Grounding & Bonding Flashcards

How is a ground fault best defined in the context of electrical installations?

Answer: An unintentional electrically conductive connection between an energized conductor and a grounded surface or metal enclosure

A ground fault is an unintentional connection that allows current to flow from an energized conductor to a grounded surface, creating a shock and fire hazard.

What type of fault does a Ground Fault Circuit Interrupter (GFCI) primarily protect against, and what is its detection threshold?

Answer: Ground faults by detecting current imbalances of approximately 4–6 milliamperes between hot and neutral

GFCIs protect personnel by sensing a current difference of 4–6 mA between the hot and neutral conductors and interrupting the circuit within milliseconds.

Per NEC 250.64(B), which wiring method is NOT permitted to protect a grounding electrode conductor from physical damage?

Answer: Flexible metal conduit

NEC 250.64(B) does not permit flexible metal conduit to protect GECs because its higher impedance can compromise grounding effectiveness.

When two ground rods are required, what is the minimum separation distance between them per NEC 250.53(B)?

Answer: 6 feet

NEC 250.53(B) requires supplemental rod electrodes to be spaced at least 6 feet apart to ensure they contact different zones of soil.

Per NEC Table 250.66, what is the maximum copper conductor size that may be required as a grounding electrode conductor for a single set of service-entrance conductors, regardless of how large those conductors are?

Answer: 3/0 AWG

NEC Table 250.66 caps the required GEC size at 3/0 AWG copper for a single set of service-entrance conductors, no matter how large the service.

Which grounding electrode type generally provides the lowest resistance to earth and is recognized by NEC 250.52(A)(3)?

Answer: A concrete-encased electrode (Ufer ground)

Concrete-encased electrodes (Ufer grounds) offer very low earth resistance because concrete retains moisture and provides a large surface area in contact with the earth.

If a single driven ground rod is installed and tested, revealing a resistance to earth of 38 ohms, what action is required by NEC 250.56?

Answer: A supplemental electrode must be added to the grounding electrode system

NEC 250.56 requires a supplemental grounding electrode when a single rod has a resistance to earth exceeding 25 ohms.