Services & separately derived systems: Texas Journeyman Electrician Practice Questions

What is the minimum rating of the service disconnecting means for a one-family dwelling?

A one-family dwelling needs a service disconnect rated at least 100 A, 3-wire.

What is the maximum number of service disconnects permitted for one service?

A service may have up to six disconnects, grouped, as 230.71 sets out.

What is the minimum clearance for service-drop conductors (300 V or less to ground) over a residential driveway?

Over residential property and driveways the minimum is 12 ft for these voltages; public streets need more.

At the service, the main bonding jumper connects:

The main bonding jumper ties the neutral to the equipment grounding conductors and the service enclosure, so fault current has a path back to the source.

The grounding electrode conductor for a service is sized from the size of:

The grounding electrode conductor is sized from the largest ungrounded service-entrance conductor (or equivalent area for parallel sets), using the table in 250.66.

A single ground rod must be supplemented by an additional electrode unless its resistance to earth is no more than:

One rod alone is acceptable only if it measures 25 ohms or less; otherwise add a supplemental electrode.

What is the minimum length of a rod or pipe grounding electrode?

Rod and pipe electrodes must be at least 8 ft long.

According to the NEC, how many services may a building generally be supplied by?

Section 230.2 limits a building to one service unless one of the listed special conditions applies (fire pumps, large loads, different characteristics and similar). Exceptions are ignored here.

According to the NEC, may branch-circuit conductors be installed in the same raceway as service conductors?

Section 230.7 keeps other conductors out of service raceways and service cables (grounding conductors and bonding jumpers are allowed). Service conductors are unprotected on the line side, so other circuits are kept apart.

According to the NEC, overhead service conductors run beside a window that opens must keep what minimum clearance from it?

Section 230.9(A) requires 3 ft of clearance from windows designed to open, doors, porches, balconies, ladders, stairs and similar locations. Conductors above the top of a window are exempt.

According to the NEC, a service drop limited to 150 V to ground that passes over a sidewalk accessible only to pedestrians needs at least what clearance above the finished grade?

Section 230.24(B) lists 10 ft over finished grade, sidewalks and pedestrian-only areas for service drops limited to 150 V to ground.

According to the NEC, what is the minimum clearance of 120/240 V overhead service conductors over a residential driveway?

Section 230.24(B) requires 12 ft over residential property and driveways (and commercial areas without truck traffic) for conductors at 300 V or less to ground.

According to the NEC, overhead service conductors over a public street or a parking area with truck traffic need at least what clearance?

Section 230.24(B) sets 18 ft over public streets, alleys, roads, parking areas subject to truck traffic and similar areas.

According to the NEC, the point of attachment of a service drop to a building must be at least how high above finished grade?

Section 230.26 requires the point of attachment to be at least 10 ft above finished grade, and high enough to give the clearances in 230.24.

According to the NEC, what is the smallest copper conductor generally permitted for overhead service conductors?

Section 230.23 sets a minimum of 8 AWG copper (6 AWG aluminum) for overhead service conductors, apart from small limited loads covered by an exception.