Wire length tables

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When designing an electrical system, it is important to pick the correct length of and size (gauge) wire for your application to minimize voltage loss and ensure safety. If there is a lot of current running through a small wire (small wire meaning a wire with a small diameter) for a long distance, there will be significant voltage drop (causing a decrease in current arriving at the load). This may also cause the wire to become hot and burn or catch fire. It is important to choose a wire big enough (big wire meaning a wire with a large diameter) for any application based on the current that is expected to run through that wire, and the wire's round trip distance (or total wire length).

Copper wire is considered in this analysis, but it can easily be used for aluminum wire (or other wire materials) simply by changing the wire materials resistivity (11.2 for copper, in Eqn. 6 on How to create your own wire length tables). The Wire Size Section contains Table 1, which can be used to determine wire size based on a few assumptions.

Wire Size Table[edit | edit source]

Table 1 shows the American Wire Gauge (AWG) size for several different round trip (RT) wire lengths based on maximum current (A) for a 12V DC system (assuming 3% maximum wire loss) with copper wires having a resistivity of 11.2[1]:

Table 1. Wire Sizes
RT length 5A 10A 15A 20A 25A 30A 40A 50A
5 ft 20 18 16 14 14 12 12 10
10 ft 18 14 12 12 10 10 8 8
15 ft 16 12 10 10 8 8 6 6
20 ft 14 12 10 8 8 6 6 4
25 ft 14 10 8 8 6 6 4 4
30 ft 12 10 8 6 6 4 4 2
40 ft 12 8 6 6 4 4 2 2
50 ft 10 8 6 4 4 2 2 1
60 ft 10 6 4 4 2 2 1 1/0
70 ft 8 6 4 2 2 2 1/0 2/0
80 ft 8 6 4 2 2 1 1/0 2/0
90 ft 8 4 2 2 1 1/0 2/0 3/0


How to create your own wire length tables explains how these values were calculated.

References[edit | edit source]

  • This table was adapted from Engineering Toolbox[1].