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