In {TAIL ~ a three wire connection} {HEAD ~ the clock pulses} are formed from the a.c. control voltage arising between the first and second neutral points 
In { TAIL ~ a three wire connection } { HEAD ~ the clock pulses } are formed from the a.c . control voltage arising between the first and second neutral points
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH