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Technical and scientific discussion of amps, cables and other topics.

I would not recommend video cable for AC.

It has neither the ampacity nor the robustness to serve reliably as an AC power cord.

I made a triaxial line cord using:

1. A teflon insulated #10AWG high strandcount single conductor wire as the core conductor. The choice of #10 was based on the desire to have ampacity of at least 20 amps. The insulation of this conductor is what I am using to maintain a dielectric strength with respect to the neutral.

2. The neutral conductor is made of 3 layers of hollow braid, each with the cross section equivalent to that of #12AWG. This is the first level of defense in the event the cord is physically compromised, as the neutral is by design, zero volts relative to safety ground. It is covered by two layers of tefzel heatshrink tubing.

This coaxial structure does not exhibit any external magnetic field as a result of current being drawn by the device..this is the most important aspect of the cable. It is also immune to external magnetic field induction hot to neutral as long as the external spacial gradient is not overly excessive, like bending the cable around the sharp edge of an E-core transformer. However, immunity to external fields is a simple consequence of the coaxial design, and was not the primary design feature.

3. The outer conductor is two layers of #12awg braid. This is the safety ground conductor. It is not a current carrying conductor, and serves only to provide NEC compliant bonding for the chassis. This is covered by one additional layer of heatshrink tubing.
Note that the conductor which serves as safety ground by design, cannot trap any flux being produced by the line cord. This is a result of two things..the hot/neutral system does not create external flux, and the coaxial positioning of the safety ground does not form a loop with respect to the hot/neutral system.

The ampacity limitation of this cord is a result of the inner #10awg being entirely enveloped within a second current carrying conductor. As such, it does not have the ampacity of a #10awg wire. My expectation is that it would suffice for 15 ampere and perhaps 20 ampere operation. However, verification of this would require pushing 20 amperes into and out of the cord in the manner in which it will be used, and monitoring the IR drop of the center conductor and neutral conductor seperately. Given the temperature coefficient of copper, it is a simple exercise to determine both conductors for temperature rise. The #10awg teflon insulation is rated higher temperature, tefzel is lower.

Cheers, John

ps. PTFE teflon is rated 260 degrees C, FEP teflon is rated at 200 C, and tefzel is rated 150 degrees C.(this from the belden master catalog, page 22.11.) The only concern I would have would be wires and plastics in the vicinity of this cable if it's external temperature were pushed to 150 C. I recommend an outer jacket rise maximum of 35 degrees C.

pps. For a coax or triax structure, one cannot use the simple current rating chart such as Belden's on page 22.4 of it's master catalog. The coax structure has a different heat transfer path from that of standard cables, so will be a tad more compromised that a simple 2 or 3 conductor cable.




Edits: 06/07/10 06/07/10 06/07/10

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  • I would not recommend video cable for AC. - jneutron 06:09:13 06/07/10 (0)

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