Question 1

On the electrician exam, what is the key difference between grounding and bonding?

Accepted Answer

Per NEC Article 100, grounding is the connection to earth (or to a conductive body serving in place of earth), while bonding is the connection of metallic parts to establish electrical continuity and an effective ground-fault current path (250.4(A)(3)). The exam frequently tests this distinction: earth itself is NOT an effective fault-clearing path.

Question 2

What is the minimum size copper grounding electrode conductor for a service with 3/0 AWG copper service-entrance conductors?

Accepted Answer

Per NEC Table 250.66, service-entrance conductors of 3/0 AWG copper (or 250 kcmil aluminum) require a minimum 4 AWG copper grounding electrode conductor. Memorize Table 250.66 ranges for the journeyman exam.

Question 3

A grounding electrode conductor connecting to a concrete-encased electrode (Ufer) is never required to be larger than:

Accepted Answer

Per NEC 250.66(B), where the GEC connects to a concrete-encased electrode, that portion is not required to be larger than 4 AWG copper. For a connection to a ground rod (250.66(A)) the limit is 6 AWG copper. Know each exception separately.

Question 4

The portion of the grounding electrode conductor that is the sole connection to a single ground rod is never required to be larger than:

Accepted Answer

Per NEC 250.66(A), the GEC to a single rod, pipe, or plate electrode need not be larger than 6 AWG copper (or 4 AWG aluminum). This is a very commonly tested figure.

Question 5

Where a single ground rod does not achieve 25 ohms or less to earth, the NEC requires:

Accepted Answer

Per NEC 250.53(A)(2) Exception, a single rod with a resistance of 25 ohms or less may stand alone; otherwise it must be augmented by one additional electrode. Installing two rods spaced at least 6 ft apart is the common way to satisfy this without measuring resistance.

Question 6

What is the minimum required separation between two driven ground rods used together?

Accepted Answer

Per NEC 250.53(A)(3), rods, pipes, and plate electrodes must be spaced at least 6 ft (1.8 m) apart. Spacing them closer reduces the benefit of the second rod because their effective resistance areas overlap.

Question 7

The minimum size of a copper equipment grounding conductor for a circuit protected by a 60-ampere overcurrent device is:

Accepted Answer

Per NEC Table 250.122, a 60-ampere overcurrent device requires a minimum 10 AWG copper equipment grounding conductor. Note 250.122 sizes the EGC by the rating of the overcurrent device, not the load.

Question 8

At a service, the connection between the grounded (neutral) conductor and the equipment grounding system is made by the:

Accepted Answer

Per NEC 250.24(B) and 250.28, the main bonding jumper connects the grounded (neutral) conductor to the equipment grounding terminal/enclosure at the service. Downstream of the service, neutrals and grounds must be kept separate (250.142).

Question 9

In a separately derived system, the connection between the derived neutral and the equipment grounding conductor is the:

Accepted Answer

Per NEC 250.30(A)(1), a separately derived system (e.g., a transformer secondary) uses a system bonding jumper to connect the derived grounded conductor to the equipment grounding conductor at a single point. The term differs from the service main bonding jumper.

Question 10

Metal water piping in a building must be bonded, and where used as a grounding electrode it is required to be supplemented because:

Accepted Answer

Per NEC 250.53(D)(2), a metal underground water pipe electrode must be supplemented by an additional electrode because future plastic repairs or meter replacements can break electrical continuity. The interior metal water piping must also be bonded per 250.104(A).

Grounding & Bonding Essentials (Article 250) Practice Questions

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