In {TAIL ~ a four wire connection} {HEAD ~ the clock pulses} are formed from the a.c. control voltage arising between the neutral point and the neutral line 
In
In { TAIL ~ a four wire connection } { HEAD ~ the clock pulses } are formed from the a.c . control voltage arising between the neutral point and the neutral line
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 OTH