MV cable terminations and shield grounds

[mull982]

When terminating 5kV cables what size wire should be used to tie the shields of the cables to the ground bus? Typically on installations I see the 3 shields from the termination kits on cables tied together with a split bolt or something and then have a wire or cable running from the split bolt to the ground bus. What size should this wire be, and does the NEC specify anything for this?

 

[weressl]

When terminating 5kV cables what size wire should be used to tie the shields of the cables to the ground bus? Typically on installations I see the 3 shields from the termination kits on cables tied together with a split bolt or something and then have a wire or cable running from the split bolt to the ground bus. What size should this wire be, and does the NEC specify anything for this?

You would want to maintain the equivalent cross section of the shields. That information is usually available from the manufacturer. If you have triple ground wires with a three condcutor cable, it is sufficient to connect the splice kits shield terminator to the ground conductor right at the breakpoint of the jacket and carry the three grounding conductors and connect it ti your ground-bus.

 

[dicklaxt]

That drain wire needn't be anything huge - the shield will pick up some inductive/capacitive current, but it won't be anything huge. You could get hold of the specs on the cable - look for capacitance of the cable per foot, multiply by feet of run, and then calculate the drain wire size for a purely capacitive load on the feeder at 60 Hz..

I don't know how to do the calcs with out some research but these PE's around here can probably help with that.

I have seen anything from #8 to #2 used on the shield grounds but think #2 is way overkill,maybe in the very high HV cable ranges

dick

 

[weressl]

That drain wire needn't be anything huge - the shield will pick up some inductive/capacitive current, but it won't be anything huge. You could get hold of the specs on the cable - look for capacitance of the cable per foot, multiply by feet of run, and then calculate the drain wire size for a purely capacitive load on the feeder at 60 Hz..

I don't know how to do the calcs with out some research but these PE's around here can probably help with that.

I have seen anything from #8 to #2 used on the shield grounds but think #2 is way overkill,maybe in the very high HV cable ranges

dick

The closest grounded conductive material to the conductor is the shield, so it will carry the ground fault current. If you were to undersize the grounding conductor it could potentially burn up before the shield and interrupt the ground-fault path causing more extensive damage and exposing people to danger for a longer period of time.