High Voltage Tap

[steve66]

I need to feed a new transformer (12.47KV to 480V). I planned on having the electrician tap an exisitng underground 4/0 Copper loop in a manhole. From there, they would run about 200' of #2 XLP sheilded cable ran underground in a single conduit. (The entire run would be outdoors.)

I read through article 240 part IX, and I'm not sure how that relates to the tap rules (specifically 240.21(B)(5)). Can I use that tap rule, or do I have to protect the #2 wire at its point of supply.

Steve

 

[jtester]

I don't think 240.21 can apply unless it is blessed by the engineering supervision required in 240.100(A). 240.101(B) would also seem to support that belief.

Jim T

 

[kingpb]

I need to feed a new transformer (12.47KV to 480V). I planned on having the electrician tap an exisitng underground 4/0 Copper loop in a manhole. From there, they would run about 200' of #2 XLP sheilded cable ran underground in a single conduit. (The entire run would be outdoors.)

I read through article 240 part IX, and I'm not sure how that relates to the tap rules (specifically 240.21(B)(5)). Can I use that tap rule, or do I have to protect the #2 wire at its point of supply.

Steve

It would not be good practice to run a reduced sized cable to the transformer without protection for the cable. If a fault were to occur in the cable you would take out the entire 12.47kV circuit. Also, in a distribution circuit, it is typical that a loop feed would go to the transformer. in no cases is anything less then # 1/0 AWG usually onsidered.

The best approach is to put in an S&C type fused switch at your tap location, and run your feed to the transformer, preferrably as a loop.