Inductance in adjacent wires

[SAF]

210406-2342 EST

SAF:

I not going to answer your question because of the forum rules. However, I will make some additional comments.

First, most electricians do not have a good understanding of basic electrical circuit theory, and therefore, don't think of many different solutions. Thus, they may not be real useful in solving your problem.

I ran an experiment with a 30 ft cable, applied 120 V to a lead, and measured the capacitively coupled voltage to another wire in the cable. With just a Fluke 27 as the load ( 10 meg input resistance ) I read 0.29 V ( 29 millivolts ). Shunt loading with 15 k ohms across the meter input the reading dropped to 0.003 V ( 3 millivolts ). 15 k is in the ballpark of a typical 120 V solid-state input.

Your problem can be solved with the correct help.

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Gar, your note is too technical for my limited electrical backrground to be sure of what it implies; I am curious whether your testing supports the stray voltage readings we are getting in the two unenergized float lines that run along with the energised one, or cast doubt on it.... can you provide that interpretation without breaking the rules? (Or maybe I shouldn't ask, now that we think we have found the solution using the resistors).

 

[gar]

210412-2034 EDT

SAF:

If you take two wires, more or less in physical parallel, that are close to one another, then you can typical measure a capacitance of about 10 to 30 pfd per foot. The captive reactance (impedance) Xc = 1/(2*Pi*f*C). At 60 Hz a 20 pfd capacitor has a reactance of 130 megohms. Twenty ft will be about 6.5 megohms. A high impedance load like a Fluke 27 is about 10 megohms with some parallel capacitance. So an unloaded isolated wire adjacent to a wire at 120 V 60 Hz with a 10 megohm meter connected to the floating wire might read about 1/2 the hot wire's voltage.

A shunt load resistor will greatly reduce this capacitively coupled voltage.

If I put an electrostatic shield around the floating wire, and connect the shield to the low voltage side of the 120 V source, then I can get very near 0 V capacitively coupled from the hot wire to the floating wire.

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