CSLB Trade — Electrical (C-10) — All Questions

For a feeder/service neutral, the portion of the maximum unbalanced load that exceeds 200 A may generally be calculated at:

• a.80%
• b.50%
• c.100%
• d.70%✓

Per 220.61(B)(2), the neutral load in excess of 200 A may be taken at 70% (subject to the restrictions of 220.61(C), such as nonlinear loads). The first 200 A is at 100%; the other percentages do not match the code demand factor.2023 NEC §220.61

A 75 kVA, 208Y/120 V transformer has an impedance of 2%. Using the infinite-bus (worst-case) method, the approximate available fault current at the transformer secondary is about:

• a.10,400 A✓
• b.4,160 A
• c.2,080 A
• d.20,800 A

Secondary full-load current = 75,000 / (1.732 x 208) = 208 A; dividing by the per-unit impedance gives 208 / 0.02 = 10,400 A. Using the wrong impedance or forgetting to divide gives the incorrect values; this infinite-bus method assumes an unlimited primary source.

When circuit conductors are run in parallel in multiple raceways, the equipment grounding conductor in each raceway must be:

• a.Divided proportionally between raceways
• b.Sized in full, based on the circuit overcurrent device, in each raceway✓
• c.Omitted in all but one raceway
• d.One size smaller in each raceway

Per 250.122(F), where conductors are run in parallel in separate raceways or cables, a full-size equipment grounding conductor sized per Table 250.122 (based on the circuit OCPD) must be installed in each raceway. It cannot be divided, reduced, or omitted, because each raceway must carry a complete fault path.2023 NEC §250.122

A 208Y/120 V, 3-phase feeder supplies a balanced 50 kVA load. The approximate line current (and therefore the minimum conductor ampacity before continuous factors) is:

• a.120 A
• b.174 A
• c.139 A✓
• d.96 A

For a 3-phase load, I = VA / (1.732 x line voltage) = 50,000 / (1.732 x 208) = about 139 A. Dividing by voltage alone or using a single-phase formula gives the incorrect answers; the sqrt(3) factor is required for three-phase current.2023 NEC §215.2

For a 200 A service where the equipment and conductors are all rated for it, the conductor ampacity used for termination sizing is normally based on which temperature column?

• a.75 degrees C✓
• b.90 degrees C
• c.60 degrees C
• d.105 degrees C

Per 110.14(C), for circuits over 100 A (or conductors larger than 1 AWG), terminations are generally rated 75 degrees C, so the 75 degrees C column of Table 310.16 is used unless equipment is listed otherwise. The 90 degrees C column is only for derating starting points, and 60 degrees C applies to smaller circuits.2023 NEC §110.14

A panelboard must have a rating (busbar ampacity) not less than:

• a.The largest single branch circuit only
• b.The minimum feeder capacity required for the load served, as computed per Article 220✓
• c.50% of the service rating
• d.Twice the neutral load

Per 408.30, a panelboard must have a rating not less than the minimum feeder or service capacity required for the load computed under Article 220. Sizing only to a single branch circuit or an arbitrary fraction of the service would leave the busbar under-rated for the actual load.2023 NEC §408.30

Service-entrance conductors installed in a raceway in a wet location (such as underground or exposed to weather) must be:

• a.Any dry-rated conductor is acceptable
• b.Type TW without a jacket
• c.Listed and marked for wet locations, such as RHW, THW, THWN, or XHHW✓
• d.Bare copper only

Per 310.10(C), conductors in wet locations (including raceways underground or exposed to weather) must be a type listed for wet locations, such as RHW, THW, THWN, or XHHW. Dry-only types or bare conductors are not permitted where moisture is present.2023 NEC §310.10

A separately derived system (such as the secondary of a transformer feeding a distribution panel) must have a system bonding jumper connecting:

• a.The grounded conductor to the supply-side bonding jumper and equipment grounding conductor at the source or first disconnect✓
• b.The neutral to a branch-circuit breaker
• c.The two ungrounded phases together
• d.Only the metal raceway to earth

Per 250.30(A), a separately derived system requires a system bonding jumper connecting the grounded conductor to the supply-side bonding jumper and/or equipment grounding conductor at a single point (at the source or the first disconnect). Bonding phases together or omitting the grounded conductor connection would not establish the required fault path.2023 NEC §250.30

A detached garage is supplied by a feeder from the main dwelling. At the garage, the code generally requires:

• a.No grounding electrode because the feeder has an equipment grounding conductor
• b.A grounding electrode (or electrode system) to be installed and connected to the building disconnect, with the equipment grounding conductor run with the feeder✓
• c.Only a single ground rod with the neutral used as the ground
• d.The neutral must be bonded to the enclosure like at a service

Per 250.32, a building or structure supplied by a feeder must have a grounding electrode connected to the equipment grounding terminal at the disconnect, and an equipment grounding conductor must be run with the feeder while the neutral remains isolated. Re-bonding the neutral downstream (the old exception) is no longer generally permitted.2023 NEC §250.32

On a 4-wire delta system where the midpoint of one phase is grounded, the conductor with the higher voltage to ground (the high leg) must be durably and permanently marked, typically colored:

• a.Orange✓
• b.White
• c.Green
• d.Blue

Per 110.15, the phase conductor having the higher voltage to ground (about 208 V on a 120/240 V high-leg delta) must be marked by an outer finish that is orange or by other effective means at every point of connection. White identifies the grounded conductor and green identifies equipment grounding, so neither can mark the high leg.2023 NEC §110.15

A service raceway enters a building from an underground distribution system. To prevent moisture and gases from entering, the raceway must be:

• a.Filled with concrete
• b.Sealed with an approved material (though a drainage provision may still be provided)✓
• c.Painted on the interior
• d.Left open for drainage

Per 230.8, a raceway entering from an underground distribution system must be sealed with an identified compound to block moisture and gases; spare or unused raceways must also be sealed. Leaving it open or filling with concrete does not meet the sealing requirement, and painting does not seal against gas migration.2023 NEC §230.8

Where multiple service disconnects are installed under the 2023 NEC, the general requirement (compared to older editions) is that they be:

• a.Operable by a maximum of six movements of the hand in one enclosure
• b.Located outdoors only
• c.Installed in separate enclosures, or in a listed assembly, rather than up to six switches in a single common enclosure✓
• d.Interlocked so only one can open at a time

The 2023 NEC changed the multiple-disconnect rule so that up to six service disconnects must be in separate enclosures (or part of a listed switchboard, switchgear, or metering-disconnect assembly), rather than as several breakers in one common enclosure. The old six-hand-movement allowance in a single cabinet is no longer the general rule.2023 NEC §230.71

When installing a surge-protective device (SPD), the best practice for the connecting conductors is to:

• a.Keep them as short and straight as practicable✓
• b.Make them as long as possible for flexibility
• c.Route them alongside the grounding electrode conductor for the full length
• d.Coil extra length behind the panel

SPD performance depends on low conductor impedance, so the leads should be kept as short and straight as practicable to minimize added voltage from lead inductance during a surge. Long or coiled leads raise the let-through voltage and reduce protection, defeating the purpose of the device.

In a standard dwelling load calculation, the general lighting and receptacle load demand factor applies 100% to:

• a.None of the load
• b.The first 3000 VA✓
• c.The first 10,000 VA
• d.All VA above 120,000

Per Table 220.42, the first 3000 VA of general lighting/receptacle load is taken at 100%, the portion from 3001 to 120,000 VA at 35%, and any remainder at 25%. The other choices misstate the thresholds of the demand-factor table.2023 NEC §220.42

A series-rated combination of overcurrent devices is permitted to protect equipment where the available fault current exceeds the interrupting rating of a downstream device, provided the combination is:

• a.Any two breakers from different manufacturers
• b.Rated only by adding the two interrupting ratings
• c.Tested and marked/listed as a recognized series combination, and the equipment is field-marked accordingly✓
• d.Field-assembled without documentation

Per 240.86, series ratings may be used only where the combination is listed and marked as a tested series combination (or engineered per 240.86(A)), and the end equipment is legibly field-marked to indicate the series-combination rating. Simply pairing arbitrary breakers or adding interrupting ratings is not permitted.2023 NEC §240.86

In a dwelling living room, general-purpose receptacles must be placed so that no point measured horizontally along the floor line of any wall space is farther than what distance from a receptacle?

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

Section 210.52(A) requires receptacles so no point along the wall line is more than 6 ft from an outlet, which effectively caps spacing at 12 ft. This lets any 6-ft appliance cord reach an outlet without an extension cord. 8, 10, and 12 ft each exceed the 6-ft reach the rule protects.2023 NEC §210.52(A)

For dwelling receptacle spacing under 210.52(A), any wall space that is how wide or wider is counted as usable wall space requiring a receptacle?

• a.4 ft
• b.1 ft
• c.18 in
• d.2 ft✓

Section 210.52(A)(2) defines wall space to include any space 2 ft or more in width, including corners. A wall segment at least 2 ft wide must be served by a receptacle. 1 ft and 18 in are below the threshold, and 4 ft is larger than the code minimum.2023 NEC §210.52(A)

Along a dwelling kitchen countertop, receptacles must be installed so that no point along the wall counter space is more than what distance, measured horizontally, from a receptacle?

• a.48 in
• b.24 in✓
• c.12 in
• d.36 in

Section 210.52(C)(1) requires countertop receptacles so no point along the wall counter line is more than 24 in from a receptacle, giving a 4-ft maximum spacing. 12 in is stricter than required; 36 and 48 in would leave points beyond the reach of a typical appliance cord.2023 NEC §210.52(C)(1)

A kitchen wall counter space is required to be served by a countertop receptacle when the counter is at least what width?

• a.6 in
• b.9 in
• c.12 in✓
• d.10 in

Section 210.52(C)(1) applies to wall counter spaces 12 in or wider. A counter narrower than 12 in is not required to have a dedicated countertop receptacle. 6, 9, and 10 in are all below the 12-in trigger.2023 NEC §210.52(C)(1)

What is the minimum number of 20-ampere small-appliance branch circuits required to serve the receptacle outlets in a dwelling kitchen, pantry, breakfast room, and dining room?

• a.4
• b.1
• c.2✓
• d.3

Section 210.11(C)(1) requires at least two 20-A small-appliance branch circuits for these areas. These circuits serve countertop and receptacle outlets and cannot supply lighting. One circuit is insufficient; three or four exceed the code minimum.2023 NEC §210.11(C)(1)

The dwelling laundry receptacle outlet(s) required by 210.52(F) must be supplied by a branch circuit of at least what rating, dedicated to the laundry?

• a.30 A
• b.20 A✓
• c.15 A
• d.40 A

Section 210.11(C)(2) requires at least one additional 20-A branch circuit for the laundry receptacle(s), and it must have no other outlets. A 15-A circuit is too small; 30 and 40 A are not the required minimum for general laundry receptacles.2023 NEC §210.11(C)(2)

A dwelling bathroom receptacle outlet must be supplied by a branch circuit of at least what rating that serves only bathroom receptacle outlets?

• a.15 A
• b.30 A
• c.10 A
• d.20 A✓

Section 210.11(C)(3) requires at least one 20-A branch circuit to supply bathroom receptacle outlets. Where that circuit supplies only a single bathroom, it may also serve other equipment in that same bathroom. 10 and 15 A are below the required rating, and 30 A is not specified.2023 NEC §210.11(C)(3)

A 125-volt, 20-ampere receptacle installed in a dwelling bathroom must have what protection?

• a.GFCI✓
• b.AFCI only
• c.Surge protection
• d.No special protection

Section 210.8(A)(1) requires GFCI protection for all 125-V through 250-V receptacles in dwelling bathrooms because of the wet environment near sinks and tubs. AFCI addresses arc faults, not shock in wet locations; surge protection and 'none' do not meet the shock-protection requirement.2023 NEC §210.8(A)(1)

Under 210.8(A), a 125-volt receptacle located within how many feet of a dwelling laundry, utility, or wet bar sink (measured from the outside edge of the sink) requires GFCI protection?

• a.10 ft
• b.3 ft
• c.4 ft
• d.6 ft✓

Section 210.8(A)(7) requires GFCI protection for receptacles located within 6 ft of the outside edge of a sink. The distance is measured to the nearest edge of the sink. 3 and 4 ft are too short, and 10 ft is beyond the code radius.2023 NEC §210.8(A)

A 125-volt, 20-ampere receptacle installed in the unfinished portion of a dwelling basement used for storage or a work area requires what protection?

• a.GFCI✓
• b.AFCI only
• c.No protection
• d.Isolated ground

Section 210.8(A)(5) requires GFCI protection for receptacles in unfinished basement areas not intended as habitable rooms, such as storage and work areas, because of the damp concrete environment. AFCI alone does not provide shock protection; 'no protection' and an isolated ground do not satisfy the rule.2023 NEC §210.8(A)(5)

Receptacles installed in a dwelling attached garage at 125 volts, 20 amperes must be provided with what protection?

• a.None if dedicated
• b.GFCI✓
• c.AFCI only
• d.Surge protection

Section 210.8(A)(2) requires GFCI protection for all 125-V through 250-V receptacles in dwelling garages and accessory buildings. This includes receptacles for freezers or door openers. AFCI, surge protection, and a 'dedicated' exception do not remove the GFCI requirement.2023 NEC §210.8(A)(2)

Under 210.8(A), outdoor receptacles at a dwelling rated 125 volts, 20 amperes generally require what protection?

• a.Weatherproof cover only
• b.No protection
• c.GFCI✓
• d.AFCI

Section 210.8(A)(3) requires GFCI protection for receptacles installed outdoors at dwellings because of exposure to moisture. A weatherproof cover is also required by 406.9 but does not replace GFCI. AFCI and 'no protection' do not address outdoor shock hazards.2023 NEC §210.8(A)(3)

Under 210.8(A), a 125-volt, 20-ampere receptacle that serves a dwelling kitchen countertop surface requires what protection?

• a.Surge only
• b.None
• c.AFCI only
• d.GFCI✓

Section 210.8(A)(6) requires GFCI protection for receptacles serving dwelling kitchen countertop surfaces due to proximity to water. AFCI is separately required for the circuit but does not satisfy the GFCI rule; surge protection and 'none' do not protect against shock.2023 NEC §210.8(A)(6)

Which protection is required for 120-volt, 15- and 20-ampere branch circuits supplying receptacle outlets in dwelling bedrooms?

• a.None
• b.Surge only
• c.AFCI✓
• d.GFCI only

Section 210.12(A) requires arc-fault circuit-interrupter (AFCI) protection for 120-V, 15- and 20-A branch circuits supplying outlets in dwelling bedrooms and many other living areas. AFCI protects against arcing faults that can start fires. GFCI addresses shock, not arcing; surge and 'none' do not meet the rule.2023 NEC §210.12(A)

In a dwelling bathroom, at least one receptacle outlet must be installed within what distance of the outside edge of each basin?

• a.6 ft
• b.3 ft✓
• c.2 ft
• d.12 in

Section 210.52(D) requires a receptacle outlet within 3 ft of the outside edge of each bathroom basin. The receptacle must be on a wall or partition adjacent to the basin, or on the countertop/basin cabinet side. 12 in and 2 ft are stricter than required; 6 ft exceeds the code limit.2023 NEC §210.52(D)

For a one-family dwelling, how many outdoor receptacle outlets are required, and where?

• a.None
• b.One, at the front only
• c.At least one at the front and one at the back, accessible from grade✓
• d.One, in the garage

Section 210.52(E)(1) requires at least one receptacle outlet accessible from grade at both the front and back of a one-family dwelling, not more than 6.5 ft above grade. A single front outlet, a garage-only outlet, and 'none' all fail to meet the front-and-back requirement.2023 NEC §210.52(E)(1)

In a dwelling, a hallway of what length or more must have at least one receptacle outlet?

• a.20 ft
• b.6 ft
• c.15 ft
• d.10 ft✓

Section 210.52(H) requires at least one receptacle outlet in dwelling hallways 10 ft or more in length, measured along the centerline without passing through a doorway. Halls shorter than 10 ft are not required to have one; 15 and 20 ft are longer than the trigger.2023 NEC §210.52(H)

What is the minimum depth of working space in front of electrical equipment operating at 0 to 150 volts to ground, where there are exposed live parts on one side and no live or grounded parts on the other (Condition 1)?

• a.3.5 ft
• b.3 ft✓
• c.4 ft
• d.2.5 ft

Table 110.26(A)(1) requires a minimum working clearance of 3 ft (Condition 1) for equipment at 0-150 V to ground. This depth allows safe access for operation and maintenance. 2.5 ft is below the minimum; 3.5 and 4 ft apply to higher voltage or more hazardous conditions.2023 NEC §110.26(A)(1)

The width of the working space in front of electrical equipment must be at least the width of the equipment or what minimum, whichever is greater?

• a.28 in
• b.24 in
• c.36 in
• d.30 in✓

Section 110.26(A)(2) requires the working space width to be the width of the equipment or 30 in, whichever is greater. The space must also permit at least a 90-degree opening of equipment doors. 24 and 28 in are below the minimum; 36 in is more than required.2023 NEC §110.26(A)(2)

What is the minimum height (headroom) of the working space about electrical equipment such as panelboards, generally required by 110.26?

• a.6 ft
• b.6 ft 6 in✓
• c.6 ft 4 in
• d.6 ft 2 in

Section 110.26(A)(3) requires the working space to be clear and extend from the grade or floor to a height of 6.5 ft (6 ft 6 in) or the height of the equipment, whichever is greater. The lower heights listed do not satisfy the minimum headroom.2023 NEC §110.26(A)(3)

Electrical metallic tubing (EMT) must be securely fastened within what distance of each outlet box, junction box, or fitting?

• a.4 ft
• b.3 ft✓
• c.5 ft
• d.6 ft

Section 358.30(A) requires EMT to be securely fastened in place within 3 ft of each box, cabinet, or termination. It must also be supported at intervals not exceeding 10 ft. 4, 5, and 6 ft all exceed the 3-ft fastening distance from boxes.2023 NEC §358.30(A)

After the required fastening near boxes, EMT must be supported at intervals not exceeding what distance?

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

Section 358.30(A) requires EMT to be supported at least every 10 ft along the run. Combined with fastening within 3 ft of boxes, this keeps the raceway secure. 8 and 6 ft are stricter than required, and 12 ft exceeds the maximum support spacing.2023 NEC §358.30(A)

Between pull points (for example, from box to box), the total number of bends in one run of EMT must not exceed the equivalent of how many degrees?

• a.450
• b.180
• c.360✓
• d.270

Section 358.26 limits the total bends between pull points to the equivalent of four quarter bends, or 360 degrees. Exceeding this makes conductor pulling difficult and risks insulation damage. 180 and 270 are below the allowed total; 450 exceeds the code maximum.2023 NEC §358.26

Liquidtight flexible metal conduit (LFMC) must be securely fastened within what distance of each box, cabinet, or fitting where the conduit is not fished?

• a.18 in
• b.12 in✓
• c.3 ft
• d.2 ft

Section 350.30(A) requires LFMC to be fastened within 12 in of each box, cabinet, or termination and supported at intervals not exceeding 4.5 ft. The larger distances of 3 ft, 2 ft, and 18 in all exceed the 12-in fastening requirement for LFMC.2023 NEC §350.30(A)

Along its length, liquidtight flexible metal conduit (LFMC) must be supported at intervals not exceeding what distance?

• a.10 ft
• b.4.5 ft✓
• c.8 ft
• d.6 ft

Section 350.30(A) requires LFMC to be supported at intervals not exceeding 4.5 ft (1.4 m) along the run, in addition to fastening within 12 in of boxes. 6, 8, and 10 ft all exceed the maximum support spacing for this flexible raceway.2023 NEC §350.30(B)

Rigid metal conduit (RMC) must be securely fastened within what distance of each outlet box, junction box, or termination?

• a.5 ft
• b.3 ft✓
• c.2 ft
• d.6 ft

Section 344.30(A) requires RMC to be securely fastened within 3 ft of each box, cabinet, or fitting. Support intervals along the run then follow Table 344.30(B). 2 ft is stricter than the code minimum, while 5 and 6 ft exceed the required fastening distance.2023 NEC §344.30(A)

For 1/2-inch through 3/4-inch trade size rigid metal conduit (RMC), what is the maximum spacing between supports on a straight horizontal run per Table 344.30(B)?

• a.8 ft
• b.6 ft
• c.10 ft✓
• d.14 ft

Table 344.30(B) permits a maximum support spacing of 10 ft for 1/2-in and 3/4-in RMC. Larger conduit sizes allow greater spacing. 6 and 8 ft are stricter than needed; 14 ft applies only to larger trade sizes such as 2.5 in and above.2023 NEC §344.30(B)

For 1/2-inch through 1-inch trade size rigid PVC conduit, what is the maximum support spacing per Table 352.30?

• a.4 ft
• b.3 ft✓
• c.6 ft
• d.5 ft

Table 352.30 requires support of rigid PVC conduit sized 1/2 in through 1 in at intervals not exceeding 3 ft because PVC is more flexible than metal raceway. Larger sizes allow wider spacing. 5, 4, and 6 ft all exceed the 3-ft maximum for these small sizes.2023 NEC §352.30(B)

Expansion fittings for rigid PVC conduit must be provided to compensate for thermal expansion and contraction where the length change is expected to be at least how much?

• a.1 in
• b.2 in
• c.1/2 in
• d.1/4 in✓

Section 352.44 requires expansion fittings where the length change of PVC due to temperature is expected to be 1/4 in or greater. PVC expands and contracts significantly with temperature. 1/2 in, 1 in, and 2 in are all beyond the 1/4-in threshold that triggers the fitting.2023 NEC §352.44

Under Table 300.5, what is the minimum burial depth for a direct-buried rigid metal conduit (RMC) installed under a residential driveway of a one-family dwelling?

• a.6 in
• b.12 in
• c.18 in✓
• d.24 in

Table 300.5 requires 18 in minimum cover for RMC and IMC located under one- and two-family dwelling driveways. General non-driveway locations allow 6 in for RMC, but the driveway column increases this. 12 in and 6 in are too shallow here; 24 in is required for direct-buried cable, not RMC under a driveway.2023 NEC §300.5

Per Table 300.5, what is the minimum cover for direct-buried UF cable (without other protection) not under a driveway, in a residential branch circuit application?

• a.12 in
• b.36 in
• c.24 in✓
• d.6 in

Table 300.5 requires 24 in of cover for direct-buried cables and conductors in the general burial column. A GFCI-protected residential 120-V, 20-A branch circuit may be reduced to 12 in, but the base direct-burial requirement is 24 in. 6 in is far too shallow; 36 in is not required in this row.2023 NEC §300.5

Where cables or raceways are run parallel to framing members, the wiring must be kept at least what distance from the nearest edge of a wood stud where nails or screws are likely, unless protected by a steel plate?

• a.3/4 in
• b.1-1/8 in
• c.1-1/4 in✓
• d.1 in

Section 300.4(D) requires cables and raceways run parallel to framing to be at least 1-1/4 in from the nearest edge where nails or screws are likely; otherwise a 1/16-in steel plate is required. The smaller distances of 3/4, 1, and 1-1/8 in do not provide the required setback.2023 NEC §300.4(D)

Branch-circuit conductors must have an ampacity not less than the maximum load to be served and, before the application of adjustment or correction factors, not less than what portion of the continuous load?

• a.125 percent✓
• b.80 percent
• c.100 percent
• d.150 percent

Section 210.19(A) requires branch-circuit conductors to be sized at not less than 125 percent of the continuous load plus 100 percent of the noncontinuous load. This margin accounts for heat buildup under sustained load. 100 and 80 percent are too small; 150 percent is more than the code requires.2023 NEC §210.19(A)

A single receptacle installed on an individual branch circuit must have an ampere rating not less than what value relative to the branch circuit?

• a.No minimum applies
• b.125 percent of the circuit
• c.The rating of the branch circuit✓
• d.50 percent of the circuit

Section 210.21(B)(1) requires a single receptacle on an individual branch circuit to have an ampere rating not less than that of the branch circuit. A 20-A individual circuit therefore needs at least a 20-A receptacle. Half the circuit rating and 'no minimum' are wrong, and 125 percent is not required for the receptacle.2023 NEC §210.21(B)(1)

On a 20-ampere branch circuit supplying two or more receptacles, a single cord-and-plug-connected utilization equipment item must not have a rating exceeding what value?

• a.10 A
• b.16 A✓
• c.12 A
• d.20 A

Section 210.23(A)(1) limits any single cord-and-plug-connected utilization equipment to 80 percent of the branch-circuit rating where the circuit supplies two or more outlets. On a 20-A circuit that is 16 A. 10 and 12 A are stricter than required; 20 A would leave no margin and exceeds the 80-percent limit.2023 NEC §210.23(A)(1)