Journeyman Electrician (NEC) — All Questions

A single ground rod need not be supplemented by a second electrode if its resistance to earth does not exceed what value?

• a.25 ohms✓
• b.1 ohm
• c.5 ohms
• d.100 ohms

A single rod, pipe or plate electrode must be supplemented unless it is shown to have a resistance to earth of 25 ohms or less. See NEC 250.53(A)(2).

A concrete-encased electrode using bare copper must be formed with at least 20 feet of what minimum conductor size?

• a.2 AWG
• b.4 AWG✓
• c.8 AWG
• d.6 AWG

A concrete-encased electrode may be at least 20 feet of bare copper not smaller than 4 AWG, or 20 feet of 1/2-inch or larger reinforcing bar, encased near the bottom of a footing. See NEC 250.52(A)(3).

Where rock bottom is encountered and an 8-foot rod cannot be driven vertically, at what maximum angle from vertical may the rod be driven?

• a.90 degrees
• b.45 degrees✓
• c.60 degrees
• d.30 degrees

If rock bottom prevents vertical driving, a rod electrode may be driven at an angle not exceeding 45 degrees from vertical, or buried in a trench at least 30 inches deep. See NEC 250.53(G).

A grounding electrode conductor connection to a ground rod buried in the earth must use what kind of fitting?

• a.A connector or clamp listed for direct burial in soil✓
• b.A tape-wrapped mechanical lug
• c.A solder joint
• d.Any indoor split-bolt connector

Connections to electrodes in contact with earth must be made with fittings listed and identified for direct soil or concrete burial as applicable. See NEC 250.70 and 250.68(A).

Under the current code, how must two to six service disconnects for a single service be arranged?

• a.Behind a single main breaker feeding sub-disconnects
• b.All mounted on a single removable panel
• c.Each in a separate enclosure, or in a listed assembly with individual enclosures, all grouped✓
• d.In any convenient locations throughout the building

The 2020 and 2023 codes require each of up to six service disconnects to be in a separate enclosure or a listed assembly with individual disconnect enclosures, grouped together. See NEC 230.71(B).

The point of attachment of overhead service-drop conductors to a building must be at least how far above finished grade?

• a.10 feet✓
• b.12 feet
• c.8 feet
• d.15 feet

The point of attachment of the service-drop or overhead service conductors must be at least 10 feet above finished grade and positioned to maintain the required conductor clearances. See NEC 230.26.

What is the minimum vertical clearance of overhead service conductors above a roof not readily accessible where the voltage does not exceed 300 volts to ground?

• a.8 feet✓
• b.10 feet
• c.12 feet
• d.3 feet

Overhead service conductors must maintain at least 8 feet of vertical clearance above the roof surface, over an area 3 feet in all directions from the roof edge, with reduced clearances only under specific listed conditions. See NEC 230.24(A).

Overhead service conductors must maintain what minimum clearance from a window designed to be opened?

• a.6 feet
• b.3 feet✓
• c.5 feet
• d.10 feet

Service conductors must keep 3 feet of clearance from windows designed to open, doors, porches, decks, stairs and similar locations. Conductors above the top of a window are exempt. See NEC 230.9(A).

What is the minimum clearance for overhead service conductors passing over a public street or road?

• a.15 feet
• b.12 feet
• c.10 feet
• d.18 feet✓

Overhead service conductors over public streets, roads, alleys and parking areas subject to truck traffic require 18 feet of clearance. See NEC 230.24(B).

Ground-fault protection of equipment is required for a solidly grounded wye service of more than 150 volts to ground when the disconnect is rated at least what value?

• a.1,000 amperes✓
• b.1,200 amperes
• c.600 amperes
• d.800 amperes

The threshold is a service disconnect rated 1,000 amperes or more on a solidly grounded wye system of more than 150 volts to ground but not over 1,000 volts phase-to-phase, such as 480Y/277. The 1,200-ampere figure is the maximum GFPE setting, not the trigger. See NEC 230.95.

Neutral current that flows onto metal enclosures and grounding conductors because of an improper neutral-to-ground connection is known as what?

• a.Inductive reactance
• b.Fault current
• c.Displacement current
• d.Objectionable current✓

A neutral-to-ground bond made on the load side of the service creates parallel neutral paths, and the resulting current on grounding paths is objectionable current, which must be eliminated by correcting the connection. See NEC 250.6 and 250.142(B).

On the load side of the service disconnecting means, may the grounded neutral conductor be used to ground equipment enclosures?

• a.Yes, where the neutral is 6 AWG copper or larger
• b.Yes, in any subpanel fed from the service equipment
• c.No; a separate equipment grounding conductor must be used✓
• d.Yes, but only in dwelling units

Downstream of the service disconnect the neutral and equipment grounding conductor must be kept separate so load current does not travel on enclosures and raceways. See NEC 250.142(B).

A 30 kVA, three-phase transformer has a 480-volt primary and is protected by primary overcurrent protection only at 125 percent. What is the maximum standard primary overcurrent device rating?

• a.60 amperes
• b.50 amperes✓
• c.45 amperes
• d.40 amperes

Primary full-load current = 30,000 / (1.732 x 480) = 36.1 A, and 36.1 x 1.25 = 45.1 A. Because that exceeds the standard 45-ampere rating, the next standard size of 50 A is permitted. See NEC 450.3(B).

What is the secondary full-load current of a 112.5 kVA transformer with a 208Y/120-volt three-phase secondary?

• a.541 amperes
• b.312 amperes✓
• c.270 amperes
• d.156 amperes

Secondary current = VA / (1.732 x E) = 112,500 / (1.732 x 208) = 112,500 / 360.3, about 312 amperes. Dividing by voltage alone gives the 541-ampere trap.

How is the bonding jumper for exposed structural metal building framing sized?

• a.From Table 250.66, based on the ungrounded service conductor size✓
• b.Always 6 AWG copper regardless of service size
• c.From Table 310.16, by the service ampacity
• d.From Table 250.122, by the overcurrent device rating

The bonding jumper for exposed structural metal that is likely to become energized is sized from Table 250.66 using the ungrounded service-entrance conductors. See NEC 250.104(C).

For a separately derived system, the grounding electrode conductor connects to the grounded conductor at the same point where what is installed?

• a.The largest branch-circuit overcurrent device
• b.The main bonding jumper at the service
• c.The system bonding jumper✓
• d.Every downstream equipment grounding bus

The grounding electrode conductor for a separately derived system connects the grounded conductor to the electrode at the same single point where the system bonding jumper is installed. See NEC 250.30(A).

A supply-side bonding jumper on the line side of the service is sized from which table?

• a.Table 220.55
• b.Table 250.102(C)(1)✓
• c.Table 310.16
• d.Table 250.122

Supply-side bonding jumpers are sized from Table 250.102(C)(1), based on the ungrounded supply conductors, not from the equipment grounding conductor table. See NEC 250.102(C).

An equipment grounding conductor of the wire type is never required to be larger than what?

• a.The circuit conductors supplying the equipment✓
• b.Twice the value shown in Table 250.122
• c.6 AWG copper in all cases
• d.The ungrounded service conductor size in every case

An equipment grounding conductor need not be larger than the circuit conductors supplying the equipment. See NEC 250.122(A).

What is the rule for a bare aluminum grounding electrode conductor near the earth?

• a.It must be installed within 18 inches of the earth
• b.It may not be used in direct contact with earth or masonry, or within 18 inches of the earth✓
• c.It may be buried directly in the earth like copper
• d.Aluminum grounding electrode conductors are prohibited entirely

Bare or exposed aluminum grounding electrode conductors may not be used in direct contact with masonry or earth or where subject to corrosive conditions, and may not be terminated within 18 inches of the earth. See NEC 250.64(A).

How must the multiple grounding electrodes present at a building be arranged?

• a.Electrodes must be at least 100 feet apart
• b.A ground rod may never be combined with a water pipe electrode
• c.All electrodes present must be bonded together to form the grounding electrode system✓
• d.Only one electrode is permitted per building

All grounding electrodes that are present, such as a water pipe, concrete-encased electrode and ground rods, must be bonded together to form the grounding electrode system. See NEC 250.50.