Wire Gauge, Fuses, and Electrical Safety Basics

Wire gauge: thicker wire carries more current

Wire is rated by AWG (American Wire Gauge), and the scale runs backwards: a smaller AWG number is a thicker wire that safely carries more current. 6 AWG is far fatter than 18 AWG.

This comes straight from the power lesson. Thinner wire has more resistance, and heat is P = I^2 x R — push too much current through too thin a wire and it overheats, melts its insulation, and can ignite. So you size wire to the current it will carry.

The FRC minimums (WPILib wiring docs and the Game Manual):

• Battery to main breaker to PDH/PDP: 6 AWG copper — this carries the full robot current.
• 40A breaker circuit: 12 AWG minimum.
• 30A breaker circuit: 14 AWG minimum.
• 20A breaker circuit: 18 AWG minimum.
• roboRIO and radio power: 18 AWG.

The principle behind the table: the breaker protects the wire. A higher-amp breaker has to feed thicker wire, never the reverse.

Fuses and breakers: the deliberate weak link

A fuse or breaker sits in series with what it protects and opens the circuit when current exceeds a safe limit — a short, or a jammed motor — before the wire or component is damaged. A fuse melts once and gets replaced; a circuit breaker trips and resets, which is why FRC motor channels use breakers.

On the robot:

• The 120A main breaker sits between the battery and the PDH/PDP. It's both the master cutoff and the top-level protection for all downstream wiring.
• Motor channels use auto-resetting Snap-Action breakers sized to the wire and motor — commonly 40A, 30A, and 20A.
• The roboRIO and radio run on smaller 10A protection.

The golden rule: the breaker's rating must match the wire it protects. A 40A breaker on 18 AWG wire is dangerous — the wire can cook long before 40A trips the breaker.

Limit current in code, too

Breakers stop catastrophic faults, but they're slow and blunt. Good teams also set current limits in software (in WPILib, on the motor controller) so a stalled mechanism backs off before it sags the battery into a brownout or nuisance-trips a breaker. Hardware and software protection work together.

Habits that prevent the worst day

1. Connect the battery last, after the circuit is built and checked — and disconnect it first before working.
2. Verify polarity: red to positive, black to negative. Reversing it instantly destroys electronics.
3. Crimp, don't twist. Loose joints add resistance, make heat, and cause flaky brownouts. Use proper crimps and Wago connectors where the manual calls for them.
4. A short circuit is the enemy. Near-zero resistance means I = V/R races toward the battery's 180A+ capability. Keep stray wire strands and tools off the battery terminals and bus bars.
5. Charge a tired battery. A pack resting at 12.5V on an idle robot should be swapped and charged before a match to avoid sag and brownouts.
6. Respect 12V. It won't shock you through dry skin, but its available current can melt a wrench and start a fire. Treat the battery terminals like they're hot.

Get wire gauge, fusing, and these habits right and the electricity from the first three lessons stays inside your wires, doing useful work.