Journeyman Electrician (NEC) — All Questions

A service uses 3/0 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.4 AWG✓
• b.6 AWG
• c.2 AWG
• d.1/0 AWG

Table 250.66 groups 2/0 and 3/0 copper service conductors together and calls for a 4 AWG copper grounding electrode conductor. The 6 AWG row applies to service conductors of 1 or 1/0 AWG, 2 AWG copper is required only above 3/0 through 350 kcmil, and 1/0 applies to service conductors above 350 through 600 kcmil.2023 NEC Table 250.66

A service is supplied by two parallel sets of 250 kcmil copper conductors per phase. What is the minimum size copper grounding electrode conductor?

• a.4 AWG
• b.2 AWG
• c.1/0 AWG✓
• d.3/0 AWG

With parallel conductors the equivalent area is the sum of the areas in one phase: 2 x 250 kcmil = 500 kcmil, which falls in the over 350 through 600 kcmil row and requires 1/0 copper. Using 2 AWG treats a single 250 kcmil conductor as the whole service, and 3/0 corresponds to services above 1,100 kcmil.2023 NEC Table 250.66

Where the grounding electrode conductor connects only to a driven ground rod, what is the largest size it is required to be?

• a.2 AWG copper
• b.4 AWG copper
• c.6 AWG copper✓
• d.1/0 AWG copper

A rod, pipe or plate electrode has a limited earth contact area, so the conductor to it is never required to be larger than 6 AWG copper regardless of what Table 250.66 would otherwise demand. The 4 AWG limit applies to a concrete-encased electrode, and larger sizes are not required for any rod connection.2023 NEC §250.66(A)

Where the grounding electrode conductor connects only to a concrete-encased electrode, what is the largest size it is required to be?

• a.2 AWG copper
• b.6 AWG copper
• c.4 AWG copper✓
• d.1/0 AWG copper

The conductor to a concrete-encased electrode is never required to be larger than 4 AWG copper. The 6 AWG cap belongs to rod, pipe and plate electrodes, and 2 AWG or 1/0 would only come from Table 250.66 before this limiting rule is applied.2023 NEC §250.66(B)

What is the minimum size copper equipment grounding conductor for a circuit protected at 60 amperes?

• a.10 AWG✓
• b.12 AWG
• c.8 AWG
• d.6 AWG

Table 250.122 is entered by the rating of the overcurrent device ahead of the circuit, and the 60-ampere row calls for 10 AWG copper. 12 AWG is listed for 20 amperes, 8 AWG for 100 amperes, and 6 AWG for 200 amperes, so all three are the wrong rows.2023 NEC Table 250.122

A 200-ampere feeder requires what minimum size copper equipment grounding conductor?

• a.3 AWG
• b.8 AWG
• c.4 AWG
• d.6 AWG✓

The 200-ampere row of Table 250.122 specifies 6 AWG copper. 8 AWG belongs to 100 amperes, 4 AWG to 300 amperes and 3 AWG to 400 amperes, so those choices come from reading adjacent rows.2023 NEC Table 250.122

What is the minimum size copper equipment grounding conductor for a 400-ampere feeder?

• a.4 AWG
• b.3 AWG✓
• c.2 AWG
• d.1 AWG

Table 250.122 lists 3 AWG copper at 400 amperes. 4 AWG is the 300-ampere value, 2 AWG the 500-ampere value and 1 AWG the 600-ampere value, so all three are one row away from the correct entry.2023 NEC Table 250.122

A 100-ampere feeder originally sized with 3 AWG copper (52,620 circular mils) is upsized to 1/0 AWG copper (105,600 circular mils) for voltage drop. What is the minimum equipment grounding conductor?

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

When ungrounded conductors are increased in size, the equipment grounding conductor must be increased in the same proportion by circular-mil area. The ratio is 105,600 / 52,620 = 2.0, and the base 100-ampere equipment grounding conductor of 8 AWG (16,510 circular mils) doubles to about 33,100 circular mils; 6 AWG has only 26,240 circular mils, so 4 AWG at 41,740 circular mils is the smallest that qualifies. Leaving it at 8 AWG ignores the proportional rule.2023 NEC §250.122(B)

A service is supplied by a single set of 500 kcmil copper ungrounded conductors. What is the minimum size copper main bonding jumper?

• a.3/0 AWG
• b.2 AWG
• c.4 AWG
• d.1/0 AWG✓

The main bonding jumper is sized from the same table used for the grounded conductor and supply-side bonding jumpers, and the over 350 through 600 kcmil row calls for 1/0 copper. The 2 AWG and 4 AWG answers come from smaller service conductor rows, and 3/0 applies to much larger services.2023 NEC §250.28(D)(1)

A service uses two parallel sets of 750 kcmil copper per phase. Using the 12.5 percent rule, what is the minimum copper main bonding jumper?

• a.250 kcmil
• b.3/0 AWG
• c.4/0 AWG✓
• d.2/0 AWG

Where the ungrounded service conductors exceed 1,100 kcmil of copper, the main bonding jumper must be at least 12.5 percent of that area: 2 x 750 = 1,500 kcmil, and 1,500 x 0.125 = 187.5 kcmil. The smallest standard conductor with at least that area is 4/0 AWG at 211.6 kcmil; 3/0 at 167.8 kcmil falls short and 250 kcmil is larger than the calculated minimum.2023 NEC §250.28(D)(2)

Service-entrance conductors supply 68 amperes of continuous load plus 120 amperes of noncontinuous load. What minimum ampacity must the conductors have?

• a.205 amperes✓
• b.188 amperes
• c.235 amperes
• d.225 amperes

Service-entrance conductors follow the same rule as feeders: noncontinuous load plus 125 percent of continuous load, or 120 + (68 x 1.25) = 120 + 85 = 205 A. The 188-ampere answer simply adds the loads, while 225 and 235 amperes apply the 125 percent factor to the entire load instead of only the continuous portion.2023 NEC §230.42(A)(1)

Using the dwelling conductor table, what is the minimum copper conductor size for a 400-ampere single-phase dwelling service?

• a.600 kcmil
• b.500 kcmil
• c.350 kcmil
• d.400 kcmil✓

The dwelling service and feeder table lists 400 kcmil copper for a 400-ampere single-phase dwelling service, reflecting the 83 percent allowance. Table 310.16 alone would push you toward 600 kcmil, and 350 kcmil is the table value for a 350-ampere service.2023 NEC §310.12

A 45 kVA, three-phase transformer has a 480-volt primary. If only primary overcurrent protection is provided at 125 percent, what is the maximum standard primary device rating?

• a.90 amperes
• b.60 amperes
• c.80 amperes
• d.70 amperes✓

Primary full-load current is 45,000 / (1.732 x 480) = 54.1 A, and 54.1 x 1.25 = 67.6 A. Because the calculated value does not correspond to a standard rating, the next higher standard size of 70 amperes is permitted. The 60-ampere answer rounds down and would nuisance trip, while 80 and 90 amperes skip past the next standard size.2023 NEC §450.3(B)

What is the secondary full-load current of a 75 kVA transformer with a 208Y/120-volt, three-phase secondary?

• a.120 amperes
• b.361 amperes
• c.208 amperes✓
• d.104 amperes

Secondary current is I = VA / (1.732 x E) = 75,000 / (1.732 x 208) = 75,000 / 360.3, or about 208 amperes. The 361-ampere answer divides by the voltage alone, 120 amperes uses the phase voltage incorrectly, and 104 amperes is roughly half the correct value.

What is the minimum length of a rod-type grounding electrode?

• a.10 feet
• b.6 feet
• c.8 feet✓
• d.5 feet

Rod and pipe electrodes must be at least 8 feet long and must have at least 8 feet in contact with the soil once installed. The 10-foot value is associated with the minimum earth contact required of a metal underground water pipe electrode, and 5 or 6 feet fall short of the rod requirement.2023 NEC §250.52(A)(5)

Where two rod electrodes are installed to make up the grounding electrode system, what is the minimum spacing between them?

• a.3 feet
• b.6 feet✓
• c.8 feet
• d.10 feet

Rods that supplement one another must be separated by at least 6 feet so their earth shells do not overlap and defeat the purpose of the second rod. The 8-foot figure is the minimum rod length rather than spacing, and 3 or 10 feet are not the code minimum.2023 NEC §250.53(A)(3)

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

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

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. Values such as 5 ohms or 1 ohm come from specialized standards for communications and lightning systems, not from this general requirement, and 100 ohms is far too high.2023 NEC §250.53(A)(2)

A metal underground water pipe qualifies as a grounding electrode only if it is in direct contact with the earth for at least what length?

• a.20 feet
• b.10 feet✓
• c.8 feet
• d.5 feet

The metal underground water pipe electrode must have 10 feet or more in direct contact with the earth, including any metal well casing bonded to it. The 20-foot value belongs to the concrete-encased electrode, and 5 or 8 feet do not meet the requirement.2023 NEC §250.52(A)(1)

A concrete-encased electrode may be formed by at least 20 feet of which of the following?

• a.Bare 4 AWG copper conductor encased in the concrete footing✓
• b.Bare 6 AWG copper conductor encased in the concrete footing
• c.Insulated 4 AWG copper conductor run through the footing
• d.Bare 8 AWG copper conductor encased in the concrete footing

A concrete-encased electrode consists of at least 20 feet of bare copper not smaller than 4 AWG, or at least 20 feet of one-half inch or larger electrically conductive reinforcing bar, encased in at least 2 inches of concrete near the bottom of a footing in direct contact with earth. Smaller conductors do not qualify, and the copper must be bare so it can couple to the concrete.2023 NEC §250.52(A)(3)

When a metal underground water pipe is used as a grounding electrode, what else is required?

• a.It must be bonded to the interior metal gas piping system, which then serves as the required supplemental grounding electrode
• b.No supplement is required if the pipe is longer than 20 feet
• c.It must be supplemented by an additional electrode of a type identified in 250.52✓
• d.It may be used as the sole electrode only if its measured resistance to earth is 25 ohms or less at installation

A water pipe electrode is never allowed to stand alone because plastic repairs or dielectric fittings can silently disconnect it from earth, so it must always be supplemented by another qualifying electrode such as a rod or a concrete-encased electrode. Pipe length does not remove the requirement, gas piping is bonded but is not permitted as an electrode, and the 25-ohm test applies to rod, pipe and plate electrodes.2023 NEC §250.53(D)(2)

What is the maximum number of service disconnecting means permitted for a single set of service-entrance conductors?

• a.Eight
• b.Two
• c.Four
• d.Six✓

Up to six service disconnects are permitted, but current code requires them to be in separate enclosures or in a listed assembly with individual disconnects, each marked as a service disconnect. Two and four are below the ceiling but are not the code maximum, and eight exceeds the limit.2023 NEC §230.71

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

• a.60 amperes
• b.100 amperes✓
• c.125 amperes
• d.200 amperes

A one-family dwelling service disconnect must be rated at least 100 amperes, 3-wire. The 60-ampere minimum applies to certain limited installations and older code cycles, while 125 and 200 amperes are common design choices but exceed the code minimum.2023 NEC §230.79(C)

What is the minimum clearance above a residential driveway for overhead service conductors limited to 150 volts to ground?

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

Residential driveways and commercial areas not subject to truck traffic require 12 feet of clearance. The 10-foot clearance applies only above finished grade, sidewalks and platforms accessible to pedestrians, and 18 feet is required over public streets, alleys and roads.2023 NEC §230.24(B)

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

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

Service conductors must keep 3 feet of clearance from windows designed to open, doors, porches, balconies, stairs and similar locations. Conductors run above the top level of a window are considered out of reach and are exempt, and the other distances do not appear in this rule.2023 NEC §230.9(A)

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

• a.800 amperes
• b.1,000 amperes✓
• c.600 amperes
• d.1,200 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 exceeding 1,000 volts phase-to-phase, which describes a typical 480Y/277-volt service. The 1,200-ampere figure is the maximum permitted setting of the ground-fault protection, not the threshold at which it is required.2023 NEC §230.95

How must a panelboard be protected against overcurrent?

• a.By an overcurrent device rated at 125 percent of the panelboard rating
• b.By the sum of the branch-circuit devices installed in it
• c.By an overcurrent device having a rating not greater than the panelboard rating✓
• d.No separate protection is required if the feeder conductors are properly sized

Each panelboard must be protected by an overcurrent device rated no higher than the panelboard rating, located either in the panelboard itself as a main or ahead of it in the feeder. Summing the branch devices routinely exceeds the panelboard rating because of diversity, and no code rule allows protecting a panelboard at 125 percent of its rating.2023 NEC §408.36

On the load side of the service disconnecting means, what is the general rule for using the grounded neutral conductor to ground equipment enclosures?

• a.It is permitted only in dwelling units
• b.It is permitted where the grounded neutral conductor is at least 6 AWG copper and runs directly to the equipment
• c.It is permitted in any panelboard or subpanel that is supplied directly from the service equipment enclosure
• d.It is not permitted; a separate equipment grounding conductor must be used✓

Downstream of the service disconnect the neutral and the equipment grounding conductor must be kept separate so that normal load current does not travel on enclosures and raceways. Bonding them together at a subpanel creates parallel neutral paths and objectionable current, and neither conductor size nor occupancy type changes this general prohibition.2023 NEC §250.142(B)

A dry-type transformer rated 112.5 kVA or less is installed indoors. What is the minimum separation from combustible material unless it is separated by a fire-resistant heat-insulating barrier?

• a.3 inches
• b.6 inches
• c.12 inches✓
• d.18 inches

Dry-type transformers of 112.5 kVA or less must be at least 12 inches from combustible material unless separated by a fire-resistant, heat-insulating barrier or unless the unit is completely enclosed except for ventilating openings. The smaller clearances listed belong to other rules such as recessed luminaire and insulation spacing, not to transformer installation.2023 NEC §450.21(A)

The interior metal water piping system of a building must be bonded to the service equipment. How is the required bonding jumper sized?

• a.From Table 250.66, based on the size of the service-entrance conductors✓
• b.From Table 250.122, based on the rating of the overcurrent device protecting the largest service conductor
• c.Always 6 AWG copper regardless of service size
• d.From Table 310.16, based on the service ampacity and the temperature rating of the terminations used

The bonding jumper for the interior metal water piping system is sized from Table 250.66 using the ungrounded service-entrance conductors, the same table used for the grounding electrode conductor. Table 250.122 sizes equipment grounding conductors by overcurrent device and does not apply to this bond.2023 NEC §250.104(A)(1)

For a separately derived system such as a transformer secondary, where is the system bonding jumper permitted to be installed?

• a.At every downstream panelboard
• b.Only at the main service disconnecting means of the building and never at the transformer, panelboard, or any other point of the separately derived system
• c.At the source of the separately derived system or at the first disconnecting means, but at only one of those points✓
• d.It is not required for separately derived systems

A separately derived system requires a single system bonding jumper connecting the grounded conductor to the equipment grounding system, installed either at the source or at the first disconnecting means but at only one location. Installing it at more than one point creates parallel neutral paths, and omitting it leaves no effective fault-clearing path for the derived system.2023 NEC §250.30(A)(1)

A single-family dwelling has a calculated demand load of 21,600 volt-amperes on a 240-volt, single-phase service. What is the minimum service disconnecting means rating permitted?

• a.90 amperes
• b.100 amperes✓
• c.125 amperes
• d.60 amperes

The calculated current is 21,600 / 240 = 90 amperes, but the service disconnecting means for a one-family dwelling must be rated at least 100 amperes, so the code floor governs. Selecting 90 amperes satisfies the calculation but violates the 100-ampere minimum, and 125 amperes exceeds the required minimum.2023 NEC §230.79(C)

The grounded (neutral) service conductor also serves as the effective ground-fault current path back to the utility. It must be sized not smaller than what?

• a.The equipment grounding conductor from Table 250.122
• b.6 AWG copper in all cases
• c.One-half the ungrounded conductor size
• d.The grounding electrode conductor value from Table 250.102(C)(1)✓

Because there is no main bonding jumper ahead of the service, the grounded conductor must carry any fault current back to the source, so it may not be smaller than the value from Table 250.102(C)(1), which mirrors Table 250.66. Sizing it from the equipment grounding conductor table would leave it too small for that duty.2023 NEC §250.24(C)

At service equipment, why are standard locknuts and bushings alone not adequate where service raceways connect through concentric or eccentric knockouts?

• a.They are in fact adequate by themselves, so no additional bonding means, jumpers, or listed fittings are needed where service raceways connect through concentric or eccentric knockouts
• b.Because service raceways must always be nonmetallic
• c.Because service bonding requires bonding jumpers, bonding bushings or other listed bonding-type fittings to ensure a low-impedance path✓
• d.Because only exothermic welding is permitted at a service

Service raceways and enclosures must be bonded by an approved means such as bonding jumpers, bonding-type locknuts or bushings, since standard locknuts across concentric or eccentric knockouts cannot be relied on for the high fault current available ahead of the service overcurrent device. Downstream of the service, standard locknuts are generally acceptable.2023 NEC §250.92(B)

A grounding electrode conductor is run from the service to a driven ground rod. What is the rule regarding splices in that conductor?

• a.Any listed split-bolt connector may be used
• b.It must be installed in one continuous length unless spliced by irreversible compression connectors, exothermic welding or connections to busbars✓
• c.Up to three twist-on wire connector splices are permitted along the run, provided that each connection is made accessible and the conductor is not reduced in size at any of the splice points
• d.Splices are permitted only inside accessible junction boxes

A grounding electrode conductor must be continuous, and where a splice is necessary it is permitted only by irreversible compression connectors listed for the purpose, exothermic welding, or bolting to busbars. Ordinary split-bolts and twist-on connectors are reversible and are not acceptable for this conductor.2023 NEC §250.64(C)

How is the load on a feeder or service neutral (grounded) conductor determined?

• a.By the maximum unbalanced load, the maximum net current between the neutral and any one ungrounded conductor✓
• b.By the sum of all ungrounded conductor currents
• c.It is always the same size as the ungrounded conductors
• d.By taking 125 percent of the load on the largest single ungrounded conductor and applying that resulting value to the neutral conductor

The neutral carries only the imbalance among the phase conductors, so its calculated load is the maximum unbalanced load, defined as the maximum net current between the neutral and any one ungrounded conductor. Loads such as 240-volt line-to-line appliances place no current on the neutral at all.2023 NEC §220.61(A)

A demand factor may be applied to the portion of a feeder neutral load that exceeds what value?

• a.100 amperes
• b.150 amperes
• c.200 amperes✓
• d.400 amperes

For a feeder or service, the portion of the maximum unbalanced neutral load that exceeds 200 amperes may be taken at 70 percent, recognizing the diversity of line-to-neutral loads at higher currents. This reduction does not apply to nonlinear loads on a wye system, where the neutral can be as heavily loaded as the phases.2023 NEC §220.61(B)

A service uses 4/0 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.4 AWG
• b.2 AWG✓
• c.1/0 AWG
• d.6 AWG

Table 250.66 places service conductors over 3/0 through 350 kcmil copper in the row requiring a 2 AWG copper grounding electrode conductor. The 4 AWG row is for 2/0 and 3/0, so reading one row low understates it. See NEC Table 250.66.

A service is supplied by a single set of 400 kcmil copper ungrounded conductors. What is the minimum size copper grounding electrode conductor?

• a.2 AWG
• b.4 AWG
• c.1/0 AWG✓
• d.3/0 AWG

Service conductors over 350 through 600 kcmil copper require a 1/0 AWG copper grounding electrode conductor. The 2 AWG row applies to over 3/0 through 350 kcmil. See NEC Table 250.66.

A service uses 1 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

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

Table 250.66 groups 1 and 1/0 AWG copper service conductors together and requires a 6 AWG copper grounding electrode conductor. The 8 AWG row is for 2 AWG and smaller. See NEC Table 250.66.

What is the minimum size copper equipment grounding conductor for a circuit protected at 100 amperes?

• a.8 AWG✓
• b.10 AWG
• c.6 AWG
• d.4 AWG

Table 250.122 is entered by the overcurrent device rating, and the 100-ampere row calls for 8 AWG copper. The 10 AWG row is 60 amperes and 6 AWG is 200 amperes. See NEC Table 250.122.

What is the minimum size copper equipment grounding conductor for a 300-ampere feeder?

• a.2 AWG
• b.6 AWG
• c.3 AWG
• d.4 AWG✓

The 300-ampere row of Table 250.122 specifies 4 AWG copper. 6 AWG is 200 amperes and 3 AWG is 400 amperes, so those are adjacent rows. See NEC Table 250.122.

What is the minimum size copper equipment grounding conductor for a 20-ampere branch circuit?

• a.14 AWG
• b.10 AWG
• c.8 AWG
• d.12 AWG✓

Table 250.122 lists 12 AWG copper at 20 amperes. 14 AWG is the 15-ampere value and 10 AWG is the 60-ampere value. See NEC Table 250.122.

What is the minimum size copper equipment grounding conductor for a 500-ampere feeder?

• a.1 AWG
• b.4 AWG
• c.3 AWG
• d.2 AWG✓

The 500-ampere row of Table 250.122 requires 2 AWG copper. 3 AWG is 400 amperes and 1 AWG is 600 amperes. See NEC Table 250.122.

A ground ring encircling a building must be formed from at least 20 feet of bare copper conductor not smaller than what size?

• a.4 AWG
• b.6 AWG
• c.2 AWG✓
• d.1/0 AWG

A ground ring must encircle the building and consist of at least 20 feet of bare copper conductor not smaller than 2 AWG. See NEC 250.52(A)(4).

A plate electrode must present at least how much surface area to exterior soil?

• a.8 square feet
• b.4 square feet
• c.2 square feet✓
• d.1 square foot

A plate electrode of iron, steel or nonferrous metal must expose at least 2 square feet of surface to the surrounding earth. See NEC 250.52(A)(7).

When ungrounded conductors are increased in size for voltage drop, how must the equipment grounding conductor be adjusted?

• a.Doubled in every case
• b.Increased proportionally to the ungrounded conductors' increase in circular-mil area✓
• c.Sized only from Table 250.122 by the overcurrent device rating
• d.Left unchanged because the overcurrent device did not change

Where ungrounded conductors are upsized, the equipment grounding conductor must be increased proportionally by circular-mil area. See NEC 250.122(B).

A service is supplied by a single set of 350 kcmil copper ungrounded conductors. What is the minimum size copper main bonding jumper?

• a.3 AWG
• b.1/0 AWG
• c.2 AWG✓
• d.4 AWG

The main bonding jumper is sized from Table 250.102(C)(1), and 350 kcmil copper falls in the over 3/0 through 350 kcmil row requiring 2 AWG copper. See NEC 250.28(D)(1).

A service uses two parallel sets of 600 kcmil copper conductors per phase. Using the 12.5 percent rule, what is the minimum copper main bonding jumper?

• a.2/0 AWG
• b.4/0 AWG
• c.3/0 AWG✓
• d.250 kcmil

Where copper service conductors exceed 1,100 kcmil, the main bonding jumper must be at least 12.5 percent of that area: 2 x 600 = 1,200 kcmil, and 1,200 x 0.125 = 150 kcmil. 2/0 (133.1 kcmil) is too small; 3/0 (167.8 kcmil) qualifies. See NEC 250.28(D)(2).

A reinforcing bar used to form a concrete-encased electrode must be at least what diameter?

• a.1/4 inch
• b.5/8 inch
• c.3/8 inch
• d.1/2 inch✓

A concrete-encased electrode may use at least 20 feet of electrically conductive reinforcing bar not smaller than 1/2 inch in diameter, encased in at least 2 inches of concrete. See NEC 250.52(A)(3).

Where two rod electrodes are installed to form the grounding electrode system, what is the minimum spacing between them?

• a.6 feet✓
• b.8 feet
• c.3 feet
• d.10 feet

Supplementary rods must be at least 6 feet apart so their earth shells do not overlap. The 8-foot figure is the rod length, not the spacing. See NEC 250.53(A)(3).

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.