Electrical Systems in Buildings Flashcards
6 cards from real Building Engineering practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Electrical Systems in Buildings flashcards as text
What is the purpose of a transfer switch in a building's electrical system?
Answer: To switch between utility power and generator power safely
A transfer switch prevents backfeeding by safely isolating utility power before connecting generator power during an outage.
Which electrical system configuration is most common in US commercial buildings?
Answer: Three-phase 4-wire 208Y/120V
Three-phase 208Y/120V wye systems supply both 120V single-phase loads and 208V three-phase equipment in commercial facilities.
What is the maximum allowed voltage drop for branch circuits in building electrical design per NEC recommendations?
Answer: 3%
NEC recommends no more than 3% voltage drop on branch circuits and 5% total from the service entrance to the farthest outlet.
Which lighting control device reduces energy use by dimming lights based on available daylight?
Answer: Daylight harvesting sensor
Daylight harvesting sensors measure ambient light and automatically dim or switch off artificial lighting when natural light is sufficient.
What ampacity is a standard 12 AWG copper conductor rated for in a 60°C environment per NEC?
Answer: 20A
A 12 AWG copper conductor has a 20A ampacity rating at 60°C, making it suitable for 20A branch circuits.
What is the function of a surge protective device (SPD) installed at a building's main panel?
Answer: To limit transient voltage spikes from entering building wiring
An SPD clamps transient voltage spikes caused by lightning or utility switching before they can damage sensitive equipment throughout the building.