NEC Article 110 Practice Questions (10 Free, With Answers)

A panelboard is 20 in. wide. What is the minimum width of the working space in front of it?

1. A20 in., the width of the panelboard
2. B24 in.
3. C30 in., and enough for the doors or hinged panels to open at least 90 degrees
4. D36 in.

A 5-ft-tall panelboard is installed indoors in a commercial building. What is the minimum height of its working space?

1. A6 ft
2. B7 ft
3. CThe height of the panelboard only (5 ft)
4. D6 1/2 ft, or the height of the equipment if that is greater

A 480Y/277-volt panelboard faces a concrete-block wall across the aisle. Nothing else near the working space has exposed live parts. What is the minimum depth of the working space?

1. A3 ft
2. B3 1/2 ft
3. C4 ft
4. D2 1/2 ft

A switchboard rated 2,000 A and 10 ft wide contains circuit breakers. Unless an exception (such as an unobstructed exit or doubled working space) applies, what access to the working space is required?

1. AAn entrance at least 24 in. wide and 6 1/2 ft high at each end of the working space
2. BOne entrance at least 30 in. wide anywhere along the working space
3. CA single entrance at least 36 in. wide at one end
4. DNo special entrance rule applies to equipment in a locked electrical room

Which arrangement satisfies the NEC illumination requirement for the indoor working space at a service panelboard?

1. ALighting is provided for the working space and is not controlled only by an automatic means such as an occupancy sensor
2. BNo lighting is required if the panelboard is in an unfinished basement
3. CLighting is required only for equipment rated 1,200 A or more
4. DLighting is required but may be controlled only by a timer

An indoor panelboard's top is 6 ft above the floor, and the structural ceiling is 15 ft high. Directly above the panelboard (its width and depth), up to what height must foreign piping and ducts be kept out of the dedicated electrical space?

1. A15 ft, the structural ceiling
2. B6 1/2 ft above the floor
3. C8 ft above the floor (2 ft above the panelboard)
4. D12 ft above the floor (6 ft above the top of the panelboard)

An aluminum conductor and a copper conductor need to be joined in the same splicing connector, with the two conductors touching. When is this permitted?

1. AWhenever an antioxidant compound is applied to the aluminum
2. BWhenever both conductors are the same AWG size
3. COnly when the connector is identified for the purpose and conditions of use, such as one listed for copper-to-aluminum splices
4. DNever; the NEC prohibits any connection between copper and aluminum

A 200-A feeder breaker has terminals with no temperature marking. 90°C-rated XHHW-2 conductors land on it. Which temperature column limits the conductor ampacity at the termination?

1. A90°C
2. B75°C
3. C60°C
4. DWhichever column gives the highest ampacity

The available fault current at the line terminals of a panelboard is 22,000 A. No series-combination rating is used. Which interrupting rating is acceptable for its circuit breakers?

1. A25,000 A (25 kA)
2. B10,000 A (10 kA)
3. C18,000 A (18 kA)
4. DAny rating, as long as the trip rating matches the conductor ampacity

At a new retail store, what must be field-marked on the service equipment under NEC 110.24?

1. AThe arc-flash incident energy and the required PPE category
2. BThe available fault current and the date the fault-current calculation was performed
3. CThe installing electrician's name and license number
4. DThe measured resistance of the grounding electrode