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If we take a typical 2- or 3-wire power line how do I estimate its parasitic capacitance, resistance and inductance?

I tried to find this information at internet sites of wire manufactures but looks like nobody needs this information except me.

Mostly for power lines using cables with 3 copper single wire conductors with 1.5 or 2.5 mm2 section:

enter image description here

Line, protective ground and neutral wire respectively.

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Because it is useless, the impedance analysis is usefull for power lines from generator to the consumer, your cable or wire (which is totally diferent geometry) has little influence. – Marko Buršič Feb 29 at 12:43

The power line is only specified at the power frequency, which is usually 50 or 60 Hz. At such low frequencies, the inductance and capacitance of wiring in your house is irrelevant. The series resistance can matter, and is something you can just look up for whatever cable you are using. For the sizes of cable used in a house, skin effect is not a issue, so the DC resistance is close enough to the actual resistance at the power frequency.

Anything much above the power frequency is unspecified. There is little guarantee what the transformer making the low voltage from the local feeder looks like at high frequencies. Some will pass RF, others will block RF, for example.

The only way to know the impedance at high frequencies is to measure it where you care. You can feed a high frequency signal onto the power line thru a capacitor and see how much it gets attenuated. You measure the result thru another capacitor. These caps need to be able to withstand the full power voltage, and you have to filter off that voltage to see the small signal that would otherwise be tiny in relation.

I actually did this at 1 MHz many years ago in a dorm at college. I don't remember the exact answer, but it was in the 10s of Ohms range. However, that measurement is only valid for that place with the transformers they used, with whatever appliances others had plugged in, etc. You really have to measure your own case to know what you have.

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It's length dependent but if you need to estimate values per metre there are formulas on the internet that can help a lot. There are calculators too.

This basic one calculates capacitance based on AWG of wire and distance between them and for instance, with 3mm separation, 12 AWG wire has a capacitance of 0.3 pF per centimetre.

The formula is: -

enter image description here

It's never going to be an exact science given all the surrounding effects such as trunking etc but it should give you a start.

You can also find similar formulas and calculators for inductance. For resistance there are plenty of tables on the internet such as this one: -

enter image description here

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Just made some real-world measurements.

So I take the cable like this:

enter image description here

The specs are the following:

  • 7 conductors in each wire
  • each conductor 0.35mm in diameter
  • 0.67 sqmm wire section
  • 2mm wire with insulation outside diameter
  • length of the wire is 20.3 m

The RLC measurements are the following:

  • 14 uH for two wires (connected on the other end)
  • 1.4 Ohm for two wires
  • 1000 pF (two unconnected wires)

The wire was formed in a bundle with 27 cm average diameter (if it's meters).

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