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Author Topic: Overloaded Extension Cords  (Read 10345 times)

Mike Sokol

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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)
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TJ (Tom) Cornish

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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!
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Jonathan Johnson

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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?
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Stop confusing the issue with facts and logic!

Mike Sokol

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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 »
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Lyle Williams

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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...
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Mike Sokol

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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...
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Geoff Doane

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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
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Mike Sokol

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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 »
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Stephen Swaffer

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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?
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Geoff Doane

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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
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Mike Sokol

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Re: Overloaded Extension Cords
« Reply #10 on: January 21, 2014, 10:27:41 pm »

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

You're right... so an amplifier rated for 1,000 watts at 4 ohms would probably only deliver around 250 watts to the speakers on stage. That's a lotta loss...
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Mark Cadwallader

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Re: Overloaded Extension Cords
« Reply #11 on: January 21, 2014, 11:14:26 pm »

You're right... so an amplifier rated for 1,000 watts at 4 ohms would probably only deliver around 250 watts to the speakers on stage. That's a lotta loss...

And thus folks can get away with 4 times RMS ratings without burning out drivers.... 
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Lyle Williams

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Re: Overloaded Extension Cords
« Reply #12 on: January 22, 2014, 01:55:29 am »

We had a drum of flex retained as an educational example if what not to do.  Operated at high current, the insulation had melted and flowed like lava out the bottom of the drum.
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Mike Sokol

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Re: Overloaded Extension Cords
« Reply #13 on: January 22, 2014, 08:30:54 am »

We had a drum of flex retained as an educational example if what not to do.  Operated at high current, the insulation had melted and flowed like lava out the bottom of the drum.

Does anyone have pictures of melted/burned wiring or plugs they can share? If so, post them here...
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Jordan Wolf

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Overloaded Extension Cords
« Reply #14 on: January 22, 2014, 10:57:35 am »

Found - still ON and plugged in - at a show last November, I think.  A gift from the overnight cleaning crew...

I don't know if the image is detailed enough, but the prong was still in the Neutral slot.

My take is that the prong was broken inside the molded plug assembly, causing a arc that totaled the strip (and probably the plug housing, too). The carpet was also singed around where the strip was.
« Last Edit: January 22, 2014, 11:00:37 am by Jordan Wolf »
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Tommy Peel

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Re: Overloaded Extension Cords
« Reply #15 on: January 22, 2014, 11:58:00 am »

I don't have a picture and this isn't audio related but a few years ago we had a '96 F250 Diesel pickup(my family owned it from '99-'12 with 280k+ miles on it when  we sold it). Anyway we had to use the 1500 watt engine block heater on it all winter while we had it and the AC cord that ran from  the grill to the heater wasn't heavy enough. We had to replace the cable once while we owned it and had to replace the plug on the cord every few years because they would overheat and get burnt looking.

Sent from my Nexus 4 running OmniROM 4.4 KitKat using Tapatalk Pro

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Greg_Cameron

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Re: Overloaded Extension Cords
« Reply #16 on: January 22, 2014, 12:48:26 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?

This is why I make them myself from 12AWG SO cord and good connectors. It's hard to find good off the shelf cords that are both hard service rated and black.
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Mike Sokol

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Re: Overloaded Extension Cords
« Reply #17 on: January 22, 2014, 02:22:50 pm »

This is why I make them myself from 12AWG SO cord and good connectors. It's hard to find good off the shelf cords that are both hard service rated and black.

If you got the $$$, then the WW Power Link stuff is great. I use these to distro between my various FOH processing racks. http://whirlwindusa.com/catalog/power-electrical-distribution/default/power-linktm

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Samuel Rees

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Re: Overloaded Extension Cords
« Reply #18 on: January 22, 2014, 02:37:18 pm »

Just got my PowerCon Quads from Ken at O.A. Windsor and they are excellent!
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Mike Sokol

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Re: Overloaded Extension Cords
« Reply #19 on: January 22, 2014, 04:10:24 pm »

Just got my PowerCon Quads from Ken at O.A. Windsor and they are excellent!

Got pics?
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Mike Sokol
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Samuel Rees

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Re: Overloaded Extension Cords
« Reply #20 on: January 22, 2014, 04:41:17 pm »

Definitely give me a few!
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Samuel Rees

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Re: Overloaded Extension Cords
« Reply #21 on: January 22, 2014, 06:37:44 pm »

Take a look! Feels like I could play catch with them - both somewhat safely for the guys throwing it and the gear! It's light and soft but feels super durable and ruggedized. I'm going to get some more, but I've spent a lot of money this month :)
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Tom Bourke

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Re: Overloaded Extension Cords
« Reply #22 on: January 22, 2014, 09:27:24 pm »

Does anyone have pictures of melted/burned wiring or plugs they can share? If so, post them here...
I have some really nasty ones from a theater that was out in the sticks I will have to dig up for you.  3.6K dimmers with ALL over current removed and 6K worth of par cans at the end of EACH line of a 12 AWG 6 ch mult.  14 awg romex jammed into the 150A 3 phase disconnect for a utility outlet.
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