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Power cords

BlueTalon

BlueTalon

Happy Cynic
Supporting Member
Mar 20, 2011
8,776
15,392
Inland Northwest
Disclosures
Endorsing Artist: Turnstyle Switch
#1
There has been some discussion here recently about 1/4" plugs and their ability to handle power, and so power handling was on my mind today as I was cleaning gaffer tape adhesive gunk off of some of my power cords.

I started looking at the information printed on the side of the cable, and I was startled to learn that the outward diameter of the cable was not a reliable indicator of the power handling! I'm sure that's old news for a lot of you, but it took me by surprise, and there might be a few of you that didn't already know this.
power cords.jpg

The conductors in those cords are, from left to right, 18AWG, 16AWG, 14AWG, 14AWG, and 18AWG.

I can't count the number of times I plugged my amp in using a wider cord because I thought it would handle the power better. Granted, my amp doesn't draw enough to stress the thinner conductors, and all my lights have LEDs, so I was never putting myself in danger by doing this, but my ignorance could have had consequences if I had equipment that drew more power.
 
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#5
I like the 12AWG cords I got. However, I don't like them because of the larger gauge wire. I like them because they have these ultra-durable, but super-supple rubber jackets and coil wonderfully.

I cringe when I see folks packing away those PC cables and bending and wrapping them in all sorts of directions before they toss them in a bag.

I don't like plugging into power-bars on stage and sometimes the nearest quad box is more than 6 feet away from me. So if I'm going to carry a longer power cable, I'd like it to have that tougher jacket that still coils easily for packing and these just happened to be 12AWG. I learned that doing PA work. One of them is a Planet Waves power cord, and the others were made for me by a PA system supply company. 12 was what they had on hand of for the lengths I wanted to own. I just make sure that the full weight of the cable is not bearing down on the IEC jack on the back of the amplifier.
 
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#14
Reciting my electrical engineering mantra:
Using an oversized (vs. factory-supplied cable) power cable has no benefit. In fact, the weight and stiffness of too-large can damage your amp by causing severe strain at the mains connector.

The 18 AWG IEC cable typically supplied with amps has ample ampacity. It’s capable of handling several times the amplifier’s maximum current draw.

OK, that’s enough spitting into the wind for this week.
 
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#16
BlueTalon said:
Could you elaborate on this a little bit, please? I don't know what that means.
Click to expand...
It actually wasn't a joke.

For audio signals, the electrical demand on the AC power source is not the rated audio power of the amp because the amp does not reproduce this continuously at 100% duty cycle. The audio signal it typically 12.5% duty cycle (that's what the test labs must use as a standardized value) though some of us design around higher duty cycles (I typically use between 30% and 40% depending on the product and how it's intended to be used). The rated audio power multiplied by the duty cycle represents the average power that the amplifier produces with an audio signal.

The calculation that the safety agency test lab uses for rated power draw is:

(rated audio power x duty cycle) / (power amp + power supply efficiency)

For an 800 watt RMS rated amp, using the test lab standard duty cycle, average total efficiency of 80%:
(800W x .125) / 0.8 = 125 watts average AC power draw, which is approximately 1 amp at 120V

Now, if you were to double the duty cycle (driving the amp into mild clipping), you would have the following:
(800W x .250) / 0.8 = 250 watts average AC power draw, which is approximately 2 amp at 120V

The power supply, because of the way it works to store energy and work with the signal's duty cycle, serves to average the AC power draw.

By this point, it should be obvious why an 18 gauge power cord (rated at 10 amps continuous) is WAY more than adequate for this application. In fact, because of the wide margin, I seriously doubt ANYBODY could tell the difference with an amp that uses the above data (like the Subway amps).
 
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#18
I've seen discussion about not only the power cabling, but also the head-to-cab amp cable. Some here have attested quite vigorously that a 1/4" speaker cable can't handle more than, say, 400 or 500W. The specifics escape me, but it was in that area. And the informed conclusions were that the 1/4" cable connection have absolutely zero problem handling any market-available juice.

As an example, my Quilter BB800 has 1/4" out, and it's rated at 800W RMS at 4 ohms. And Mr. Pat Quilter knows that daisychaining cabs is common, so would not have included a 1/4" output if it posed a danger. This, however, is a combo of tangent and red herring. Also, audio cables, not really measured by gauge, are waaaay higher in estimated gauge (meaning way thinner), and they're not safe for high-wattage transmission. There's a point where copper thickness matters, but it's not at 12 or 14 gauge. It'd be like, what, 40 gauge? 60 gauge?

As for the original thing, power cords... I look at it like this. An 18-ga extension cord at Kroger or Food Lion or Piggly Wiggly or wherever may not be of the same build quality as something APC puts out. But a known reputable maker of power cords will have cords rated for uses faaaaar outstripping us running our bass amp setup. Like, they're looking at generators and pro light rigs and extra-output boat motors and things. 18-gauge.

Whoever actually needs 12-gauge copper connections is probably also hardwiring conduit. Bass & guitar amps and a space heater all at once. 30 amps at 120V kind of thing.
 
#19
Real Soon said:
I've seen discussion about not only the power cabling, but also the head-to-cab amp cable. Some here have attested quite vigorously that a 1/4" speaker cable can't handle more than, say, 400 or 500W. The specifics escape me, but it was in that area. And the informed conclusions were that the 1/4" cable connection have absolutely zero problem handling any market-available juice.

As an example, my Quilter BB800 has 1/4" out, and it's rated at 800W RMS at 4 ohms. And Mr. Pat Quilter knows that daisychaining cabs is common, so would not have included a 1/4" output if it posed a danger. This, however, is a combo of tangent and red herring. Also, audio cables, not really measured by gauge, are waaaay higher in estimated gauge (meaning way thinner), and they're not safe for high-wattage transmission. There's a point where copper thickness matters, but it's not at 12 or 14 gauge. It'd be like, what, 40 gauge? 60 gauge?

As for the original thing, power cords... I look at it like this. An 18-ga extension cord at Kroger or Food Lion or Piggly Wiggly or wherever may not be of the same build quality as something APC puts out. But a known reputable maker of power cords will have cords rated for uses faaaaar outstripping us running our bass amp setup. Like, they're looking at generators and pro light rigs and extra-output boat motors and things. 18-gauge.

Whoever actually needs 12-gauge copper connections is probably also hardwiring conduit. Bass & guitar amps and a space heater all at once. 30 amps at 120V kind of thing.
Click to expand...
What are you talking about, most of what you posted makes no sense whatsoever.
 
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#20
agedhorse said:
The power supply, because of the way it works to store energy and work with the signal's duty cycle, serves to average the AC power draw.
Click to expand...
Thank you for the explanation. I think this part of it was the part I was missing, and why I didn't understand your previous post.
 
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