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

For a single service, what is the maximum number of service disconnecting means permitted (for one set of service-entrance conductors)?

• a.10
• b.6✓
• c.4
• d.8

Per 230.71, the service disconnecting means for each service is limited to a maximum of 6, each in a separate enclosure or in listed switchgear/switchboard. 4 is more restrictive than required, and 8 or 10 exceed the code maximum.2023 NEC §230.71

As a general rule, how must a panelboard be protected against overcurrent?

• a.By the branch-circuit breakers only
• b.It requires no separate overcurrent protection
• c.By an OCPD not exceeding the panelboard rating, on the supply side✓
• d.By a GFCI device

Per 408.36, each panelboard must be protected by an overcurrent device not exceeding its rating, located on the supply side (or within the panelboard as main). Branch breakers alone do not protect the busbar, and GFCI protects people, not the bus rating.2023 NEC §408.36

What is the minimum depth of working space in front of a 120/240 V panelboard (Condition 1, exposed live parts on one side)?

• a.3.5 ft (1.07 m)
• b.4 ft (1.2 m)
• c.2 ft (0.6 m)
• d.3 ft (0.9 m)✓

Per Table 110.26(A)(1), Condition 1 for systems 0-150 V to ground requires 3 ft (900 mm) of clear working depth. 2 ft is too shallow, and 3.5 ft/4 ft apply to higher-voltage or Condition 2/3 situations.2023 NEC §110.26

Service-entrance conductors must have an ampacity not less than which of the following?

• a.The physical size of the meter socket
• b.The computed load per Article 220, with continuous loads at 125%✓
• c.The neutral load only
• d.Half the service rating

Per 230.42, service conductors are sized to the load calculated under Article 220, applying 125% to continuous loads. Meter-socket size, half the rating, and neutral-only are not the sizing basis.2023 NEC §230.42

As a general rule, how many sets of service-entrance conductors may supply each service drop or lateral?

• a.Two sets always
• b.Up to six sets
• c.One set (with listed exceptions)✓
• d.Unlimited sets

Per 230.40, each service drop/lateral generally supplies only one set of service-entrance conductors, with specific exceptions (e.g., multiple-occupancy buildings). 'Two always,' 'up to six,' and 'unlimited' misstate the general rule.2023 NEC §230.40

Overhead service-drop conductors passing above a residential roof that is not readily accessible generally must maintain what minimum vertical clearance above the roof?

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

Per 230.24(A), service conductors must generally clear a roof by at least 8 ft (2.5 m) within 3 ft horizontally of the edge; various reduced-clearance provisions exist but 8 ft is the baseline. 3 ft and 12 ft are not the general roof-clearance value.2023 NEC §230.24

Under the 10-ft feeder tap rule, the tap conductors must have an ampacity not less than what value relative to the load and the device they supply?

• a.The load served, and at least the rating of the device/overcurrent it supplies✓
• b.25% of the feeder OCPD
• c.50% of the feeder ampacity
• d.Equal to the feeder OCPD

Per 240.21(B)(1), 10-ft tap conductors must have an ampacity not less than the combined computed load and not less than the rating of the device or OCPD they terminate in. Fixed percentages of the feeder OCPD/ampacity are not the correct basis for the 10-ft rule.2023 NEC §240.21(B)

Where service-entrance conductors are run in parallel in separate raceways, how is the supply-side bonding jumper sized in each raceway?

• a.One 6 AWG total for the whole service
• b.Not required for parallel runs
• c.Same as the neutral in all cases
• d.Sized per Table 250.102(C)(1) based on the largest ungrounded conductor in that raceway✓

Per 250.102(C)(2), when raceways are in parallel the supply-side bonding jumper in each raceway is sized from Table 250.102(C)(1) using the largest ungrounded conductor in that raceway. A single 6 AWG, matching the neutral, or omitting the jumper are all incorrect.2023 NEC §250.102(C)

A service uses 600 kcmil copper ungrounded conductors. Per Table 250.66, what is the minimum copper GEC?

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

Table 250.66 row 'over 350 through 600 kcmil' requires 1/0 copper. 2 AWG is for up to 350 kcmil, 2/0 is for over 600 through 1100 kcmil, and 3/0 is for over 1100 kcmil.2023 NEC §250.66

A feeder is protected by a 60 A overcurrent device. Per Table 250.122, what is the minimum copper EGC?

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

Table 250.122 requires a 10 AWG copper EGC for overcurrent devices from 40 A up to and including 60 A. 12 AWG serves only up to 20 A, and 8 AWG/6 AWG are for 100 A/200 A respectively.2023 NEC §250.122

A service supplies a continuous load of 80 A and a noncontinuous load of 100 A. What is the minimum required ampacity of the service-entrance conductors?

• a.160 A
• b.180 A
• c.200 A✓
• d.225 A

Service-entrance conductors must have an ampacity not less than the noncontinuous load plus 125% of the continuous load: 100 + (80 x 1.25) = 200 A. Simply adding the loads (180 A) ignores the 125% continuous factor, and 225 A applies the factor to the total load in error.2023 NEC §230.42

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

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

For a one-family dwelling, the service disconnecting means must be rated not less than 100 A, 3-wire. The 60 A rating applies to smaller occupancies such as certain limited loads, while 200 A and 125 A are common but not the code-required minimum.2023 NEC §230.79

For a single service, the maximum number of service disconnects permitted for each service permitted by 230.40 is:

• a.Four
• b.Six✓
• c.Three
• d.Two

Section 230.71 permits up to six service disconnects for each service; in the 2023 NEC each must be in a separate enclosure, or be part of listed switchgear/switchboard/metering assemblies. The lower numbers are not the code limit.2023 NEC §230.71

Overload protection for service-entrance conductors must be provided by an overcurrent device in series with:

• a.The grounded conductor only
• b.The equipment grounding conductor
• c.Each ungrounded service conductor✓
• d.The grounding electrode conductor

Per 230.90(A), each ungrounded service-entrance conductor must have overload protection, generally an overcurrent device rated not more than the conductor ampacity. The grounded (neutral) conductor is not fused this way, and grounding/grounding-electrode conductors never carry service overcurrent devices.2023 NEC §230.90

A feeder supplies a continuous load of 40 A and a noncontinuous load of 60 A. The minimum feeder conductor ampacity before applying any adjustment factors is:

• a.100 A
• b.125 A
• c.110 A✓
• d.105 A

Feeder conductors must have an ampacity of at least the noncontinuous load plus 125% of the continuous load: 60 + (40 x 1.25) = 110 A. The 100 A option omits the continuous multiplier, and 125 A over-applies it to the entire load.2023 NEC §215.2

A feeder overcurrent device protecting a feeder that supplies continuous loads must have a rating not less than:

• a.150% of the continuous load
• b.100% of the total connected load
• c.125% of the continuous load plus 100% of the noncontinuous load✓
• d.80% of the continuous load

Per 215.3, where a feeder supplies continuous load(s), the overcurrent device rating must be at least 125% of the continuous load plus 100% of the noncontinuous load (unless the assembly is listed for 100% operation). The other options misstate the required factor.2023 NEC §215.3

A service is supplied with 3/0 AWG copper service-entrance conductors. Using Table 250.66, the minimum size copper grounding electrode conductor is:

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

Table 250.66 requires a 4 AWG copper grounding electrode conductor for service conductors sized over 2/0 through 3/0 AWG copper. A 6 AWG is too small for this range, while 2 AWG and 1/0 AWG exceed what the table requires.2023 NEC §250.66

At a grounded AC service, the grounded (neutral) conductor run to the service disconnecting means must be sized:

• a.Only large enough to carry the neutral load
• b.The same as the equipment grounding conductor
• c.Not smaller than required by Table 250.102(C)(1) and never less than the neutral load✓
• d.No smaller than 6 AWG copper in all cases

Per 250.24(C), the grounded conductor brought to the service must be at least the size shown in Table 250.102(C)(1) (based on the ungrounded conductors), and also not smaller than needed to carry the neutral load. Sizing it only for neutral load can leave it too small to serve as the effective fault-current path.2023 NEC §250.24

The main bonding jumper in service equipment serves to:

• a.Bond the metal water pipe to the gas pipe
• b.Provide overcurrent protection for the neutral
• c.Connect the grounded conductor to the service equipment enclosure✓
• d.Connect two grounding electrodes together

Per 250.28, the main bonding jumper connects the grounded (neutral) conductor to the equipment grounding conductor and metal enclosure at the service, establishing the fault-return path. It is not a jumper between electrodes, a piping bond, or any form of overcurrent protection.2023 NEC §250.28

A feeder is protected by a 100 A overcurrent device. Using Table 250.122, the minimum size copper equipment grounding conductor is:

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

Table 250.122 lists an 8 AWG copper equipment grounding conductor for circuits protected at 100 A. A 10 AWG is the value for 60 A, and 6 AWG is for larger ratings up to 200 A, so both miss the 100 A row.2023 NEC §250.122

At other than dwelling units, service equipment must be legibly field-marked with:

• a.The rating of the largest branch circuit
• b.The utility transformer size
• c.The maximum available fault current and the date the calculation was performed✓
• d.The service voltage only

Section 110.24 requires service equipment to be field-marked with the maximum available fault current, including the date of the calculation, and updated if modifications change that value. The transformer size, voltage, or branch-circuit rating alone do not satisfy this marking.2023 NEC §110.24

The interrupting rating of an overcurrent device must be:

• a.Equal to the conductor ampacity
• b.Not less than the available fault current at its line terminals✓
• c.Equal to the load current
• d.At least 65,000 A in all cases

Per 110.9, equipment intended to interrupt current at fault levels must have an interrupting rating at least equal to the available fault current at its line terminals. A device with too low an interrupting rating can fail catastrophically. Load current and conductor ampacity are unrelated to interrupting rating.2023 NEC §110.9

The short-circuit current rating (SCCR) of equipment such as a panelboard means the equipment can:

• a.Withstand the available fault current at its terminals without extensive damage until the overcurrent device clears✓
• b.Interrupt fault current by itself
• c.Carry continuous load indefinitely
• d.Operate at 125% of its rating

Per 110.10, the SCCR ensures the assembly can safely withstand the let-through energy of the available fault current until the protective device opens, preventing extensive damage. It is not a measure of continuous carrying capacity, and the panelboard itself does not interrupt the fault.2023 NEC §110.10

In general, conductors may be connected in parallel (electrically joined at both ends) only where the individual conductors are:

• a.250 kcmil and larger
• b.2 AWG and larger
• c.1/0 AWG and larger✓
• d.4 AWG and larger

Per 310.10(G), paralleling of ungrounded and grounded conductors is generally permitted only in sizes 1/0 AWG and larger. The smaller sizes are not allowed under the general rule, and requiring 250 kcmil would be more restrictive than the code.2023 NEC §310.10(G)

When conductors are installed in parallel, the paralleled conductors of each phase, neutral, or grounded circuit conductor must:

• a.Be different lengths to balance impedance
• b.Only match in the ungrounded conductors
• c.Be the same length, same conductor material, same size, and have the same insulation type and termination✓
• d.Use different sizes in each raceway

Per 310.10(G)(1), all parallel conductors of the same circuit designation must be the same length, material, cross-sectional area (size), and insulation, and terminate the same way, so current divides evenly. Different lengths or sizes cause unequal current sharing and overheating.2023 NEC §310.10(G)

A feeder has a maximum unbalanced (neutral) load of 250 A. Applying the neutral demand provisions, the minimum neutral conductor ampacity is:

• a.250 A
• b.235 A✓
• c.200 A
• d.175 A

Per 220.61(B), the first 200 A of unbalanced load is at 100% and the portion above 200 A may be taken at 70%: 200 + (50 x 0.70) = 235 A. Sizing at the full 250 A ignores the permitted demand, and 175 A/200 A understate the required capacity.2023 NEC §220.61

For a 200 A single-phase dwelling service, the minimum aluminum service-entrance conductor permitted by the dwelling service conductor provisions is:

• a.250 kcmil copper
• b.4/0 AWG aluminum✓
• c.1/0 AWG copper
• d.3/0 AWG aluminum

Section 310.12 (dwelling services and feeders) permits 4/0 AWG aluminum for a 200 A single-phase dwelling service. 3/0 aluminum is undersized for 200 A, while the copper options are permitted but are not the minimum aluminum answer asked for.2023 NEC §310.12

Each panelboard must be protected by an overcurrent device having a rating:

• a.Equal to the largest branch circuit
• b.Exactly twice the panelboard rating
• c.Determined only by the feeder length
• d.Not greater than that of the panelboard✓

Per 408.36, a panelboard must be individually protected by an overcurrent device rated not greater than the panelboard's rating, located on the supply side (with limited exceptions). Doubling the rating or sizing to a single branch circuit would leave the busbar unprotected.2023 NEC §408.36

Under the 2023 NEC, the maximum number of overcurrent devices permitted in a lighting and appliance branch-circuit panelboard is:

• a.Not limited to a fixed number; governed by the panelboard's listing✓
• b.42
• c.60
• d.30

The former 42-circuit limit was removed; per 408.54 a panelboard must not have more overcurrent devices than the number for which it is designed, rated, and listed. There is no universal fixed cap such as 30 or 42; the manufacturer's listing controls.2023 NEC §408.54

Under the 2023 NEC, the service supplying a dwelling unit must be provided with a:

• a.Second grounding electrode only
• b.GFCI at the service
• c.Surge-protective device (SPD)✓
• d.AFCI at the service

Section 230.67 (new emphasis in recent editions) requires dwelling unit services to be provided with a surge-protective device, located within or adjacent to the service equipment. GFCI and AFCI protection are branch-circuit requirements, not a service-level SPD substitute.2023 NEC §230.67

Which type of surge-protective device is permitted to be connected on the line side of the service overcurrent device (service disconnect)?

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

Per Article 242, a Type 1 SPD is permitted to be connected on the line side of the service disconnect overcurrent device. Type 2 devices are connected on the load side of the service disconnect, and Type 3 are point-of-utilization devices installed near equipment.2023 NEC §242.14

A concrete-encased electrode (Ufer) must consist of at least 20 ft (6.0 m) of:

• a.6 AWG copper stapled to a stud
• b.Bare 4 AWG copper conductor or 1/2 in. (13 mm) rebar encased in concrete near the earth✓
• c.12 AWG insulated wire in conduit
• d.8 AWG aluminum in a wall

Per 250.52(A)(3), a concrete-encased electrode is at least 20 ft of one or more 1/2 in. or larger steel reinforcing bars, or at least 20 ft of bare 4 AWG copper, encased in at least 2 in. of concrete in contact with the earth. The other options are not qualifying electrode materials or lengths.2023 NEC §250.52

A single made rod electrode is measured at 40 ohms resistance to earth. The code requires that it be:

• a.Augmented with one additional electrode (or otherwise meet 25 ohms)✓
• b.Replaced with a copper water pipe
• c.Bonded to the neutral only
• d.Left as is because 40 ohms is acceptable

Per 250.53(A)(2), a single rod, pipe, or plate electrode that does not have a resistance to earth of 25 ohms or less must be supplemented by one additional electrode. Because 40 ohms exceeds 25 ohms, a second electrode is required; leaving it or bonding only to the neutral does not comply.2023 NEC §250.53

Overhead service conductors (service drop) over a residential driveway with no truck traffic must maintain a minimum vertical clearance above grade of:

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

Per 230.24(B), 12 ft (3.7 m) is required over residential property and driveways where the voltage does not exceed 300 V to ground. The 10 ft clearance applies only over limited areas like accessible-to-pedestrians-only locations, while 18 ft applies to public streets/truck traffic.2023 NEC §230.24

The general minimum vertical clearance of overhead service conductors above a roof surface (voltage not over 300 V to ground) is:

• a.3 ft
• b.10 ft
• c.6 ft
• d.8 ft✓

Per 230.24(A), the general clearance above a roof is 8 ft (2.5 m), measured over the area where the conductors pass. Reduced clearances (such as 3 ft) apply only under specific listed exceptions like limited slope or attachment conditions.2023 NEC §230.24

The point of attachment of overhead service conductors to a building must be at least what height above finished grade?

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

Per 230.26, the point of attachment must not be less than 10 ft (3.0 m) above finished grade and must be located so the minimum service-drop clearances of 230.24 are still met. Lower values do not satisfy the code minimum, and 12 ft/15 ft exceed the required attachment height.2023 NEC §230.26

A feeder supplies a single continuous load of 100 A. The minimum feeder conductor ampacity and overcurrent device rating is:

• a.125 A✓
• b.100 A
• c.110 A
• d.115 A

For a continuous load, both the conductor ampacity and the overcurrent device must be at least 125% of the load: 100 x 1.25 = 125 A. Selecting 100 A ignores the continuous-load factor entirely, and 110 A/115 A fall short of the required 125%.2023 NEC §215.2

A supply-side bonding jumper on the line side of the service, used to bond service raceways and enclosures, is generally sized based on:

• a.The service conductors, using Table 250.102(C)(1)✓
• b.The branch-circuit rating
• c.The equipment grounding conductor Table 250.122
• d.The grounding electrode conductor only

Per 250.102(C), a supply-side bonding jumper is sized from Table 250.102(C)(1) based on the size of the ungrounded service conductors (with proportional rules for parallel/large conductors). Table 250.122 is for load-side equipment grounding conductors, not supply-side bonding.2023 NEC §250.102

Metal water piping system(s) in or attached to a building must be:

• a.Bonded to the service equipment enclosure, grounded conductor, or grounding electrode conductor✓
• b.Connected only to the gas piping
• c.Used as the sole grounding electrode
• d.Left unconnected to avoid stray current

Per 250.104(A), the interior metal water piping system must be bonded, with the bonding jumper sized per Table 250.102(C)(1) based on the service conductors. Metal water piping alone cannot be the sole electrode, and it must not be left unbonded or bonded only to gas piping.2023 NEC §250.104

Ground-fault protection of equipment is generally required for solidly grounded wye services of more than 150 V to ground but not exceeding 1000 V phase-to-phase, where the service disconnect is rated:

• a.2000 A or more
• b.400 A or more
• c.100 A or more
• d.1000 A or more✓

Per 230.95, ground-fault protection of equipment is required on such services where the service disconnecting means is rated 1000 A or more. The other ampere thresholds do not match the code trigger for this GFP requirement.2023 NEC §230.95

In a typical utility service arrangement, the electric meter (metering equipment) is normally connected:

• a.After the first branch-circuit panel
• b.On the supply (line) side of the service disconnecting means✓
• c.On the load side of the main breaker
• d.Inside the sub-panel only

Metering equipment is generally located on the supply side of the service disconnect so it measures all energy entering the premises. Placing the meter on the load side of the main or after a panel would fail to record the total service usage, which is why utilities require line-side metering.

A feeder is the main power feeder to a single dwelling and carries the entire load. What allowance does the dwelling feeder provision give for sizing this conductor?

• a.It may be sized at 83% of the service rating using the dwelling conductor provisions✓
• b.It cannot be smaller than 250 kcmil
• c.It must be sized at 150% of the service rating
• d.It must always match the utility transformer

Section 310.12(B) permits the main feeder to an individual dwelling (that carries the total load) to be sized using the reduced dwelling-service-conductor values, effectively 83% of the service rating. The other options misstate or invent sizing rules not found in the code.2023 NEC §310.12

As a general rule, each service drop or service lateral is permitted to supply:

• a.An unlimited number of sets
• b.One set of service-entrance conductors (with specific exceptions)✓
• c.Three sets minimum
• d.Always two sets of service-entrance conductors

Per 230.40, each service drop, overhead service, or lateral is generally permitted to supply only one set of service-entrance conductors, with defined exceptions (such as multiple occupancies with separate disconnects grouped together). The other choices misstate the general one-set rule.2023 NEC §230.40

Six current-carrying conductors are installed in a single raceway. The ampacity adjustment factor that must be applied to each conductor is:

• a.70%
• b.100%
• c.50%
• d.80%✓

Per Table 310.15(C)(1), for 4 through 6 current-carrying conductors the adjustment factor is 80%. Seven through nine conductors use 70%, and 100% would apply only to three or fewer conductors, so those factors do not fit six conductors.2023 NEC §310.15

A grounded (neutral) service conductor larger than 6 AWG is permitted to be identified by:

• a.Green tape at both ends
• b.Orange marking
• c.No identification at all
• d.A continuous white outer finish, or by white/gray marking (such as tape) encircling the conductor at terminations and accessible points✓

Per 200.6(B), grounded conductors larger than 6 AWG may be identified either by a continuous white or gray outer finish, or by distinctive white/gray marking (like tape or paint) at terminations at the time of installation. Green identifies equipment grounding, and leaving it unmarked or orange (high leg) is incorrect.2023 NEC §200.6

Where a service has two to six service disconnects for a single service, they must be:

• a.Spaced at least 25 ft apart
• b.Wired in series with each other
• c.Grouped, unless otherwise permitted, with each marked to indicate the load served✓
• d.Located in separate rooms of the building

Per 230.72, the two to six disconnects must be grouped (except for specific separate loads like fire pumps) and each marked to indicate the load it serves. Placing them in separate rooms, spacing them widely, or wiring them in series would defeat the purpose of a single, identifiable point of disconnection.2023 NEC §230.72

The minimum depth of working space in front of a 208Y/120 V panelboard (0-150 V to ground, Condition 1: exposed live parts on one side, no live or grounded parts on the other) is:

• a.3 ft✓
• b.4 ft
• c.6 ft
• d.2.5 ft

Per Table 110.26(A)(1), for equipment 0-150 V to ground under Condition 1, the minimum working clearance is 3 ft (900 mm). Greater depths (4 ft, 6 ft) apply to higher voltages or worse conditions, and 2.5 ft is never a permitted minimum for this equipment.2023 NEC §110.26

When a panelboard is used as service equipment, the main bonding jumper must be:

• a.Omitted because the neutral is isolated
• b.Replaced by the equipment grounding conductor
• c.Installed only in a downstream sub-panel
• d.Installed to connect the grounded conductor to the panelboard enclosure✓

At service equipment, 250.24(B) and 250.28 require a main bonding jumper connecting the grounded (neutral) conductor to the enclosure. In a downstream sub-panel the neutral is instead isolated, so the main bonding jumper belongs only at the service, never omitted or moved downstream.2023 NEC §250.24

Where the grounding electrode conductor connects to a concrete-encased electrode, that portion of the conductor is not required to be larger than:

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

Per 250.66(B), the grounding electrode conductor to a concrete-encased electrode is not required to be larger than 4 AWG copper. 6 AWG applies to a rod/pipe/plate electrode under 250.66(A), and the other sizes are not the code cap for this connection.2023 NEC §250.66

Where the grounding electrode conductor connects to a made rod, pipe, or plate electrode, that portion of the conductor is not required to be larger than:

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

Per 250.66(A), the portion of the grounding electrode conductor that is the sole connection to a rod, pipe, or plate electrode need not be larger than 6 AWG copper. The 4 AWG limit is for concrete-encased electrodes, and larger sizes exceed the code requirement for a ground rod.2023 NEC §250.66