Automatic Transfer Switch Function Flashcards
7 cards from real EGSA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Automatic Transfer Switch Function flashcards as text
In an ATS system, what is the purpose of the 'commit-to-transfer' point?
Answer: The point in a closed-transition transfer after which the ATS will complete the transfer even if the in-phase window is missed
The commit-to-transfer point ensures that once a closed-transition transfer has been initiated and both sources are paralleled, the ATS completes the transfer rather than re-opening, preventing extended parallel operation.
What is the maximum permissible parallel operation time for a closed-transition ATS per NFPA 110?
Answer: 100 milliseconds
NFPA 110 limits closed-transition parallel operation to 100 milliseconds to prevent synchronizing torques, circulating currents, and utility interconnection issues.
What does a 'source available' indicator on an ATS signify?
Answer: The source voltage and frequency are within acceptable limits for connection
A 'source available' indication confirms that the monitored source meets the ATS controller's programmed voltage and frequency acceptance criteria and is ready for load connection.
Which factor most directly determines whether a four-pole ATS is required instead of a three-pole ATS?
Answer: Whether the generator is a separately derived system with its own neutral-ground bond
NEC 250.30 requires the neutral to be switched when a separately derived system (generator with a neutral-ground bond) is used, preventing objectionable current from flowing on the grounding electrode conductors of both systems simultaneously.
What is the role of the 'test' function on an ATS controller?
Answer: To simulate a utility failure and exercise the generator and transfer sequence without interrupting the load
The test function initiates a generator exercise sequence, transferring the load to generator power or running the generator unloaded, allowing verification of the entire emergency power system without an actual utility outage.
A 'mechanically held' ATS contactor differs from an 'electrically held' contactor in that it:
Answer: Maintains contact position without continuous coil current, using a mechanical latch
Mechanically held contactors use a mechanical latch to maintain contact position, drawing coil current only during the act of opening or closing, which improves efficiency and prevents contact dropout during control power disturbances.
What is the function of the 'engine cooldown' timer in an ATS sequence?
Answer: Keeps the generator running unloaded after retransfer to utility to allow thermal cooldown before shutdown
The engine cooldown timer keeps the generator running at no-load after the load has been transferred back to utility, allowing the engine and turbocharger to cool gradually before shutdown, extending engine life.