Rail Size

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Short Definition

Various sizes of rail are available to represent main lines, branches, and sidings, as usage/tonnage would require.

Rail sizes are expressed using the term Code.

Rail profile.svg

Code 100 rail (commonly found in train sets or used to model heavy rail used on the mainlines, is 0.1 inches, or 100 thou (thousands) in height.

Many sizes of rail are used, to represent the way the prototype used rail for mainlines, yards, and sidings, depending on the loads and usage.

Common to HO are Code 100, Code 83 and Code 70. N scale modellers would use even lighter rail, otherwise in proportion to the model, Code 100 would look huge. Narrow gauge modellers would employ light rail, such as Code 70 or Code 55, to better recreate the look of a narrow gauge railroad.

One issue that is very important is voltage drop. Proper feeder installation is important, as rail behaves just like wire: The smaller the cross sectional area, the more resistance. See the table below.

This is why the track must be wired using a power bus with feeders at regular intervals.

Rail Resistance, Nickel Silver

The following table gives the impedance of various codes of rail. The impedance was found with 1A (at 60Hz) current flowing through the sample, using a comparator feeding a detector set at 50μV. By injecting a negative impedance, the impedance of the rail is found when the measuring system is brought into balance.

Code of Rail Impedance per metre, mΩ Equivalent Wire Gauge Strands/Gauge
100 76 24 7/32
83 108 26 19/38
70 206 28 19/40

The wire used for an equivalent is stranded. Since the measurements were made at 60Hz, impedance better reflects the results.

Rail resistance measurement accuracy is >100ppm. Actual resistance will vary by manufacturer due to alloy and profile.