Battery & Electrical Safety

The robot's power system is the one place in the pit where carelessness can burn you, melt a tool, or start a fire. None of it is scary if you respect it — here's what every team member should understand before touching the battery or the wiring.

##Your battery can dump over 500 amps

The robot runs on a single 12V, ~18Ah sealed lead-acid (SLA) battery — rule R601 allows exactly one (17–18.2 Ah). It is deceptively powerful: fully charged it can briefly supply over 180 A, and a dead short across the terminals can arc at over 500 A. SLA batteries have no built-in short-circuit protection, so a short does not trip anything — it just pours current until something melts, sparks, or the battery vents.

A wrench or piece of scrap laid across both battery terminals can heat red-hot in seconds and weld itself in place. It will not throw a large arc-flash, but it can absolutely cause burns and start a fire.

Rules of thumb:

• Never let any metal bridge the two battery terminals.
• Rule R607 requires every terminal on the battery, the main breaker, and their wire connections to be fully insulated at all times — tape any exposed lug.
• When you connect the battery, tape over the terminal you are not working on so a slipped tool cannot short across both.

##The danger zone: battery → main breaker

The 120 A main breaker is both the robot's power switch and its protection device — but it only protects what is downstream of it. The short run of wire between the battery and the main breaker is unprotected.

• A fault downstream of the breaker trips it and shuts off, limited by the breaker's time/current curve.
• A fault upstream — on that battery-to-breaker run — is limited only by the battery, which is why those leads can glow hot.

This is also why rule R611 ("the ROBOT frame is not a wire") requires all wiring electrically isolated from the frame, verified by inspectors with a >120 Ω resistance check between the battery posts (at the PDP/PDH) and the frame. If worn insulation lets a battery lead touch the chassis, and a second fault grounds the other lead, you have shorted the battery straight through your robot. Route wiring away from moving and sharp parts, and bolt the SB50 connector to the frame using the 6-32 holes in the housing so it cannot be yanked loose.

##12V will not shock you — usually

12V DC is "safe extra-low voltage." The international threshold (IEC 61140) for extra-low voltage is 120 V ripple-free DC / 50 V AC, so 12V is far below the level that can push dangerous current through dry skin. You can handle the robot's 12V wiring without getting shocked.

The one variable is resistance: salt water, sweat, or broken skin lowers your body's resistance, and a cut across a live terminal can sting. So on the robot, 12V is a heat-and-short hazard, not a shock hazard.

##Shop power (120V AC) is the real shock hazard

The thing in the shop that can actually hurt a person is 120V wall power — the battery charger, drills, soldering irons.

• Shorting or crushing a 120V cable produces a real arc and flash (normal breakers limit the energy and duration).
• Touching a live 120V conductor will shock you, with real risk of burns, involuntary muscle lock, and cardiac arrest.
• If you find someone stuck on a live line, do NOT grab them — you will become a second victim. Cut the power if you can. If you cannot, use a dry, non-conductive object — a dry 2×4, PVC pipe, or wooden broom handle — to push them clear (OSHA: any dry non-conductive object works for ≤600 V), then call for help immediately.

##The short version

• Treat the battery as always live — no metal across the terminals, ever.
• Insulate every terminal; tape the spare while you connect.
• The battery-to-breaker run is the danger zone — keep all wiring isolated from the frame.
• 12V = heat/short hazard. 120V wall power = the real shock hazard.

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This lesson was prompted by feedback from mentor Weldingrod1 on Chief Delphi, and every claim was verified against the WPILib documentation, the FRC Game Manual (R601 / R607 / R611), IEC 61140, and OSHA electrical-safety guidance.