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