Primary cable 15KV

[newt]

I was at a job where utility allowed the electrician to use tape shielded cable on 12.7KV primary.The padmount was wired Y,Utility said if you ran a 1/0 along with tape shield It would be ok.(parralled conductors).My understanding is that you can not parr. two different type conductors and the tape shield is not ment to carry return neutral current.Will the tape shield termination be stressed from carrying current?

 

[Nick]

Re: Primary cable 15KV

The tape shield is there for just what it states...shielding. It is not meant and in most cases not rated to Carry fault or neutral current. Therefore you have to run separate equipment grounding conductors and neutral conductors with the circuit conductors. Yes it creates a parallel path and that is why its common practice to bond the shield and EGC at every termination and splice.
You stated the pad mount is wired Y. Is that primary, secondary or both? Is the 12.7KV the primary or secondary? Is there neutral current being generated somewhere? If so then concentric neutral cable is a better choice or a separate neutral (which can be 600V insulated).

 

[newt]

Re: Primary cable 15KV

The shield and the egc are the same,They are ment to cary fault current not neutral current.The termination on 15 KV shielded cable is a spring type connection,if you had current across it it would not be a good conection and I believe it would create stress leading to cable failure.The tape shield is sized to carry fault current only,similiar to egc on inside wiring it is much smaller than the grounded conductor.The code states that parr. conductors be the same size, and made of same type material ect. This application does not fit normal practise or does it?This installation is a Y-Y underground. My suggestion was to bond only one end of the tape shield breaking this extra path for neutral current but still giving the cable protection from dig ins ect.Any thoughts?