Practice Questions: Grounding & Bonding
Real questions from our bank, each cited to the exact NEC section. Tap “Show explanation” after you answer.
Per NEC 250.52(A)(2), a metal in-ground support structure shall qualify as a grounding electrode when which condition is met?
- AThe structure is over three stories tall
- BThe structure is in direct contact with the earth vertically for 10 ft (3.0 m) or more, with or without concrete encasement
- CThe structure supports electrical equipment
- DThe building has a lightning protection system
Show explanation
Per NEC 250.52(A)(2), one or more metal in-ground support structures (such as pilings, casings, or other structural metal) qualify as grounding electrodes when they are in direct contact with the earth vertically for 3.0 m (10 ft) or more, with or without concrete encasement. The phrase 'effectively grounded' does not appear in this section and is not the specified condition.
Per NEC 250.53(A)(2) Exception, a single rod electrode that does not have a resistance to earth of 25 ohms or less shall be supplemented by an additional electrode. Per 250.53(A)(3), what is the minimum spacing between the two rod electrodes?
- A3 feet
- B6 feet
- C8 feet
- D10 feet
Show explanation
NEC 250.53(A)(2) requires a single rod, pipe, or plate electrode to be supplemented by an additional electrode unless it has a resistance to earth of 25 ohms or less. Per 250.53(A)(3), where multiple rod, pipe, or plate electrodes are installed to meet this requirement, they shall be not less than 1.8 m (6 ft) apart.
Per NEC 250.119, equipment grounding conductors may be identified by which of the following methods?
- AContinuous green color or green with yellow stripes
- BWhite or gray insulation
- CBlue insulation
- DRed insulation
Show explanation
NEC 250.119 requires EGCs to be identified by continuous green insulation, green with one or more yellow stripes, or bare copper.
Per NEC 250.64(A), a grounding electrode conductor made of aluminum or copper-clad aluminum shall not be installed in which location?
- AInside rigid metal conduit
- BIn direct contact with masonry or the earth, or where subject to corrosive conditions
- CIn PVC conduit
- DInside EMT
Show explanation
NEC 250.64(A) prohibits aluminum or copper-clad aluminum grounding electrode conductors from being installed where in direct contact with masonry, the earth, or subject to corrosive conditions.
Per NEC Table 250.122, what is the minimum size copper equipment grounding conductor required for a branch circuit protected by a 60-ampere overcurrent device?
- A12 AWG
- B10 AWG
- C8 AWG
- D6 AWG
Show explanation
Per NEC Table 250.122, a branch circuit protected by a 60 A overcurrent device requires a minimum 10 AWG copper equipment grounding conductor. The EGC is sized based on the rating of the overcurrent device, not the size of the phase conductors.
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