Is it safe to supply a single phase machine from a 3 phase 5 pin commando socket?

This question is the sort that will never get a simple answer.

The obvious answer is "yes, of course it is".  But nobody actually wants to stick their neck out and say it.

It's like asking "are polar bears white?"  Nobody is going to say "yes".  Instead, they will all try to find reasons why the answer is "no" or "maybe".

• Their fur isn't really white.  It's transparent, so it scatters the light.  It only looks white from a distance.  And looking at a polar bear from a long way away is probably the best place to be.
• They always look a bit off-white when I see them on TV.
• They won't be white if they have been swimming through an oil slick.  Or algae, or whatever.  So they are usually white.
• And so on...

This question is the sort that will never get a simple answer.

The obvious answer is "yes, of course it is".  But nobody actually wants to stick their neck out and say it.

It's like asking "are polar bears white?"  Nobody is going to say "yes".  Instead, they will all try to find reasons why the answer is "no" or "maybe".

• Their fur isn't really white.  It's transparent, so it scatters the light.  It only looks white from a distance.  And looking at a polar bear from a long way away is probably the best place to be.
• They always look a bit off-white when I see them on TV.
• They won't be white if they have been swimming through an oil slick.  Or algae, or whatever.  So they are usually white.
• And so on...

Simon Barker said:

The obvious answer is "yes, of course it is".  But nobody actually wants to stick their neck out and say it.

Give or take the issues of correct overcurrent protection (according to the manufacturer's requirements), whether the socket-outlet is RCD protected, and whether the machine requires additional cpc arrangements because of high protective conductor currents.

Everyone is entitled to their opinion on whether those issues are important for safety ... but a court might not agree with your decision if someone is exposed to danger that could have easily been prevented for the want of checking, and, if necessary, fitting/upgrading when the machine is put into / returned to service.