Electrical & Control Systems Flashcards
7 cards from real CET practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical & Control Systems flashcards as text
What is the purpose of a 'top-of-car inspection' (TOCI) station in elevator electrical design?
Answer: Transfers control authority to the car top, limits speed to inspection speed, and requires continuous pressure operation
The TOCI station transfers control to the car top, restricts speed to no more than 150 ft/min (inspection speed), and requires constant-pressure operation for safe personnel movement.
In a solid-state relay (SSR) used in an elevator controller, what triggers the output switching?
Answer: A low-power control signal that activates the internal semiconductor switch
An SSR uses a low-level DC or AC control signal to switch a semiconductor device (triac, SCR, or transistor) that controls the load circuit with no moving mechanical parts.
What is the significance of the 'unswitched' (always-hot) conductor requirement for elevator machine room lighting per NEC Article 620?
Answer: Lighting must remain on even when the main line disconnect is opened
NEC 620.23 requires machine room lighting to be on a circuit that remains energized even when the elevator main line disconnect is open, ensuring technicians have light while working on de-energized equipment.
What does a 'brake pick' coil do in a dual-coil electromagnetic elevator brake?
Answer: Both provides initial high current to open the brake and maintains release with lower current
In a dual-coil brake, the pick (lift) coil provides high initial current to rapidly open the brake while the hold coil then maintains the open position at lower power, reducing heat generation.
When troubleshooting an elevator that won't respond to hall calls but runs normally on car calls, which system is most likely at fault?
Answer: The hall call system — buttons, wiring, or the hall call input circuit in the controller
Normal car call operation confirms the drive, safety circuit, and car controls are functional, isolating the fault to the hall call input circuits, hall buttons, or the controller's hall call processing.
What is the purpose of a 'final limit switch' at the terminal landings of an elevator?
Answer: Cuts power to the motor and brake if the car travels past the normal stopping zone
Final limit switches are the last line of electrical protection at terminal floors; if the car passes the normal stopping position, they cut power to the motor and brake to halt movement.
What is 'hunting' in an elevator leveling system and what commonly causes it?
Answer: The car overshooting and repeatedly correcting around the landing level, often caused by excessive leveling gain or a faulty encoder
Leveling 'hunting' occurs when the car oscillates above and below the landing level repeatedly, typically due to over-tuned leveling gain, a noisy encoder signal, or a sticking leveling vane.