Steve,

This one is just a straight 4 wire 2 phase type of Animal. I have a drawing [somewhere] that shows where the common neutral would be connected to, which would make this one a 5 wire system. I seem to remember it coming from a common connection to separate coils, so maybe it's a tap from the jumper which connects the outside coils' ends [??].

In Article 220-22, you can see there's a reference to both 2 phase 3 and 5 wire systems with a common neutral. A 5 wire system would be like the one shown in this schematic - just this one is lacking the before mentioned common neutral tap, but that system would be from a full 3 transformer bank.
The 3 wire system would be from two transformers connected in the "TEE" method. On that arrangement, one end from each coil are connected together to form a common connector [which would be the choice for grounding - if the system is to be grounded].
That guy would be the common neutral for the 3 wire 2 phase system.

I'll post the TEE connection schematics also, hust for fun. Now those are some odd looking Animals!!

Hope everyone likes this schematic! You will probably never see any of these 2 phase systems in your lifetime - unless accidentally stumbling across them in really old areas of Chicago, Ill. or Long Beach, CA.
I have only seen one, which was the result of pulling a serious "Mission" [Linked Image] to find it.

Scott SET - bringing you large assortments of exotic Animals

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!