Electrical Systems and Lighting Flashcards

In a 208Y/120 V three-phase system, what is the voltage measured from any phase conductor to neutral?

Answer: 120 V

In a wye system, line-to-neutral voltage equals line-to-line voltage divided by 1.732, so 208 / 1.732 ≈ 120 V.

In many U.S. commercial buildings with a 480Y/277 V service, what is the 277 V line-to-neutral circuit most commonly used for?

Answer: Large fluorescent and LED lighting systems

Commercial lighting is often fed at 277 V to reduce current and conductor size.

Which standard covers electrical safety in the workplace, including arc-flash risk assessment and PPE?

Answer: NFPA 70E

NFPA 70E sets requirements for electrical safety-related work practices, including arc-flash hazard analysis.

Which type of occupancy sensor works best in a restroom with stall partitions, where occupants may be out of direct line of sight?

Answer: Ultrasonic

Ultrasonic sensors fill the space with sound waves and detect motion around obstructions, unlike line-of-sight PIR sensors.

What is the main effect on a three-phase motor of even a small voltage imbalance between phases?

Answer: It causes a larger current imbalance and extra heating

A small percentage of voltage imbalance produces a much larger current imbalance, which raises winding temperature and shortens motor life.

The Color Rendering Index (CRI) of a lamp indicates:

Answer: How accurately it shows object colors compared with a reference source

CRI, on a scale up to 100, rates how faithfully a light source renders colors compared with a reference illuminant.

A ballast or driver has a ballast factor of 0.88. What does this mean?

Answer: The lamp produces about 88% of its rated lumen output

Ballast factor is the ratio of the lamp's lumen output on that ballast to its rated lumen output on a reference ballast.