The scans from the catalog don't show it very well, but yes, the earth pin is slightly smaller in the vertical dimension, and it also has a horizontal notch at the top to make it slightly T-shaped.
The "non standard" heading says it all though. I'm not aware of any other manufacturer that makes plugs compatible with these outlets (although this being well-respected MK it may be that somebody will decide to do so). As I said above though, these are marketed mainly for "clean earth" (isolated ground) usage, and would normally be wired for standard 220/240V rather than 110V.
Other manufacturers have also devised non-standard fittings for such use. Here's Crabtree's version:
It may be that a particular facility in Ireland has adopted the MK non-standard plugs for 110/120V, but I think you would need to inquire on an individual basis. There may well be other places (I'm guessing we're talking about the numerous computer plants that have sprung up in the R.o.I. in recent years) that just use normal NEMA American plugs for any 120V gear. Both MK and Crabtree make outlets which will take NEMA 5-15 plugs but which are designed to fit British mounting boxes (I think they're aimed mainly at the Middle Eastern market where 127V supplies are used in some areas with British-style switches, boxes, etc.).
I'm not aware of any U.S. suppliers of MK equipment, but it might be worth contacting MK's head office to inquire. Failing that, you could order whatever you need and have them ship it directly to you from England.
Caradon MK Electric Ltd.
The Arnold Centre
Essex, SS14 3EA
Tel. +44 1268 563307
Fax +44 1268 563483
(These are "customer enquiry" which seem the most likely numbers!)
For what it's worth, they have a website: www.mkelectric.co.uk
[This message has been edited by pauluk (edited 08-18-2002).]