To me, a CNC machine does not fall within the scope of 'household and similar use', therefore 553.1.201 does not apply. Using an interlocked industrial socket will provide comparable protection to shuttering.
They should be used for specific purposes, which in this case is the CNC machine but could similarly be for any other piece of workshop equipment.

Use the interlock version, RCD the circuit, crack on.

Apparently a small workshop in a shed or garage is not typical of 'domestic use' even if it is part of a household. (at the risk of a H and S failure, in my household I beg to differ. *)

Equally the other way one might stretch the household and similar to include domestic type equipment used in a domestic way but in a work setting - a hotel or a small office you would expect the vacuum cleaner and kettle to be used with 13A shuttered sockets, but really not the 3 phase industrial oven in the hotel kitchen.

In a case like that,  if you really had to, you could probably make a case for not being too worried about the shutters or the interlocks either if access was restricted to folk who know what they are doing.

After all the free ends of commando cables with un-shuttered sockets get draped around on caravan and camp sites and festivals and so on,  by folk I'd consider to be at best to be 'instructed' but not always that 'skilled' and that's a comparable, perhaps greater, level of risk given water and vehicles.

Interlocking and shuttering achieve a similar end - exposed metal is dead, live metal is not exposed. Its a pretty solid argument.

Mike.

* At my place I've got a few 16 amp ones on a 20A circuit for the lathe, welder and similar abnormal household appliances so perhaps I'm biased. Just don't put them on a 32A breaker with the 13A sockets.

I agree with pww235.

At some stage, machinery gets too big for "household" use. One might even say that is when a BS 1362 fuse is not man enough to withstand the start-up current.

Good point.

In some places BS 7671 uses the term "household and similar use" in others we see e.g.  at 411.3.4 [additional protection on luminaries] that it refers to domestic premises.

So for example the lighting circuit to a home workshop must protected by a 30mA RCD because it's in a dwelling. But a socket outlet in the workshop would have under the blue book wording of 411.3.3 have also have needed additional protection because it's physically in a dwelling, in the brown books wording of 411.3.3 I can omit it subject to risk assessment given it's not a space for the use of persons of capability BA1&2.

So I think there's a lot of weight in your comment here. 

One place I do often see 16A commandos in a domestic is caravan owners where they certainly are BA1&2. So I don't think that would enjoy a non-household application exemption. But I do think a departure from 553.1.201 should be reasonable if the socket is interlocked.

Good point.

In some places BS 7671 uses the term "household and similar use" in others we see e.g.  at 411.3.4 [additional protection on luminaries] that it refers to domestic premises.

So for example the lighting circuit to a home workshop must protected by a 30mA RCD because it's in a dwelling. But a socket outlet in the workshop would have under the blue book wording of 411.3.3 have also have needed additional protection because it's physically in a dwelling, in the brown books wording of 411.3.3 I can omit it subject to risk assessment given it's not a space for the use of persons of capability BA1&2.

So I think there's a lot of weight in your comment here. 

One place I do often see 16A commandos in a domestic is caravan owners where they certainly are BA1&2. So I don't think that would enjoy a non-household application exemption. But I do think a departure from 553.1.201 should be reasonable if the socket is interlocked.