The cross-section of the wire from the junction box to the machine is determined by the following factors:
Maximum load current:
Determine the maximum current that will be consumed by the protected load. This can be found on the equipment nameplates or from the manufacturer.
Allowable current density:
Each wire has an allowable current density, which is the maximum amount of current that can pass through the wire without overheating. For residential premises this figure is usually 9 amperes per mm?.
Wire length:
The longer the wire, the greater the voltage drop will occur. A thicker wire will have a lower voltage drop.
Wire type:
Copper wires are usually used for internal wiring.
Wiring method:
If the wire is laid in a pipe or corrugation, a smaller cross-section is allowed than with an open installation.
Recommended wire sizes for various load currents:
* 16 amps: 2.5 mm?
* 25 amps: 4 mm?
* 32 amps: 6 mm?
* 40 amp: 10 mm?
* 50 amp: 16 mm?
* 63 amps: 25 mm?
Example: If the protected load consumes a maximum current of 20 amperes, and the length of the wire from the junction box to the machine is 10 meters, it is recommended to use a wire with a cross-section of at least 4 mm?.
Note: To accurately calculate the wire cross-section, you can use the formula:
“`
S = (I * L) / D
“`
Where:
* S – wire cross-section in mm?
* I – maximum load current in amperes
* L – wire length in meters
* D – permissible current density in amperes per mm?