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

A dwelling's standard-method net calculated load is 28,600 VA on a 240 V service. What is the smallest standard service size that will carry it?

• a.110 A
• b.100 A
• c.125 A✓
• d.150 A

28,600 ÷ 240 = 119 A, so the service must exceed 119 A; the next standard size is 125 A. A 100 A or 110 A service would be too small for a 119 A demand.

Using Table 250.66, for copper service-entrance conductors of 3/0 AWG, what is the minimum size copper grounding electrode conductor?

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

Per Table 250.66, service conductors over 2/0 through 3/0 AWG copper require a 4 AWG copper grounding electrode conductor. 8 AWG serves 2 AWG or smaller, and 2 AWG GEC is for larger service conductors.2023 NEC §250.66

In a bid, what does overhead refer to?

• a.The profit added to the price
• b.The direct labor installed on the job
• c.Indirect business costs allocated to the job✓
• d.The direct material used on the job

Overhead is the indirect cost of running the business (office rent, insurance, vehicles, tools, administrative staff) that must be recovered across jobs. Direct material, direct labor, and profit are separate line items in a bid.

Estimators add a waste factor to material quantities to account for what?

• a.Material lost to cutting, scrap, and errors✓
• b.Overtime labor hours
• c.Contractor profit
• d.Permit fees

A waste factor increases ordered quantities to cover material that is cut off, scrapped, or mistakenly used so the job does not run short. It is not related to labor overtime, permit fees, or profit.

A home run is 60 ft long and pulls 3 conductors. Adding 10% for waste, approximately how much conductor should be ordered?

• a.198 ft✓
• b.540 ft
• c.60 ft
• d.180 ft

Wire length = 60 ft × 3 conductors = 180 ft, then × 1.10 for waste = 198 ft. Forgetting the three conductors (60 ft) or the waste (180 ft) gives the low distractors.

If a receptacle takes 0.5 labor-hour to install, how many labor-hours should be estimated to install 30 receptacles?

• a.60 hours
• b.30 hours
• c.7.5 hours
• d.15 hours✓

Labor = 30 units × 0.5 hr = 15 labor-hours. Multiplying by 2 (60) or by the count alone (30) misapplies the labor unit, and 7.5 uses the wrong quantity.

Using the optional method, a dwelling's 220.82(B) loads compute to 19,280 VA, plus 5,000 VA of air conditioning at 100%. On a 240 V service (about 101 A), what is the minimum standard service size?

• a.125 A✓
• b.175 A
• c.100 A
• d.150 A

Total = 19,280 + 5,000 = 24,280 VA; 24,280 ÷ 240 = 101 A. Since the demand exceeds 100 A, the next standard size, 125 A, is required. A 100 A service would be slightly undersized.2023 NEC §220.82

The California Electrical Code is essentially the NEC as modified by what?

• a.IEEE standards
• b.Local utility company rules
• c.UL product listings
• d.California state amendments✓

California adopts each NEC edition and then modifies it with California-specific amendments to create the CEC (Title 24, Part 3). Utility rules, IEEE standards, and UL listings are separate documents, not what creates the CEC.

In code language, what does the abbreviation AHJ stand for?

• a.Authority Having Jurisdiction✓
• b.American Home Journal
• c.Annual Home Inspection
• d.Approved Housing Judge

AHJ means Authority Having Jurisdiction, the office or official responsible for enforcing the code and approving equipment and installations. The other choices are not code terms.

For a set of service-entrance conductors, the service disconnecting means is generally limited to a maximum of how many switches or circuit breakers?

• a.6✓
• b.8
• c.4
• d.2

The service disconnecting means is limited to a maximum of six switches or circuit breakers for a given set of service conductors. Modern code also requires them to be in separate enclosures, but the six-disconnect limit still governs.2023 NEC §230.71

The 2023 NEC requires one- and two-family dwellings to have an emergency disconnect installed where?

• a.Inside the dwelling only
• b.In the attic
• c.It is not required
• d.At a readily accessible outdoor location✓

An emergency disconnect must be installed in a readily accessible outdoor location so first responders can shut off power. It is required, and an interior or attic location would not meet the readily accessible outdoor requirement.2023 NEC §230.85

For 120/240 V equipment likely to require examination while energized (Condition 1), what is the minimum depth of working space in front of it?

• a.4 ft
• b.1 ft
• c.2 ft
• d.3 ft✓

Under Condition 1, the minimum working-space depth for equipment operating at 0-150 V to ground is 3 ft. Two feet or one foot is too little, and 4 ft applies to higher-voltage or worse conditions.2023 NEC §110.26(A)(1)

What is the minimum width of working space in front of electrical equipment (or the width of the equipment, whichever is greater)?

• a.30 in✓
• b.18 in
• c.36 in
• d.24 in

The working space must be at least 30 in wide, or the width of the equipment, whichever is greater. Narrower dimensions such as 24 in or 18 in do not meet the minimum.2023 NEC §110.26(A)(2)

What is the minimum headroom (height) of working space about electrical equipment such as panelboards?

• a.6 ft 6 in✓
• b.6 ft 3 in
• c.6 ft
• d.7 ft

The minimum headroom of working space is 6 ft 6 in (or the height of the equipment if taller). The lesser heights do not satisfy the requirement, and 7 ft exceeds the minimum.2023 NEC §110.26(A)(3)

What is the line current of a 30 kVA, three-phase load supplied at 208 V?

• a.100 A
• b.144 A
• c.83 A✓
• d.72 A

For a three-phase load, I = VA ÷ (V × 1.732) = 30,000 ÷ (208 × 1.732) = 30,000 ÷ 360 = 83 A. Dividing by 208 alone or by 120 gives the incorrect single-phase-style results.

A complete bid price for an electrical project generally consists of which of the following?

• a.Permit fees only
• b.Material only
• c.Labor only
• d.Material, labor, overhead, and profit✓

A full bid adds up direct material, direct labor, overhead (indirect business costs), and profit. Leaving out any of these, such as bidding labor or material alone, would not cover the true cost of doing the work.

The NEC is updated on a three-year cycle. The 2023 NEC directly follows which prior edition?

• a.2017 NEC
• b.There is no prior edition
• c.2014 NEC
• d.2020 NEC✓

On the three-year cycle, the edition immediately before the 2023 NEC is the 2020 NEC. The 2017 and 2014 editions are earlier cycles, not the one directly preceding 2023.

You opened the disconnect for a 480V motor circuit and applied your personal lock and tag. What is the FINAL step required before you may treat the conductors as safe to touch?

• a.Test the conductors with an adequately rated voltage tester, then re-test the tester on a known live source to prove it works✓
• b.Wait 30 minutes for any capacitors to bleed off
• c.Confirm the tag is signed and dated
• d.Notify the building owner in writing

Verifying the absence of voltage with a rated tester, and proving the tester is functioning before and after (live-dead-live), is the required final step. Waiting and checking the tag are part of lockout/tagout but do not confirm zero energy. Notifying the owner is not a safety verification of the conductors.Cal/OSHA Title 8 §3314

Which sequence correctly describes the basic lockout/tagout procedure before servicing electrical equipment?

• a.Apply locks first, then shut down, verify, and notify workers
• b.Notify affected employees, shut down, isolate/disconnect the energy source, apply locks and tags, release stored energy, then verify zero energy✓
• c.Shut down, energize a test circuit, remove guards, then lock
• d.Verify zero energy, apply tags, shut down, then isolate

The correct order is to notify, shut down, isolate, lock and tag, release stored energy, and finally verify zero energy. You cannot lock before shutting down, and verification must come at the end—not before isolation. Removing guards on a live test circuit is unsafe.Cal/OSHA Title 8 §3314

A crew of four electricians is servicing the same de-energized 480V feeder. How should lockout be handled?

• a.Only the foreman needs to apply a lock
• b.One shared lock is hung on a hook by the panel
• c.Each authorized worker applies their own individual lock so the energy cannot be restored while anyone is exposed✓
• d.The first person in applies the lock and the last person out removes it for everyone

In group lockout, every exposed worker applies their own lock (often on a lockbox or hasp) so power stays off until the last person removes their lock. A single foreman lock or shared lock leaves others exposed if someone else re-energizes. Relying on the first-in/last-out person defeats individual protection.Cal/OSHA Title 8 §3314

An electrician left the jobsite for the day and forgot to remove his lockout lock. How may it be removed?

• a.Any journeyman on site may simply cut it off
• b.Leave it in place and abandon the circuit permanently
• c.The foreman removes it immediately with no documentation
• d.Only under the employer's documented procedure after verifying the worker is off site and making a reasonable effort to notify them✓

A lock is normally removed only by the person who applied it. When that is not possible, the employer must follow a documented removal procedure, verify the worker has left, and make a reasonable effort to inform them before restoring energy. Cutting a lock off without that procedure risks energizing a circuit while someone is still working.Cal/OSHA Title 8 §3314

On a construction site, which receptacles must have GFCI protection for personnel?

• a.All 125-volt, 15-, 20-, and 30-ampere receptacles that are not part of the permanent building wiring✓
• b.None, as long as the power tools are double-insulated
• c.Only receptacles inside finished rooms
• d.Only receptacles rated above 250 volts

Temporary construction power requires GFCI protection on all 125V, 15/20/30A receptacles that are not part of the permanent wiring (or an assured equipment grounding conductor program). Voltage rating and room finish do not exempt them, and double-insulated tools do not remove the receptacle requirement.2023 NEC §590.6

A Class A GFCI intended to protect people trips at approximately what ground-fault current?

• a.About 5 milliamperes (in the 4-6 mA range)✓
• b.About 20 milliamperes
• c.About 100 milliamperes
• d.About 1 ampere

A Class A GFCI for personnel protection trips when ground-fault current reaches roughly 4 to 6 mA, low enough to protect against dangerous shock. 20 mA, 100 mA, and 1 A are all far above the let-go and ventricular-fibrillation thresholds and would allow a lethal shock.

What is the difference between a Class A (personnel) GFCI and a 30-milliampere 'equipment' ground-fault protection device?

• a.The 30 mA device protects people better than the 5 mA device
• b.They are identical in function
• c.A Class A GFCI (about 5 mA) protects people from shock, while a 30 mA device protects equipment/wiring against fire and is not intended for personnel protection✓
• d.Only the 30 mA device is allowed on construction sites

Class A GFCIs trip near 5 mA to protect people from electric shock, while equipment ground-fault protection (up to 30 mA) is designed to protect wiring and equipment and limit fire risk, not to protect a person. A 30 mA trip point is too high to reliably prevent a dangerous shock.

The arc flash boundary is best defined as the distance at which:

• a.The electrician can no longer physically reach the equipment
• b.The incident energy equals 1.2 cal/cm², the onset of a second-degree burn to bare skin✓
• c.The restricted approach boundary begins
• d.The voltage on the conductors drops to zero

The arc flash boundary is the distance from a potential arc source where incident energy is 1.2 cal/cm²—the level that would cause a second-degree burn to unprotected skin. It is a thermal (burn) boundary, not a reach limit or a shock (approach) boundary, and it has nothing to do with voltage reaching zero.NFPA 70E

In NFPA 70E, the 'limited approach boundary' is best described as:

• a.A boundary that applies only to DC systems
• b.A distance from an exposed energized part within which a shock hazard exists; an unqualified person must not cross it without a qualified escort and appropriate PPE✓
• c.The distance within which a full arc-flash suit is always mandatory
• d.Exactly the same distance as the arc flash boundary

The limited approach boundary is a shock-protection boundary; crossing it means a shock hazard is present, so unqualified persons need a qualified escort and PPE. It is distinct from the arc flash (thermal) boundary and applies to both AC and DC. The full arc suit is tied to incident energy, not this line.NFPA 70E

Crossing the restricted approach boundary toward an exposed energized part requires:

• a.No special precautions because it is close to the equipment
• b.A hard hat and nothing else
• c.Only safety glasses
• d.A qualified person, a documented plan/energized work permit, and appropriate shock PPE such as voltage-rated gloves✓

The restricted approach boundary is close to the live part, where an increased risk of shock from inadvertent movement exists. Only a qualified person may cross it, and only with a plan/permit and shock PPE (e.g., rated gloves). Glasses or a hard hat alone are inadequate for the shock hazard at that distance.NFPA 70E

An arc-flash study shows an available incident energy of 8 cal/cm² at the working distance. The arc-rated clothing and PPE must have an arc rating of:

• a.Less than the incident energy so it breathes better
• b.Any untreated cotton clothing is acceptable
• c.Exactly 1.2 cal/cm²
• d.At least equal to or greater than the available incident energy (8 cal/cm² or more)✓

Arc-rated PPE must have an arc rating equal to or greater than the available incident energy—here at least 8 cal/cm². Choosing PPE below the incident energy, or ordinary cotton (which can ignite), would not protect the worker. The 1.2 cal/cm² figure is the arc flash boundary threshold, not a PPE rating for this task.NFPA 70E

Rubber insulating gloves used for energized work on a 480V system must be:

• a.Cotton gloves worn under nitrile gloves
• b.Only required for work above 1,000 volts
• c.Rated for the voltage, worn with leather protectors, and inspected/air-tested before use✓
• d.Any leather work glove that fits

Voltage-rated rubber gloves must match or exceed the system voltage, be worn with leather protector gloves to prevent mechanical damage, and be inspected (and often air-tested) before each use. Leather or cotton alone provide no shock protection, and shock protection is required well below 1,000 volts.

Under Cal/OSHA and NFPA 70E, the primary/preferred way to protect workers from electrical hazards is to:

• a.Use insulated tools only and skip other protections
• b.Put on an arc-flash suit and work the equipment while energized
• c.De-energize the equipment and establish an electrically safe work condition whenever it is feasible✓
• d.Post a warning sign near the panel

The hierarchy of controls makes de-energizing and creating an electrically safe work condition the primary protection; energized work is only permitted when de-energizing is infeasible or introduces greater hazards. PPE, insulated tools, and signs are supplemental and do not replace de-energizing when it can be done.Cal/OSHA Title 8 §2320.2

An energized electrical work permit is generally required when:

• a.The job simply takes longer than eight hours
• b.Energized work is justified because de-energizing would introduce additional hazards or is infeasible, and the work is within the restricted approach or arc flash boundary✓
• c.Working on a 24-volt control circuit
• d.Any electrical work is performed, even de-energized

An energized work permit is required when justified energized work occurs within the restricted approach or arc flash boundary. Routine de-energized work does not need one, job duration is irrelevant, and very low-voltage circuits below the shock/arc thresholds generally do not require the permit.NFPA 70E

Before you rely on a voltage detector to verify absence of voltage, you should:

• a.Assume it works if the battery indicator light is on
• b.Test it on a known energized source before and after the check to confirm it is functioning (live-dead-live test)✓
• c.Do nothing, because meters never fail
• d.Only test after your hand is already on the conductors

A voltage tester must be proven functional on a known live source immediately before and after checking the circuit, so a failed meter cannot fool you into treating a live circuit as dead. A battery light does not prove the tester reads voltage, and touching first defeats the purpose of verification.

You are servicing a circuit that feeds a variable frequency drive (VFD) with large DC-bus capacitors. After disconnecting power you must:

• a.Allow/assist the stored energy to dissipate and verify the capacitors are discharged before contact✓
• b.Ignore stored energy because it is a low-voltage system
• c.Short the source to ground while it is still energized
• d.Immediately touch the terminals to test them

Capacitors in VFDs can hold a dangerous charge after power is removed, so you must let them discharge (per manufacturer's time/procedure) and verify they are discharged before touching. Touching immediately or ignoring stored energy risks a shock, and shorting an energized source is dangerous and can cause an arc flash.

You are installing a 480Y/277V panelboard with exposed live parts likely to require examination while energized. There is a concrete (grounded) wall on the opposite side of the working space (Condition 1). What is the minimum working-space depth in front of the panel?

• a.3 feet✓
• b.4 feet
• c.2 feet
• d.2½ feet

For nominal voltages of 151-600V, Condition 1 requires a minimum clear working-space depth of 3 feet in front of the equipment. The 3½- and 4-foot figures apply to Conditions 2 and 3 in that voltage range, and 2 or 2½ feet is never permitted for this equipment.2023 NEC §110.26

A 480V panel is installed so the worker stands between two energized sections with exposed live parts on both sides of the working space (Condition 3). What minimum working-space depth is required?

• a.3½ feet
• b.6 feet
• c.3 feet
• d.4 feet✓

For 151-600V equipment, Condition 3 (exposed live parts on both sides of the worker) requires a minimum 4-foot clear depth. 3 feet is Condition 1 and 3½ feet is Condition 2 at this voltage; 6 feet is not required for 480V.2023 NEC §110.26

The clear working space in front of a panelboard must be at least how wide and how high?

• a.36 inches wide and 7 feet high
• b.18 inches wide and 6 feet high
• c.24 inches wide and 5 feet high
• d.30 inches wide (or the width of the equipment, whichever is greater) and 6½ feet high✓

Working space must be at least 30 inches wide, or the width of the equipment if greater, and at least 6½ feet high (or the height of the equipment). 18, 24, or 36 inches and the other heights do not match the code minimums for width and headroom.2023 NEC §110.26

The 'dedicated equipment space' above an indoor panelboard or switchboard:

• a.Extends only 1 foot above the equipment
• b.Extends only 6 inches above the equipment
• c.Extends from the top of the equipment to 6 feet above it (or to a structural ceiling), and must be kept clear of foreign piping and ducts✓
• d.Extends only 3 feet above the equipment

The dedicated space extends from the top of the equipment upward 6 feet or to a structural ceiling, whichever is lower, and no foreign systems (piping, ducts) may occupy it. The 6-inch, 1-foot, and 3-foot answers understate the code-required dedicated space above electrical equipment.2023 NEC §110.26

For electrical equipment rated 1,200 amperes or more and over 6 feet wide, how many entrances to the working space are generally required?

• a.One 24-inch door is enough
• b.No entrance requirement applies
• c.Two entrances/means of egress, one at each end of the working space (with limited exceptions)✓
• d.A window at one end

Large equipment (1,200A or more and over 6 feet wide) generally requires an entrance/egress at each end of the working space so a worker can escape an arc flash. One door or no requirement leaves a worker potentially trapped behind an arcing fault. A window is not an approved means of egress here.2023 NEC §110.26

Live parts operating at 50 volts or more must be guarded against accidental contact by:

• a.Painting the parts a bright red color
• b.Approved enclosures, or location in a room/vault accessible only to qualified persons, or suitable elevation✓
• c.Wrapping them in electrical tape
• d.A warning sign posted nearby

Guarding of live parts is achieved through approved enclosures, access limited to qualified persons, or elevation out of reach. A sign, paint, or tape does not physically prevent accidental contact and is not an acceptable guarding method for exposed energized parts at 50V or more.2023 NEC §110.27

An electrical room containing exposed live parts that is accessible only to qualified persons must have:

• a.No signage of any kind
• b.Only a fire sprinkler and nothing else
• c.Entrances marked with conspicuous warning signs forbidding unqualified persons from entering✓
• d.Carpeting on the floor

Rooms or enclosures with exposed live parts restricted to qualified persons must have entrances marked with conspicuous warning signs that prohibit unqualified persons from entering. Omitting signage, adding carpet, or providing only a sprinkler does not satisfy the requirement to warn and restrict access.2023 NEC §110.27

The primary safety purpose of equipment grounding (bonding metal enclosures to the equipment grounding conductor) is to:

• a.Provide a low-impedance fault-current path so overcurrent devices open quickly and metal parts do not stay energized✓
• b.Reduce the customer's electric bill
• c.Eliminate the need for GFCI protection
• d.Improve voltage regulation on the circuit

Equipment grounding provides a low-impedance path for fault current so the breaker or fuse clears the fault fast and enclosures do not remain energized to a dangerous voltage. It does not regulate voltage, lower the bill, or replace GFCI protection, which detects small leakage currents to protect people.2023 NEC §250.4

Which statement about the grounded (neutral) and equipment grounding conductors is correct?

• a.The equipment grounding conductor normally carries load current
• b.They may be bonded together again at every subpanel
• c.Neutrals and grounds are effectively the same conductor everywhere
• d.They are bonded together only at the service (or separately derived source) and kept separate downstream in subpanels✓

The neutral and equipment grounding conductor are bonded only at the service or source; downstream subpanels keep them isolated so normal load current does not flow on grounding conductors and enclosures. Re-bonding at subpanels or treating them as one conductor creates parallel neutral paths and shock hazards.2023 NEC §250.24

A single ground rod electrode that does not achieve a resistance to earth of 25 ohms or less must be:

• a.Left as-is with no further action
• b.Replaced with a length of copper water pipe
• c.Supplemented by one additional electrode (such as a second rod) spaced at least 6 feet away✓
• d.Removed and left ungrounded

If a single made electrode does not meet 25 ohms or less, the Code requires adding one supplemental electrode located at least 6 feet from the first. Leaving it inadequate or removing it defeats the grounding, and a random copper pipe is not the prescribed supplemental electrode method.2023 NEC §250.53

The purpose of the main bonding jumper at a service is to:

• a.Bond the neutral bar only to the ground rod
• b.Connect two separate service panels together
• c.Carry the lighting load for the building
• d.Connect the equipment grounding conductor/metal enclosure to the grounded (neutral) conductor at the service✓

The main bonding jumper ties the equipment grounding system and service enclosure to the grounded (neutral) conductor at the service, completing the fault path back to the source. It is not a tie between two panels, not merely a neutral-to-rod link, and it never carries normal load current.2023 NEC §250.24

An excavation or trench that is how deep generally requires a protective system (sloping, shoring, or shielding) unless it is entirely in stable rock?

• a.20 feet or deeper
• b.2 feet or deeper
• c.10 feet or deeper
• d.5 feet or deeper✓

Trenches 5 feet deep or more must have a protective system (sloping/benching, shoring, or a trench shield) unless made entirely in stable rock. The 2-foot answer is too shallow, and waiting until 10 or 20 feet would leave workers unprotected in the depth range where fatal cave-ins commonly occur.Cal/OSHA Title 8 §1541.1

Who must inspect an excavation for hazards (before each shift and as conditions change) and classify the soil?

• a.A competent person who can identify hazards and is authorized to take prompt corrective action✓
• b.The city electrical inspector
• c.Any laborer available that day
• d.The electric utility company

Excavations must be inspected by a competent person—someone able to recognize hazards and authorized to take immediate corrective action, including ordering workers out. An untrained laborer, the electrical inspector, or the utility does not meet the competent-person requirement for trench safety.Cal/OSHA Title 8 §1541

Excavated soil (spoil) and equipment must be kept at least how far back from the edge of a trench?

• a.6 inches from the edge
• b.2 feet from the edge✓
• c.There is no setback requirement
• d.10 feet from the edge

Spoil piles and equipment must be kept at least 2 feet from the trench edge (or be restrained) so the surcharge load does not trigger a cave-in and material does not roll back onto workers. 6 inches is too close, 10 feet is more than required, and 'no requirement' is incorrect.Cal/OSHA Title 8 §1541

In a trench 4 feet or more deep, a stairway, ladder, or ramp must be provided so that:

• a.Only one is provided per trench regardless of its length
• b.Workers can jump out if needed
• c.It is optional as long as the trench is short
• d.No worker has to travel more than 25 feet of lateral distance to reach a means of exit✓

Trenches 4 feet or deeper require a ladder, stairway, or ramp located so that lateral travel to a means of exit is no more than 25 feet. Expecting workers to jump out, allowing only one regardless of length, or making it optional does not meet the egress requirement for deep trenches.Cal/OSHA Title 8 §1541

Before excavating a trench 5 feet or more deep into which a person must descend, a California employer generally must obtain:

• a.A building fire permit
• b.Nothing beyond a shovel
• c.A Cal/OSHA excavation/trench permit (project or annual) for trenches 5 feet or deeper that a worker will enter✓
• d.A city business license

Cal/OSHA requires a permit for construction of trenches 5 feet or more deep into which a person must descend. A business license or fire permit does not authorize the excavation, and 'nothing' ignores the permit requirement that helps ensure protective systems are planned.Cal/OSHA Title 8 §341

Before digging near underground utilities in California, you are required to:

• a.Do nothing if the work is on private property
• b.Contact the regional one-call center (DigAlert/811) at least two working days in advance to have utilities marked✓
• c.Call the fire department for a spotter
• d.Just dig carefully by hand and hope for the best

California law requires notifying the regional notification/one-call center (DigAlert, 811) at least two working days before excavating so member utilities can mark their lines. Digging blindly, calling the fire department, or assuming private property is exempt all risk striking energized or gas lines.