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