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NCCER Electrical practice questions

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Question 1Electrical Safety

Under a typical lockout/tagout program, who may remove a lock that has been applied to an energy-isolating device?

  1. Any journeyman on the crew
  2. The site superintendent
  3. The safety officer on duty
  4. The worker who applied it Correct answer.

Explanation

Removing another person's lock could expose that worker to unexpected energization. Only the person who applied the lock removes it, unless the employer's documented special removal procedure is followed when that person is unavailable.

Question 2Electrical Safety

Rubber insulating gloves protect the wearer primarily against which hazard?

  1. Falling objects
  2. Chemical splashes
  3. Cuts and abrasions only
  4. Electric shock Correct answer.

Explanation

Rubber insulating gloves are dielectric PPE, selected and tested for the voltage involved. Leather protectors worn over them handle abrasion and cuts, not the electrical protection itself.

Question 3Electrical Safety

Which extinguisher class is specified for fires involving energized electrical equipment?

  1. Class A
  2. Class D
  3. Class C Correct answer.
  4. Class B

Explanation

Class C extinguishers use nonconductive agents suitable for energized electrical equipment. Once the equipment has been de-energized, the fire is classified by the burning material instead.

Question 4Electrical Safety

How does a ground fault circuit interrupter protect a worker using a portable tool?

  1. It trips when current leaks to ground Correct answer.
  2. It reduces voltage at the receptacle
  3. It limits fault current to a safe level
  4. It opens the circuit on overload only

Explanation

A GFCI compares the current leaving the source with the current returning; a small imbalance trips the device. It is a personnel protection device, not an overload or current-limiting device.

Question 5Electrical Safety

Which ladder type is preferred when work must be performed near energized electrical equipment?

  1. Any metal ladder with rubber feet
  2. Steel-reinforced
  3. Aluminum
  4. Fiberglass or wood Correct answer.

Explanation

Nonconductive ladders made of fiberglass or wood reduce the chance of establishing a path to ground. Metal ladders remain conductive regardless of the feet or coatings attached to them.

Question 6Electrical Safety

A coworker is being held by a live conductor and cannot let go. What should you do first?

  1. Pull the person away by the arm
  2. Call for a supervisor first
  3. Shut off the power source Correct answer.
  4. Begin CPR immediately

Explanation

The circuit must be de-energized before anyone touches the victim, or the rescuer becomes a second victim. CPR and medical aid follow only after the electrical hazard has been removed.

Question 7Electrical Safety

Danger signs posted on a construction site indicate which of the following?

  1. PPE required for the area
  2. An immediate hazard that may cause death Correct answer.
  3. Traffic and parking restrictions in the plant
  4. The location of first aid stations and exits

Explanation

Danger signs mark an immediate hazard that could cause death or serious injury and use red as the signal color. Caution signs, in yellow, mark lesser hazards, while safety instruction signs give general guidance.

Question 8Electrical Safety

Before touching a conductor that is supposed to be de-energized, a qualified worker must do what?

  1. Check the disconnect handle position
  2. Test it with a meter rated for the voltage Correct answer.
  3. Look at the panel schedule
  4. Ask a journeyman to confirm it is off

Explanation

Test-before-touch with a tester rated for the voltage confirms the absence of voltage at the point of work. Switch position and paperwork are not proof of an electrically safe condition.

Question 9Electrical Safety

The arc flash boundary is the distance from energized equipment at which which condition exists?

  1. The circuit is de-energized and grounded
  2. The equipment is considered isolated
  3. Shock protection is not required
  4. Incident energy equals 1.2 cal/cm² Correct answer.

Explanation

The arc flash boundary is set where incident energy is 1.2 cal/cm², the level at which a second-degree burn can occur. Inside that boundary, arc-rated PPE is required.

Question 10Electrical Safety

Stored energy such as charged capacitors or compressed springs must be handled how during lockout/tagout?

  1. Tagged and left in place
  2. Left charged until work begins
  3. Inspected by a supervisor
  4. Released or blocked before work Correct answer.

Explanation

Lockout/tagout requires more than isolating the supply; stored energy must be dissipated or restrained and then verified. Otherwise the circuit can re-energize or parts can move when touched.

Question 11Electrical Safety

Entry past the restricted approach boundary is permitted only under which condition?

  1. The circuit is treated as de-energized
  2. Only qualified persons with PPE may cross Correct answer.
  3. Arc-rated clothing is no longer required
  4. Unqualified persons may pass without PPE

Explanation

The restricted approach boundary marks the distance at which shock risk rises sharply. Only qualified persons using shock-protective PPE and insulated tools may cross it.

Question 12Electrical Safety

How often must rubber insulating gloves be electrically retested to remain in service?

  1. Every six months Correct answer.
  2. Every month
  3. Once a year
  4. Every three months

Explanation

Gloves must be electrically tested before first issue and every six months thereafter. A visual inspection and air test are performed before each day's use in addition to the periodic retest.

Question 13Electrical Safety

For lines rated under 50 kV, the minimum approach distance that unqualified persons must maintain from overhead lines is which of the following?

  1. 20 ft
  2. 15 ft
  3. 25 ft
  4. 10 ft Correct answer.

Explanation

The minimum approach distance for unqualified persons near overhead lines rated up to 50 kV is 10 ft. Equipment must also be positioned and operated so that no conductive part can encroach on that distance.

Question 14Electrical Safety

A portable tool marked as double-insulated has which characteristic?

  1. Requires an equipment grounding conductor
  2. Is approved only for dry locations
  3. Has two layers of insulation Correct answer.
  4. Must be tested before each shift

Explanation

Double-insulated tools have a supplementary insulation system over the basic insulation, so they are built without a grounding conductor. They still require cord inspection and GFCI protection where the job calls for it.

Question 15Electrical Safety

Before entering a permit-required confined space, the entrant must do which of the following?

  1. Wear a hard hat and safety glasses
  2. Ask the attendant to watch from outside
  3. Ventilate the space for five minutes
  4. Test the atmosphere and get an entry permit Correct answer.

Explanation

Atmospheric testing is performed before entry and the results are recorded on the entry permit along with rescue provisions and attendant assignment. Ventilation alone does not replace testing.

Question 16Electrical Safety

Arc-rated clothing is defined by which of the following?

  1. It is always made of wool or cotton
  2. It is required only for utility linemen
  3. It carries an arc rating in cal/cm² Correct answer.
  4. It cannot be worn near energized equipment

Explanation

Arc-rated garments have been tested and assigned an arc rating, usually expressed in cal/cm². Flame-resistant clothing that has not been arc-tested cannot be substituted where an arc rating is required.

Question 17Electrical Safety

Energized electrical work is permitted only under which circumstance?

  1. De-energizing adds risk or is infeasible Correct answer.
  2. The circuit is rated below 600 volts
  3. The customer requests it in writing before work
  4. The job takes less than one shift

Explanation

Energized work is allowed only when de-energizing would introduce additional or increased hazards, or when it is infeasible, and then only with a documented energized work permit and appropriate PPE.

Question 18Electrical Safety

Where would you find the health hazards, PPE requirements, and first aid measures for a solvent used on the job?

  1. The arc flash label
  2. The lockout procedure
  3. The panel schedule
  4. The safety data sheet Correct answer.

Explanation

The Hazard Communication standard requires a safety data sheet for each hazardous chemical. Its standardized sections cover hazards, safe handling, exposure controls, and first aid measures.

Question 19Electrical Safety

A test instrument with a CAT III rating is intended for use on which type of circuit?

  1. Telecommunications lines
  2. Resistance measurements only
  3. Fixed distribution circuits Correct answer.
  4. Low-voltage electronics only

Explanation

Category ratings reflect the transient energy a meter can withstand. CAT III covers fixed distribution installations, while CAT IV covers service entrances and outdoor feeders.

Question 20Electrical Safety

What does an assured equipment grounding conductor program require?

  1. Grounding every tool with an individual rod
  2. Testing GFCI receptacles monthly
  3. Documented testing of cords and tools Correct answer.
  4. Using only double-insulated tools

Explanation

The program requires that cord sets, receptacles, and equipment be visually inspected and continuity-tested at set intervals, with the results recorded. It is an alternative to GFCI protection for certain temporary receptacles.

Question 21Electrical Safety

At a given working distance, incident energy from an arcing fault is most strongly determined by which pair of factors?

  1. Fault current and clearing time Correct answer.
  2. Ambient temperature and humidity
  3. Wire size and conduit type
  4. Conductor insulation color

Explanation

Incident energy rises with the magnitude of the arcing fault current and the time the arc persists. Reducing either one, through faster clearing or lower available fault current, reduces the calculated energy.

Question 22Electrical Safety

Class 2 rubber insulating gloves are rated for what maximum use voltage?

  1. 36,000 V AC
  2. 26,500 V AC
  3. 5,000 V AC
  4. 17,000 V AC Correct answer.

Explanation

Class 2 gloves have a proof-test voltage of 20,000 V AC and a maximum use voltage of 17,000 V AC. Wearing a class below the system voltage defeats the protection.

Question 23Electrical Safety

Under a group lockout, which practice is required?

  1. Each worker applies a personal lock Correct answer.
  2. One lock for the entire crew is sufficient
  3. Tags replace locks for short jobs
  4. Locks are applied by the supervisor

Explanation

Each worker exposed to the hazard places a personal lock on the group lockout device or hasp, so equipment cannot be re-energized until every lock has been removed by its owner.

Question 24Electrical Safety

Arc-rated PPE selected for a task must have an arc rating that is which of the following relative to incident energy?

  1. At least equal to the incident energy Correct answer.
  2. Half of the incident energy
  3. Twice the incident energy
  4. No greater than the incident energy

Explanation

The arc rating of the garment must meet or exceed the calculated incident energy at the working distance. PPE with a lower rating may be ignited or fail under the thermal exposure.

Question 25Electrical Safety

A live conductor has fallen to earth and a worker is standing nearby. The hazard that requires shuffling away with the feet close together is which one?

  1. Step potential in the earth Correct answer.
  2. Direct contact with the fallen line
  3. Arc flash from the fallen conductor
  4. Induced voltage in nearby conduit

Explanation

Current flowing through the earth creates a voltage difference between the worker's two feet. Keeping the feet close together and shuffling reduces that potential difference and the current through the body.

Question 26Electrical Safety

A ground-fault circuit interrupter (GFCI) intended to protect personnel opens the circuit at a ground-fault current of approximately:

  1. 30 milliamperes
  2. 5 milliamperes Correct answer.
  3. 15 amperes
  4. 100 milliamperes

Explanation

Personnel-protection GFCIs trip at about 4 to 6 milliamperes, which is below the level that can cause sustained muscle contraction. This low threshold limits the duration of a shock and reduces the chance of serious injury.

Question 27Electrical Safety

A lock and tag are applied to a disconnect by an electrician who then leaves the site. Who may remove that lock?

  1. Any supervisor who witnessed the lockout
  2. Any qualified worker on the same crew
  3. The site safety officer without authorization
  4. The worker who applied it, per procedure Correct answer.

Explanation

A lockout lock is removed by the person who applied it. If that person is unavailable, the employer's written procedure must be followed, including steps to verify the worker is not in danger.

Question 28Electrical Safety

Which ladder material is preferred when work must be performed near energized electrical equipment?

  1. Wet wood
  2. Steel
  3. Fiberglass Correct answer.
  4. Aluminum

Explanation

Fiberglass is nonconductive and is the preferred ladder material for electrical work. Metal ladders conduct electricity, and wet wood cannot be relied on to provide insulation.

Question 29Electrical Safety

The minimum clear working space in front of an electrical panelboard rated 600 volts or less is generally:

  1. 36 inches Correct answer.
  2. 30 inches
  3. 12 inches
  4. 24 inches

Explanation

Electrical working-space rules require at least 36 inches of clear depth in front of panelboards in the usual case. Greater depth may be required by the specific voltage and condition of the equipment.

Question 30Electrical Safety

A portable extension cord is found with a missing grounding pin on its plug. What is the correct action?

  1. Use it only with double-insulated tools
  2. Wrap the plug with tape and continue
  3. Remove it from service and tag it Correct answer.
  4. Plug it into a GFCI receptacle and use it

Explanation

A missing grounding pin defeats the equipment grounding path and creates a shock hazard. The cord must be removed from service and tagged so it cannot be used until repaired or discarded.

Question 31Electrical Safety

The current level at which a person grasping an energized conductor may be unable to let go is approximately:

  1. 1 ampere
  2. 1 milliampere
  3. 10 milliamperes Correct answer.
  4. 100 milliamperes

Explanation

At about 10 milliamperes, sustained muscle contraction can prevent a person from releasing a grasped conductor. Currents near 1 milliampere are usually just perceptible, while 100 milliamperes or more can cause ventricular fibrillation.

Question 32Electrical Safety

What is the primary purpose of bonding in an electrical installation?

  1. To keep exposed conductive parts at the same potential Correct answer.
  2. To reduce the resistance of the earth electrode
  3. To provide a low-impedance path that opens the overcurrent device during a fault
  4. To limit voltage surges from lightning

Explanation

Bonding connects conductive parts so they remain at substantially the same potential, which prevents dangerous voltage differences between them. Grounding to earth and providing a fault-current path are related but separate functions.

Question 33Electrical Safety

Which document identifies the specific lockout points, energy sources, and shutdown sequence for a particular machine?

  1. The job hazard analysis
  2. The energy control procedure Correct answer.
  3. The manufacturer's warranty
  4. The arc flash risk assessment

Explanation

A machine-specific energy control procedure lists each energy source, the means to isolate it, the lockout points, and the sequence for shutting down and verifying zero energy. Generic hazard analyses do not contain that machine-specific detail.

Question 34Electrical Safety

When verifying absence of voltage on a 480-volt, three-phase motor branch circuit, the tester should be applied to:

  1. Between each phase and ground only
  2. All phase-to-ground and phase-to-phase points Correct answer.
  3. The motor frame and ground only
  4. Across any one phase pair only

Explanation

Absence of voltage must be verified across every phase-to-phase combination and from each phase to ground. Checking only one point can miss a backfeed or a phase-to-phase potential.

Question 35Electrical Theory and Circuits

A 12 Ω resistor is connected across a 120 V source. What current flows through the resistor?

  1. 10 A Correct answer.
  2. 132 A
  3. 0.1 A
  4. 1440 A

Explanation

Ohm's law states that current equals voltage divided by resistance, so 120 V ÷ 12 Ω = 10 A. The relationship applies to any purely resistive circuit.

Question 36Electrical Theory and Circuits

A 120 V circuit carries a current of 15 A. What is the power consumed by the load?

  1. 1800 W Correct answer.
  2. 135 W
  3. 8 W
  4. 2400 W

Explanation

Power in a resistive DC circuit equals voltage multiplied by current, so 120 V × 15 A = 1800 W. The same result is obtained with P = I²R once the resistance is known.

Question 37Electrical Theory and Circuits

Three resistors rated 5 Ω, 10 Ω, and 15 Ω are connected in series. What is the total resistance of the circuit?

  1. 7.5 Ω
  2. 30 Ω Correct answer.
  3. 15 Ω
  4. 3.3 Ω

Explanation

In a series circuit the total resistance is the sum of the individual resistances. Adding 5 Ω + 10 Ω + 15 Ω gives 30 Ω.

Question 38Electrical Theory and Circuits

In a parallel circuit, which quantity is the same for every branch?

  1. Voltage Correct answer.
  2. Power
  3. Current
  4. Resistance

Explanation

Each branch of a parallel circuit is connected directly across the same two points, so the voltage across every branch is equal to the source voltage. The branch currents then depend on each branch's own resistance.

Question 39Electrical Theory and Circuits

Conventional current is described as flowing in which direction through an external circuit?

  1. In both directions at once
  2. From positive to negative Correct answer.
  3. From negative to positive
  4. Only in alternating-current circuits

Explanation

Conventional current is defined as moving from the positive terminal, through the external circuit, to the negative terminal. Electron flow is in the opposite direction, from negative to positive.

Question 40Electrical Theory and Circuits

A 60 Hz alternating-current waveform completes how many full cycles each second?

  1. 60 Correct answer.
  2. 3600
  3. 120
  4. 30

Explanation

Hertz means cycles per second, so a 60 Hz waveform completes 60 full cycles every second. Each full cycle contains two alternations, one positive and one negative.

Question 41Electrical Theory and Circuits

Which unit is used to express opposition to current flow in a circuit?

  1. Ampere
  2. Volt
  3. Watt
  4. Ohm Correct answer.

Explanation

The ohm is the unit of resistance, defined as the resistance that allows one ampere to flow when one volt is applied. Volts, amperes, and watts describe potential, current, and power respectively.

Question 42Electrical Theory and Circuits

A conductor's length and material are held constant while its cross-sectional area is increased. What happens to its resistance?

  1. It decreases Correct answer.
  2. It doubles
  3. It increases
  4. It is unchanged

Explanation

Resistance is inversely proportional to cross-sectional area, so a larger area provides more paths for current and lowers resistance. Doubling the area halves the resistance.

Question 43Electrical Theory and Circuits

A 240 V source supplies a series circuit containing a 4 Ω resistor and an 8 Ω resistor. What is the voltage across the 8 Ω resistor?

  1. 80 V
  2. 240 V
  3. 160 V Correct answer.
  4. 60 V

Explanation

Total resistance is 12 Ω, so the current is 240 V ÷ 12 Ω = 20 A. The drop across the 8 Ω resistor is then 20 A × 8 Ω = 160 V.

Question 44Electrical Theory and Circuits

Two 12 Ω resistors are connected in parallel. What is the equivalent resistance of the combination?

  1. 12 Ω
  2. 6 Ω Correct answer.
  3. 0.17 Ω
  4. 24 Ω

Explanation

For two equal resistors in parallel, the equivalent resistance is half of one resistor's value, so 12 Ω ÷ 2 = 6 Ω. The general reciprocal formula gives the same result.

Question 45Electrical Theory and Circuits

A 240 V appliance draws 10 A and runs for 5 hours. How much energy does it consume?

  1. 12 kWh Correct answer.
  2. 1.2 kWh
  3. 2.4 kWh
  4. 24 kWh

Explanation

Power is 240 V × 10 A = 2400 W, or 2.4 kW. Multiplying by 5 hours gives 12 kWh of energy.

Question 46Electrical Theory and Circuits

Voltage drop in a two-wire feeder is calculated with VD = 2KIL/CM. What does the factor of 2 represent?

  1. The current's return path Correct answer.
  2. The conductor temperature
  3. The load power factor
  4. The insulation thickness

Explanation

The formula accounts for the fact that current must travel out to the load and back to the source, so the conductor length is counted twice. That is why the constant K and the one-way length L are doubled.

Question 47Electrical Theory and Circuits

In a balanced three-phase system, total power is calculated with which expression?

  1. V × I × PF
  2. V × I ÷ PF
  3. 3 × V × I
  4. √3 × V × I × PF Correct answer.

Explanation

For a balanced three-phase load, total power equals the square root of three times line voltage times line current times power factor. The √3 factor arises from the relationships between line and phase quantities.

Question 48Electrical Theory and Circuits

Power factor is defined as the ratio of which two quantities?

  1. Voltage to current
  2. Apparent power to true power
  3. Reactive power to true power
  4. True power to apparent power Correct answer.

Explanation

Power factor is the ratio of true power, measured in watts, to apparent power, measured in volt-amperes. It equals the cosine of the phase angle between voltage and current.

Question 49Electrical Theory and Circuits

What happens to capacitive reactance as the frequency of the applied voltage increases?

  1. It decreases Correct answer.
  2. It stays constant
  3. It increases
  4. It is zero at every frequency

Explanation

Capacitive reactance is inversely proportional to frequency and capacitance, so raising the frequency lowers the reactance. A capacitor passes higher-frequency current more readily.

Question 50Electrical Theory and Circuits

A sine wave has an RMS value of 120 V. What is its approximate peak value?

  1. 120 V
  2. 85 V
  3. 240 V
  4. 170 V Correct answer.

Explanation

Peak value equals RMS value multiplied by about 1.414, so 120 V × 1.414 ≈ 170 V. The RMS value is the equivalent heating value of the waveform, not its maximum.