Ground conductors

[WasGSOHM]

Is this a solution in search of a problem? Is it a solution at all?

Let’s say you want to find out which way power is flowing through a #14 ground conductor 100’ long, and it’s not Direct Current so you can’t check the current direction.

The power is supposed to go into the ground, right?

But suppose due of other current paths and PoCo, the power is coming out of the ground and into the load.

How can you tell?

As a last resort, put a 1/4 ohm resistor between the ground connection and the conductor. The ground current will be halved by this and hopefully this does not screw things up.

With respect to the ground rod connection, measure the voltage on other end of the resistor and
on the other end of the ground conductor (use an extension cord conductor or a long, skinny wire as a test lead).

If the power is going into the ground, this last voltage will be the higher one.

Otherwise the power is coming out, with the ungrounded end of the resistor having the higher AC voltage.

Depending on the ground conductor current, small voltage differences may be hard to resolve (I’ve never done this).

For a 10A ground conductor current the resistor needs to dissipate 25w. 60’ or so of #16 or less length of a smaller gauge will probably work for the resistor.
The wire will heat up and change resistance but this change may be negligible for a 1 or 2 second test duration.

A better choice is a length of Nichrome wire, if you can find it.

 

[infinity]

Can you specify what you mean by ground conductor?

 

[WasGSOHM]

Sorry, that post was nuts.

Pencil, paper and calculator tells me that the current (for a residence) in the thick wire that runs from the panel to a clamp on the nearest water pipe should be about 3 mA due to capacitive coupling between the hot wire and the ground wire in the Romex, assuming no load faults to ground.

The trick is to get the equivalent circuit correct.

It seems I measured this once somehow but I can't seem to confirm this value on the Web.

I think there is a way to measure currents this small through heavy conductors without using a millivoltmeter but I need to do more on this before I go shooting my mouth off.

 

[don_resqcapt19]

If the grounding electrode conductor is connected to a metal underground water pipe that is common to other buildings, it is a parallel path for the service neutral conductor. It is not uncommon to find 25% of the total neutral conductor current on the water pipe where there is a common metal underground water piping system.

 

[gar]

201220-1057 EST

My response to the first post is ---
The circuit under consideration is not sufficiently well defined.

A resistor or current measuring shunt has a voltage drop across it that is in phase and proportional to the current thru the resistor.

Suppose I have a DC circuit ( an AC circuit, for the purpose here, at an instant of time is the same as a DC circuit ) and a resistance (shunt ) to measure the circuit current. The voltage drop across that resistance including polarity, with no other information available, is insufficient to tell me the direction of power flow.

.

 

[hbiss]

Pencil, paper and calculator tells me that the current (for a residence) in the thick wire that runs from the panel to a clamp on the nearest water pipe should be about 3 mA due to capacitive coupling between the hot wire and the ground wire in the Romex, assuming no load faults to ground.

Better sharpen your pencil and replace the batteries in that calculator.

-Hal

 

[suemarkp]

One of your initial assumptions is wrong. "Ground" is not explicitly a source or a sink. It is just another conductive path (assuming the power system is connected to it). On an AC circuit, the current will flow into and then out of the earth as the current changes direction in the AC cycle. A DC system could be wired with current flowing into the earth or out of the earth (really, since it takes two connections for a conductor to function, one earth electrode will have current going in while the other earth electrode will have current leaving it if there are only 2 earth connections). On utility systems, earth currents are going every which way because every building with a ground electrode is passing neutral current to/from each utility pole ground electrode. The utility pole with the transformer feeding a given building should have the most current, but pole electrodes further away will also take some current but it is less since they have more wire resistance to go through to hit that source transformer.