12AWG for 20A

[Tom Morrow]

I'm building some stingers (extension cords) that I want to use with 2k lights. Is 12AWG wire big enough or do I need 10AWG? My NEC 1999 "Wiring Simplified" book says that 12AWG has an ampacity of 20A (even buried underground), but I'm not clear about whether coiling would be worse than direct burial.

Here's another NEC ampacity chart:

http://www.usawire-cable.com/pdfs/NEC%20AMPACITIES.pdf

[Jacques Mersereau]

12 gauge is fine depending on length and use. I think 12 ga is approved for 20 AMP @ 100 feet.

Do you plan on actually drawing a full 20 AMPS through this? Inside or outside?
Reason being, outside in the SUMMER heat and direct sunlight can make a huge difference.
Heck, a black cable with nothing being put through it, on a black tarmac on a 100º day in the Sun gets real hot by itself.

If you are installing Edison plugs, then try to make sure you've got the 20 AMP rated.

[Jacques Mersereau]

I would recommend buying the best cable the first time out - the fire you don't have is worth it.

[Chris Medico]

The table you reference there is for specialized cable that isn't the kind of cable you would make stingers from.

Cable you would run for stingers would be SO or SJ. They are rated for 12ga @ 20a up to 50'. Over 50' for 20a would be 10ga.

[Garrett Low]

Hey Tom, you should talk to Bob Nelson in SC. He's actually an electrician and might even be able to hook you up with some deals on materials.

[Chris Medico]

I'm also a licensed electrician. :)

[Garrett Low]

Hey Chris, didn't intend to question your advice. Bob is someone that is in the same film coop as Tom so he might be able to give some hands on help.

[John Nantz]

When one wants to determine the wire size for a certain amperage and voltage drop, then the round-trip distance should used and not just the extension cord length.

To get the idea of the relationship I found a couple web pages that display that but, unfortunately, there for DC applications. AC would be different but the curves would be similar. At least one can get the idea.

Blue Sea web site: Voltage Drop in Conductor - Wire Sizing Chart - Blue Sea Systems

West Marine web site: The West Advisor: Marine Wire

Voltage drop will also occur if there is a conductor connection that isn't really solid, such as a set screw for example. In the case of a poor contact, such as the set screw just mentioned that isn't well seated, the increased resistance will cause heat to build up and depending on the amount, cause a meltdown, or worse.

If there is a splitter handy it could be plugged in at the end of the extension cord and a multimeter could be used to measure the voltage with the load turned on. At least that should be close enough.

As the saying goes, "The devil is in the details"

Disclaimer: I'm no electrician like Chris

[Chris Medico]

Originally Posted by Garrett Low

Hey Chris, didn't intend to question your advice. Bob is someone that is in the same film coop as Tom so he might be able to give some hands on help.

Oh No Garrett, I didn't take it that way. I was just being playful.

[Chris Medico]

Originally Posted by John Nantz

When one wants to determine the wire size for a certain amperage and voltage drop, then the round-trip distance should used and not just the extension cord length.


Voltage drop will also occur if there is a conductor connection that isn't really solid, such as a set screw for example. In the case of a poor contact, such as the set screw just mentioned that isn't well seated, the increased resistance will cause heat to build up and depending on the amount, cause a meltdown, or worse.

If there is a splitter handy it could be plugged in at the end of the extension cord and a multimeter could be used to measure the voltage with the load turned on. At least that should be close enough.

As the saying goes, "The devil is in the details"

Disclaimer: I'm no electrician like Chris

Common AC circuits that anyone will encounter using normal plugs and outlets aren't wired that way so trip length isn't an issue.

All conductors in the path are accounted for in the tables I posted so you are good there. Just remember they are MINIMUM CODE. I personally go one size above minimum when weight/cost/flexibility aren't issues.

Poor connections are indeed a serious concern. They can easily start a fire. I recommend having at least one person on watch when using high current devices. This would include a 2k connected up in a residential stetting. The watch person should monitor from the breaker box to the device. If you hear or smell something odd stop and check it out. Loose connections and bad breakers sometimes buzz when you start drawing current through them. Better yet if you have an electrician on the site have them check all the screws in the panel. Takes 5 minutes and can save a lot of down time looking for a replacement breaker.

Its also a good idea if you are working in a residential setting to exercise the breakers before you get started. You can find a bad one that way. When you flip the on and off it cleans the contacts which reduces the chance of a problem there as well. You should do that once a year for every breaker in your house actually.

Voltage drop is a good thing to check but it won't necessarily find a loose connection. If you drop 2v on a 20a load you have 40w of energy getting turned into heat. You won't notice that on a volt meter and you'll still melt the connector and/or set the house on fire.

[John Nantz]

Chris - That's a good tip about flicking the breakers. Never thought about it before. The one problem that I'll have, though, is so many circuits in my house have electronics or electrical stuff with digital clocks on them that will have to be reset.

Table: By the way, I was interested in that table you mentioned but couldn't spot it.

[Bruce Watson]

Originally Posted by Tom Morrow

I'm building some stingers (extension cords) that I want to use with 2k lights. Is 12AWG wire big enough or do I need 10AWG? My NEC 1999 "Wiring Simplified" book says that 12AWG has an ampacity of 20A (even buried underground), but I'm not clear about whether coiling would be worse than direct burial.

Here's another NEC ampacity chart:

http://www.usawire-cable.com/pdfs/NEC%20AMPACITIES.pdf

One thing you might want to think about is what you are going to plug this stinger into. If you're thinking you can plug it into a standard wall outlet (in the US), you're probably wrong. Nearly all wall outlets have 15 amp sockets. A 20 amp plug won't plug into it. For very good reasons.

While it's theoretically possible to run a 2k light off of a single house circuit, it's not actually practical. I would only do it if I had an electrician inspect that circuit first -- tighten down all the screws in the breaker box, check the house ground and make sure it's sound, etc. But not many houses have actual 20 amp circuits available (with 20 amp receptacles), so it's sort of a moot point.

[Chris Medico]

Originally Posted by John Nantz

Chris - That's a good tip about flicking the breakers. Never thought about it before. The one problem that I'll have, though, is so many circuits in my house have electronics or electrical stuff with digital clocks on them that will have to be reset.

Table: By the way, I was interested in that table you mentioned but couldn't spot it.

Sorry John, I thought I had posted it but didn't. This chart takes into account the cord type and the number of load bearing conductors.

UL Ampacity Guidance Chart

[John Nantz]

Chris - thanks for the Ampacity link.

My experience with electrical conductors stems primarily from maintaining my boat; hence the marine related references in my previous post. With 12 volts and a Fluke 77 multimeter one can read out to several significant places and it's easy to see the voltage drop from a battery bank. Electrical motor start-up voltage (forced air heater, water pump, microwave, etc.) is another issue though, and some day I'd like to get a scope or something like that so plot the voltage.

UL:

One thing of interest to me is that it is a Underwriters Lab UL chart and not something like NEC or so. There are a lot of "standards" organizations for all kinds of things and this is, I think, the first time I've ever come across what is apparently a UL one. Also noticed the little "Footnote 1" at the bottom of the chart.

A little UL side story:
Going back a few years, I was working my way through college in California and my job was 32 hours per week in a tool and die shop. The owner came up with a lamp product to be used on machine tools because at the time there weren't any really good lights that one could adjust. He called it the Cobra because the arm was made using stamped and formed "knuckles" and the two conductor (everything was two conductor back then) wire ran inside it.

He sent two (maybe three) samples of the lamp to UL (I think in New York) for approval along with, of course, a cover letter and their other required documents and the payment for the approval. One of the light samples was partially disassembled so UL could see how it was made and how it went together. UL took one look at one of the partially disassembled and disapproved the application. UL would not reconsider and insisted a resubmittal, with another payment of course.

For our small shop the cost for a UL approval was a lot of money. My boss, the owner, was incensed at ULs handling of the submittal so given how they acted with it he decided to market it without their approval. While he did sell quite a few of the lights it wasn't enough to stay in production and we quit making them. Not having a UL approval at the time was starting to be an impact on sales. Also, the lamp filled a niche market mostly in manufacturing operations so that was another factor.

Needless to say, as this occurred in my young life this experience has left a sour taste for UL.

As for standards organizations in general, it almost seems like some of them are a business model unto themselves. National Electrical Code, National Fire Protection Association, National Building Code, Uniform Building Code, American Association of State Highway Transportation Officials, just to name a few big ones I'm familiar with.

Bruce:
Very good point! How did we miss that?
On my boat I carry all kinds of connectors for 15A, 20A, and 30A. The 20A is definitely different than 15A.

[Chris Medico]

I chose that one because it is the same as the NEC charts AND everything is in one place.

With NEC charts you get multiple charts that are all subtly different and it can be overwhelming which one to read. Also much of that info is behind a pay wall which I can see with my NEC subscription but its not allowable to post it on a website. Since this one was already public and easy to read I figured it would be a good resource to reference.

I feel your pain with UL stuff. I deal with it every day with proprietary equipment for the BioPharmaceutical industry. Its driven by insurance companies. You don't want to see me get started there...