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 'buffer stopping switch' in the elevator pit electrical circuit?
Answer: Opens the safety circuit when the car strikes an oil or spring buffer
The buffer stopping switch opens the safety circuit when the car or counterweight contacts a buffer, cutting power and preventing further car movement.
In a duplex elevator group, what does 'dispatching logic' in the group controller determine?
Answer: Which car responds to a hall call based on position, direction, and load
Dispatching logic assigns hall calls to the most efficient car based on real-time factors such as car position, travel direction, and passenger load.
What does 'harmonic distortion' from an elevator VFD affect in a building electrical system?
Answer: Other equipment connected to the same electrical distribution system
VFDs generate harmonic currents that travel through the building's electrical distribution system and can cause overheating, nuisance tripping, and interference with sensitive equipment throughout the building.
What is the function of a 'door reversal device' in the elevator door control circuit?
Answer: Detects an obstruction and signals the door operator to reverse from closing to opening
The door reversal device (such as a safety edge, light curtain, or pressure sensor) detects an obstruction and immediately commands the door operator to reverse direction and reopen.
In an elevator safety circuit, what is a 'series circuit' configuration used for?
Answer: Ensuring that ALL safety contacts must be closed for the elevator to run
Safety devices are wired in series so that opening ANY single safety contact interrupts the entire circuit and stops elevator operation, providing a fail-safe architecture.
What is 'load weighing' used for in a modern elevator control system?
Answer: Both adjusting motor torque and triggering the overload alarm
Load weighing devices serve dual purposes: they feed load data to the drive for pre-torque (smooth starts) and trigger full-load or overload bypasses and alarms.
What must be verified before energizing an elevator system that has had the traveling cable replaced?
Answer: That all conductors are correctly landed, insulation resistance is acceptable, and no short circuits exist
Before energizing, technicians must verify correct terminations at both ends, perform a megger test for insulation integrity, and confirm continuity without shorts between conductors.