Heyyyy, More Power to Ya!
     

I’ve been writing this column for years and years, but there’s one kind of cable I have never talked about, one kind you use every day. I’d bet you touch these cable as much, or even more, than audio cables. What kind of cable is that? Power cords!

I am not going to talk about those super-high-end power cords, the ones with timed-delivery, multilayered, silver-plated oxygen-free conductors, jacketed with Unobtanium, made by virgins during a full moon. We’re told that those power cords make such a dramatic difference with your audio quality.

Of course, I won’t mention that 99.99 percent of the cable before that power cord, the stuff between your wall and the power plant, is simple solid copper wire. No, no, that last three feet makes such a difference!

I also won’t mention that the foil or braid shield in a power cord has virtually no effect at 60 Hz, or any harmonic up to 1,000 Hz. I also won’t mention that the alternating current delivered to the device is usually converted to DC by a power supply, so whatever difference there was is converted away. On the other hand, if you paid $800 for a power cord, it’d better sound different.

I would think that different power supplies would have more of an effect than different power cords.

So are there good and bad power cords? Sure there are. And there are lots of real reasons to choose between cords.

IEC-320

Your first choice is to buy a pre-made power cord or make your own.

In Europe, it is now illegal to make your own power cord. Guess too many people electrocuted themselves with the 240 volts over there. In Europe you can now only buy pre-made cables. And pre-made molded end power cords are the most common on this side of the world as well, not the least because they come “free” with the gear you buy.

On most equipment made now, the power input is one worldwide standard connector called an IEC-320. It’s got three flat pins in a “rectangular” jack. Unfortunately, for the do-it-yourselfer, this is a hard connector to install. The other end, the standard three-pin power plug, is much easier to install.

Of course, you know that larger gage will handle higher current. So how big do you need? 18 AWG? 16 AWG? 14? 12? 10? Bigger? The accompanying table shows you the current these different gage size can carry.

So what is the limit on current? It’s not the conductor. Copper won’t melt until 1,085 degrees C. As Ohm’s Law and Watt’s Law say, P = I2R. If you have a given amount of current (I), then more resistance (R) means more of this electrical energy will be converted to heat (P). Smaller wires have more resistance than bigger wires. So the limit on a power cord is the melting point of the plastic around the conductors. Note that the chart above lists the wire’s gage and current by temperature.





GaugeAdd Ambient Temperature to
10°C35°C
185 amps8 amps
166.5 amps10.2 amps
148 amps17 amps
1210.2 amps22 amps
1017 amps29 amps


First, you have to know the ambient temperature where your cord is being used. A power cord in Antarctica can handle more current than one in the Sahara Desert because the colder one can absorb more heat generated before it affects the jacket.

So the second thing you need to know is the melting point of the jacket material. Sometimes this is actually printed on the jacket. Common temperatures are 60, 75, 90 or 105 degrees C. If it’s not printed on the cord, you can look it up in the manufacturer’s catalog or Web site. So now you can see one of the reasons why they have higher temperature plastics.

I am worried that some high-end consumer company will read this and realize that a Teflon-insulated and -jacketed power cord would handle higher current. Teflon melts at higher temperatures than most other plastics, some Teflon formulations as high as 260 degrees C. That would make one stiff and expensive power cord. Of course, just putting in a bigger wire would also handle more current.

One word of caution to the do-it-yourselfer. There’s an obvious liability with power cords that is way more lethal that regular audio and video wiring. Many “companies” (guys in their garages) who make those Unobtainium made-by-hand cords may have overlooked this. There are safety standards for power cords. And there are independent test labs, such as UL (Underwriter’s Labs) that do third-party testing to verify safety. Many of those “custom” guys ignore all this. You be the judge on the wisdom of this approach.

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Comment List:

Steve Lampen said "Of course, I won’t mention that 99.99 percent of the cable before that power cord, the stuff between your wall and the power plant, is simple solid copper wire." But that forgets about the high voltage distribution lines that are mostly aluminum (with steel cores).
By Anonymous on 8/20/2010

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