Power cords

[frankie5string]

Just don't abuse the power cable that came with your rig and you'll be fine.
If anything, watch out for dodgy power bars and extension cords. Those are a far larger risk to you and your gear than the cable that ships with your amp.

 

[iiipopes]

Just don't abuse the power cable that came with your rig and you'll be fine.
If anything, watch out for dodgy power bars and extension cords. Those are a far larger risk to you and your gear than the cable that ships with your amp.

This^ Agedhorse has shown that the power supply, or mains, cord that ships with any unit is sufficient due to well-received regulatory specs. But wear and tear, scuffing of the insulation, too much flexing which induces metal fatigue, and inferior items such as cheap power strips, etc., are much more of a concern to a gigging musician. ALWAYS check your power supply system (cords, strips, buffers, even conditioners [Furman being the best known brand] at EVERY gig to make sure everything is secure and won't open or short at a critical juncture.

This brings me to another point: the actual power supply at a gig. When I am playing a venue I have not played before, or a venue that has "rewired the stage to make it better," I keep in my gig box a polarity checker. Just because the house wiring appears clean doesn't mean someone could have made a mistake and flipped the hot and the neutral on the jack, or didn't get the third prong wired correctly. ALWAYS check your polarity as well as the condition of the cords. I have been shocked when, in the old days of non-polarized plugs, someone accidentally tripped over a plug, and wanting to be "helpful," plugged it back in - upside down. I have also avoided shock when, at the expense of the guys getting aggravated at me for the delay in setting up, I checked the sockets, and the owner of the venue (not being a qualified electrician, of course) on the cheap had wired some of them backwards. To me, checking the polarity of the wall sockets and checking for wiring integrity, both at the jacks and between the jacks and the mains input for any particular unit, are much, much more important issues than which power cord is being used, so long as the power cord meets regulatory specs.

 

[OogieWaWa]

I think I'd be somewhat more concerned about the ampacity of that power strip and cord that all has all those loads shown plugged in on the OP's post. Some loads really do use their rated current.

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

Thanks for the info in that post, Agedhorse. I was trying to add up all of our power requirements and had to assume some efficiencies for the amps. I went a little more conservative than those realistic numbers you gave because I was never sure before. At least now I'm more confident that we (over)sized our power distribution well enough.

 

[Ross W. Lovell]

Do the same calculation using current rather than voltage and you will see the other limiting factor.



Sounds like something was defective, most certainly not due to the wire gauge.


Factory supplied power cords supplied are generally independent not chosen based on cost. They are chosen based on the minimum required gauge, length, jacket requirements for the application, flexibility and safety agency global approvals.

If there is a “low voltage situation”, the cord won’t warm up, nor will it “pop fuses”. Please review Ohm’s law regarding non-rotating (non-motor) loads.

On conventional power supply amps, the cord will theoretically run cooler. Even on few amps with PWM regulated power supplies, the current only increased by about 12% at 100V which would rest in an unmeasurable theoretical increase in temperature. The agency approvals include under-voltage testing to -10% at 120V (~108V) for US market products and -10% for Japanese market products (~90V).

NEMA and the NEC has nothing to do with power cord sizing for plug connected devices. That is covered under UL 60065 and UL 63368 in the US market, which specifies the gauge for the current profile that the regulations define, the ground bonding and over current protection in the equipment, and other aspects of isolation and consumer safety as it applies to the equipment.

The supply capacity and NEMA connectors (type and current) are defined so that when the manufacturer provides or specifies a plug connected connection, the supply will confirm to the safety listing details that the equipment is designed and approved to. (Voltage, current, phase, configuration, and grounding).

I have dealt with this my entire professional life, industrial controls and power systems was the specialty of my EE degree. It applies very much to audio electronics as well.

Cords have to support the load, which is what the gauge size designates, cost of that particular size gauge varies.

Voltage drop, occurs in long runs. NEMA specifies that when a run is 75' or more a conductor size upgrade is warranted.

Your next to,last paragraph, how is that different from what I have stated?

 

[OogieWaWa]

and the owner of the venue (not being a qualified electrician, of course) on the cheap had wired some of them backwards

The scariest words I hear when setting up are "Oh, I know the power is good, I wired it myself." Always test.

 

[Slevage]

#18 is good though if I had a big tube amp (SVT sized), I wouldn’t replace the AC pigtail with anything smaller than #16.

This doesn’t mean you should run a 50’ extension cord that you use for your Christmas lights, to run your audio gear.

 

[Sid Fang]

If it’s getting warm to the touch in operation, it’s too small a gauge…

 

[SoCal80s]

...(800W x .250) / 0.8 = 250 watts average AC power draw, which is approximately 2 amp at 120V...

So if I'm reading this right, an 800W amplifier does not draw more (or much more) than 2 amps of electricity?

 

[Killing Floor]

You now go by waist size?

Yeasss, pandemic pounds!

 

[agedhorse]

Thanks for the info in that post, Agedhorse. I was trying to add up all of our power requirements and had to assume some efficiencies for the amps. I went a little more conservative than those realistic numbers you gave because I was never sure before. At least now I'm more confident that we (over)sized our power distribution well enough.

The efficiency numbers I used are for typical SMPS/class D amps. Class AB amps are typically less efficient.

Cords have to support the load, which is what the gauge size designates, cost of that particular size gauge varies.

Voltage drop, occurs in long runs. NEMA specifies that when a run is 75' or more a conductor size upgrade is warranted.

Your next to,last paragraph, how is that different from what I have stated?

Because the power cord supplied with the amp is limited by regulations to less than 10 feet. The NEC applies to branch wiring beyond the plug of the listed equipment. Extension cords themselves are not specifically covered under the NEC either, there are covered under different UL regulations.

The NEC does address voltage drop but only from the service entrance to the branch circuit receptacle, as well as type of insulation, jacket and ampacity for general purpose applications. This is all different than the power cord that ships with an amp, which is governed by UL product safety regulations.

#18 is good though if I had a big tube amp (SVT sized), I wouldn’t replace the AC pigtail with anything smaller than #16.

This doesn’t mean you should run a 50’ extension cord that you use for your Christmas lights, to run your audio gear.

If it’s getting warm to the touch in operation, it’s too small a gauge…

 

[Ross W. Lovell]

So if I'm reading this right, an 800W amplifier does not draw more (or much more) than 2 amps of electricity?

I think your confusing amp audio output with what the amplifier actually uses to make that 800w?

Hopefully Agedhorse will weigh in on this.

 

[agedhorse]

So if I'm reading this right, an 800W amplifier does not draw more (or much more) than 2 amps of electricity?

Correct, for the example I provided.

Important factors are the duty cycle that the amp is being driven to, the amp’s efficiency and the understanding that this is the average power consumption under these conditions.

 

[agedhorse]

I think your confusing amp audio output with what the amplifier actually uses to make that 800w?

Hopefully Agedhorse will weigh in on this.

The amplifier doesn’t deliver 800 watts continuously because the bass signal is not a continuous sine wave. A bass signal had dynamics, attack and decay envelopes, and follows peak to average characteristics. The power supply averages all of this out.

 

[Phalex]

18-3 SJ cord is rated for 10A. At 120 Volts that’d be good up to 1200 Watts give or take.

 

[Killing Floor]

I know this is a bass forum…

but I grew up playing Cowboy Chords.

 

[Ross W. Lovell]

The efficiency numbers I used are for typical SMPS/class D amps. Class AB amps are typically less efficient.



Because the power cord supplied with the amp is limited by regulations to less than 10 feet. The NEC applies to branch wiring beyond the plug of the listed equipment. Extension cords themselves are not specifically covered under the NEC either, there are covered under different UL regulations.

The NEC does address voltage drop but only from the service entrance to the branch circuit receptacle, as well as type of insulation, jacket and ampacity for general purpose applications. This is all different than the power cord that ships with an amp, which is governed by UL product safety regulations.

Correct, for the example I provided.

Important factors are the duty cycle that the amp is being driven to, the amp’s efficiency and the understanding that this is the average power consumption under these conditions.

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.
View attachment 4322669
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.

Agedhorse,

So if my Hiwatt is supplied 80-90 VAC because the venue has a refrigeration circuit on the one stage our side of the stage..........

Will my amp draw more and pop a fuse?

Will my amp supply cord get warm?

 

[OogieWaWa]

The efficiency numbers I used are for typical SMPS/class D amps. Class AB amps are typically less efficient.

I actually took that into account! I used to work with a bunch of industrial electrical design and field engineers and was always bugging them with questions. But there aren't many Class D amps in a power plant, so it was unfamiliar territory for them.

 

[agedhorse]

18-3 SJ cord is rated for 10A. At 120 Volts that’d be good up to 1200 Watts give or take.

Yes, for a connected or IEC power cord less than 3.3 meters long.

This may not apply to extension cords that are long (length in a listed cord is factored into the gauge) or are connected together. The voltage drop must also be factored into the use of extension cords, especially long ones.

Another factor that relates to this discussion is the term continuous load, which has different meanings depending on the application. An audio amp is not considered a continuous load due to the duty cycle, which is why the earlier calculations are done to provide an average power consumption number. On the other hand, a lighting (and motor, heating and process) loads is considered continuous when it can potentially exist for a 4 hour period of time. Where this exists, the ampacity must be sweated to 80% of the conductor’s ampacity.

In the NEC, there is additional delaying terms for multiple conductors in a raceway or jacket, and ambient temperature.

 

[swarfrat]

I find 12 gauge gives me the best tone.

Rev Peyton fan?

 

[agedhorse]

Agedhorse,

So if my Hiwatt is supplied 80-90 VAC because the venue has a refrigeration circuit on the one stage our side of the stage..........

Will my amp draw more and pop a fuse?

Will my amp supply cord get warm?

If the voltage drops to 80-90V on a 120V circuit, you have MUCH bigger problems related to fire safety. This is WAY beyond the NEC requirement that the total circuit voltage drop not exceed 5% at the branch circuit’s rated current.

In this case, your amp would draw considerably less current (if it worked at all). Many amps have under-voltage shutdown protection that for US models shut the amp down (to protect the amp from damage) around 100-105V.