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...