CSLB C-10 Electrical ContractorEquipment and InstallationMedium
An electrician is installing a 200-ampere, 120/240-volt single-phase panelboard in a retail store. The panelboard will serve general lighting and receptacle loads. What is the minimum required working space depth in front of this panelboard if the panelboard is opposite a grounded masonry wall?
- A48 inches (1.2 m)
- B36 inches (900 mm)
- C42 inches (1.07 m)
- D30 inches (750 mm)
Show answer & explanationAnswer & explanation
Correct answer: B. 36 inches (900 mm)
According to NEC Table 110.26(A)(1) for equipment operating at 0-150 volts to ground, Condition 1 (exposed live parts on one side, grounded surface on the other) requires a minimum working space depth of 3 feet (36 inches). A 120/240V system has 120V to ground.
Why the other options are wrong
- A. 48 inches is required for 151-600 volts to ground, Condition 2 or 3.
- C. 42 inches is required for 151-600 volts to ground, Condition 1, or 0-150 volts to ground, Condition 2.
- D. 30 inches is the minimum width, not depth, of working space.
Electrical Working Space Depth (NEC 110.26(A)(1))
The minimum clear space required in front of electrical equipment, determined by voltage to ground and the type of obstruction opposite the equipment, to allow for safe operation and maintenance.
- Determined by voltage to ground and conditions (1, 2, or 3).
- Condition 1: Exposed live parts on one side, grounded surface on the other.
- Condition 2: Exposed live parts on one side, no live or grounded parts on the other, or live parts on both sides that are effectively guarded.
- Condition 3: Exposed live parts on both sides of the working space.
Memory trick: Working Space: 'V'oltage and 'C'ondition are Key.