Bonding requirements for conductive poles
Increasing load density at electric utilities has driven the trend toward larger distribution conductors and higher settings on overcurrent protective equipment. Not only are pickup values of feeder breakers and reclosers increasing, the protective curves are often slower to achieve coordination with downstream devices. Where there are larger conductors and slower protective settings you will often find more application of conductive distribution poles to carry the structural loads imposed by larger conductors. The potential problem arises with the possibility of the distribution pole becoming electrically detached from the distribution neutral. If a conductor makes direct contact with an unbonded pole the fault current is limited to a much lower value. Proper tripping of the faulted line section may not take place due to the combination of limited fault current and high pickup levels on the feeder protection equipment. This paper will examine typical feeder ground trip settings and the effect these will have on the sizing of bonding jumpers for conductive distribution poles. The effect of loss of bonding jumpers on contact voltage is addressed.