NEC Wiring and Protection 5

Question 1

A service has 3/0 AWG copper ungrounded service-entrance conductors. Per NEC Table 250.66, what is the minimum copper grounding electrode conductor size?

Accepted Answer

4 AWG

Answer

Table 250.66 requires 4 AWG copper for 2/0 or 3/0 copper service conductors.

Question 2

Per NEC 250.53(A)(2), when a single rod, pipe, or plate electrode does not have a resistance to earth of 25 ohms or less, what must be done?

Accepted Answer

Supplement it with an additional electrode

Answer

The single electrode must be supplemented by an additional electrode, unless it measures 25 ohms or less.

Question 3

When multiple rod electrodes are installed to meet NEC 250.53, what is the minimum spacing between them?

Accepted Answer

6 ft

Answer

NEC 250.53(B) requires at least 6 ft between rod, pipe, or plate electrodes.

Question 4

Per NEC 250.66(A), when a grounding electrode conductor is the sole connection to a rod, pipe, or plate electrode, it need not be larger than which copper size?

Accepted Answer

6 AWG

Answer

For the portion connecting only to rod, pipe, or plate electrodes, 6 AWG copper is the maximum required size.

Question 5

Per NEC 230.24(B), what is the minimum clearance for service-drop conductors (300 V to ground or less) over a residential driveway not subject to truck traffic?

Accepted Answer

12 ft

Answer

NEC 230.24(B)(2) requires 12 ft over residential property and driveways for voltages not exceeding 300 V to ground.

NEC Practice Test

NEC Practice Test

NEC Wiring and Protection 5