a protective relay for producing a breaker opening command when {HEAD ~ a fault} occurs on {TAIL ~ a load side} of the breaker 
occurs on
a protective relay for producing a breaker opening command when { HEAD ~ a fault } occurs on { TAIL ~ a load side } of the breaker
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH