Metal enclosure with 3rd amendment.

[bernardgreen]

If memory serves me right I recall from decades ago fuse boxes had to be made out of non conductive material ( mostly wood ) to prevent people getting shocks from them in the event of insulation failure.

There are fires started by a CU bursting into flames so they should be made from non combustible material but to make them conductive is in my opinion a back ward step.

If there is a problem with the electrics the first place a person will go to is the consumer unit. If the earth connection to the case of the consumer unit has failed as well as the other fault the case of the consumer unit could be lethal to the touch if the person has a good second point of contact to ground.

 

[JohnW2]

If memory serves me right I recall from decades ago fuse boxes had to be made out of non conductive material ( mostly wood ) to prevent people getting shocks from them in the event of insulation failure.

If that were ever true, it must have been very many decades ago. I was brought up with cast iron fuse boxes, which were in situ when we moved into the house in the mid-50s, and fairly obviously had been there for a few decades prior to that.

There are fires started by a CU bursting into flames so they should be made from non combustible material but to make them conductive is in my opinion a back ward step.

As I have implied, I agree - but who am I to have an opinion?! However, what I can say (and have said) is that I would personally be less comfortable with a metal CU (whether its earth connection were present or 'failed') - and, for that reason, will certainly do all I can to stick with ('non-combustible') plastic ones for evermore!

Don't forget that Amd3 (hence JPEL/64) have not said that CUs have to be metal - despite what a lot of people seem to think - and, as I've said, I have a sneaky suspicion that there will be far less of a move to metal CUs than many people seem to be assuming.

Kind Regards, John

 

[bernardgreen]

Yes it was many decades ago. The 1950's.

Yes there were cast iron cut outs and metal boxes with switches with mechanical interlocks. The switch had to be turned OFF before the cover over the fuse could be removed and without the cover back in place the switch could not be switched back ON. ( that could be defeated ).

But also the earth was often a separate connection via the network ( often the lead sheave of the supply cable ) to a true ground ( and not shared with the Neutral conductor ) and backed up by the metallic water supply network.

It does seem to be that over past decades almost all the "improvements" have had a cost cutting component. The expensive VOELB was only introduced because the lower cost earth systems could no longer be guaranteed to carry enough current to take out a fuse when there was a Live - CPC fault.

Food for thought ?

 

[JohnW2]

Yes it was many decades ago. The 1950's.

As I said, I think it would have been long before the 1950s when wooden fuse boxes were last installed!

Yes there were cast iron cut outs and metal boxes with switches with mechanical interlocks. The switch had to be turned OFF before the cover over the fuse could be removed and without the cover back in place the switch could not be switched back ON. ( that could be defeated ).

Yes, those are what I was 'brought up on', and they were well established long before the 50s. Once (switched off and) opened, there were often exposed live parts.

But also the earth was often a separate connection via the network ( often the lead sheave of the supply cable ) to a true ground ( and not shared with the Neutral conductor ) and backed up by the metallic water supply network.

Well, in my case it was long after the 50s that I first met a TN earth; like many others, I was brought up on TT.

It does seem to be that over past decades almost all the "improvements" have had a cost cutting component. The expensive VOELB was only introduced because the lower cost earth systems could no longer be guaranteed to carry enough current to take out a fuse when there was a Live - CPC fault.

I'm not sure what you mean by 'lower cost earthing systems'. On the face of it, it sounds as if you are probably talking of TN-C-S - but that surely is the least likely earthing system to 'not be able to carry enough current to take out a fuse' ... so I'm a bit confused!

Kind Regards, John

 

[flameport]

It does seem to be that over past decades almost all the "improvements" have had a cost cutting component.

Definitely.

Consumer units with single screws for wires instead of 2
Steel screws instead of brass
Screws made of weak metal which shear off when tightening.
Busbars which fall out on the floor and can be fitted incorrectly.
Plastic cases so thin, they inevitably bend and distort regardless of how they are fixed to the wall.
Blank plates for unused ways which clip into the front panel, and can be removed easily without tools.

This is what the regulation actually says:

Untitled

• flameport
• 25 Jan 2015
• 2

 

[ban-all-sheds]

Do they define "non-combustible"?

Nope, no definition, other than a requirement that it complies with BS EN 61439-3 (does that define it?)

Apparently not:

... shall comply with BS EN 61439-3 and shall ...

 

[JohnW2]

Do they define "non-combustible"?

Nope, no definition, other than a requirement that it complies with BS EN 61439-3 (does that define it?)

Apparently not:

... shall comply with BS EN 61439-3 and shall ...

Yes, I noted that, but I have very limited faith in what one can conclude from the exact wording of the regs. For example, it could be that the "and" should have been something like "in particular".

If the Standard does not define what is regarded as "non-combustible", then the whole thing is totally ridiculous, since there would be no way of determining whether or not any particular CU complied with the new regulation, unless it was made out of ferrous metal!

Perhaps stillp will be able to tell us what, if anything, the Standard has to say about this.

Kind Regards, John

 

[JohnW2]

Do they define "non-combustible"?

Nope, no definition, other than a requirement that it complies with BS EN 61439-3 (does that define it?)

Apparently not: .....

In the Doepke document which was recently brought to our attention (click here), in supporting/justifying the compliance of their CUs with Amd3, they say:

Independent glow wire tests completed as per BSEN 61439-3 2012 10.2.3.2
Verification of resistance of insulating materials to abnormal heat and fire due to internal electric effects by
Test to IEC60695-2-11: Materials used for retention of current carrying parts tested at 960°C .
Other parts not current carrying tested at 650°C
Issued by KA Testing Nottingham- TRN 41951/4/5/6

This rather seems to imply that BS EN 61439-3 and/or IEC 60695-2-11 may specify tests of 'non-combustibility'.

Kind Regards, John

 

[mfarrow]

In the Doepke document which was recently brought to our attention (click here), in supporting/justifying the compliance of their CUs with Amd3, they say:

Independent glow wire tests completed as per BSEN 61439-3 2012 10.2.3.2
Verification of resistance of insulating materials to abnormal heat and fire due to internal electric effects by
Test to IEC60695-2-11: Materials used for retention of current carrying parts tested at 960°C .
Other parts not current carrying tested at 650°C
Issued by KA Testing Nottingham- TRN 41951/4/5/6

This rather seems to imply that BS EN 61439-3 and/or IEC 60695-2-11 may specify tests of 'non-combustibility'.

Kind Regards, John

Indeed, there are, and I think I remember reading these through the discussion regarding the DPC.

I really can't understand therefore the knee-jerk reaction of the likes of Hager to reinvent their CUs. Material changes are most probably easier to accomplish, unless they really think their Design range of boxes looks better than the old ones, which I'd doubt!

 

[JohnW2]

Indeed, there are, and I think I remember reading these through the discussion regarding the DPC. ... I really can't understand therefore the knee-jerk reaction of the likes of Hager to reinvent their CUs. Material changes are most probably easier to accomplish, unless they really think their Design range of boxes looks better than the old ones, which I'd doubt!

Quite so. As I've said, I rather suspect that any manufacturers who have already 'knee-jerked' into plans to 'drop' plastic CUs may well find themselves having to do some serious back-peddling if they don't want to lose most of their domestic market share!

Kind Regards, John

 

[bernardgreen]

In the Doepke document which was recently brought to our attention

*When using any Metal enclosure there is an increased risk of electrocution from indirect contact with an exposed conductive part under single fault conditions.

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.

Unless they are considering the case when the earthed metal case is the second point of contact for a person being shocked by a fault not involving the CU case.

 

[stillp]

Here's an extract from the relevant standard. The product standard is 61439-3, but it refers to 61439-1 for tests to validate resistance to abnormal heat and fire. Sorry about the formatting, it doesn't copy well.

BS EN 61439-1:2009

The resistance of insulating materials to normal heat shall be verified in accordance with IEC 60695-10-2. The test shall be carried out on one representative sample of each of the insulating materials taken from enclosures, barriers and other insulating parts.
The temperature of the tip of the glow-wire shall be as follows:
– 960 °C for parts necessary to retain current-carrying parts in position;
– 850 °C for enclosures intended for mounting in hollow walls;
– 650 °C for all other parts, including parts necessary to retain the protective conductor.
The specimen is considered to have withstood the glow-wire test if
– there is no visible flame and no sustained glowing, or if flames and glowing of the specimen extinguish within 30 s after removal of the glow-wire.

 

[JohnW2]

*When using any Metal enclosure there is an increased risk of electrocution from indirect contact with an exposed conductive part under single fault conditions.

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. ... Unless they are considering the case when the earthed metal case is the second point of contact for a person being shocked by a fault not involving the CU case.

I have to say that I interpreted it as per your "Unless...." - i.e. just as with a (otherwise floating) metal bath or whatever if one 'unnecessarily' increases the amount of earthed metal around, one increases the risk of electric shock in the event of a single fault (in something else) - not to mention (again!) the increased risk to a person 'dabbling' inside a CU built out of earthed metal.

Kind Regards, John

 

[JohnW2]

Here's an extract from the relevant standard. The product standard is 61439-3, but it refers to 61439-1 for tests to validate resistance to abnormal heat and fire. Sorry about the formatting, it doesn't copy well.

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

If so, as BAS asked (and I had previously wondered) what do you think the new reg means when it says that a CU "... shall comply with BS EN 61439-3 and shall have their enclosure manufactured from non-combustible material..."?? Would it be possible for a CU not manufactured out of 'non-combustible material' to be compliant with 61439-3?

Kind Regards, John

 

[stillp]

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. However I can't remember where, and I'm not about to search through the several hundred standards I keep.
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.