The control voltage for {TAIL ~ the three wire configuration} is {HEAD ~ the voltage} between the two neutral points 
The control voltage for { TAIL ~ the three wire configuration } is { HEAD ~ the voltage } between the two neutral points
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH