Electrical Systems, Wiring, and Control Circuits
Power, control, and safety chain
Elevator electrical work follows NFPA 70 Article 620 in addition to ASME A17.1 and A17.5. The motor branch circuit has a disconnect, overcurrent protection, and conductors sized for the load. Control circuits may be Class 1, 2, or 3; Class 2 and 3 wiring must not be mixed with power conductors unless permitted. The safety chain is a series circuit of protective devices: door interlocks, pit stop switch, top-of-car stop switch, governor switch, final limits, and other safety contacts. If any contact opens, the main contactor drops and the car cannot run. Grounding and bonding must be continuous.
Worked example
A car door interlock fails to prove closed. The interlock contact in the safety chain remains open. The main contactor coil cannot energize, so the motor cannot start even though the controller has a run command. The correct diagnosis is to trace the safety chain and repair the interlock, not to bypass it. Jumpering the interlock would allow motion with an open door and is a serious code violation.
Traps that cost marks
Do not confuse the motor disconnect with a lighting switch. Do not assume a controller fault always means a failed board; an open safety-chain contact is common. Do not mix control and power conductors improperly. Never bypass door interlocks, pit switches, or final limits to “test” a car.