Grounded conductor (neutral) and earth voltage

[Bro8898]

A high voltage or any "hot" conductor making contact with the EP bonded items, or even earth will attempt to "flow" current back to the source.

It almost seems as if the ep bonded “area” and ep bonded objects are like an extension of the hot conductor if or when it comes in contact with something that’s ep bonded. And exactly what you said, if you were a bird on a wire that’s the only thing you would be touching.

EP bonding is why in the video even at 220kv the person was able to "bare hand" the live wire.

This may or may not be related, but does he really need the faraday suit? I’m sure from a ppe standpoint yes, but if he’s completely isolated from the ground on the scaffold it would seem that no further protection would be necessary.

Also, what potential is the technician at when he standing on the scaffold? Is he at zero volts, or “not” zero volts? I understand that once he bonds himself to the live wire he is at 220k and when he’s in contact with the ground he’s at 0, but what about once he stands on the isolated scaffold?

Thanks

 

[Fred B]

but does he really need the faraday suit?

Yes he really does need the faraday suit, the difference of potential from the right had to the left hand is enough to kill at 220kV. Clamping on the the conductor to the faraday suit puts him at the same potential across his body. Even with that, been told by someone that does this, that he still feels a static tingle all over as he attaches.
True the tower is likely totally isolated being fiberglass, but at that high voltage given the right circumstances it could flash over to earth. That is why the ground crew is moving it with non conductive ropes and remove themselves from contact when the lineman goes to attach himself to the conductor. You can even see the Arc when he hooks on or when he removes the feeder conductor off the main line even though the feeder if disconnected from any load.

 

[Bro8898]

the difference of potential from the right had to the left hand is enough to kill at 220kV

That is very interesting, especially this part. I’ve enjoyed learning about this. Appreciate you all so much.

 

[ActionDave]

My brother in law was a lineman. When he was with a rookie he would take his bonding lanyard and touch it to the power line and then pull it away slowly which would draw an arc about a foot long, he would then lean his head in a little bit and light a cigarette.

 

[LarryFine]

I made a Jacob's ladder with a 30kv neon transformer, and I have ignited stuff in the arc, but it has never occurred to me to stick my face within a few inches of it.

 

[kwired]

kwired said:
What is less obvious is when there is just a rise in voltage on the EGC of say 10 volts that is imposed on the tank.

What might cause this? Is it due to a short from a hot conductor to something that the egc is bonded to - in this case the breaker should trip right?

When it is a low voltage it is usually because of voltage drop on the grounded conductor.

Not just the neutral of the local 120/240 (or whatever service voltage is) but the POCO primary neutral is bonded to secondary neutral so any VD on that is imposed on your service neutral. You can have your main disconnects off and still measure this voltage on the grounded conductor at your facility. Disconnect the service neutral and it goes away. Obviously you can't disconnect that and still operate your facility without creating other problems though. The more unbalanced the primary is the more current the neutral will carry, the more potential there is for rise in voltage on the network of grounded conductors. Voltage drop on your service neutral does contribute as well.

 

[Bro8898]

Not just the neutral of the local 120/240 (or whatever service voltage is) but the POCO primary neutral is bonded to secondary neutral so any VD on that is imposed on your service neutral. You can have your main disconnects off and still measure this voltage on the grounded conductor at your facility.

Is this the same neutral to earth voltage that Zipse wrote about where the earth is a parallel path for neutral current to flow, in a normally functioning system? Most of the return current flows back on the neutral conductor but some flows through the earth proportional to the amount of resistance. I’m pretty sure Mike Holt had a video about it. I’ll try to find it. Does that sound like the same thing?

The more unbalanced the primary is the more current the neutral will carry, the more potential there is for rise in voltage on the network of grounded conductors. Voltage drop on your service neutral does contribute as well.

I appreciate you pointing this out. I might need to study this more and understand voltage drop on a conductor over long distances. Thanks for the response.

 

[kwired]

Is this the same neutral to earth voltage that Zipse wrote about where the earth is a parallel path for neutral current to flow, in a normally functioning system? Most of the return current flows back on the neutral conductor but some flows through the earth proportional to the amount of resistance. I’m pretty sure Mike Holt had a video about it. I’ll try to find it. Does that sound like the same thing?

I appreciate you pointing this out. I might need to study this more and understand voltage drop on a conductor over long distances. Thanks for the response.

The old saying that current takes the path of least resistance isn't entirely true. Current takes all possible paths, though the least resistance path carries the majority of the current.

Now also consider the fact that there is no perfect conductor and will be some resistance in our intended conductors as well. Rules for parallel resistors in a circuit still apply and if you calculate things out yes the bulk of current still flows in the intended conductor but there is current in other paths that is proportional to the resistance of those paths. Add some unintended resistance to the intended conductor either via a bad connection or due to basic voltage drop of an undersized conductor for the load it is carrying and you increase the amount of current that will end up flowing in those other unintended paths.

Utility systems with multi-grounded, current carrying neutrals set us up for these possibilities of current flowing where not desired. The more current the neutral is carrying the more voltage drop will occur across the conductor the more current will be flowing in alternate/incidental pathways.