3rd Amendment Metal Consumer Units - best practice advice please

[The General]

Afternoon all,

I've been doing domestic electrics for about 4yrs now and although I've done a few circuit alterations on metal clad consumer units I'd say that 95% of my work has been with plastic ones. I'm totally comfortable with replacing a consumer unit and all that it entails, but I've not done any commercial or industrial work - so I've had very little exposure to the actual 'physical experience' of working with metal boxes.

I'm hoping that those more experienced than me may be able to offer some help/advice on working with a metal clad box.

For instance, are there any handy little tools which I'm going to need to buy which will make life easier?
Are there any pearls of wisdom you can offer which might save me from a lot of cursing and swearing!??

I know that often, experience can only be gained by actually doing it, but I'm hoping that I might be able to learn from good examples before I end up making too many mistakes.

Thanks in advance for your input,

 

[telectrix]

i'm confused. where in hell can i buy blue mini trunking?

 

[shanky887614]

i'm confused. where in hell can i buy blue mini trunking?

looks like aa protective film like you get on daodo

 

[Deleted member 9648]

It's best not to use top entry knockouts,doing so will compromise the fire integrity of the enclosure.

 

[Midwest]

So why have the manufacturers put them there?

 

[Octopus]

It's best not to use top entry knockouts,doing so will compromise the fire integrity of the enclosure.

Hum.... 10's of thousands of older CU's have cable entry from above, tight against the ceiling and the cables are not long enough - so what do you do? Extend all the cables including the tails or fit the replacement unit tight against the ceiling and do all the connections up nice and tight?

I can just see the muppets at the IET banning top cable entries for the 18th ed.

 

[Midwest]

We've had this argument before. Reg 421.1.201 only specifies that the enclosure is made of non combustible materials (or in non combustible cupboard etc). It make no mention of it containing a fire, although I've seen someone post an IET link, banging on about good workmanship, sealing etc. This reg is ill conceived, and different bodies are interpreting the reg differently. Hopefully at some point we will get proper direction!

 

[telectrix]

We've had this argument before. Reg 421.1.201 only specifies that the enclosure is made of non combustible materials (or in non combustible cupboard etc). It make no mention of it containing a fire, although I've seen someone post an IET link, banging on about good workmanship, sealing etc. This reg is ill conceived, and different bodies are interpreting the reg differently. Hopefully at some point we will get proper direction!

direction is clear. it's all gone south. instead of addressing the cause of the problem ( poor terminals and sloppy, undertrained sparks' workmanship ), the IET is blundering about without any thought of the impact on our industry due to having to pass on increased costs to customers who want to pay as little as possible.

 

[Deleted member 9648]

Common sense. Whether the regulation is ill conceived or not...(it is)...common sense dictates that heat and flame rises, therefore it is good practice not to reduce the integrity of the top cover in order to comply with the requirements of the regulation. If the top cover K/O's are simply grommeted,covered with plastic trunking or boxed in with MDF as has been suggested then the enclosure is no longer fire containing. Of course other measures may be taken to reinstate the fire resistance of the top cover K/O's but IMO it is far better not to use the top K/O's.

 

[Deleted member 9648]

Hum.... 10's of thousands of older CU's have cable entry from above, tight against the ceiling and the cables are not long enough - so what do you do? Extend all the cables including the tails or fit the replacement unit tight against the ceiling and do all the connections up nice and tight?

I can just see the muppets at the IET banning top cable entries for the 18th ed.

You do what you have to do to comply with the requirements, if you open top K/O's without further measures then the enclosure will no longer contain a fire and will not comply with the requirements.

 

[Midwest]

You do what you have to do to comply with the requirements, if you open top K/O's without further measures then the enclosure will no longer contain a fire and will not comply with the requirements.

I can't see anywhere in reg 421.1.201 to 421.1.6 that mentions anything about fire containment?

 

[Richard Burns]

Midwest has made it clear, the requirements of the regulations do not refer in any way to fire containment only the material of which the consumer unit is made.
The fact that the IET then state that the intent of the regulation has a different purpose to the wording of the regulation is quite annoying as this could have been specified in the regulation.
I assume that there are different opinions in the IET and the opinion of those that write the regulations got priority, then the opinion of those who write the guidance notes introduce a new "requirement" that is not present in the regulations.

Best practice would indicate that we should follow all guidance available from the organisation writing the rules but it does get irritating when the guidance is inconsistent.
(it is a bit like GN7 having some additional "special locations" that apparently were not important enough to write into the regulations)

 

[rattlehead85]

The only solution to using the top knockouts which is a bit if a bodge would be to use blind grommets opened enough to accept the cables and then seal with Intumescent mastic or sealer. This can be bought at any reputable builders merchant. It aint the best solution no doubt but at least you have endeavoured to seal and fire proof the points of entry.

 

[Midwest]

I've been advised by Elecsa, that Amd 3 enclosures should be non combustible, replacing plastic with metal removes a source of fuel for a fire,If, for a minute, we suggested a metal CU was to contain a fire, the lid held in place (designed by some manufactures) by gravity, is not going to contain a fire. So I can't see any point, in trying to install a CU to contain a fire, with that design in place. As Richard says, it's irritating when guidance is inconsistent.

 

[rattlehead85]

Some of the regs really are ridiculous when the root of the problem is either caused by overloading or poor connections in the first place.

 

[Midwest]

The only solution to using the top knockouts which is a bit if a bodge would be to use blind grommets opened enough to accept the cables and then seal with Intumescent mastic or sealer. This can be bought at any reputable builders merchant. It aint the best solution no doubt but at least you have endeavoured to seal and fire proof the points of entry.

Why is it a bodge, and why do you need to seal them? I'm sounding a bit like Davesparks, sorry Dave no offence!