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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: charles strickland on March 30, 2021, 06:04:54 PM

Title: coiling feeder cable
Post by: charles strickland on March 30, 2021, 06:04:54 PM
  Is there a better way to coil extra feeder cable than using a figure eight ? ( when powered up )  4/4
Title: Re: coiling feeder cable
Post by: Frank Czar on March 30, 2021, 08:19:33 PM
In over thirty years in the business I use 4/4 a lot and can only recall one time that I got noise from havening the cable in a single coil and re-doing it into a figure eight cured the noise.
Title: Re: coiling feeder cable
Post by: Tim McCulloch on March 30, 2021, 08:20:16 PM
It gives better heat dissipation and the cris-crossing helps hold down induction heating.

Is there a particular issue you're trying to solve or just sussing out best practices?
Title: Re: coiling feeder cable
Post by: Kevin Graf on March 31, 2021, 08:30:25 AM
It gives better heat dissipation and the cris-crossing helps hold down induction heating.
Induction heating?
If all the current is returning in the same cable, it's resistance heating.
Title: Re: coiling feeder cable
Post by: Chris Hindle on March 31, 2021, 08:50:48 AM
Induction heating?
If all the current is returning in the same cable, it's resistance heating.
But also induction heating to the closely coupled loops of cable.... as I understand it.
At a "big show" I teched one winter last century, the over/under 50 odd feet of 400A feeder made a nice hand warmer. The feeder itself (away from the loop) was cool to the touch.
Chris.
Title: Re: coiling feeder cable
Post by: Stephen Swaffer on March 31, 2021, 12:36:20 PM
Take a look at conduit conductor count deratings to get a picture of how quickly heat dissipation can become an issue.  Conductor ampacities are based on insulation temperature ratings-most of these are high enough to make a hand warmer.  Bundle a bunch together and you have lots of heat.   Just common sense-if you think about the physics behind the rules in the NEC.  Just like thinking about the physics involved in setting up a sound system.
Title: Re: coiling feeder cable
Post by: Dave Garoutte on March 31, 2021, 12:44:34 PM
But also induction heating to the closely coupled loops of cable.... as I understand it.
At a "big show" I teched one winter last century, the over/under 50 odd feet of 400A feeder made a nice hand warmer. The feeder itself (away from the loop) was cool to the touch.
Chris.
A stacked coil of 'heater' wire will have way less surface area to dissipate said heat compared to a single strand laid out.
Title: Re: coiling feeder cable
Post by: Erik Jerde on March 31, 2021, 05:24:44 PM
Take a look at conduit conductor count deratings to get a picture of how quickly heat dissipation can become an issue.  Conductor ampacities are based on insulation temperature ratings-most of these are high enough to make a hand warmer.  Bundle a bunch together and you have lots of heat.   Just common sense-if you think about the physics behind the rules in the NEC.  Just like thinking about the physics involved in setting up a sound system.

I can attest to that.  I was climbing in an attic space over a stage once and I laid hands on a very warm piece of 3/4Ē EMT that was serving the lighting system.  I donít know how many circuits or what the conduit fill was but it was just a hair uncomfortable to hold onto.  Fortunately there was other structure around more appropriate to use for climbing.
Title: Re: coiling feeder cable
Post by: Curt Sorensen on April 01, 2021, 02:33:19 PM
A friend toured with Brit Row and was taught to alternate a coil (loop) and an eight. He said it evened out the build-up from the cross-overs when only figure eights are used. I assume every other coil is over-under. Luckily I don't deal with much bundled feeder these days, so no personal experience with that approach.
Title: Re: coiling feeder cable
Post by: charles strickland on April 01, 2021, 05:01:25 PM
I asked the question mainly for best practice reasons. on occasion I have an extra 20 ft or so cable to deal with, heat build up was my main concern.  Thank you for the advice. 
Title: Re: coiling feeder cable
Post by: Ed Hall on April 02, 2021, 08:21:18 AM
Just common sense-if you think about the physics behind the rules in the NEC.  Just like thinking about the physics involved in setting up a sound system.

This was so much easier before physics got involved!  ;D
Title: Re: coiling feeder cable
Post by: doug johnson2 on April 03, 2021, 06:27:42 PM
Dave Rat has some thoughts on the subject:
https://www.youtube.com/watch?v=jgq8-4m133o
Title: Re: coiling feeder cable
Post by: Stephen Swaffer on April 05, 2021, 12:36:33 PM
Speaker cable and feeder cable are not the same thing and usually have different considerations.
Title: Re: coiling feeder cable
Post by: Dave Garoutte on April 05, 2021, 04:06:06 PM
Speaker cable and feeder cable are not the same thing and usually have different considerations.
He did mention that power cables also have inductive issues, just not the same ones.
Title: Re: coiling feeder cable
Post by: Brian Jojade on April 05, 2021, 05:08:26 PM
Induction heating?
If all the current is returning in the same cable, it's resistance heating.

While I agree, most of the heating issues of coiled cable has to do with resistance heating and dissipation.  However, I have experienced a couple of times where it appeared something else is at play.  I've done an event several times over the years where the setup involves a bit of excess feeder cable that ends up coiled under a stage.  Wrapped in a normal loop fashion and tucked away 6/4 cable, less than 30 amp load, which was never a problem. .  Never got even warm to the touch.

One show, during our setup, we smelled something hot and found the coil of wire so hot it couldn't be touched.  The we did note that someone set a coffee can full of nuts and bolts inside the coil.

Now, it's possible that the exact wrap of the wire happened to be slightly different, or slightly neater, but since I'm the one that put the coil there each time, it's hard to believe that it was THAT different that particular year to cause such a difference.

Removed the coffee can and bolts and spilled the wire around a bit, and all was well.  Definitely a very strange scenario.
Title: Re: coiling feeder cable
Post by: Chris Hindle on April 05, 2021, 05:33:13 PM
While I agree, most of the heating issues of coiled cable has to do with resistance heating and dissipation.  However, I have experienced a couple of times where it appeared something else is at play.  I've done an event several times over the years where the setup involves a bit of excess feeder cable that ends up coiled under a stage.  Wrapped in a normal loop fashion and tucked away 6/4 cable, less than 30 amp load, which was never a problem. .  Never got even warm to the touch.

One show, during our setup, we smelled something hot and found the coil of wire so hot it couldn't be touched.  The we did note that someone set a coffee can full of nuts and bolts inside the coil.

Now, it's possible that the exact wrap of the wire happened to be slightly different, or slightly neater, but since I'm the one that put the coil there each time, it's hard to believe that it was THAT different that particular year to cause such a difference.

Removed the coffee can and bolts and spilled the wire around a bit, and all was well.  Definitely a very strange scenario.
You made a big ass iron core coil......
Chris.
Title: Re: coiling feeder cable
Post by: Geoff Doane on April 05, 2021, 08:50:59 PM
You made a big ass iron core coil......


Yeah, but with 6/4 shouldn't the current, and therefore the magnetic field around the cable, cancel out to zero?

I'm not saying the cable didn't get hot (obviously, it did), but I'm not sure that "induction" is what is going on here.

GTD
Title: Re: coiling feeder cable
Post by: Chris Hindle on April 06, 2021, 08:07:11 AM
Yeah, but with 6/4 shouldn't the current, and therefore the magnetic field around the cable, cancel out to zero?

I'm not saying the cable didn't get hot (obviously, it did), but I'm not sure that "induction" is what is going on here.

GTD

i can't think of any other way to explain why the loop of feeder got so hot, when he has done it many times without the "core", and had no problems. I guess one of our many experts has to chime in... Where's Mike Sokol. I bet he has an easy answer for us.
Chris.
Title: Re: coiling feeder cable
Post by: Brian Jojade on April 06, 2021, 10:49:31 AM
You made a big ass iron core coil......
Chris.

That was my thought, however, the current going both directions in the wire should have cancelled things out.  I don't have a logical explanation as to why this happened.
Title: Re: coiling feeder cable
Post by: Art Welter on April 06, 2021, 04:26:49 PM
Yeah, but with 6/4 shouldn't the current, and therefore the magnetic field around the cable, cancel out to zero?
The ferromagnetic core made by the can of iron nuts and bolts inside the coil could increase the magnetic field and inductance of the AC wire coil by hundreds of times over what it would be without the core.  Like a stalled induction motor, the coils heat up due to increased currents in the armature.

There probably was also plenty of 60Hz hum in the mess before the can of iron nuts and bolts was removed...