Electrical Exam 1

Arcing is defined as a luminous discharge of electricity across an insulating medium. Electric arcs operate at temperatures between ______ and expel small particles of very hot molten material.

5,000 and 15,000°F

When a motor starts, the current drawn is approximately ______ times the motor FLA; this is known as "motor locked-rotor amperes" (LRA).

6

A GFCI-protection device contains an internal monitor that prevents the device from being turned on if there is a neutral-tocase connection downstream of the device, but this only occurs if there is a load on the circuit.

False

A holding relay is primarily used for worker convenience.

False

A clamp-on ac ammeter has a coil that is clamped around the conductor and detects the rising and falling ______ field being produced due to the ac flow through the conductor.

Magnetic

For ac circuits, the ac ______ of a conductor must be taken into consideration.

Skin effect

According to the Conventional Current Flow Theory, electrons travel from positive to negative.

True

According to the Electron Current Flow Theory, electrons flow away from the negative terminal of the source, through the circuit and load, toward the positive terminal of the source.

True

Available short-circuit current is the current in amperes available at a given point in the electrical system.

True

Circuit breakers and fuses are intended to interrupt the circuit, and they must have an ampere interrupting rating (AIR) sufficient for the available short-circuit current.

True

The major advantage of ac over dc is the ease of voltage regulation by the use of a transformer.

True

The opposition to current flow results in voltage drop.

True

Typically, when a GFCI-protection device fails, the switching contacts remain closed and the device will continue to provide power without GFCI protection.

True

Unsafe arcing faults can occur in one of two ways, as series arcing faults or as parallel arcing faults. The most dangerous is the parallel arcing fault.

True

The total resistance of a parallel circuit can be calculated by the ______ method.

equal resistance or product-over-sum or reciprocal

The formulas in the power wheel apply to ______.

dc or ac with unity power factor

The energy transfer ability of a transformer is accomplished because the primary electromagnetic lines of force induce a voltage in the secondary winding.

true

When describing the relationship between voltage and current, the reference waveform is always ______.

voltage

Because of the dangers associated with an open neutral conductor, the continuity of the ______ conductor cannot be dependent upon the receptacle.

grounded

The induced voltage in a conductor carrying alternating current opposes the change in current flowing through the conductor. The induced voltage that opposes the current flow is called "______."

(a) CEMF (b) counter-electromotive force (c) back-EMF

The purpose of overcurrent protection is to protect the conductors and equipment against excessive or dangerous temperatures because of overcurrent. Overcurrent is current in excess of the rated current of equipment or conductors. It may result from a(n) ______.

(a) overload (b) short circuit (c) ground fault

To protect against electric shock or to prevent a fire, a dangerous ______ must quickly be removed by opening the circuit's overcurrent protection device.

(a) overload (b) short circuit (c) ground fault

Factors that affect the available short-circuit current include transformer ______.

(a) voltage (b) kVA rating (c) impedance

Three-phase ac generators have three equally spaced windings, ______ out-of-phase with each other.

120 degrees

Inverse time breakers operate on the principle that as the current decreases, the time it takes for the device to open decreases.

False

A GFCI is designed to protect persons against electric shock. It operates on the principle of monitoring the imbalance of current between the circuit's ______ conductor.

Grounded or ungrounded

If the rotating part of the motor winding is jammed so that it cannot rotate, no CEMF will be produced in the motor winding. Result—the motor operates at ______ and the windings will be destroyed by excessive heat.

LRC (locked rotor current)

The expanding and collapsing magnetic field within the conductor induces a voltage in the conductors (CEMF) that repels the flowing electrons toward the surface of the conductor. This is called "______."

Skin effect

In an ac induction motor, the stator produces a rotating magnetic field that induces current in the rotor windings. The rotor current generates a magnetic field in opposition to the magnetic field of the stator, thereby causing the rotor to turn.

True

Lightning frequently terminates to a point of elevation and strikes nonmetallic as well as metallic objects with the same frequency.

True

Metal parts of premises wiring must be bonded to a lowimpedance path designed so that the circuit protection device will quickly open and clear a ground fault.

True

People become injured and death occurs when voltage pushes electrons through the human body causing the heart to go into ventricular fibrillation.

True

Providing a path to the earth often helps reduce electrostatic charge.

True

Severe electric shock or death can occur if a person touches the ungrounded and the neutral conductors at the same time, even if the circuit is GFCI-protected.

True

The current flowing on the neutral conductor of a multiwire circuit is called "unbalanced current."

True

The severity of an electric shock is dependent on the current flowing through the body, which is impacted by circuit voltage and contact resistance.

True

When power supplies are connected in parallel, the voltage remains the same, but the current or amp-hour capacity will be increased.

True

______ motors are fractional horsepower motors that operate equally well on ac and dc and are used for vacuum cleaners, electric drills, mixers, and light household appliances.

Universal

Ohmmeters measure the ______ or opposition to current flow of a circuit or component.

resistance

The megger is used to measure very high-______ values, such as those found in cable insulation, or motor and transformer windings.

resistance

The ______ of a generator is forced to rotate while it is being subjected to the magnetic field of the stator.

rotor

The ______ of an ac generator contains the electromagnetic field, which cuts through the stationary conductor coils.

rotor

The magnetic time-delay circuit breaker operates on the solenoid principle where a movable core, held with a spring, is moved by the magnetic field of a(n) ______.

short circuit ground fault

In a(n) ______ motor, the rotor is locked in step with the rotating stator field and is dragged along at the speed of the rotating magnetic field.

synchronous

The ______ sensing element causes the circuit breaker to open when a predetermined calibration temperature is reached.

thermo

Factors that affect the available short-circuit current include circuit conductor ______.

(a) material (b) size (c) length

In a dc circuit, the only opposition to current flow is the physical resistance of the material. This opposition is called "reactance" and is measured in ohms.

False

Because of the earth's ______ resistance to current flow, it cannot be used for the purpose of clearing a line-to-case ground fault.

High

Electrons leaving a power supply are always trying to return to the same power supply; they are not trying to go into the earth.

True

Even when power is removed from the circuit, capacitors can store large amounts of energy for a long period of time. They can discharge and arc if inadvertently shorted or grounded out.

True

If a conductor carrying current is next to another conductor carrying current in the opposite direction, the electromagnetic field attempts to push the conductors apart.

True

If the protection device is not rated to interrupt the current at the available fault values at its listed voltage rating, it can explode while attempting to clear the fault.

True

If the ungrounded conductors of a multiwire circuit are not terminated to different phases, this can cause the neutral current to be in excess of the neutral conductor rating.

True

It is not the force of the magnetic field through a conductor that produces electricity; it is the relative motion of the field to the electrons within the conductor that produces the movement of electrons.

True

Kirchoff's Voltage Law states, "In a series circuit, the sum of the voltage drops across all of the resistors will equal the applied voltage."

True

Self-induced voltage opposes the change in current flowing in the conductor. This is called "inductive reactance" and it is abbreviated ______.

Xl

The abbreviation for impedance is ______.

Z

Wasteful circulating ______ in the iron core cause(s) the core to heat up without any useful purpose.

eddy currents

______ can be reduced by dividing the core into many flat sections or laminations.

eddy currents

Transformers are rated in ______.

kVA

The electric motor works on the principle of the attracting and repelling forces of ______ fields.

magnetic

Improper wiring or mishandling of multiwire branch circuits can cause ______ connected to the circuit.

overloading of the neutral conductors or destruction of equipment because of overvoltage

Dual-voltage ac motors are made with two field windings. The field windings are connected in ______ for low-voltage operation and in ______ for high-voltage operation.

parallel, series

Kirchoff's Current Law states, "In a series circuit, the current is ______ through the transformer, the conductors, and the appliance."

the same

The heating from harmonic currents is proportional to the square of the harmonic current.

true

Voltage induced in the secondary winding of a transformer is dependent on the number of secondary turns as compared to the number of primary turns.

true

Swapping ______ of the line conductors can reverse a three phase ac motor's rotation.

two

A balanced 3-wire, 120/240V, single-phase circuit is connected so that the ungrounded conductors are from different transformer phases (Line 1 and Line 2). The current on the neutral conductor will be ______ percent of the ungrounded conductor current.

0

If the primary phase voltage is 480V and the secondary phase voltage is 240V, the turns ratio is ______.

2:1

An electrical arc blast can approach ______, which vaporizes metal parts and produces an explosive and deadly pressure wave.

30,000°F

Three-phase, ______, wye-connected systems can overheat because of circulating odd triplen harmonic currents.

4 wire

AC inductive or capacitive reactive loads cause the voltage and current to be in-phase with each other.

False

Lightning protection is intended to protect the building itself, as well as the electrical equipment on or inside the structure.

False

Magnetic lines of force can cross each other and they are called flux lines.

False

Nonmagnetic metals are ferrous, meaning they do not contain any iron, and cannot be magnetized.

False

The best conductors, in order of their conductivity, are gold, silver, copper, and aluminum.

False

The motor FLA rating is used when sizing motor conductor size or circuit protection.

False

The termination of the lightning stroke is unlikely to ignite combustible materials.

False

To prevent fires and electric shock, the NEC specifies that neutral current can flow on metal parts of the electrical system.

False

A nonsinusoidal waveform is created when ______ loads distort the voltage and current sine wave.

Nonlinear

Equipment must have a(n) ______ current rating that permits the protection device to clear a short circuit or ground fault without extensive damage to the components of the circuit.

Short Circuit

According to Kirchoff's Current Law, the total current provided by the source to a parallel circuit will equal the sum of the currents of all of the branches.

True

The opposition offered to the flow of ac current by a capacitor is called "capacitive reactance," which is expressed in ohms and abbreviated ______.

Xc

As current flows through the transformer, the iron core is temporarily magnetized. The energy required to realign the core molecules to the changing electromagnetic field is called "______" loss.

hysterisis

The total opposition to current flow in ac circuits is called "______" and measured in ohms.

impedance

The effective value is equal to the peak value ______.

times 0.707

An AFCI-protection device provides protection from an arcing fault by recognizing the characteristics unique to an arcing fault and by functioning to de-energize the circuit when an arc fault is detected.

true

Because of conductor resistance, flux leakage, eddy currents, and hysteresis losses, not all of the input power is transferred to the secondary winding for useful purposes.

true