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What is the effect of dust and dirt between joints of permissible equipment?
Joints cannot be closed tightly enough to get the required cooling action; therefore permissibility is destroyed.
If you read an open circuit between A1 and A2 of a DC motor, it indicates that:
The armature circuit is open.
What happens if the two line leads to a DC series motor are reversed?
Direction of rotation remains the same.
The direction in which a motor rotates depends upon the:
Direction of the current flow through the armature.
If you read a low resistance between leads S1 and S2 of a series motor, means that:
The series field is good.
How is the rotation of a direct current, series motor reversed?
By changing the direction of the current flow in either the armature or series field.
The thermal heater element of an overload relay is generally connected in:
Series with the motor lead.
When compared to the resistance of the series fields and armature circuit, the shunt fields of a motor will have:
When dealing with electrical equipment, grounding:
Provides a return path to the earth and prevents voltage from existing on the frames of the equipment.
A solid state device most commonly used to control power output in a DC circuit is:
Silicon controlled rectifier.
What is the purpose of a frame ground in a trailing cable?
To protect the operator from shock by keeping the equipment at earth potential.
When comparing the resistance of the shunt field of a DC motor to the series field, the shunt field resistance is usually:
What purpose is served by a starting resistor in a motor circuit?
It limits the starting current during start-up by reducing the voltage.
If an equipment frame grounding wire was not provided:
There would be a real potential for electrical shock.
Which of the following methods is NOT recommended for removing a victim from contact with electricity?
Knock the victim off with a nonconductive object.
Through what piece of equipment is alternating current fed in order to lower its voltage?
If 1,100 amps leave a rectifier on one conductor, how many amps will return to that rectifier on the other conductor?
The function of the capacitor trip device and circuit is to:
Provide sufficient energy to trip the breaker, even after the power goes off.
If the overcurrent condition continues for a long time, and at a great enough magnitude, an overcurrent device will trip the:
If circuit breakers are too small for the equipment they are protecting:
The circuit breaker will not stay closed.
The ampere capacity of a circuit breaker is:
The amount of current that a breaker can carry under normal conditions.
When an overcurrent device detects an overload condition, the breaker should trip:
All three phases at the same time.
The difference between a time delay and an instantaneous overcurrent relay:
Lies primarily in how quickly they trip a circuit breaker.
The idea behind a capacitor trip device and circuit is to:
Provide sufficient energy to trip the breaker, even after power goes off.
When a circuit breaker has an overload trip, what causes the circuit breaker to de-energize the circuit?
A thermal element heats up and actuates the contacts.
Thermal heater strips in circuit breakers or line starters are used to provide what protection?
A 3-phase motor continues to operate when one lead has been severed or cut in two; then, when stopped, will not start again. The motor is said to be:
If under normal load a 30-amp fuse becomes hot the most likely reason for this is:
The clips holding the fuse are loose.
If a 120-volt direct current source is connected to a 10:1 step-down transformer, the output on the secondary side is:
Two resistors (Resistor 1 and Resistor 2) are connected in parallel and Resistor 2 burns open. What would happen?
Current in the circuit would be reduced.
If an ohmmeter shows continuity across an SCR with no gate voltage applied, the SCR is probably:
Which of the following is a true statement concerning the operational characteristics of an SCR?
It will allow current flow in only one direction once it is gated.
The heater element in a motor circuit overload relay is connected in:
Series with the motor circuit.
If neither indicating light were on, and the coil would not energize, what component is most likely defective?
What is wrong with replacing a blown fuse with a piece of copper wire?
The copper wire will not provide adequate overcurrent protection.
If a system designed for a 20-amp fuse blows, and an electrician replaces it with one rated at 30 amps:
A fire may result or the equipment may become damaged.
When fuses are too big for the current requirement of the equipment being protected:
Too much current could be allowed to pass through, overheating. equipment and burning off insulation.
What is used to prevent the Forward and Reverse contactors in a motor reversing control from operating at the same time?
Electrical and/or mechanical interlocks.
The DC motor that uses both a series and shunt winding and combines the characteristics of both is called a:
What will happen to a DC shuttle car series wound motor if the chain or drive shaft would break?
The motor will overspeed to the point of destruction.
To reduce the hazard of electrical shock, which of the following should be installed?
Frame ground conductor.
What device may be installed in the neutral of a three-phase wye connected system to limit the current if a ground fault occurs?
When checking resistance in an AC circuit when troubleshooting, what initial precaution must be taken?
Disconnect the source voltage.
The overload relay contacts of a thermal overload are generally connected in:
Series with the operating coil.
Which of the following is not a characteristic of a series motor?
Current remains the same at all loads.
The component attached to the donut coil on one phase lead, between the contactors and motor, is normally used as a (an):
If a thermal overload activates, causing a circuit to be de-energized, what must you do before the circuit can be re-energized?
Allow it to cool.
If you were to peel the insulation off a No. 14 AWG stranded conductor, you would expect to find:
Smaller wires which are not insulated from one another.
If you were to lockout and tag the motor to begin repair work, the safest and most convenient place to do this would be at the:
Disconnect switch located near the motor.
If a voltmeter were placed across the fuse and no voltage was indicated, you could correctly assume that:
The fuse was good
The system using one ground wire and three hot wires, whose voltage is balanced 120 degrees apart is called:
The safest way to de-energize a motor running on full load is:
Through the control circuit which will open the line contactors.
Which system requires only two power conductors and is generally used for control, lighting, and small loads?
If a float switch on a pump closes because the water level rises:
The pump should start because the float switch completed an electrical circuit
If a voltmeter were placed across the fuse and the scale indicated 120 volts, you could correctly assume that:
The fuse was blown.
What is electrolysis?
The action of an electrical current which carries away particles of a conductor.
When testing a diode with an ohmmeter, what will be the reading of a good diode?
A low resistance reading in one direction and a very high reading in the other direction.
What purpose is served by a blowout coil used as a DC contactor?
It helps to extinguish the arc when the contactor opens.
A small sump pump blows a 20-amp fuse. The pump under full load draws 12 amps of current and receives its power through a No. 12 AWG cable. After repairing the problem, you discover you only have a 15-amp and a 30-amp fuse. You should:
Install the 15-amp fuse
The wires of a transformer have a 10:1 ratio. When stretched out side by side:
One wire would be ten times the length of the other.
If you checked a resistor marked 50 ohms and your meter read the resistance extremely high (your meter would not measure the amount), you would be most correct in assuming that:
The resistor has burned open.
If four cables all have the same insulation and circular mil value, which cable would be the most flexible?
A shuttle car tramming up a steep grade at the feeder blows a fuse. Before knocking the power and tagging-out the circuit you must:
Block the machine so it doesn't move.
The part of a disconnect switch which has metal blades that pivot at one end is called a (an):
The safest way to check an electrical load to see if it is an open circuit is with a (an):
Ohmmeter with power off.
If a circuit breaker with thermal overload protection has just tripped and you immediately try to re-energize the circuit and find that the breaker will not hold in, you should:
Wait for the thermal element in the breaker to cool sufficiently so that it will hold in the tripping mechanism.
There are three types of electrical diagrams. Which of the following is NOT an electrical diagram?
A transformer has primary windings of 460 volts and secondary windings of 115 volts. What can you correctly assume about wire size?
The secondary windings would be larger in size (AWG) than those on the primary side.
If the motor developed an internal "direct short" between phases, the device to de-energize the circuit would be the:
If you wanted to check the insulation on wire for damage, the instrument you would use is a (an):
If a belt conveyor loaded with coal was turned on, the starting torque would be greatest when the motor:
If you wanted to find information concerning a motor's duty cycle characteristics, you could find it most easily by:
Looking at the tag attached to the motor housing
If the continuous miner stops operating, and the only component that is energized on the miner is its methane monitor, you could do all of the following EXCEPT:
Jumper-out the methane monitor.
Which will cause the power center circuit breaker for a continuous miner to trip faster?
The shuttle car runs over the miner cable causing two conductors to come in contact with each other.
If a transformer was believed to be shorted because of a breakdown in its insulation, what instrument would you use to check it?