As required, {HEAD ~ a separator} may be employed between {TAIL ~ the positive and negative electrodes} to prevent a short circuit 
employed between
As required , { HEAD ~ a separator } may be employed between { TAIL ~ the positive and negative electrodes } to prevent a short circuit
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH