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Novice question, sorry if it has been asked. I couldn't find it.

I'm currently working on a project and I'll be powering 2 LED strips connected together. They each require 12V (24W, 2 amps).

I need wires to run about 15 feet. In my research I'm finding AWG charts are all pretty conflicting. Some are trying to tell me 20 AWG would do the job, others are saying I should use 12 AWG, 14 AWG... etc...

As someone who sincerely doesn't want to start a fire, is there some trust-worthy source for this information?

Thanks in advance.

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  • \$\begingroup\$ Did any of them list/ask for an acceptable temperature increase? \$\endgroup\$ Nov 24, 2017 at 0:21
  • \$\begingroup\$ @IgnacioVazquez-Abrams Some charts do mention temperatures. For instance, the chart on wikipedia has 3 columns for 60, 75, and 90 deg C. Although I'm not sure exactly what it is referring to there. Other charts I've found don't reference temperature at all. For instance, based on this: link 20 awg would be fine (I think) But based on this: link I would need 16 AWG \$\endgroup\$
    – darkcammo
    Nov 24, 2017 at 1:12
  • \$\begingroup\$ You read the second link wrong. The minimum current in that table is 5 A, while your current is only 2 A. \$\endgroup\$ Nov 24, 2017 at 1:14
  • \$\begingroup\$ Right, I went with the closest value of 5 amps. A wire that can handle 5 amps could handle 2 amps (or in this case with 2 led strips, 4 amps). \$\endgroup\$
    – darkcammo
    Nov 24, 2017 at 1:26

1 Answer 1

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This is not a matter of "trust-worthy", it is a matter of understanding of basics of electricity. One should always remember that any wire is a resistor. As a resistor in a circuit with current flowing, it

(a) dissipates energy, and therefore produces Joule heat, and

(b) voltage drops along the wire.

These are two major restrictions imposed by wires in DC applications. That's it.

The wire gauge system is based on restriction (a), to what extent the design can tolerate increase of wire temperature. The temperature raise depends, in turn, on ambient conditions, whether it is assumed to hang in open air, or moving air, or encapsulated into equipment or thick insulation jacket. That's why different sources might differ in assumptions about the acceptable level of temperature increase, or duration of current pulse, etc., and give slightly different results.

The second effect is (b), voltage drop, so in voltage-sensitive application (like LED steep forward voltage), the drop might have a strong effect. According to Wikipedia, 20 AWG wire has resistance of 10 mOhms/foot, so 15 feet will have 0.15 Ohm resistance. With 2 A current it will result in voltage drop of 0.3 V one way, or 0.6V less at the load (accounting for ground return wire drop). For a 12-V setup this sounds like tolerable, unless there is a design error in LED hook-up.

The same source indicates that a 20 AWG wire can sustain 7.5A with 20 C raise in temperature, so 2 A shouldn't be any problem either.

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  • \$\begingroup\$ Thank you for your clear, concise reply. My gut was telling me that 20 AWG would be okay for my application. I think I am just not fully understanding the temperature ratings. For instance in the wikipedia chart, it appears the copper cable can handle more (11 amps) at a higher temperature (75 deg C). That is counter-intuitive. At a higher temp, I would expect it to perform more poorly (less current). \$\endgroup\$
    – darkcammo
    Nov 24, 2017 at 1:22
  • \$\begingroup\$ That's not counter intuitive. It's saying that it can do more amps of you are okay with the temperature increasing. Normal conductors like copper will not have performance issues as current/temperature increases. The insulation will fail and the copper will fuse at a certain temperature though. \$\endgroup\$
    – Passerby
    Nov 24, 2017 at 1:54
  • \$\begingroup\$ Copper has a very low positive temperature co-efficent resistance. There are conductors that have a high PTC or NTC, where they will have performance difference as the conductor heats up. \$\endgroup\$
    – Passerby
    Nov 24, 2017 at 1:56

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