"Consumer's Panel"

[JohnW2]

I do feel the London Fire Brigade are being given a bad deal over this. They are not the only fire brigade to have raised concerns about plastic consumer units but they seem to be the only brigade betting the "blame".

We obviously don't have the full facts, but it is our understanding that it was the LFB that essentially brought about this change. It has even been suggested to us (by someone who had reason to have some inside information) that JPEL/64 were essentially 'bullied' by the LFB to make this change to BS7671, under threat of resort to political/legal approaches if they did not comply - the implication perhaps being that JPEL/64 were far from convinced that the change was appropriate/needed.

Of course the risk of electric shock is increased slightly if the consumer unit case is Earthed metal.

Exactly my point - so it is only a justifiable change if one is pretty sure that that 'slight increase' is balanced by at least an equal 'slight decrease' in risks due to CU-related fires.

( Does it have to be Earthed ).

Definitely. To have an unearthed exposed-conductive part would certainly increase risks, as well as being non-compliant with regs.

I am sure that the Fire Investigation Officers of the brigades advocating a change had thought this out and based on their decades of experience of investigating the causes of fires decided that inflamable consumer units should not be installed.

As I said, they don't seem to have 'thought it out' all that well. If they truly believe that a significant number of house fires result from a plastic CU case catching on fire as a result of something within it initiating a fire, they should at least have demanded some requirement for 'fire containment' (which, after all, is a major consideration in terms of fire safety requirements) - but they didn't.

In any event, even if they had required 'fire containment', as was often said in discussions when this change was first proposed, if the problem is that components within a CU are catching on fire, then one really ought to try to find a way of addressing that problem, rather than taking measures to slow the spread of such fires. If an aircraft engine developed a reputation for exploding in flight, sending shrapnel through the fuselage, one hopes that measures would be taking to reduce the risk of such explosions, rather than strengthening the 'containment' around the engine to reduce the risk of shrapnel escaping and doing harm!

Kind Regards, John

 

[ban-all-sheds]

I am sure that the Fire Investigation Officers of the brigades advocating a change had thought this out and based on their decades of experience of investigating the causes of fires

Not decades of the practice of ascribing "electrical fault" to fires whose cause was otherwise unknown?

How many installers have carried out forensic investigation of the burned out equipment they are replacing ?.

How many of the fire investigators are trained forensic engineers?

How many considered whether requiring better engineered connections to address the root cause of fires starting in CUs might be better than requiring a tin box to address the symptoms?

It was a knee-jerk reaction, poorly thought out, ungrounded in any reasonable engineering practice, driven solely by the PR need to be perceived to have Done Something.




PS. To pre-empt JW2 quoting himself, I started this post before I saw #16

 

[ericmark]

Which is why Fire Brigade FIOs investigate fires to discover the cause of the fire and then if necessary give advice on how to prevent other fires starting from the same source.

My point is a metal CU does not stop fires from starting, all it does is contain a fire if it starts. What was needed was a CU which does not over heat in the first place.

It seems some MCB's when the terminal is opened do not force the clamp open but allow it to open or close, this is a problem when the CU is mounted in a restrictive space, the MCB can be inserted, with the terminal fully slack, and then the terminal tightened to the required torque, but the tag on the bus bar is not actually clamped, it is just pushed against the terminal, the clip on the DIN rail makes it feel as if the MCB is properly connected, and the loop impedance will also show a good connection. However once a high current is draw then it starts to over heat.

Good makes of MCB actually force the terminal open so this error can't be made, it was just some cheap versions where the error was possible. It really was cracking a nut shell with sledge hammer when the metal consumer unit was specified. And there was very little done to actually cure the problem, which would have involved a recall on certain MCB's.

 

[bernardgreen]

How many of the fire investigators are trained forensic engineers?

They are well trained in determining where the fire started and then determining what was the cause of the fire. Evidence they provide is accepted by Coroners and Courts.

 

[ban-all-sheds]

They are well trained in determining where the fire started and then determining what was the cause of the fire. Evidence they provide is accepted by Coroners and Courts.

So none of these fires were caused by poor connections within the CUs?

Every single one was caused by the plastic enclosure?

 

[bernardgreen]

So none of these fires were caused by poor connections within the CUs?

Did I say that NO... I DID NOT

Probably the majority of fires in consumer units are caused by over heating of terminals. They may be accelerated by a non fire resistant case
.
There is another reason for metal cases. Heat from an over heating terminal can soften the plastic enough that components ( MCB RCD bus bars etc ) are no longer held in place and apart from each other. What was a contained overheating terminal then results in further faults of shorting conductors with a greater risk of reaching ignition temperatures

 

[JohnW2]

My point is a metal CU does not stop fires from starting ....

That was indeed one of my point, but ....

... all it does is contain a fire if it starts.

The available metal CUs undoubtedly do to some extent, but that's no thanks to the new regulation or the LFB - since, as I said, the regulation includes no requirements in relation to containment. A metal CU full of 'ventilation holes' would be compliant with the new reg, and probably compliant with all regs provided that it did not violate IP rating requirements.

What was needed was a CU which does not over heat in the first place.

Quite - per my aircraft engine analogy, it is far better to address the underlying cause than to try to 'contain' its effects.

Kind Regards, John

 

[JohnW2]

There is another reason for metal cases. Heat from an over heating terminal can soften the plastic enough that components ( MCB RCD bus bars etc ) are no longer held in place and apart from each other.

Most plastic CUs have/had metal din rails, and I would certainly regard that as highly desirable. However, it's failure (melting) of the (plastic) clips on the devices themselves which would cause those devices to detach from the rail and become 'mobile'.

What was a contained overheating terminal then results in further faults of shorting conductors with a greater risk of reaching ignition temperatures

I'm not sure that's very logical. Other than in the one culprit device, things in general would probably not start melting until ignition had already occurred - and, in any event, as above, it's not melting/burning of the case which would be the real issue.

Indeed, and a little ironically, if there were a requirement for extensive ventilation of the case (rather than that it should be metal), it would take longer for anything (even the 'culprit device') to reach ignition temperature, so the fire might not start in the first place!

Kind Regards, John

 

[mattylad]

I would expect plastic CU's to be EL94V compliant and to self extinguish within 10 seconds of any heat likely to start a fire.
If it does then I'd be happy to have such a CU in my house.

 

[JohnW2]

I would expect plastic CU's to be EL94V compliant and to self extinguish within 10 seconds of any heat likely to start a fire. If it does then I'd be happy to have such a CU in my house.

I don't know whether they were/are required to be self-extinguishing (**) (and don't even know what EL94V is), but I am sure that adequately self-extinguishing plastics are available and could be used for CUs - in which case, like you, I would be more than happy to have such a CU in my house.

** one has to wonder, since we have seen videos and photos of burning plastic CU enclosures which appear to be doing anything but 'self-extinguishing'.

Kind Regards, John

 

[EFLImpudence]

No manufacturer has made a fuss and said that their plastic CUs were like that, although I am sure some were (CED?).

They just seem to have caved in and gone over to metal ones.

Perhaps they know the power of suggestion and realised no electrician would buy plastic ones any more.

 

[JohnW2]

No manufacturer has made a fuss and said that their plastic CUs were like that, although I am sure some were (CED?). They just seem to have caved in and gone over to metal ones. Perhaps they know the power of suggestion and realised no electrician would buy plastic ones any more.

I suspect/fear that all of that is very true.

I think the problem may be that the reg contains this ridiculous requirement for "non-combustible" material, in addition to the requirements (which I think already include 'hot wire tests' etc.) of the relevant product Standards.

Given the absence of any attempt at a definition of "non-combustible" in BS7671, that means that manufacturers really have no way of knowing what would satisfy the reg, other than the one example (ferrous metal) given of something that would be 'deemed to'satisfy the requirements of the reg. Quite apart from the unknown requirements in relation to (any) plastic materials, I don't think one could even be sure that aluminium, copper or brass etc. would necessarily satisfy the requirement.

Kind Regards, John

 

[ericmark]

Would it be really that hard to include in the RCD an over temperature trip which would isolate board before a fire starts? OK the MCB gets hot anyway so maybe not in MCB but in the RCD it could even be two terminals for a remote temperature sensor placed in top of board.

Even with metal case, inside the insulating parts are not metal so still they can melt or burn causing more shorts.

I went to skip site other day, notice said "Hard Plastic" is not that contradictory? How can anything be hard and plastic?

 

[JohnW2]

Would it be really that hard to include in the RCD an over temperature trip which would isolate board before a fire starts? OK the MCB gets hot anyway so maybe not in MCB but in the RCD it could even be two terminals for a remote temperature sensor placed in top of board.

There are all sorts of measures one could take to reduce the risk of fires starting within CUs and/or to sound an alarm if they do. However, the LFB don't seem interested in that but, instead, seem to prefer to allow the fires to start, without any warning, and then merely require that the enclosure itself cannot burn easily (although I imagine that, with a raging fire within, it would soon get hot enough to ignite nearby items).

I went to skip site other day, notice said "Hard Plastic" is not that contradictory? How can anything be hard and plastic?

A lot of the materials now described as 'plastics' are not really significantly plastic. It seems that the word is now widely used to refer to almost any polymer, and even some composites.

However, I suppose that the answer to your question depends upon what one means by 'hard' - since, for example, many metals (which I would usually regard as 'hard') are pretty plastic (at least, once stressed beyond their {low} elastic limit).

Kind Regards, John

 

[ban-all-sheds]

Did I say that NO... I DID NOT

So were you saying that the forensic engineers employed to establish the causes of fires identified the causes and then decided that nothing should be done to address those causes?