Are you inquiring about a back plate within an enclosure? If referring to BS 7671 I’m thinking Regulation 527.1.1: This reg aims to minimize the risk of fire spread. 416.2, focuses on preventing live contact and generally Regulation 522, external influences.

Edit: I think BS EN 61439-2, switchgear etc

- Andrew

Hi Andrew.

Many thanks for your reply. Yes correct I meant backplate within the enclosure. Does the material has to be steel? 

The reg that explicitly mandates the use of non-combustible materials is Regulation 421.1.201, which applies to domestic consumer units and similar switchgear assemblies. The requirement for non-combustible materials may vary depending on the specific installation context. Does the material have to be steel ? I don’t think so.

Does the material has to be steel?

It would be unusual for a standard to specify an exact material - usually they just give performance requirements (passing a glow wire test or flame retardant or non-combustible sort of thing) and leave it to the designer to pick something suitable for their particular application. In this case it sounds like it's not a BS 7671 matter, more likely an equipment standard (of which there are quite a few) or even down to the enclosure manufacturer's instructions to ensure compatibility with the enclosure.

   - Andy.

It can be insulating, or a suitable metal ... selection of this would be in line with the enclosure itself to prevent electrolytic  corrosion.

For controlgear or switchgear panels, these are out of scope of BS 7671, and BS EN IEC 61439 series is a common standard, perhaps with BS EN 60204-1 if it involves machinery as defined in the Supply of Machinery (Safety) Regulations.

If you mean the false back  inside an enclosure, that carries DIN rails, terminals and so on, that will be whatever the enclosure makers recommend - it could well be steel and in a steel box it usually is, but it could also be thick fibreglass or even Tufnol for certain situations where there are terminal bars to attach.

If you mean the back panel that switch gear or similar is screwed to, that historically has been plywood or chipboard in the UK, but can be almost anything - in  a sense the whole point is that the switchgear enclosure contains all the bits that might go bang or glow re in a fault. In really old installations you may encounter asbestos fibre boards in which case some care is needed.

As far as I know, no-one has made 'backless' boxes or fittings that are in effect an open square  that relies on the wall behind to complete the enclosure since the early 1980s - that would not be accepted today. (though if done well it can be fine, sadly it was not always done well... slightly live damp masonry anyone ?)

Mike.