Shielded versus not shielded cable.....?

[REVCAM_Bob]

I have some servo motors 1kw to hook up. The first time thru I used
shielded 15 awg 3 conductor for the motor drive hook up. Checking on prices
I find they now want $450 for 100 ft. of this wire. I know non shielded would
be way less, like probably $50 down at the electrical supply house.

I understand the necessity to shield the signal cables, but
is it necessary to shield the power cables?

Thanks again, you guys are great!

[gar]

070523-0734 EST USA

You need to study electrical circuits and fields.

What do you mean by shield? I assume electrostatic.

If you have a loop of wire and pass a current thru the wire what are the fields generated?

A conductive and non-magnetic shield around a pair of current carrying wires will have essentially no effect on the magnetic field associated with these wires at low frequencies. This type of shield will be classified as an electrostatic shield. Usually made of a copper braid or aluminum tape.

An electrostatic shield acts like one plate of a capacitor and the wires as the other plate or plates. Apply a voltage between the wires and the shield and you create an electric field between them. If the shield is fully around the wires and it is a 100% shield, then there is no electric field outside the shield due to a voltage between the internal wires and the shield.

There is no need to electrostatically shield your power wires other than to reduce noise coupled to other circuits. You should use twisted pairs to reduce magnetic coupling to other circuits. But this is complex for a multiphase motor. External coupling into the power circuits of your servos will be negligble relative to the voltage or currents in those circuits.

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