I have the same refractor bucket here....we have some of those NEMA heads in service around here....I hope to have a fixture in my nema head collection one day!
The Ballast on this Nema Hangs from the Top of the Head Right?.....thats my Favorite Style...some others have the Ballast Mounted from the Bottom with the characteristic Buldges in the Bottom Sides of the Head.
I have one similar by Thomas and Betts which was kindly sent to me by a fellow US collector, due to the ballast had burnt out, however as we don't have these type of lights in the UK I have had to put a 150w HPS ballast in mine as we don't have 175w Mercury Lamps or Ballasts, however I can use a 175w mercury on a UK 150w HPs Ballast as they are near enough Electrically Identical.
I have one similar by Thomas and Betts which was kindly sent to me by a fellow US collector, due to the ballast had burnt out, however as we don't have these type of lights in the UK I have had to put a 150w HPS ballast in mine as we don't have 175w Mercury Lamps or Ballasts, however I can use a 175w mercury on a UK 150w HPs Ballast as they are near enough Electrically Identical.
All the Best
Colin