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I am trying to understand the relationship between these. I have 24AWG 300V copper PVC insulated wire. From what I have learned, this wire can be used to connect a Panel LED that draws <20 mA @ 110V to a 110V main power terminal strip.

I have read that voltage drop would be a problem with increasing lengths of wire at smaller gauges. This wire's length is less than 2 feet and at room temperature. Using a calculator, the Vdrop is on the order of a thousandths of a volt. Am I doing my math correctly? I have only been able to find examples of this situation where people used 14 gauge wire, which has to be way overkill.

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  • \$\begingroup\$ 14 awg might be overkill, but if you're talking about something installed by an electrician it might just be what they have lying around, because 14 awg is commonly used for 10 A circuits (in the US). A couple of feet of 14 awg is something that would be lying around as scrap during any electrical installation work. \$\endgroup\$ – The Photon Mar 6 '14 at 19:03
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    \$\begingroup\$ @ThePhoton: Actually, that would be 15A circuits in the US. AWG12 is normally used for 20A circuits. \$\endgroup\$ – Dave Tweed Mar 6 '14 at 19:10
  • \$\begingroup\$ @DaveTweed, Yes you're right. Brain freeze. Anyway I think Spehro got the right answer: You need to pick the wire gage according to how it's fused. \$\endgroup\$ – The Photon Mar 6 '14 at 19:51
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Voltage drop is one consideration, there are others.

Think about the potential fault current and fusing for that circuit.

You want the wire to be sufficiently large gauge to be able to blow the fuse or trip the breaker without causing a hazardous situation (such as the wire going incandescent). In many cases that may be prescriptively spelled out by safety regulations (NEC, UL or whatever).

There may also be minimum gauge requirements just for mechanical robustness (for example AWG20 is the minimum wire gauge allowed in some situations).

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  • \$\begingroup\$ I see. That makes sense. In this situation, the LED would probably burn out before the wire though right? \$\endgroup\$ – user2558042 Mar 6 '14 at 19:21
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    \$\begingroup\$ Sure, but the wires could be shorted to each other. \$\endgroup\$ – Spehro Pefhany Mar 6 '14 at 19:26
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According to my copper wire table, #24 wire has close to 26 ohms per thousand feet. So about a millivolt drop is about right. Sometimes wire larger than necessary is used because it is less fragile than the smaller wire that meets the electrical requirements.

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