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.
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.
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|
- 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. The samples were Micro Engineering flex track
Why Different Sizes
The rail size or code indicates the height, and is used to represent the various types of rail used by the prototype. (H0 Scale)
|H0 Scale||Prototype Rail|
|Code||Pounds per yard||Height, inches||Application|
|100||152||8.7||PRR Heavy rail (155lb) used in the mountains|
|83||126||7.1||Main line applications|
|75||114||6.5||Main line, passing sidings|
|55||83||4.7||Sidings, industrial, Narrow gauge railways|
|40||60||3.5||Narrow gauge and industrial railways|
In general, heavier tonnage, heavier rail. For N scale, divide the code number by 2, or for 0, multiply by two to get an approximate size. For Example, the C83 equivalents for N are 45, and 0, 148. So C40 and C150 are appropriate. The NMRA recommends C40 for all applications in N Scale. For more details see NMRA Data Sheet D9r Rail Size. Choosing the appropriate rail size will make your models look much more like a model.
In the 19th century, rail weights of 40 to 80 lbs were typical. In the 20th century, weights increased to the 112 to 145 lbs seen today. For most modellers, Code 83 is the best compromise for main line trackage. Lighter rails can be represented by C70 and C55 rail for sidings, yards or lightly used branch lines. C100 can be used to represent the 155 lb. rail used by the Pennsylvania Railroad in their mountain districts.