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American, British, and Metric
Standard Wire Gauge
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Sizes, Resistance, Voltage Drop, and Uses |
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Standard |
WG |
Approx.
O.D. |
Square |
Resistance |
Voltage Drop at 5 Amps |
Used For |
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Inches |
MM |
Inches |
MM |
Ohms/Ft |
Ohms/Meter |
Volts/Ft |
Volts/Meter |
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British |
12 |
0.1040 |
2.64 |
0.0085 |
5.48 |
0.001 |
0.003 |
0.0050 |
0.0164 |
Power Bus Lengths over 100ft |
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American |
10 |
0.1019 |
2.59 |
0.0082 |
5.26 |
0.001 |
0.003 |
0.0052 |
0.0171 |
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Metric |
25 |
0.0984 |
2.50 |
0.0076 |
4.90 |
0.001 |
0.004 |
0.0056 |
0.0183 |
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British |
13 |
0.0920 |
2.34 |
0.0066 |
4.29 |
0.001 |
0.004 |
0.0064 |
0.0210 |
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American |
12 |
0.0808 |
2.05 |
0.0051 |
3.31 |
0.002 |
0.005 |
0.0082 |
0.0272 |
Power Bus Lengths
50ft-100ft |
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British |
14 |
0.0800 |
2.03 |
0.0050 |
3.24 |
0.002 |
0.006 |
0.0084 |
0.0277 |
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Metric |
20 |
0.0787 |
2.00 |
0.0049 |
3.14 |
0.002 |
0.006 |
0.0087 |
0.0287 |
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British |
15 |
0.0720 |
1.83 |
0.0041 |
2.63 |
0.002 |
0.007 |
0.0104 |
0.0342 |
Power Bus Lengths
30ft-50ft |
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Metric |
18 |
0.0709 |
1.80 |
0.0039 |
2.55 |
0.002 |
0.007 |
0.0107 |
0.0353 |
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American |
14 |
0.0641 |
1.63 |
0.0032 |
2.08 |
0.003 |
0.009 |
0.0131 |
0.0432 |
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British |
16 |
0.0640 |
1.63 |
0.0032 |
2.07 |
0.003 |
0.009 |
0.0131 |
0.0433 |
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Metric |
16 |
0.0630 |
1.60 |
0.0031 |
2.01 |
0.003 |
0.009 |
0.0136 |
0.0447 |
Power Bus Lengths
00ft-30ft |
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British |
17 |
0.0560 |
1.42 |
0.0025 |
1.59 |
0.003 |
0.011 |
0.0172 |
0.0566 |
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Metric |
14 |
0.0551 |
1.40 |
0.0024 |
1.54 |
0.004 |
0.012 |
0.0177 |
0.0585 |
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American |
16 |
0.0508 |
1.29 |
0.0020 |
1.31 |
0.004 |
0.014 |
0.0208 |
0.0688 |
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British |
18 |
0.0480 |
1.22 |
0.0018 |
1.17 |
0.005 |
0.015 |
0.0233 |
0.0770 |
Short splices to Power
Bus. |
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Metric |
12 |
0.0472 |
1.20 |
0.0017 |
1.13 |
0.005 |
0.016 |
0.0241 |
0.0797 |
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American |
18 |
0.0403 |
1.02 |
0.0013 |
0.82 |
0.007 |
0.022 |
0.0331 |
0.1093 |
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British |
19 |
0.0400 |
1.02 |
0.0013 |
0.81 |
0.007 |
0.022 |
0.0336 |
0.1110 |
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Metric |
10 |
0.0394 |
1.00 |
0.0012 |
0.79 |
0.007 |
0.023 |
0.0347 |
0.1144 |
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British |
20 |
0.0360 |
0.91 |
0.0010 |
0.66 |
0.008 |
0.027 |
0.0415 |
0.1370 |
Short Splices and
Feeders |
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Metric |
9 |
0.0354 |
0.90 |
0.0010 |
0.63 |
0.009 |
0.028 |
0.0429 |
0.1417 |
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American |
20 |
0.0320 |
0.81 |
0.0008 |
0.52 |
0.011 |
0.035 |
0.0525 |
0.1734 |
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British |
21 |
0.0320 |
0.81 |
0.0008 |
0.52 |
0.011 |
0.035 |
0.0525 |
0.1734 |
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Metric |
8 |
0.0315 |
0.80 |
0.0008 |
0.50 |
0.011 |
0.036 |
0.0542 |
0.1789 |
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British |
22 |
0.0280 |
0.71 |
0.0006 |
0.40 |
0.014 |
0.045 |
0.0686 |
0.2264 |
Drop Feeders, Rail to
Bus |
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Metric |
7 |
0.0276 |
0.70 |
0.0006 |
0.39 |
0.014 |
0.047 |
0.0706 |
0.2330 |
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American |
22 |
0.0253 |
0.64 |
0.0005 |
0.32 |
0.017 |
0.055 |
0.0840 |
0.2773 |
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British |
23 |
0.0240 |
0.61 |
0.0005 |
0.29 |
0.019 |
0.062 |
0.0934 |
0.3082 |
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Metric |
6 |
0.0236 |
0.60 |
0.0004 |
0.28 |
0.019 |
0.064 |
0.0966 |
0.3187 |
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British |
24 |
0.0220 |
0.56 |
0.0004 |
0.25 |
0.022 |
0.073 |
0.1111 |
0.3668 |
Drop Feeders, Rail to
Bus |
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American |
24 |
0.0201 |
0.51 |
0.0003 |
0.20 |
0.027 |
0.088 |
0.1332 |
0.4394 |
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British |
25 |
0.0200 |
0.51 |
0.0003 |
0.20 |
0.027 |
0.089 |
0.1345 |
0.4438 |
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Metric |
5 |
0.0197 |
0.50 |
0.0003 |
0.20 |
0.028 |
0.091 |
0.1386 |
0.4574 |
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Resistance and Voltage Drop of Common Rail Sizes |
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Nickel Silver Rail |
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Ohm's per |
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Voltage Drop at 5 Amps per |
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Code |
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Foot |
Meter |
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Foot |
Meter |
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100 |
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0.0275 |
0.09075 |
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0.275 |
0.9075 |
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83 |
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0.0424 |
0.13992 |
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0.424 |
1.3992 |
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70 |
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0.0757 |
0.24981 |
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0.757 |
2.4981 |
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55 |
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0.1107 |
0.36531 |
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1.107 |
3.6531 |
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Brass Rail |
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100 |
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0.0016 |
0.00528 |
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0.016 |
0.0528 |
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83 |
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0.0024 |
0.00792 |
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0.024 |
0.0792 |
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70 |
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0.0044 |
0.01452 |
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0.044 |
0.1452 |
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55 |
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0.0064 |
0.02112 |
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0.064 |
0.2112 |
Wire Gauge Standards
AWG = American Wire Gauge BWG = British Wire Gauge [Imperial] MWG = Metric Wire Gauge
Every Circuit Requires a Return Path.
When calculating wire distance for resistance and/or voltage drops,
figure the wire distance to include out and back. As example, if the physical distance from source to control
is 50ft, the wire length will be 100ft, 50ft out and 50ft back
Voltage drop figures for rails already include both rails. The resistance is for a single rail.
The Coin Test
No matter what wire size is used for Power Bus and Drop Feeders. Shorting across the rails with a metallic
object will be the final test. Do this
at all power districts across the layout, at different points inside
each district and in all reverse sections. Mainly at the distant most points of each. This should result in
a booster or power management unit tripping to fault protection almost instantly, usually 1/8th second or less.
If not, then
this indicates there is high resistance somewhere. Either in wire size being to small for the
distance required and/or possible high resistance in connection points. All will cause excess voltage drop
and not allow the booster/s or power manager to trip into fault mode. In any case the
cause of the excess
voltage must be corrected.
The #1156 Automotive Tail Lamp.
This lamp is very commonly used as a ballast or current limit device. It is a single filament bayonet base.
Any basic 12V 25W lamp should work the same. For reference the #1156 has a cold filament resistance of
0.4356 Ohm
Note:
All values are approximate, and based on the actual material used, this is an alloy and will vary from
manufacturing process.
All resistance values for wire are based on the square area of copper, see the above note.
All wire values are based on solid wire. Stranded wire will vary above and below based on the strand size
and number of strands.