Ian:
yes that is a nema " 14-30" that serves the dryer in this case, the connecter you see is actually a missing K/O that got plugged.. you will notice at the top of that box the romex is not installed into the connector properly.
Just a note those "new" dryer and stove plugs are a pain to work with, the mounting screws tend to slip out of the 'keyway" that retains the receptacle to the box sometimes... Thety are made by Leviton and come in black and white.. But really who cares its normally behind a stove or dryer anyway, and if you do see it in a laundry room, who really cares anyway right?
Pauluk:
That receptacle is mounted on a 4 11/16" box
