long power cable run

[Rick Auricchio]

Loops in an extension cord aren't as bad as some make them out to be.

Yeah, but who wants dizzy electrons?

 

[billfitzmaurice]

Yeah, but who wants dizzy electrons?

Power cord loops do cause EMI. But the level is miniscule in comparison to that created by the power transformers in amps, so it's not a concern unless said loop is wrapped around your pickups.

 

[anonymous122511]

Without knowing how long is "long" (25 feet? 2000?), I'll have to agree with Bill Fitzmaurice that playing outdoors tends to require a lot more power than indoors, so you were probably just pushing it a lot more than you usually do.

Loops in an extension cord aren't as bad as some make them out to be.

As long as we're in "de-bunk" mode it's HIGHLY unlikely that a bass amp under any circumstance would be drawing enough to heat up an AC cable unless there was a problem with the cable, a problem with the amp or a problem with the power. It's utterly ridiculous to think 14/3 is gonna heat up with powering a bass amp of ANY kind. If the cord heated up there was another problem.

If you think a coiled cable can offer no trouble on stage plug in a 1K PAR can to a cord with 20' of tightly coiled cable and see how long it takes the jacket to melt and cause a short. You're right it won't make a difference with a bass amp but it's something anyone working on stage should be aware of. I'm a stagehand for almost thirty years. I deal with this stuff daily and I'm not talking outta my ass here.

 

[rodl2005]

So, here in AUS, with our 240V mains.... What's the situation?? all these 1/2 = double in elec's freak me out ;-/

Does it mean 50' should be our 'min acceptable length' in ext leads for a high amp load???

 

[Bob Lee (QSC)]

Power cord loops do cause EMI. But the level is miniscule in comparison to that created by the power transformers in amps, so it's not a concern unless said loop is wrapped around your pickups.

Loops in a power cord have current flowing in both directions in equal amounts, so they don't really change the EM field appreciably. However, if you separate the conductors and loop them individually (which, BTW, is a useful tool for measuring current in the individual AC legs), then you'd get some good hum fields going.

 

[Pilgrim]

As long as we're in "de-bunk" mode it's HIGHLY unlikely that a bass amp under any circumstance would be drawing enough to heat up an AC cable unless there was a problem with the cable, a problem with the amp or a problem with the power. It's utterly ridiculous to think 14/3 is gonna heat up with powering a bass amp of ANY kind. If the cord heated up there was another problem.

If you think a coiled cable can offer no trouble on stage plug in a 1K PAR can to a cord with 20' of tightly coiled cable and see how long it takes the jacket to melt and cause a short. You're right it won't make a difference with a bass amp but it's something anyone working on stage should be aware of. I'm a stagehand for almost thirty years. I deal with this stuff daily and I'm not talking outta my ass here.

Jeff, no argument on the 14/3 AC cord. My concern is that some of the cheapies out there have tiny wire but add a lot of cheap vinyl covering to make the cord feel more substantial.

There are many cases where the bass amp isn't the only plugged into a long extension cord - there may be a number of things connected to it.

Question: what's a "1K PAR?" No clue here. My background is radio/TV production, not stage work. Are you referring to a 1 KW stage light?

 

[Bob Lee (QSC)]

If you think a coiled cable can offer no trouble on stage plug in a 1K PAR can to a cord with 20' of tightly coiled cable and see how long it takes the jacket to melt and cause a short. You're right it won't make a difference with a bass amp but it's something anyone working on stage should be aware of. I'm a stagehand for almost thirty years. I deal with this stuff daily and I'm not talking outta my ass here.

It would not be wise to run an amp and a 1K PAR can on the same extension cord. If you get significant heating with 8.3 A of steady current, then that 20' cord has too much resistance. If it's, say, 14 AWG, that 20' length would have about 0.1Ω resistance round trip and would dissipate about 7 watts--probably not enough to feel warm to the touch unless it's damaged.

 

[anonymous122511]

Jeff, no argument on the 14/3 AC cord. My concern is that some of the cheapies out there have tiny wire but add a lot of cheap vinyl covering to make the cord feel more substantial.

There are many cases where the bass amp isn't the only plugged into a long extension cord - there may be a number of things connected to it.

Question: what's a "1K PAR?" No clue here. My background is radio/TV production, not stage work. Are you referring to a 1 KW stage light?

Yep. Parabolic Aluminized Reflector is what PAR stand for....looks like a car headlight. Very widely used type of stage lighting fixture.

I agree with you about the molded end thing bigtime.....you wouldn't use a molded end cable to plug yer bass into yer amp.

 

[Bob Lee (QSC)]

Question: what's a "1K PAR?"

A PAR lamp has a parabolic aluminum reflector built into the bulb itself. The can is the fixture it screws into.

 

[anonymous122511]

It would not be wise to run an amp and a 1K PAR can on the same extension cord. If you get significant heating with 8.3 A of steady current, then that 20' cord has too much resistance. If it's, say, 14 AWG, that 20' length would have about 0.1Ω resistance round trip and would dissipate about 7 watts--probably not enough to feel warm to the touch unless it's damaged.

I'm almost sorry I jumped in here......
Ok, folks DON'T plug lights into the same circuit as ANY audio gear. Ever. For any reason. It never occurred to me I needed to make that clear. I only brought it up for those doing their own stage lighting as you're a whole lot more likely to incur heat issues there than plugging yer bass amp in. I guess I went there too because in over thirty years of live gigs I've never significantly heated up the AC cable my amp was plugged into. My mind went immediately to lighting.

One reason I've never had an issue powering my amp is that I've always used $10 ground fault tester that's saved me from bad power several times. No gigging musician should EVER plug in to ANY power without using one first. I'd bet what the OP experienced was related to a ground fault of some sort that could have easily been avoided.

 

[Jim Campbell]

A PAR lamp has a parabolic aluminum reflector built into the bulb itself. The can is the fixture it screws into.

ergo no adjustment for spot/flood can be gained by moving the bulb back or forward in the housing.....the lamp kits usually contain variety of lenses for that purpose....or bulbs can be swapped for the cans

 

[billfitzmaurice]

I'd bet what the OP experienced was related to a ground fault of some sort that could have easily been avoided.

That bet you'd lose. Ground faults don't cause amps to clip. But your point is well taken. As I already mentioned long extensions and outdoor gigs don't mix, especially if you're not on a stage, and that has everything to do with proper grounding. In that circumstance the distance from your rig to the point where the AC line is grounded at the service entrance can be literally hundreds of feet, and that's a lot of resistance in the run of wire to get there. OTOH the distance from your feet to ground is the thickness of your shoe soles, and if you're barefoot that distance is zero. And as the old saying goes electricity always takes the shortest path to ground. You don't want that path to be through you. That's why outdoor stages must have their own grounded service entrance at the stage, and should have at least GFCI outlets, if not GFCI breakers.

 

[anonymous122511]

That bet you'd lose. Ground faults don't cause amps to clip.

OK, I have to defer to your superior knowledge on amp clipping. What I have a problem with is the idea that long AC runs to a bass amp pose a significant heat threat when I regularly run 100' to 1000w lights with no issues. Or are you guys saying a long AC run drops the voltage enough to cause problems other than heat? I can't argue the numbers on paper with you...I don't have the math. What I'm basing my statements on are years of working with long runs of AC and the stagehand rules of thumb regarding them. I've never heard of anyone worrying about a 50' to 100' AC run to audio gear. By the time power breaks out of the distro to all the places it needs to go it's most often way over 50'. What am I misunderstanding here?

I think mostly we are on the same page though. I wholeheartedly agree with you on the subject of GFIs. Accurate reference to ground saves gear and lives.

 

[Bob Lee (QSC)]

+1 on what Bill said. A ground fault will cause safety issues if the AC shorts internally in a piece of equipment, or even if there's just too much leakage current to the chassis. But it won't cause clipping.

GFCIs don't reference to ground. They just always compare the hot current to the neutral current, and as long as they're exactly the same everything's fine. But if there's an imbalance, like the neutral current is less than the hot current--i.e., some of it's returning through somewhere else, perhaps a bass player--it will interrupt the circuit.

Reduced AC voltage to the amp will cause premature clipping because the supply rails in the amp will sag proportionally to the voltage dip. The voltage drop (E) is equal to the wire resistance (R) times the current (I).

E = I * R

So the longer the extension lead, or thinner its wire gauge, the more voltage drops. And because the current drawn by the amp is dynamic, and can vary in large spurts, the voltage sag can jump up and down too. That can cause problems. If you use an extension, don't use one that's longer or thinner than necessary.

But I think the main thing the OP was observing was just that it takes a lot more power to play outdoors, where there are no walls and ceiling to contain the sound.

 

[anonymous122511]

So the longer the extension lead, or thinner its wire gauge, the more voltage drops. And because the current drawn by the amp is dynamic, and can vary in large spurts, the voltage sag can jump up and down too. That can cause problems. If you use an extension, don't use one that's longer or thinner than necessary.

I'm learning here so don't think I'm being argumentative. I've heard ticket electricians speak of GFI as reference to ground and from your explanation I can see how you could look at it that way even if by the technical letter of the law that's not accurate.

I understand voltage drop. I've seen instances where it is a problem. I've never seen it be a problem with AC going 50' to 100' to audio gear. The numbers on paper aside have you? I'm assuming pro quality cables of adequate gauge.

 

[ulrich]

Very long cable runs, can prevent breakers tripping.

Example: 20ea 100W bulbs (16amps), and 13 amp Sawzall, on short run - 20 amp breaker pops.

Same gear at the end of a 300 foot run - lights dim, Saw runs very slow, breaker doesn't trip.

So, you get voltage drop from the long run, plus drop from running more gear than would normally be possible. Do not want.

On another note - warm cable OK, hot bad.

 

[billfitzmaurice]

I understand voltage drop. I've seen instances where it is a problem. I've never seen it be a problem with AC going 50' to 100' to audio gear.

I haven't either. The distance from the wall outlet to the entrance may be that far as well, that's why code standards allow for 100% gauge oversizing. With insufficient gauge cable the insertion loss might be enough to give voltage drop, but it's mainly the current capacity that would be problematic.

 

[Bob Lee (QSC)]

I'm learning here so don't think I'm being argumentative. I've heard ticket electricians speak of GFI as reference to ground and from your explanation I can see how you could look at it that way even if by the technical letter of the law that's not accurate.

I understand voltage drop. I've seen instances where it is a problem. I've never seen it be a problem with AC going 50' to 100' to audio gear. The numbers on paper aside have you? I'm assuming pro quality cables of adequate gauge.

Like I described before, voltage drop = resistance times current. The current draw of an amp can be pretty low on average but have frequent peaks many times higher. The voltage drop in the extension cord and any other wiring in series with it will be proportional to the current. A high-power amp driven hard enough might pull short peaks that exceed the circuit breaker's rating but are too transient to trip it. But those will cause significant voltage dips if the wire resistance is relatively high.

I've known of DJs, for example, trying to run two or three good sized amps off a single 100-foot extension cord with 2- and 4-ohm loads on each channel, and they wonder why the things clip unexpectedly.

So don't use an extension that's significantly longer than you need. And the longer you need it to be, the larger the wire gauge it'll have to be made with.

 

[Munjibunga]

I made the mistake one time of using a 100-foot 16X3 extension cord to run the whole band. The stage amps and PA kept dying out on loud passages. I was lucky not to lose some gear over that.

 

[GrowlerBox]

I made the mistake one time of using a 100-foot 16X3 extension cord to run the whole band. The stage amps and PA kept dying out on loud passages. I was lucky not to lose some gear over that.

But ... you just look so damn smart in your avatar pic!