A grounding question please

[MUTNAV]

Ok... It's possible I'm not expressing myself clearly.

My idea is that in a 240 Volt home power system, if there is an imbalance in loads between the two phases (although I guess it's technically called a single phase system.) The imbalance goes to the neutral, which is connected to the ground at the entry panel.

Shouldn't there be be some sort of current on the ground system, although most should go to the neutral back to the transformer? AND if there is another grounded system nearby, there should be a potential difference that could be exploited?

The second part of my "issues" (in a nice sense "issues") is that The N.E.C. says that the down-lead on the mast (which should have a lightning rod) can't be near the feed-line, which is just about impossible for most of us.

Maybe I'm just brain blocking the understanding of having to keep the feed-line and ground separated by a distance that isn't practical.

These two illustrations shows the general idea, a lightning down-conductor would be right next to the feedline on the mast (the TV looking one).






Thanks to Mike Holt for the illustrations.

Joel

 

[AC9KH]

Shouldn't there be be some sort of current on the ground system, although most should go to the neutral back to the transformer? AND if there is another grounded system nearby, there should be a potential difference that could be exploited?

No, because the ground does not complete the AC circuit back to the generator, transformer or inverter. The neutral does. Power will only flow on the ground in the event of a fault to ground.

The power system in question is indeed single phase, but technically split-phase because the two phases are 180° out of phase. A split-phase 240V electric motor only requires the two phases to it to run. No neutral or ground required. However, without the ground conductor to it, in the event of a ground fault in the motor the motor will become "hot" and you do not want to touch it. The neutral is only used for half-voltage (120V) loads that require a return path to the source.

The source, in this case, is not your service entrance panel or the powerplant. It is the secondary winding in your transformer that feeds your service panel. That winding has a center tap for the neutral.

And yes, there is differences in ground potential, but this is not "free" power. It is due to leaks in wiring, transformers, insulators etc.. It is a man-made phenomenon due to running too many wires all over tarnation with a national grid system that's only about 40% efficient due to I^2R losses and "leak" losses to ground.

 

[MUTNAV]

I take free power to mean anything I personally am not directly paying for, ie a crystal radio getting "free" power from radio waves.

Thanks
Joel

 

[AC9KH]

I take free power to mean anything I personally am not directly paying for, ie a crystal radio getting "free" power from radio waves.

You can string a wire under a HV powerline and get "free" power from it with capacitive coupling of the EMF off the line. But I don't know how practical it is. I would imagine if you put a voltage regulator downstream of the rectifier you could probably charge a battery with it.

Edit: I'll add that capacitive coupling with earth ground under HV powerlines "leaks" millions of dollars worth of electricity every year. It is an elaborate network of 60Hz radiators strung all over tarnation.

 

[MUTNAV]

You can string a wire under a HV powerline and get "free" power from it with capacitive coupling of the EMF off the line. But I don't know how practical it is. I would imagine if you put a voltage regulator downstream of the rectifier you could probably charge a battery with it.

Edit: I'll add that capacitive coupling with earth ground under HV powerlines "leaks" millions of dollars worth of electricity every year. It is an elaborate network of 60Hz radiators strung all over tarnation.

I've always wondered though, would the 60hz radiation be the best "target" (I NEVER intend on doing anything like this, this is more of a mental exercise), or would 180Hz be more appropriate, depending on location, since (I assume) it's 3 phase, and there may be overlapping fields?

Thanks
Joel

 

[AC9KH]

I've always wondered though, would the 60hz radiation be the best "target" (I NEVER intend on doing anything like this, this is more of a mental exercise), or would 180Hz be more appropriate, depending on location, since (I assume) it's 3 phase, and there may be overlapping fields?

I don't think so. It's still 60Hz on every phase, just that they're 120° separation. The simplest three-phase transmission line will have three conductors on the bottom, with a single ground conductor on top. You'll notice that ground conductor is connected to earth with ground rod at every pole and it's conduit'd up high enough so you can't touch it. And there's a sign on the pole that says it's really stupid to try to climb up the pole and touch that ground wire. That's because there's current on it. It's purpose is not to ground anything to it - it's there in the hope that if lightning strikes the line it will hit the ground wire and get shunted to earth instead of blowing transformers. This scheme only works about 20% of the time. Usually the EMF from the strike sends a big surge down the lines anyway and blows equipment that I work on all to smithereens before it burns the fuse links off on the pole pigs.

Or the other one that will cause me to fire up the Cat in my service truck and head out to fix stuff - somebody hits a power pole with a car and you get a phase-to-phase slap on the lines.

The service grounds you are concerned with are derived at each service entrance and they are in no way shape or form connected to those transmission line grounds.