Electrical Controls and Wiring
Electrical Controls and Wiring
This domain covers the elevator power supply, disconnecting means, control circuits, and the wiring methods that keep safety circuits reliable. The exam expects you to apply NEC Article 620 and ASME A17.1 electrical requirements together, and to troubleshoot a dead car without bypassing safety devices.
Power and disconnecting means
- Each elevator needs a dedicated branch circuit and a single mainline disconnect that opens all ungrounded conductors, is lockable in the open position, and is located in the machine room where it is accessible.
- The disconnect must be labeled with the elevator identification. Control power, lighting, and receptacles are separate circuits and must not be fed through the elevator disconnect.
- Grounding and bonding must be continuous; the machine room, controller enclosure, and raceways require proper bonding.
Control and safety circuits
- Safety devices are wired in series in the safety chain. An open switch drops the chain and stops the car.
- Door interlocks, final limits, pit switches, and governor switches must not be bypassed for troubleshooting.
- Traveling cables and hoistway wiring must be protected from abrasion and flexing damage.
Worked example
A car will not run and the controller shows the safety chain open. With the mainline disconnect closed, measure voltage across each series device. If a door interlock shows approximately full control voltage across its terminals, that interlock is open, because the voltage is dropped across the open contacts. Trace and correct the door-lock circuit; do not jumper the interlock to move the car.
Traps
Using the elevator disconnect for machine-room receptacles; bypassing a safety switch; confusing control voltage with line voltage; and failing to lock out the disconnect before working on wiring.