How to Choose Wire Gauge and Length for Your 3d Printer

How can you calculate the wire gauge and length for 3d printer wiring? Most 3D printers use either 12V or 24V. The hotend of a 3D printer may draw up to 4A, while a heated bed draws nearly 12A. If the wire is not large enough or longer than needed, it will have more resistance which means less watts going through the wire. Copper wire size uses American Wire Gauge (AWG) which determines how much current it can handle safely. To calculate 3d printer wiring calculations, divide Current in Amps by Length in Feet to identify the correct size of wire material needed for your 3D printing project.”

Stepper Motor Wiring

Rated Current is the maximum current that can pass through both windings at the same time. Set the motor current to no more than about 85% of the rated current. To get maximum torque out of your motors without overheating them, you should choose motors with a current rating no more than 25% higher than the recommended maximum stepper driver current. 

• Nema 17 Stepper Motors: 22 AWG wire with 4 conductors
• NEMA 17 motor wires are 26 AWG

Most motor torque data assumed 24 Volts, at 1.1 amp to 1.5 amp. Roughly 26 to 36 Watts, but remember that’s “chopped” or pulsed.

Wire size is based on power transmission requirements and length of wire.

If your wire gauge is not large enough or longer than needed the resistance will be higher This means less watts going through the wire. Copper wire size uses the American Wire Gauge (AWG). The lower the gauge number, the less resistance the wire has and therefore the higher current it can handle safely.

Most motor torque data assumed 24 Volts, at 1.1 amp to 1.5 amp. Roughly 26 to 36 Watts, but remember that’s “chopped” or pulsed. Wire size is based on power transmission requirements and length of wire.

Recommended Wire Size

• 10 gauge wire – 30 amps
• 12 gauge wire – 20 amps
• 14 gauge wire – 15 amps
• 16 gauge wire – 10 amps
• 18 gauge wire – 7 amps
• 20 gauge wire – 3 amps (or slightly more)
• 22 gauge wire – 2 amps

• Maximum motor current 1.5A peak => Stepper motor rated current <= 1.9A
• Maximum motor current 2.5A peak  => Stepper motor rated current <= 3.0A
• Maximum motor current 1.6A peak with good fan cooling  => Stepper motor rated current <= 1.7A. 

3d printing at a higher speed uses more current and can cause wire overheating if wire thickness is not thick enough. Use motors with lower rated current (e.g. 1.0 to 1.2A) and 24V power, then the drivers will run cooler.

Duet 3 Current

Duet 3 Mainboard 6HC and Expansion board 3HC has a recommended maximum motor current 6.3A peak/4.45A RMS) => Stepper motor rated current <= 6A

Duet 3 Toolboard has a recommended maximum motor current 1.4A peak) => Stepper motor rated current <= 1.75A

One solution is twisted pairs of wire to have one wire carrying the current while the other brings the current back. Use a shielded 4-core high current wire, so that the wiring creates much less capacitive and induced interference or a twisted pair of twisted pairs.

Each individual winding should have a twisted pair, and these two pairs should be twisted (in the opposite sense) together. Twisted pair will reduce induced interference to a minimum, and twist-on-twist is a very flexible way to combine 4 wires. Alas the construction will couple capacitively to nearby signal cables, so it pays to keep separate from them, or ensure all signal cables are shielded. Signal cables are things like limit switch wiring, encoders, etc….

Using a cordless drill and a bench vice, keep enough tension to prevent kinking, and reverse briefly to lose any torsion before releasing the wires.

Wire Connectors

The Molex 4 pin connector are rated at about 14 Amps (.093 inch / 2.36 mm diameter terminals.

Calculating the wire size

A higher voltage means a lower current for the same amount of power. This gives you the opportunity to use smaller wires for the same job. Voltage is proportional to the current.  A higher voltage means a lower current. Wire size influences the amount of current that can pass through it.

• A thicker wire will have less resistance per length
• Less resistance means loss
• The less loss means less temperature increase

In terms of wire size, 24V has an advantage over 12V, as the wires can be much smaller. A power supply of 300 watts running at 12V or 24V, will use less wire.

Wire Sizing Chart and Formula

Calculate the Voltage Drop Index (VDI) using the following formula:

1. VDI = AMPS x FEET ÷ (% VOLT DROP x VOLTAGE)
2. Determine the appropriate wire size from the chart above.

To compensate for voltage-drop, heat and current changes it is recommended to use 6 gauge wire and 4 gauge for over 15 feet.

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