ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3  All   Go Down

Author Topic: Overloaded Extension Cords  (Read 10362 times)

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3354
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Overloaded Extension Cords
« on: January 21, 2014, 04:53:29 pm »

The biggest issue we face is voltage drop from high-current loads at the end of too long/too small cords.  Our industry should host a mass bonfire to rid the world of 16-ga orange extension cords, followed by mass psychotherapy to rid the idea that 20,000 watts of amp power and 100,000 watts of PAR lights are necessary for 50-cap bars.

Hey, I don't just talk about it.... I bring it to the party...! Here's a pic of my NSZ demonstration on what happens to a 16-ga orange extension cord when you overload it with 28-amps of current. In less than 5 minutes the surface temp of the extension cord was over 200 degrees F and still climbing. Much longer and it would cause the bonfire you're requesting...

Too much fun!!!!  8)
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

TJ (Tom) Cornish

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4264
  • St. Paul, MN
Re: Overloaded Extension Cords
« Reply #1 on: January 21, 2014, 05:23:27 pm »

Hey, I don't just talk about it.... I bring it to the party...! Here's a pic of my NSZ demonstration on what happens to a 16-ga orange extension cord when you overload it with 28-amps of current. In less than 5 minutes the surface temp of the extension cord was over 200 degrees F and still climbing. Much longer and it would cause the bonfire you're requesting...

Too much fun!!!!  8)
Nice!
Logged

Jonathan Johnson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2990
  • Southwest Washington (state, not DC)
Re: Overloaded Extension Cords
« Reply #2 on: January 21, 2014, 06:57:44 pm »

Hey, I don't just talk about it.... I bring it to the party...! Here's a pic of my NSZ demonstration on what happens to a 16-ga orange extension cord when you overload it with 28-amps of current. In less than 5 minutes the surface temp of the extension cord was over 200 degrees F and still climbing. Much longer and it would cause the bonfire you're requesting...


Incomplete information here... why do you have what appears to be a black wire and a white wire wire-nutted together?
Logged
Stop confusing the issue with facts and logic!

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3354
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Overloaded Extension Cords
« Reply #3 on: January 21, 2014, 07:22:28 pm »

Incomplete information here... why do you have what appears to be a black wire and a white wire wire-nutted together?

Here's the full circuit layout. Instead of trying to run a full 28 amp load in my office, I used a Glo-Melt resistance soldering transformer to generate 3 volts at 40 amps (it's a 120 watt transformer). I'm only pulling around 1 amp from the wall outlet for this demonstration.  This works because wire heating is only caused by voltage drop (not actual voltage), so by looping the current back around in the same wire I get 28 amps going each way. I needed to make a bundled cross section of wires for the infrared thermometer to read since at that range it has a 1" by 1" acceptance window. If I would have just pointed it at a single width of extension cord it would average the small surface area of the cord with a 1 square inch of measured area which would give an abnormally low temp reading. Of course, I could have used a thermocouple on a single wire to measure the surface temp, but a laser pointer on the infrared thermometer looks much more scientific. Here's the full video: http://www.youtube.com/watch?v=WZznobYGF_c

Sharks with lasers.... That's all I'm asking for.
« Last Edit: January 21, 2014, 07:25:11 pm by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Lyle Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1556
Re: Overloaded Extension Cords
« Reply #4 on: January 21, 2014, 08:14:14 pm »

The market for cheap extension cords makes it hard to buy good ones.  Who wants to buy a $200 extension cord when there is a $20 one at the hardware store?  A heavy gauge, thickly insulated, braided cord with IP66 connectors is expensive.  Fortunately nobody's PA is playing sine waves, and not all the lights are on all the time...
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3354
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Overloaded Extension Cords
« Reply #5 on: January 21, 2014, 08:39:03 pm »

The market for cheap extension cords makes it hard to buy good ones.  Who wants to buy a $200 extension cord when there is a $20 one at the hardware store?  A heavy gauge, thickly insulated, braided cord with IP66 connectors is expensive.  Fortunately nobody's PA is playing sine waves, and not all the lights are on all the time...

I did this video for RV owners who are notorious for using a $20, 16 gauge extension cord to power their $250,000 motor homes via adapters of all types. They'll try to run a coffee maker and 1,500 watt blow dryer at the same time, or crank up a big rooftop air conditioner, then wonder why they burn up their extension cords.

Of course, most music usually has a pretty high crest factor (peak to average ratio) so the average amperage on the extension cords are lower than you might think, unless you're playing hip-hop which can have a lot of sine wave action. That's when the overheating begins...
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Geoff Doane

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 816
  • Halifax, NS
Re: Overloaded Extension Cords
« Reply #6 on: January 21, 2014, 08:53:19 pm »

I needed to make a bundled cross section of wires for the infrared thermometer to read since at that range it has a 1" by 1" acceptance window. If I would have just pointed it at a single width of extension cord it would average the small surface area of the cord with a 1 square inch of measured area which would give an abnormally low temp reading.

Of course, in fairness to the extension cord, bundling it makes the temperature rise even higher, for the same reason we're supposed to derate cables with multiple current carrying conductors.  Still it's a pretty good demo, even if you are preaching to the choir here.

I'm sure I've seen vinyl extension cords somewhere that had partially melted, and the twisted wires inside had imprinted themselves on the jacket.  Ignorance is bliss!  ::)

GTD
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3354
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Overloaded Extension Cords
« Reply #7 on: January 21, 2014, 09:52:28 pm »

Still it's a pretty good demo, even if you are preaching to the choir here.

I certainly HOPE that most of you on the forum know this already, but I've got to tell you there's a LOT of entry level sound technicians who don't understand the concept of voltage drop over long/undersized cables. I've lost count of the times I've seen a TRS return pair on a snake used to send amplifier power to a passive monitor speaker on stage. Yikes!!! 

Here's a quick review of that scenario. Assume the return snake is 24 gauge twisted pair. According to the chart below, that gauge wire has about 2.5 ohms resistance per 100 ft which totals 5 ohms for both legs for a 100 ft snake. So now you're inserting 5 ohms in series with perhaps a 4 ohm (2-speaker) load, which results in throwing away more than 50% of your wattage in the wire. Due to its long length it's doubtful that you'll catch the wire in the snake on fire, but you've now destroyed the damping factor of your amp while losing around 4 dB of headroom.
« Last Edit: January 21, 2014, 10:15:54 pm by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2215
Re: Overloaded Extension Cords
« Reply #8 on: January 21, 2014, 09:54:24 pm »

I wish I had a picture-where  I used to work we had a bunch of hoists wired with 14-4 festoon cable, the hoists ran on nylon rollers and were used to place parts on tables for welders.  Every so often someone would forget to hook up their ground cable to the table (usually after cleaning at shift change) leaving the #14 ground wire in the festoon the only return path for the weld current.  They could weld for bit-but #14 AWG and 150 A weld current was never pretty.  I was always afraid that when the ground became a fuse and blew , sooner or later the end going to the table would end up melting through to a phase conductor and putting 480 VAC on the table.

For sound purposes the voltage drop is probably more of  concern than melting-although with many univeral power supplies being happy at 100 Volts maybe not so much, but at some point it would have to start affecting amps, especially subs wouldn't it?
Logged
Steve Swaffer

Geoff Doane

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 816
  • Halifax, NS
Re: Overloaded Extension Cords
« Reply #9 on: January 21, 2014, 10:13:05 pm »

So now you're inserting 5 ohms in series with perhaps a 4 ohm (2-speaker) load, which results in throwing away more than 50% of your wattage in the wire.

It's even worse than that.  You are using half your power to heat up the speaker cable (instead of heating up voice coils  :( ), but because you've added that extra resistance, the amp is now only putting out about half the power you thought it would.

GTD
Logged
Pages: [1] 2 3  All   Go Up
 


Page created in 0.029 seconds with 24 queries.