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,

 

[charlie76]

Yes,
Section 3.8.1 consumer units and similar assemblies in domestic properties
[Description of regulation]
The intent of regulation 421.1.201 is, as far as is reasonably practicable, to contain any fire within the non-combustible enclosure or cabinet and to minimise the emission of flames to the surroundings or into conduits trunking or ducting.
It then goes on to say the enclosure should be a complete envelope and that the installer must seal all openings into the enclosure for cables ducting trunking that remain after cable installation.

There is an easier option albeit not cheap Wylex NMCE1 7x20mm + 3x32mm Membrane Fire Retardant Cable Entry Kit - Edwardes

 

[sam400]

I ve used mastic around cables entering knockouts on the top surface of a consumer unit to maintain the IP4X for years and I ve never realised it was a bodge?

I ll be swapping to the 30min fire rated stuff on metal boards after reading this thread.

cheers

 

[Midwest]

Yes,
Section 3.8.1 consumer units and similar assemblies in domestic properties
[Description of regulation]
The intent of regulation 421.1.201 is, as far as is reasonably practicable, to contain any fire within the non-combustible enclosure or cabinet and to minimise the emission of flames to the surroundings or into conduits trunking or ducting.
It then goes on to say the enclosure should be a complete envelope and that the installer must seal all openings into the enclosure for cables ducting trunking that remain after cable installation.

Hmmmm, don't suppose you could let me have the publication date for that, cos it conflicts with the guidance being given by 'Certsure' tech support.

 

[Richard Burns]

Oddly enough it was published in 2015, I think GN4 came out in January and I do not think that they have issued a corrected version.
This is what they say

 

[Richard Burns]

There is an easier option albeit not cheap Wylex NMCE1 7x20mm + 3x32mm Membrane Fire Retardant Cable Entry Kit - Edwardes

I think I would prefer to buy 10m of intumescent glazing tape and wrap it round / over the cable entries, cheaper, easier to do once complete and fulfills the spirit of the guidance, but possibly not the practicalities.

 

[Octopus]

Oddly enough it was published in 2015, I think GN4 came out in January and I do not think that they have issued a corrected version.
This is what they say
View attachment 30361

Hum..... most of us are fed up with having to buy the big book and OSG without feeling you HAVE to buy all the GN's too.

The IET needs to include ALL the salient information in BS7671 and not in additional books that some people seem unaware exist, let alone buy and read!

 

[Richard Burns]

I totally agree, BS7671 should provide all the information you need.
Expansion of the information in BS7671 can be provided separately, but not the introduction of new information.
One of the ones that springs to mind is the use of GN3 as an absolute requirement because there is a specific training course but this also introduces new information.

 

[Octopus]

I totally agree, BS7671 should provide all the information you need.
Expansion of the information in BS7671 can be provided separately, but not the introduction of new information.
One of the ones that springs to mind is the use of GN3 as an absolute requirement because there is a specific training course but this also introduces new information.

Theres no wonder the "stream" of questions seems endless on here - a lot are simply people who aren't sparks, but loads just need to buy more and read more.... which for some is out of the question!

 

[Andy78]

I'll be installing consumer units to the letter of the regs, no more no less. Sod the intention. I'll change my habits when they clear things up in the next edition and it's there in black and white.

 

[Electric Magic]

So if we are supposed to seal all openings does anyone have any good ideas about how to do that for rear cable entry where you've mounted the cu on a board with a gap at the back (or will this no longer be a sensible option?). A lot of cu's have a few very large rear cable entry points (so I'm not sure manufacturers have been considering this), do we just drill smaller ones and use grommets, or are there going to be a lot of messy installations out there because people use gallons of intumescent mastic instead ( also, might not that much mastic have an affect on the temperature of the cables?).

 

[Octopus]

So if we are supposed to seal all openings does anyone have any good ideas about how to do that for rear cable entry where you've mounted the cu on a board with a gap at the back (or will this no longer be a sensible option?). A lot of cu's have a few very large rear cable entry points (so I'm not sure manufacturers have been considering this), do we just drill smaller ones and use grommets, or are there going to be a lot of messy installations out there because people use gallons of intumescent mastic instead ( also, might not that much mastic have an affect on the temperature of the cables?).

I'm with Andy78 on this. Non combustible enclosure meets the regs.

 

[Midwest]

Oddly enough it was published in 2015, I think GN4 came out in January and I do not think that they have issued a corrected version.
This is what they say

Thanks Richard, I can feel another email coming on!

 

[Octopus]

Thanks Richard, I can feel another email coming on!

To or from who?

 

[Midwest]

So if we are supposed to seal all openings does anyone have any good ideas about how to do that for rear cable entry where you've mounted the cu on a board with a gap at the back (or will this no longer be a sensible option?). A lot of cu's have a few very large rear cable entry points (so I'm not sure manufacturers have been considering this), do we just drill smaller ones and use grommets, or are there going to be a lot of messy installations out there because people use gallons of intumescent mastic instead ( also, might not that much mastic have an affect on the temperature of the cables?).

Couldn't agree more, this thing about sealing around cable entry is just nonsense IMO. What about large unsealed gap left by the lid that covers the mcb's etc, do we have to seal that with mastic! If that's what the bodies want, why have we got to provide the fire containment system. You don't get fire rated down lights, and have to provide the intumescent seal.

 

[Andy78]

I'm with Andy78 on this. Non combustible enclosure meets the regs.

Cheers Murdoch.
To my mind it's an ill thought out and poorly implemented regulation. I don't have anything against fitting metal boards as such, especially now the prices have stabilised. But it was designed to combat fires resulting from poor installation and dodgy components, neither of which I feel apply to a fully qualified and experienced electrician as myself. If the intention was other than is stated then more fool the IET for not being able to agree on the wording of a paragraph to fulfil a clear intention.