Why doesn't the NEMA 6-50 plug go into the 14-50 receptacle?

[rszimm]

This is something I've always wondered about. When they came out with the 5-15 standard, they made it backwards compatible with the old 1-15 (i.e. a 1-15 plug will go into a 5-15 receptacle.). It would seem that a similar argument could be made for the 6-50 plug going into the 14-50 receptacle and just picking up the two hots and ground. I'm sure there's got to be some history behind this as it seems like it should be obvious to me...

 

[Jraef]

Maybe because a 6-50 is for single phase, and a 14-50 is for 3 phase...

 

[rszimm]

NEMA 14 is not three phase. (maybe you're thinking of 11, 15 and 18, which are 3 phase?). INEMA 14 is hot-hot-neutral-ground whereas NEMA 6 is hot-hot-ground. If they had designed the 6-50 plug "correctly" it could plug into the hot-hot-ground ports of the 14-50 receptacle. As it is, it's just a tad too narrow to fit...

 

[Jraef]

You're right, it's not 3 phase, it is 3 poles.