Building Engineering Electrical Systems in Buildings 2

Question 1

What is the purpose of a transfer switch in a building's electrical system?

Accepted Answer

To switch between utility power and generator power safely

Answer

A transfer switch prevents backfeeding by safely isolating utility power before connecting generator power during an outage.

Question 2

Which electrical system configuration is most common in US commercial buildings?

Accepted Answer

Three-phase 4-wire 208Y/120V

Answer

Three-phase 208Y/120V wye systems supply both 120V single-phase loads and 208V three-phase equipment in commercial facilities.

Question 3

What is the maximum allowed voltage drop for branch circuits in building electrical design per NEC recommendations?

Accepted Answer

3%

Answer

NEC recommends no more than 3% voltage drop on branch circuits and 5% total from the service entrance to the farthest outlet.

Question 4

Which lighting control device reduces energy use by dimming lights based on available daylight?

Accepted Answer

Daylight harvesting sensor

Answer

Daylight harvesting sensors measure ambient light and automatically dim or switch off artificial lighting when natural light is sufficient.

Question 5

What ampacity is a standard 12 AWG copper conductor rated for in a 60°C environment per NEC?

Accepted Answer

20A

Answer

A 12 AWG copper conductor has a 20A ampacity rating at 60°C, making it suitable for 20A branch circuits.

Building Engineering Practice Test