Calculator for maximum cable length - SmartRelay AX Classic
You can use the form to provide a rough estimate for copper cables. The form takes into account the maximum cable length resulting from the voltage drop. It does not test for other interferences such as transition resistances or electromagnetic interference fields that limit the maximum cable length to 300 m. The following formula is used:
Symbol | Value/Input |
|---|---|
| Maximum cable length in m |
| Input voltage in V |
| Cross-section of the cable used in mm² |
| Reader power consumption at 8 V = 0.2 A |
| Specific electrical resistance (copper) = 0.01786 Ωmm²/m |
The result is the maximum cable length resulting from the voltage drop. This length comprises both the outward and return path.
To increase operational reliability, you should use a separate power supply unit for the reader from 75% of the maximum calculated length.
Enter the following values in the calculator:
Value | Explanation |
|---|---|
Supply voltage VIN [V] | Voltage of the connected power supply unit. Read the value on the power supply unit or ask the electrician responsible. Enter the number without a unit and separate decimal places with a decimal point (e.g. 13.5). |
Cable cross-section A [mm²] | Cross-section of the installed or planned cable. Read the value on the cable or ask the electrician responsible. Enter the number without a unit and separate decimal places with a decimal point (e.g. 0.5). |
The following table contains the maximum lengths for commonly used cable cross-sections and supply voltages.
0.1022 mm² (=AWG27) | 0.14 mm² | 0.2 mm² | 0.6 mm² | |
9 V | 14 m | 19 m | 27 m | 83 m |
12 V | 57 m | 78 m | 111 m | 300 m |
24 V | 223 m | 300 m | 300 m | 300 m |
32 V | 300 m | 300 m | 300 m | 300 m |