As specified in IEC 60974-1, 10.4."
and what I quoted before were the words from 60974.1. So for industrial _or_ layman use they both must have plugs able to supply Iieff.
And yes you are now splitting hairs if you say that your industrial sized welder isn't industrial because you use it in a domestic setting,
ERAC rules specifically state that is not so. In fact they have a certification database (which I haven't had a look through yet) which I suspect will show the plug size required and I also suspect it won't be 15A on welders with Iieff greater than 15A.
SWK