Fire resistant electrical "cupboard"

[Tim Watts]

I will be wiring lighting soon (hooray) and I have determined the way I
want to do it is bring all cables back to 4 sets of places in my dormer
- near the ouside where the cable trays run.

Each of these 4 locations will be a "cupboard" on the dormer uprights in
some semi dead space (where the ceiling is low) but usefully accessible.
I'm not a fan of junction boxes all over the place even if that's how
it's usually done.

I will stick SELV transformers here too.

There'll be a 5th cupboard housing a small sub-CU for all external
circuits (sheds, outside power, pond, whatever) fed by a distribution
circuit from an MCB in the main CU.


So it seems sensible to make these cupboards, which are mounted on
timber framing in a very wooden part of the house, a little more fire
resistant - just in case a SELV transformer goes ape, or a JB gets hot
from a fault.


I was thinking ply lined inside with 12mm plasterboard. Simple. All we
are talking about is if something gets hot, as in ignition point of
paper type hot and melts, that it is unlikely to set the enclosure alight.


Or is there a better/easier way? I've seen a reference to fire resistant
ply:

http://www.alsfordtimber.com/sheet-materials/plywood/fire-rated-plywood.html

What does that mean???

[Nightjar]

Wouldn't it be easier to use a ready made steel enclosure?

http://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/CM_Metal_Enclosures/index.html

--
Colin Bignell

[Tim Watts]

On 03/09/14 23:58, Nightjar <"cpb"@ insert my surname here> wrote:

> Wouldn't it be easier to use a ready made steel enclosure?
>
> http://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/CM_Metal_Enclosures/index.html

No -

I'd prefer something I can screw and cable clip to.

Most people would probably just use ply. I was wondering what I could do
for minimal extra effort to give it a bit of belt and braces :)

[harryagain]

"Tim Watts" <tw_u...@dionic.net> wrote in message
news:uialdb-...@squidward.local.dionic.net...

If you are that worried by fire as nightjar says, the way to go is steel
enclosure (and steel conduits and trunking)

Use all metalclad switch gear/switches/sockets etc

This is all properly designed stuff, unlike anything you cobble together
which might even be counter productive.

[Nightjar]

On 04/09/2014 06:40, Tim Watts wrote:
> On 03/09/14 23:58, Nightjar <"cpb"@ insert my surname here> wrote:
>
>> Wouldn't it be easier to use a ready made steel enclosure?
>>
>> http://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/CM_Metal_Enclosures/index.html
>>
>
> No -
>
> I'd prefer something I can screw and cable clip to.

A steel enclosure with a sheet of ply mounted inside?

> Most people would probably just use ply. I was wondering what I could do
> for minimal extra effort to give it a bit of belt and braces :)

The fire retardant ply you mentioned seems to limit the surface spread
of flame, rather than being completely fire proof. So lining with
plasterboard is probably better, as well as most likely cheaper, perhaps
with an ordinary ply or MDF sheet at the back as a mounting board. For a
one hour fire wall in one of my factories, we had to use two layers of
12mm plasterboard, with the joints not aligned. The doors might be a
problem unless you make those from metal.


--
Colin Bignell

[Tim Watts]

On 04/09/14 08:53, Nightjar <"cpb"@ insert my surname here> wrote:
>
> The fire retardant ply you mentioned seems to limit the surface spread
> of flame, rather than being completely fire proof. So lining with
> plasterboard is probably better, as well as most likely cheaper, perhaps
> with an ordinary ply or MDF sheet at the back as a mounting board. For a
> one hour fire wall in one of my factories, we had to use two layers of
> 12mm plasterboard, with the joints not aligned. The doors might be a
> problem unless you make those from metal.

Does sound like the way to go...

Doors - I was thinking to cover the inside in plasterboard too - at
least a big enough bit that will mostly go into the hole when they close.

Am less worried about the doors as they will not be in direct contact
with the equipment[1]. I was thinking more about the SELV PSUs going up
in smoke.

Right now, the only one I have is on an open rafter and open rafters are
really hard to set alight. But in an enclosed space with thinner ply, it
becomes slightly more credible that a bit of really really bad luck
could start a fire.

PB is cheap and quick so not much effort for a small but significant
gain I feel...


[1] I have a main CU mounted on ply. But it's a small bit on a brick
wall up against the ceiling - so even if the ply catches fire it cannot
really set anything else alight. It was mounting lots of equipment
especially with power electronics in against a load of structural timber
in the roof that got me thinking...

[Andrew]

On 03/09/2014 23:25, Tim Watts wrote:

Any sheet material that is decribed as class O should be suitable.

Here is chapter and verse from the people who know :-

http://www.british-gypsum.com/~/media/Files/British-Gypsum/FIRE-BOOK/FIRE-BOOK-Full-Publication.pdf

[John Rumm]

On 03/09/2014 23:25, Tim Watts wrote:

Probably just ply impregnated / treated with flame retardants. It does
not make it fire proof as such (it will still burn if exposed to one),
but ensures it won't in itself sustain a fire.

I would have though plasterboard would be a quicker and cheaper option.
You can clad it in ply for easy "nailability" and cocoon it in
fibreglass quilt if you are really annal ;-)


--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[Dave Plowman (News)]

In article <h4hkdb-...@squidward.local.dionic.net>,

Tim Watts <tw_u...@dionic.net> wrote:
> I was thinking ply lined inside with 12mm plasterboard. Simple. All we
> are talking about is if something gets hot, as in ignition point of
> paper type hot and melts, that it is unlikely to set the enclosure alight.

Plasterboard is probably the easiest way of providing a degree of fire
retardation. But being a cupboard, if you really think there is a danger
of this some form of alarm inside would be a good idea?

--
*i souport publik edekashun.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[Tim Watts]

On 04/09/14 11:11, John Rumm wrote:
> Probably just ply impregnated / treated with flame retardants. It does
> not make it fire proof as such (it will still burn if exposed to one),
> but ensures it won't in itself sustain a fire.
>
> I would have though plasterboard would be a quicker and cheaper option.
> You can clad it in ply for easy "nailability" and cocoon it in
> fibreglass quilt if you are really annal ;-)
>

Thanks John (and Andrew, Dave) - all interesting :)

[Nightjar]

On 04/09/2014 11:29, Dave Plowman (News) wrote:
> In article <h4hkdb-...@squidward.local.dionic.net>,
> Tim Watts <tw_u...@dionic.net> wrote:
>> I was thinking ply lined inside with 12mm plasterboard. Simple. All we
>> are talking about is if something gets hot, as in ignition point of
>> paper type hot and melts, that it is unlikely to set the enclosure alight.
>
>
> Plasterboard is probably the easiest way of providing a degree of fire
> retardation. But being a cupboard, if you really think there is a danger
> of this some form of alarm inside would be a good idea?
>

In the days of halon fire extinguishers, you used to be able to buy ones
with a length of plastic tube attached for use in small enclosed spaces.
If there was a fire, the tube would melt and release the gas, putting
the fire out.

--
Colin Bignell

[meow...@care2.com]

Don't forget ventilation needed - vent through a metal tube to stop fire spread. Food cans wired together perhaps?


NT

[Tim Watts]

On 04/09/14 15:41, meow...@care2.com wrote:

> Don't forget ventilation needed - vent through a metal tube to stop fire spread. Food cans wired together perhaps?

I don't think that will be a problem with maybe 1 PSU per cabinet -
should be able to lose heat by conduction.

But if it were, and intumescent vent is probably what I'd go for (self
seals in a fire).

Everything else is just wago terminals - this is just me being belt and
braces with a "what-if" something got hot because of a bad contact
(happens).

[Nightjar]

On 04/09/2014 16:10, Tim Watts wrote:
> On 04/09/14 15:41, meow...@care2.com wrote:
>
>> Don't forget ventilation needed - vent through a metal tube to stop
>> fire spread. Food cans wired together perhaps?
>
> I don't think that will be a problem with maybe 1 PSU per cabinet -
> should be able to lose heat by conduction.
>
> But if it were, and intumescent vent is probably what I'd go for (self

> seals in a fire)....

Use the Davy lamp principle and fit a fine mesh over the vent.


--
Colin Bignell

[Tim Watts]

That would also work - best not use ali mesh though :)

[meow...@care2.com]

On Thursday, September 4, 2014 4:10:15 PM UTC+1, Tim Watts wrote:
> On 04/09/14 15:41, meow...@care2.com wrote:

> > Don't forget ventilation needed - vent through a metal tube to stop fire spread. Food cans wired together perhaps?

> I don't think that will be a problem with maybe 1 PSU per cabinet -
> should be able to lose heat by conduction.

Would need to be a bigger cabinet then.

> But if it were, and intumescent vent is probably what I'd go for (self
> seals in a fire).

How quickly after fire escapes do they block?


NT

[spuorg...@gowanhill.com]

On Wednesday, September 3, 2014 11:25:53 PM UTC+1, Tim Watts wrote:
> Each of these 4 locations will be a "cupboard" on the dormer uprights in
> some semi dead space (where the ceiling is low) but usefully accessible.

You could use meter cupboards. Fireproof metal box, f/r backing board for fixing things to, and a neat(ish) door and frame with a cam-lock.

[Tim Watts]

Too deep. No this is more of an in place fabrication.

It'll start as a bit of board over the studwork - then get sides and a
door as renovation progresses.

I am settles with the idea of ply with a bit of PB stuck inside - all it
needs to do is cope with an item running hot if it goes horribly wrong.

I'm convince PB will do that OK :)

[The Natural Philosopher]

On 04/09/14 20:54, spuorg...@gowanhill.com wrote:

Build with masterboard/multiboard instead of plasterboard, though even
plasterboard has reasonable fire resistance

It skims and paints fine.

My experience of house fires is that hot gas and flame do the most
damage, not just a high temperature.

Serious fireproof is double metal or ceramic (brick?) with insulation
between. a bit OTT?




--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. – Erwin Knoll

[Tim Watts]

On 04/09/14 22:06, The Natural Philosopher wrote:
> On 04/09/14 20:54, spuorg...@gowanhill.com wrote:
>> On Wednesday, September 3, 2014 11:25:53 PM UTC+1, Tim Watts wrote:
>>> Each of these 4 locations will be a "cupboard" on the dormer uprights in
>>> some semi dead space (where the ceiling is low) but usefully accessible.
>>
>> You could use meter cupboards. Fireproof metal box, f/r backing board
>> for fixing things to, and a neat(ish) door and frame with a cam-lock.
>>
> Build with masterboard/multiboard instead of plasterboard, though even
> plasterboard has reasonable fire resistance

Thank you - I like the look of that:

http://www.travisperkins.co.uk/p/promat-masterboard-2440-x-1220-x-6mm/559000/3893471

> It skims and paints fine.
>
> My experience of house fires is that hot gas and flame do the most
> damage, not just a high temperature.

Indeed. One time in a million some PSU or JB will fry badly.

As I've taken the decision to keep my lighting JBs bundled in groups for
accessibility, one in each corner of the roof, it would make sense to
mount them on a bit of 18mm ply fixed to the dormer uprights.

From there it was a tiny step to make them part of a wall (the upper
parts of the wall will have celotex, so we have some "spare" depth going
anyway).

From there it was a tiny step to say "how can we take the 1:1000000
risk of a PSU gettind red hot and stop it being a risk to the timber
that surrounds it.

That's the trouble with "brownfield" development.

Greenfield - you just say "meh - this is the perfect layout, make it so".

Already developed - well your stuffed and make do.

Brownfield - contrains everywhere but just enough freedom to say "how
can we do this really nicely to be easy to maintain"...