to 30 because of the number of accidents caused by people doing 70. Clearly what is required is to catch the people doing 70 rather than reduce the speed limit further.

The special stuffing gland with two holes for incoming tails is of course not the only problem any hole in the consumer unit can allow it's contents to pour out all glands would need to be fire resisting and the only method is to have enough metal in the gland to sink any heat produced so it would need all SWA type glands. Any other type really removes the whole point of a steel enclosure.

What happened to KISS the problem is getting too hot these

have been made for years. Sticking one on a consumer unit gives a visual warning of something amiss before it reaches the fire stage. Clearly adapted for a consumer unit likely amber and red with writing on them over heated switch off and call an electrician to test electrical connections. So cheap and so easy to retro fit OK will not work in all locations and will not auto disconnect but people do not habitually test the heat of a consumer unit and even if they did they would likely not know how hot means there is a fault.

The are other methods to alert of over heating from a buzzer to some method to trigger the RCD cracking a nut with a sledge hammer will normally destroy the nut using a more reasonable approach can leave the nut in an edible state. Alerting before the fire is to me correct approach not containing the fire by which time it's too late.

 

[ericmark]

Deleted

 

[Taylortwocities]

Eric

While I can see your point, but from a practical point of view, you would be expecting your average householder to periodically check a stick on temperature display.

It just isn't going to happen. Like it or not, most consumer units are in hard to get at and/or out of the way places. They are in garages and hidden behind piles of boxes etc, or under stairs where the brooms and vacuum cleaner accessories just pile up over them.

You can't even get people to test their smoke alarms and replace the batteries on a regular basis so this isnt going to work.

Pehaps a heat sensor in the CU that posts a tweet on Twitter may get some attention?