Rear Knockouts on Metal Units

[stmartin1991]

Hey All,

So query I have had for a long time is this:

Why supply special entry glands for a metal unit (top and bottom) to help stop the spread of fire/dust ingress/water/fingers etc

then go and have a bloody great big knockout at the back which only needs a grommet strip to protect the cables...

Am I missing something?

 

[Pretty Mouth]

Hey All,

So query I have had for a long time is this:

Why supply special entry glands for a metal unit (top and bottom) to help stop the spread of fire/dust ingress/water/fingers etc

then go and have a bloody great big knockout at the back which only needs a grommet strip to protect the cables...

Am I missing something?

There's no requirement for special glands for metal units, just regular ones will do. That's fire dealt with. IP4X doesn't prevent water or dust, so ignore those too. That leaves fingers, which can't get into the back of a board, because it's mounted on a wall.

 

[MJPD29]

I agree. Absolutley no requirement to use special glands or fire seal or anything like it.

 

[nicebutdim]

I agree. Absolutley no requirement to use special glands or fire seal or anything like it.

At least, not outside the world of certain Youtube sparks.

 

[Dustydazzler]

I thought we are supposed to fill the entire board with expanding foam ?

 

[Lister1987]

I query your understanding of regulation group 527.2, it talks about sealing cable enteries thatgo through building fabric; to me that is rear entry or top entry where the unit is butted right up to the ceiling/wall intersect, otherwise you've got a chimney effect, no?

 

[nicebutdim]

I thought we are supposed to fill the entire board with expanding foam ?

Seen a couple of them pretty much do just that. I'd have some choice words if trying to bring a cable through that stuff.

 

[Dustydazzler]

Empty a can of this inside the board and nobody getting in there

Hand Held Expanding Foam

• Quick setting• Expands up to 50 times it's original volume• Insulates• Sound deadens• Interior and exterior use Easy to use one part polyurethane expanding foam for general construction and home improvement. Bulk pack available (code 35897).

www.toolstation.com

 

[Dartlec]

I query your understanding of regulation group 527.2, it talks about sealing cable enteries thatgo through building fabric; to me that is rear entry or top entry where the unit is butted right up to the ceiling/wall intersect, otherwise you've got a chimney effect, no?

View attachment 91506

That says that any hole should be sealed to the same degree of fire-resistance (if any) of the construction affected.

Most consumer units are placed on stud walls built with non-fire rated plasterboard, or brick walls/dot&dab, which don't have a specific fire rating as far as I know?

So I'd not see that as being applicable, unless the surface it is mounted onto is fire rated - but I'm open to being corrected...

It's the same issue as people who suggest that all downlights have to be fire rated when they are going into a ceiling that has no fire rating requirements...

 

[Dartlec]

Empty a can of this inside the board and nobody getting in there

Hand Held Expanding Foam

• Quick setting• Expands up to 50 times it's original volume• Insulates• Sound deadens• Interior and exterior use Easy to use one part polyurethane expanding foam for general construction and home improvement. Bulk pack available (code 35897).

www.toolstation.com

with a side bonus that no connections can work loose if there's no space for movement taps forehead

 

[Pretty Mouth]

I query your understanding of regulation group 527.2, it talks about sealing cable enteries thatgo through building fabric; to me that is rear entry or top entry where the unit is butted right up to the ceiling/wall intersect, otherwise you've got a chimney effect, no?

View attachment 91506

No, it is I who queries YOUR understanding of etc

Think plastic dry lining boxes. If you can fit those into a stud wall without additional fire protection, then you can fit a consumer unit to the same wall with rear knockouts knocked out. Same deal with ceilings. Unless the wall/ceiling forms a fire barrier, no need for fancy intumescent sealant.

One exception to the above is where the joists above the ceiling are of the manufactured OSB I-beam type. I have been led to believe that these are destroyed very quickly by fire, and the plasterboard ceiling below is expected to protect them for a certain amount of time. In that case, fire rated downlights should be used. However, happy to be corrected on this point if anyone knows more about this.

 

[MJPD29]

I query your understanding of regulation group 527.2, it talks about sealing cable enteries thatgo through building fabric; to me that is rear entry or top entry where the unit is butted right up to the ceiling/wall intersect, otherwise you've got a chimney effect, no?

View attachment 91506

Hole should be sealed to the same degree of fire resistance (if any) of the construction affected. At no point does that regulation state or even imply that we should use fire retardant grommets or any form of fire seal on a consumer unit. It directs us to seal any holes in fire barriers that we create hole in by passing through. Unless you are directly mounting the board on a fire barrier and creating a large hole in it for cable entry then again the is absolutley no requirement to use fire seal or anything like it. Considering most consumer units are mounted on a piece of timber or something like it, it would be rather pointless to waste fire retardant sealant on a highly combustible surface.

 

[stmartin1991]

Hey Guys, thanks for all your insights, every day is a school day and I much appreciate all your help. (Except filling a CU with expanding foam XD )