The secondary power supply must automatically provide power to the protected premises within a certain number of seconds whenever the primary power supply voltage is sufficient. How many seconds is required?

The secondary power supply must automatically provide power to the protected premises within a certain number of seconds whenever the primary power supply voltage is sufficient. How many seconds is required?

• A. 5
• B. 10
• C. 15
• D. 30

Answer: (B)

Ten seconds. The idea being tested is how quickly automatic standby power must take over when the normal power source fails. An automatic transfer switch is designed to sense the loss of primary power and switch to the secondary source, and the typical requirement is that this transfer happens within about 10 seconds. This keeps critical loads powered without a noticeable interruption, while still being a practical and achievable interval with standard equipment. Shorter times (like five seconds) are harder to guarantee universally, and longer times (15 or 30 seconds) would result in visible outages for the protected premises.

Ten seconds. The idea being tested is how quickly automatic standby power must take over when the normal power source fails. An automatic transfer switch is designed to sense the loss of primary power and switch to the secondary source, and the typical requirement is that this transfer happens within about 10 seconds. This keeps critical loads powered without a noticeable interruption, while still being a practical and achievable interval with standard equipment. Shorter times (like five seconds) are harder to guarantee universally, and longer times (15 or 30 seconds) would result in visible outages for the protected premises.