Journeyman Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A commercial occupancy has a 200-ampere, 120/208V, 3-phase, 4-wire service. The feeder supplying a panelboard has an overcurrent protective device rated for 150 amperes. What is the minimum required working space depth in front of this panelboard, assuming exposed live parts on one side and a grounded wall on the other, for a voltage to ground of 120V?
- A48 inches (122 cm)
- B42 inches (107 cm)
- C30 inches (76 cm)
- D36 inches (90 cm)
Show answer & explanationAnswer & explanation
Correct answer: D. 36 inches (90 cm)
According to NEC Table 110.26(A)(1) for equipment rated 600V nominal or less to ground, Condition 1 (exposed live parts on one side, grounded wall on other) requires a minimum working space depth of 3 feet (36 inches) for voltages 0-150V to ground. Since the voltage to ground is 120V, Condition 1 applies.
Why the other options are wrong
- A. 48 inches would apply to Condition 3 (exposed live parts on one side, other side has exposed live parts) or higher voltage ranges.
- B. 42 inches would apply to Condition 2 (exposed live parts on both sides) or higher voltage ranges.
- C. 30 inches is not a standard working space depth for this condition.
Electrical Equipment Working Space
NEC 110.26(A) mandates minimum clear working space around electrical equipment to ensure safe operation and maintenance, based on voltage to ground and the condition of the opposing wall.
- Working space depth depends on voltage to ground.
- Three conditions (1, 2, 3) define the opposing wall.
- NEC Table 110.26(A)(1) provides specific dimensions.
Memory trick: Voltage to ground and the opposite wall's condition tell you the clear space.