Electrical Power, Wiring, and Controls
What you must know
Gate operators typically run on line voltage (120/240 VAC single-phase or three-phase) or low-voltage DC with a transformer. Know the NEC requirements for a disconnecting means within sight of the operator, GFCI protection where required, grounding and bonding, and conduit/wire sizing for voltage drop. Control wiring includes loop detectors, keypads, card readers, and safety devices - often low-voltage and separated from line voltage. Understand control board inputs (open, close, stop, safety, shadow) and the difference between a safety input and a shadow input.
Traps
Questions test voltage drop over long runs - undersized wire causes low voltage at the operator and erratic behavior. Another trap: mixing line and low-voltage conductors in one conduit without proper separation or rating. Watch for confusion between a safety edge (reverses) and a shadow loop (prevents closing when a vehicle is present). Also, a disconnect must be lockable and within sight; a breaker in a distant panel is not sufficient.
Rule of thumb
Separate power and control wiring, size conductors for voltage drop (not just ampacity), and label every control input. If the operator behaves erratically, measure voltage at the operator under load first.
Worked example
A 300-ft run of 14 AWG to a 120 VAC operator causes the gate to stall. Voltage at the operator reads 98 VAC under load. Correct fix: increase conductor size to reduce voltage drop, not replace the motor.