If my project uses 30A DC, what wire gauge should I be using?

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    Instead of asking a dozen separate (and extremely basic) questions about wiring, how about you look up some reference guides first, and decide what you really need help with rather than shotgunning this site. – Carl Witthoft Apr 19 '16 at 19:32
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    I say, shotgun away. As long as you're not asking duplicate questions, there's no problem asking "basic" questions. – Tester101 Apr 19 '16 at 19:51
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    However, make sure the questions are on topic. If this project does not relate to home improvement, it might be better suited to Electrical Engineering. – Tester101 Apr 19 '16 at 19:53
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    Where do you have 30A DC in your home? – BMitch Apr 19 '16 at 20:17
  • @BMitch In a 12V 30A power supply, but yeah, it's a 3d printer project. – leeand00 Apr 19 '16 at 20:25

#10 AWG is code compliant for 30 amp circuits.

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  • Do you have a source? – leeand00 Apr 19 '16 at 19:36
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    Yes table 310.15(B)(16) of the National Electrical Code. That is for THHN/THWN. You could buy more expensive wire and use a smaller wire but why. barr-thorp.com/wp-content/uploads/2011/04/… – ArchonOSX Apr 19 '16 at 19:40
  • #12 is listed for 30 amps at 90ºC but you can't find breakers or terminals rated for 90ºC plus the asterisks point you to a part of the code that limits #12 to 20 amp circuit protection. – ArchonOSX Apr 19 '16 at 19:44
  • 10 AWG is code compliant for 60°C conductor temperatures, with 30°C ambient temperatures, with not more than three current carrying conductors in a raceway, and where the length of wire does not cause an unacceptable voltage drop. To simply say 10 AWG = 30 amperes, is not correct. – Tester101 Apr 20 '16 at 0:21
  • I think you are overthinking it for this particular question. Without all those other details the default is #10 before any adjustments. – ArchonOSX Apr 20 '16 at 0:25

The gauge of wire you use depends on:

  • how much voltage drop is acceptable. You can use a voltage drop calculator to estimate this. Voltage drop depends on the voltage, current, length of wire, and resistance of wire (i.e. the wire gauge, material, construction).
  • how much heat is acceptable. This depends partly on the specific application, and also the insulation on the wire. Running current through a wire causes some heating due to electrical resistance, and a smaller wire will heat up more. That's not necessarily a problem, unless the heating is excessive and creates a fire or melting risk.

(These two points are really just two ways of looking at the same phenomenon: loss of electric power due to heat. But they often have different ramifications or solutions so I think it is helpful to consider them separately.)

Since you haven't provided any information about the voltage, length of wire involved, application, or insulation, it is not possible to give a reasonable number.

The wiring standards that are used in building construction are based on common assumptions about voltage, acceptable losses, typical temperature ranges, etc. They may or may not be applicable in your situation.

P.S. - I don't know what project you are working on but make sure it is properly protected from over-current conditions. Most "household" breakers, switches, etc. are not rated for DC. DC fuses are cheap and easy to use... make sure the fuse is always the weakest link in the entire project.

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We're on DIY.stackexchange, so the context here is house repair. For architectural wiring, 10 AWG is required by code. However on projects, UL deems 12 gauge acceptable in short runs inside equipment. Check the guidelines.

You may want to go higher still if you are going long distances and don't want to lose a lot of your voltage to Ohm's Law. In some cases this is required.

Edit: See also, this, which is not official but gives you a sense of the difference between "chassis" and "pole line transmission": http://www.powerstream.com/Wire_Size.htm

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