Bonding Conduit At Utility Pole

[jtester]

Re: Bonding Conduit At Utility Pole

romeo

I read your most recent plea, and will try to shed a bit of light, and some sorrow, on your predicament.

The utility system is generally exempt from the NEC, and 250.66 probably does not apply in this case, to any bonding connection being made to the utility system. I say that because if the utility installed the conduit, clearly 250.66 couldn't apply at all. I think the district engineer is probably right.

The NESC, the utility Code, does require equipment frames, enclosures, and all nonenergized conducting components within reach, to be bonded to create a low impedance path for fault currents to flow and devices to operate. I don't have a current NESC in front of me, but that was quoted from 93 C 7 in the 1993.

Now the really bad news. If the utility transformer is a large kva unit, say 50 kva or up, it is possible that the cutout fuse will never blow at all. I have seen numerous secondaries laying on the ground, sparking away. Having an isolated piece of conduit bonded to a pole ground will do little to increase the fault current in a significant number of instances.

Not to dispair, If I was the utility engineer, and you asked me about the specific grounding requirements, you should check the section against the current NESC, I would at least think a little more before I offered answers. You should be able to make the NESC stick.
Jim T

 

[don_resqcapt19]

Re: Bonding Conduit At Utility Pole

Charlie,

If you are building a riser, you could be using a ? X 8" listed Copperweld rod and #6 Cu. running to it (that also is acceptable in the NESC).

This is permitted without a connection back to the transformer grounded conductor? What purpose would it serve? It would not reduce the touch potential to a safe level in the event of a fault to the riser.
Don

 

[highkvoltage]

Re: Bonding Conduit At Utility Pole

Charlie I apologize it's just a sore spot. Here we have two major utilities. We install the conductors to the base of the pole and they install the conduit and conductor up the pole (as long as utility owned). The other we install everything. In both cases they do all the connections.

 

[charlie]

Re: Bonding Conduit At Utility Pole

Don, the pole down ground is for the primary lightning protection and the tank of the transformer is also connected to the pole ground. The system neutral is jumpered to that same ground. Internally, the grounded end of the primary coil (H0) is connected to the tank.

The transformer secondary is brought out and the center point of the coil is grounded just below the bushing with a strap. The neutral is then taken from the secondary to the system neutral and then to the customer with the phase conductors.

The pole down ground is never used as a current carrying conductor if the transformer is connected correctly.

 

[highkvoltage]

Re: Bonding Conduit At Utility Pole

iwire. If what you and charlie post then most of the bonding done by the utility companies would fail allot. But they don't so they must be sized well enough to do there job. Also I assumed that he was talking about protecting the riser conduit not connecting the neutral from the service you are suppling to clear a fault there is a difference.

 

[don_resqcapt19]

Re: Bonding Conduit At Utility Pole

Charlie,
I misunderstood your post. I thought that you were saying that NESC permitted the use of a rod by itself to bond the metal riser pipe.
Don

 

[charlie]

Re: Bonding Conduit At Utility Pole

Highvoltage, for the grounding to fail a lot, there would have to be a lot of faults that would need to be cleared. That is not the case and the risers are usually very safe. My concern is the one fault that does happen and the failure of the bonding jumper to carry the fault current if the bonding conductor is even tied back to the transformer secondary neutral.