16 gauge melts with 20A at DVinfo.net

Tom Morrow · September 29th, 2013, 05:28 PM

I always find that failures are great learning. So I wanted to share one I observed. We all know that it's possible to push ratings on current a little bit in most circumstances, but I'm always curious how far is too far.

I found out the other day when someone accidentally plugged in a 120V 2k light with a 16 gauge extension cord (cheapo workforce brand 100' 10A rated). The light worked successfully for about 10 minutes and then went out. I discovered that the cable was coiled up the jacket melted and fused together. Thermal breakdown. What's amazing is that a Ohmeter shows that both the hot and neutral have opened up (not short circuit) although the ground still conducts current.

Good lesson.

Seth Bloombaum · September 29th, 2013, 06:18 PM

Although it is a good lesson, almost burning down the house is not a good way to learn it.

Don't mean to preach at you, Tom. Glad you posted it.

I'm just saying, for future readers of this thread, who might be inexperienced in such matters, that this is the kind of situation that can result in fire, damage, injury, or loss of life. Be safe out there.

Tom Morrow · September 29th, 2013, 06:41 PM

Yeah, it's not something to do intentionally, but the reality is that people do it unintentionally all the time and most of the time it doesn't cause problems other than a warm cable and some wasted power heating the wire.

Tom Morrow · September 29th, 2013, 06:42 PM

And to clarify it wasn't me who accidentally plugged this in.

Edward Carlson · September 30th, 2013, 12:28 AM

Also leaving it coiled might have had something to do with it. Coils create induction loops that create heat. Cables carrying large currents are wrapped figure 8 or run back and forth to take up slack to avoid the possibility of induction loops. (Also they are 12/3 SJO or larger instead of 16/3!)

Steven Digges · September 30th, 2013, 06:39 PM

The same guy that ran that stinger is probably the same guy that would drop a coil of XLR on top of it. Then wonder why his audio sounds bad. Orange AC cables are for weed whackers and coffee makers.

Another A/C cable problem that drives me nuts is when someone uses their leatherman tool to remove the ground pin instead of lifting the ground properly when necessary. And of course, when I find it with the missing pin, everyone dummys up and says I would NEVER do that. Yea right. All they had to do was ask, I always have ground lifts with me on set.

Steve

John Nantz · October 1st, 2013, 01:43 AM

That story is a good case of someone who didn't know what they were doing. When something is pushed to the max "stuff" can happen. And the person who did that probably blamed the problem on the extension cord.

Well, it could have been the extension cord. There are different wire size gauges and it wouldn't be the first time that a different gauge was used in the manufacture from what was UL approved. Anyway, assuming it was the proper gauge there are other considerations.

Ambient air: What was the current rating based on? The 10 Amps was most likely based on the wire cable having proper cooling. Since it was coiled up it obviously wasn't able to get proper air cooling, hence the current capacity drops.

The table on the West Marine web site at The West Advisor: Marine Wire provides acceptable current reductions for various situations. In the case of engine spaces (this is for boats) where it is assumed the ambient air temperature is assumed to be 20ºC hotter than non-engine spaces (50ºC vice 30ºC) then the design ampacity needs to be reduced by 15%.

It gets really interesting when the conductors are bundled (similar to coiled?) and the ampacity needs to be reduced by ..... get this, 40%. That is a serious reduction!

The web page also notes the figures are for AWG and not for SAE wire sizes. This is important because manufacturers can, and do, mix things up. I had a project using 00 cables (double zero) and had to swage some terminals on. The cable and the terminals were both Ancor brand yet the terminals wouldn't fit. After analyzing the situation with the retailer it was determined that the terminals were the wrong size. Since Ancor buys their components from other companies there was probably a mix-up somewhere along the supply chain. Ancor is a respected brand in marine cables and electrical components.

If the rating is based on 120V and the outlet voltage is less because the circuit load has had a voltage drop due to other loads on it then that causes additional problems.

I'm wondering what the circuit breaker was doing in all this. And couldn't someone smell something was hot? Like hot plastic?

Thanks, Tom, for posting your story. We all need a little safety heads-up from time to time. "The devil is in the details."

September 29th, 2013, 05:28 PM	#1
Tom Morrow Major Player Join Date: Feb 2011 Location: San Francisco, CA Posts: 416	16 gauge melts with 20A I always find that failures are great learning. So I wanted to share one I observed. We all know that it's possible to push ratings on current a little bit in most circumstances, but I'm always curious how far is too far. I found out the other day when someone accidentally plugged in a 120V 2k light with a 16 gauge extension cord (cheapo workforce brand 100' 10A rated). The light worked successfully for about 10 minutes and then went out. I discovered that the cable was coiled up the jacket melted and fused together. Thermal breakdown. What's amazing is that a Ohmeter shows that both the hot and neutral have opened up (not short circuit) although the ground still conducts current. Good lesson.

September 29th, 2013, 06:18 PM	#2
Seth Bloombaum Inner Circle Join Date: Sep 2003 Location: Portland, Oregon Posts: 3,420	Re: 16 gauge melts with 20A Although it is a good lesson, almost burning down the house is not a good way to learn it. Don't mean to preach at you, Tom. Glad you posted it. I'm just saying, for future readers of this thread, who might be inexperienced in such matters, that this is the kind of situation that can result in fire, damage, injury, or loss of life. Be safe out there. __________________ 30 years of pro media production. Vegas user since 1.0. Webcaster since 1997. Freelancer since 2000. College instructor since 2001.

September 29th, 2013, 06:41 PM	#3
Tom Morrow Major Player Join Date: Feb 2011 Location: San Francisco, CA Posts: 416	Re: 16 gauge melts with 20A Yeah, it's not something to do intentionally, but the reality is that people do it unintentionally all the time and most of the time it doesn't cause problems other than a warm cable and some wasted power heating the wire.

September 29th, 2013, 06:42 PM	#4
Tom Morrow Major Player Join Date: Feb 2011 Location: San Francisco, CA Posts: 416	Re: 16 gauge melts with 20A And to clarify it wasn't me who accidentally plugged this in.

September 30th, 2013, 12:28 AM	#5
Edward Carlson Major Player Join Date: Mar 2007 Location: North Hollywood, CA, United States Posts: 807	Re: 16 gauge melts with 20A Also leaving it coiled might have had something to do with it. Coils create induction loops that create heat. Cables carrying large currents are wrapped figure 8 or run back and forth to take up slack to avoid the possibility of induction loops. (Also they are 12/3 SJO or larger instead of 16/3!)

September 30th, 2013, 06:39 PM	#6
Steven Digges Trustee Join Date: Oct 2002 Location: Phoenix, AZ Posts: 1,828	Re: 16 gauge melts with 20A The same guy that ran that stinger is probably the same guy that would drop a coil of XLR on top of it. Then wonder why his audio sounds bad. Orange AC cables are for weed whackers and coffee makers. Another A/C cable problem that drives me nuts is when someone uses their leatherman tool to remove the ground pin instead of lifting the ground properly when necessary. And of course, when I find it with the missing pin, everyone dummys up and says I would NEVER do that. Yea right. All they had to do was ask, I always have ground lifts with me on set. Steve __________________ www.CorporateShow.com Been at this so long I'm rounding my years of experience down...not up!

October 1st, 2013, 01:43 AM	#7
John Nantz Trustee Join Date: Jun 2010 Location: Seattle WA Posts: 1,254	Re: 16 gauge melts with 20A That story is a good case of someone who didn't know what they were doing. When something is pushed to the max "stuff" can happen. And the person who did that probably blamed the problem on the extension cord. Well, it could have been the extension cord. There are different wire size gauges and it wouldn't be the first time that a different gauge was used in the manufacture from what was UL approved. Anyway, assuming it was the proper gauge there are other considerations. Ambient air: What was the current rating based on? The 10 Amps was most likely based on the wire cable having proper cooling. Since it was coiled up it obviously wasn't able to get proper air cooling, hence the current capacity drops. The table on the West Marine web site at The West Advisor: Marine Wire provides acceptable current reductions for various situations. In the case of engine spaces (this is for boats) where it is assumed the ambient air temperature is assumed to be 20ºC hotter than non-engine spaces (50ºC vice 30ºC) then the design ampacity needs to be reduced by 15%. It gets really interesting when the conductors are bundled (similar to coiled?) and the ampacity needs to be reduced by ..... get this, 40%. That is a serious reduction! The web page also notes the figures are for AWG and not for SAE wire sizes. This is important because manufacturers can, and do, mix things up. I had a project using 00 cables (double zero) and had to swage some terminals on. The cable and the terminals were both Ancor brand yet the terminals wouldn't fit. After analyzing the situation with the retailer it was determined that the terminals were the wrong size. Since Ancor buys their components from other companies there was probably a mix-up somewhere along the supply chain. Ancor is a respected brand in marine cables and electrical components. If the rating is based on 120V and the outlet voltage is less because the circuit load has had a voltage drop due to other loads on it then that causes additional problems. I'm wondering what the circuit breaker was doing in all this. And couldn't someone smell something was hot? Like hot plastic? Thanks, Tom, for posting your story. We all need a little safety heads-up from time to time. "The devil is in the details."