IEC Grounding and Bonding 5 — Questions and Answers
Question 1: In a feeder circuit, if the equipment grounding conductor is increased in size above the minimum required by Table 250.122, what must also be increased proportionally?
- The neutral conductor (Correct answer)
- The ungrounded (hot) conductors
- Nothing — only the EGC needs to increase
- The grounding electrode conductor
Correct answer: The neutral conductor
Per NEC 250.122(B), if the ungrounded conductors are increased in size, the equipment grounding conductor must be increased proportionally — and the neutral must also be evaluated for proper sizing.
Question 2: Per NEC 250.64(B), a grounding electrode conductor installed exposed on the exterior of a building must be protected from physical damage by:
- Only rigid metal conduit
- Iron or steel conduit, PVC conduit, EMT, or other approved means (Correct answer)
- Burial at least 12 inches deep
- A listed weatherproof cable tray
Correct answer: Iron or steel conduit, PVC conduit, EMT, or other approved means
NEC 250.64(B) permits the grounding electrode conductor to be protected by iron/steel conduit, PVC conduit, EMT, or other approved means when exposed to physical damage.
Question 3: When multiple electrodes are installed to meet code requirements, what is the minimum spacing between driven ground rods per NEC 250.53(B)?
- 3 feet
- 4 feet
- 6 feet (Correct answer)
- 8 feet
Correct answer: 6 feet
NEC 250.53(B) requires that where multiple rod, pipe, or plate electrodes are installed, they must be spaced at least 6 feet apart.
Question 4: Which of the following conditions allows a single ground rod to serve as the only grounding electrode without a supplemental electrode?
- When the rod is at least 10 feet long
- When the resistance to ground is 25 ohms or less (Correct answer)
- When the rod is made of solid copper
- When the service is 200 amperes or less
Correct answer: When the resistance to ground is 25 ohms or less
Per NEC 250.56, a single rod electrode does not require supplemental electrodes if the measured resistance to ground is 25 ohms or less.
Question 5: What NEC section governs bonding requirements for swimming pools, hot tubs, and similar installations?
- Article 250
- Article 410
- Article 680 (Correct answer)
- Article 700
Correct answer: Article 680
Article 680 covers the special requirements for swimming pools, fountains, and similar installations, including the equipotential bonding requirements.
Question 6: The term 'effective ground-fault current path' as defined in the NEC is an intentionally constructed, permanent, low-impedance path that facilitates what?
- Carrying normal load current safely to earth
- The operation of the overcurrent protective device during a ground fault (Correct answer)
- Reducing voltage drop in long branch circuits
- Equalizing voltage between grounding electrodes
Correct answer: The operation of the overcurrent protective device during a ground fault
An effective ground-fault current path is designed to carry enough fault current to quickly operate the overcurrent protective device and clear the fault.
Question 7: Per NEC 250.30(A), a separately derived system must establish a grounding electrode conductor connection at which location?
- At the first overcurrent device downstream from the transformer
- At the nearest subpanel supplied by the transformer
- At the source of the separately derived system (the transformer itself) (Correct answer)
- At the service entrance of the building
Correct answer: At the source of the separately derived system (the transformer itself)
NEC 250.30(A) requires the grounding electrode conductor for a separately derived system to connect at the source — the transformer — not at downstream equipment.
IEC Grounding and Bonding 5
In a feeder circuit, if the equipment grounding conductor is increased in size above the minimum required by Table 250.122, what must also be increased proportionally?