# Wire sizes: Wire Resistance Table

Summary: Different guard wires have varying degrees of resistance.

### American Wire Gauge

The following table gives the size of various conductors, with the diameter in Mils. One Mil is 0.001 inches, or one one-thousand of an inch.

The temperature all measurements (volume, length and resistance) were made at is **20º C**.

It is worthwhile to note that cross-sectional dimensions are chosen such at each *decrease* in gauge number represents a 25% *increase* of the *cross-sectional area.* On this basis, a decrease of *three* gauge numbers will represent an *increase* of the cross-sectional area of 1.25 × 1.25 × 1.25, for an approximate increase of 2:1. Similarly a change of ten gauge numbers will represent approximately an 9:1 change in cross-sectional area.

Since doubling the cross-sectional area cuts the resistance in half, a decrease of three gauge numbers will decrease the resistance of a given length of wire by half.

Applying the rule of 1.25^{(Number of steps)} allows for quick calculations for the increase or decrease in resistance between various wire gauges.

For example, AWG 22 has almost **9** times the resistance as that of 12 AWG (10 steps). Or 14 AWG has 1.25^{2} or 1.6 times that of AWG 12's resistance.

Using that knowledge, a 10 foot run of AWG 14 is equivalent to 16 feet of AWG 12.

To calculate the approximate resistance of a wire, start with AWG 10 = 1Ω per thousand feet. Using the rule above will allow you to calculate the approximate resistance of any wire using the calculated multiplier. Example:

- 14AWG, 10 – 14 = 4 steps, 1.25^4 =
**2.44**

Therefore 14AWG is approximately 2.44Ω per thousand feet. (If you use 1.26^4 the result is closer at 2.52. The 1.25 factor is easier to remember.)

### Conductor Sizes

The temperature all measurements (volume, length and resistance) were made at is **20º C**.

AWG Number |
Diameter, in Mils |
Ohms per thousand feet |
---|---|---|

10 | 101.9 | 0.9989 |

11 | 90.74 | 1.260 |

12 | 80.81 | 1.588 |

13 | 71.96 | 2.003 |

14 | 64.05 | 2.525 |

15 | 57.07 | 3.184 |

16 | 50.82 | 4.016 |

17 | 45.26 | 5.064 |

18 | 40.30 | 6.385 |

19 | 35.89 | 8.051 |

20 | 31.96 | 10.15 |

21 | 28.46 | 12.80 |

22 | 25.35 | 16.14 |

### Recommended Wire Gauge Chart

Wire Gauge Guidelines for a DCC Power Bus | ||||||||||||
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American Wire Gauge (AWG) | ||||||||||||

https://dccwiki.com/Wire_Sizes_and_Spacing | ||||||||||||

Scale | G | 0 | S | H0 | 00 | TT | N | Z | N−Trak | |||

Ratio | 1:20.3 | 1:29 | 1:48 | 1:64 | 1:87.1 | 1:76.2 | 1:120 | 1:160 | 1:220 | |||

Bus Length |
< 21 ft | < 6m | 12 | 14 | 14 | 16 | 16 | |||||

21 − 40 | 6 − 12m | 10 | 12 − 14 | 14 | 14 | |||||||

> 40 ft | > 12m | 8 | 12 | 12 | ||||||||

Feeder Wire Length |
< 5 ft | < 1.5M | 16 | 18 − 22 | 20 | 18 − 22 | 18 − 22 | |||||

< 10 ft | < 3m | 14 | 18 − 20 | 18 − 20 | 18 − 20 | |||||||

Recommended Wire Gauge | ||||||||||||

N−Trak is based on the N−Trak Wiring RP for DCC http://ntrak.org/ntrak_powerpole_rp.htm | ||||||||||||

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