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274 Cards in this Set
- Front
- Back
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(201) Name three major parts of any DC motor. |
1. Frame 2. Armature 3. Endbells |
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(201) What is the relationship of the commutator to the armature? |
The armature is the rotating part of DC motor, while the commutator segments connect the stationary terminals (or brush circuit) to the rotating armature windings. |
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(201) How are the field assembly pole pieces attached to the frame? |
They are bolted to the inside of the frame. |
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(201) Where are the field coils placed? |
The field coils are placed around the pole pieces. |
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(201) How is a circuit completed from the commutator to the external power? |
By means of brushes. |
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(201) What is the primary function of the endbells? |
To keep the armature in position. |
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(202) The magnetic law that applies to the operation of DC motors states that unlike magnetic poles do what? |
Attract. |
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(202) What determines the polarity of an electromagnet? |
The direction in which the current flows through the winding of an electromagnet determines the polarity. |
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(202) What rule could you use to determine the polarity of an electromagnet coil? |
Right-hand rule. |
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(202) What force(s) causes the armature of a DC motor to rotate? |
The attracting or repelling force of the magnetic fields. |
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(202) Name the three types of DC motors. |
1. Series 2. Shunt. 3. Compound. |
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(202) Which DC motor should not be operated without a load?
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Series. |
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(202) State the type of DC motor that you should use in each of the following cases: a. When high starting torque is required and rapid fluctuations of torque occur b. When constant speed is desired and high starting torque occur. c. When high starting torque is required with good speed control |
1. Series 2. Shunt 3. Compound |
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(203) What are the basic parts of a three-phase induction motor? |
1. Stator 2. Rotor 3. Endbells |
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(203) Other than housing the stator windings, what function does a stator serve?
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Provides an attachment point for the supply voltage. |
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(203) What is the purpose of the rotor in an AC motor? |
The rotor provides a point to convert electrical energy to mechanical energy and to attach the motor to the load. |
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(203) Name the parts of a squirrel-cage rotor. |
1. Laminated iron core. 2. Rotor bars. 3. End rings. 4. Shaft |
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(203) Which type of rotor has sliprings for variable speed control? |
Wound rotor |
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(203) When is the use of a wound rotor desirable? |
For variable speed control and low starting current. |
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(203) What functions do the endbells perform on a motor? |
House the bearings, align the rotor and shaft, and complete the frame. |
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(204) On what does the operation of a three-phase motor depend? |
Rotating magnetic field. |
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(204) What factors are necessary for producing a rotating magnetic field in a three-phase motor? |
1. The difference in amount of current flow in the three-phase power. 2. Reversal in direction of current flow 3. The arrangement of the field winding in the stator. |
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(204) What factors determine motor speed? |
1. Frequency 2. Number of poles |
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(204) If frequency increases, what happens to motor speed?
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The motor speed increases. |
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(204) What is the synchronous speed of a four-pole motor operating on 50 cycle power?
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1500 RPM=hertz x 120/poles = 50 x 120/4 =1500 |
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(204) What is the difference in speed between the rotor and rotating magnetic field called?
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Slip |
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(204) What is the normal slip for an induction motor?
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2 to 5 percent |
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(204) What percentage of slip causes the rotor to stall or lock in an induction motor? |
25 percent |
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(205) What are the two types of internal connections for a three-phase motor? |
1. Wye 2. Delta |
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(205) How many leads does a single-voltage three-phase motor require? A dual-voltage motor? |
3 leads for single voltage; 9 leads for a dual-voltage motor. |
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(205) How are the windings of a three-phase, dual-voltage, whether wye or delta, connected for high voltage? |
Series |
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(205) What s the symbol for a wye-connected motor? A delta-connected motor? |
Y, △. |
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(205) Which type of winding connection causes a motor to draw more current, series, or parallel? |
Parallel |
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(205) Which leads of a three-phase wye motor connect to the power source leads when connected high voltage? |
Leads #1,2,3 |
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(205) To which leads are the 480-volt, 3 phase power source connected? |
Leads #1,2,3 |
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(206) List the two windings found in a split-phase motor. |
1. Run winding
2. Start winding |
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(206) What is the purpose of the centrifugal switch in a split-phase motor? |
To de-energize the start windings after the rotor reaches a predetermines rpm. |
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(206) How are the contacts of the centrifugal switch connected in relation to start winding? |
In series with the start winding. |
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(206) How is the addition of a capacitor in the start winding of a capacitor-start motor beneficial? |
It increases starting torque. |
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(206) Which percentage of full speed opens the centrifugal switch? |
75 percent of full speed. |
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(206) Which type of AC motor uses a capacitor in series in the start winding but no centrifugal switch? |
Permanent-split capacitor motor. |
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(206) In which devices are shaded-pole motors used? |
Small fans, timers, and various light-load control devices. |
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(206) What is the use of a shaded-pole motors used? |
It is used in place of a start winding. |
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(207) List the three kinds of repulsion-type commutator motors. |
1. Repulsion 2. Repulsion-start induction-run 3. Repulsion-induction |
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(207) What are the operating characteristics of a simple repulsion motor?
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High starting torque and low starting current draw. |
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(207) Which type of repulsion motors would provide power to conveyers, small compressors, and woodworking equipment?
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The simple repulsion motor. |
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(207) What purpose do the compensating windings in a repulsion-start induction-run motor serve? |
They improve the power factor during the starting period. |
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(207) Why does a repulsion-induction motor start as a repulsion motor?
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Because of the low rate of current flow in the squirrel-cage windings at low speed. |
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(207) What causes a repulsion-induction motor to operate as an induction motor? |
The increased current flow in the squirrel-cage windings when the motor reaches operating speed. |
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(207) What type of motor can operate on either AC or DC power? |
Universal motor. |
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(207) What factor determines the operating speed of a universal motor? Explain. |
The load. The motor operates at low speed with a heavy load and at a high speed with a light load. |
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(208) How many external leads are necessary for a single-voltage, non-reversible-type AC motor?
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Two (T1 & T2) |
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(208) To connect a dual-voltage motor for high voltage, the run winding must be connected how? |
In series |
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(208) How must the start winding be connected to the run windings? |
Parallel |
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(208) What leads are reversed to change the rotation of a single-phase reversible induction motor? |
Leads 5 and 8 |
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(209) List the two types of across-the-line AC motor controls. |
1. Manual 2. Magnetic |
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(209) What is a manual motor-control device? |
A device mechanically operated to control a motor from a single point. |
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(209) How are the overload devices connected in a three-phase manual controller? |
In series with each of the main contacts. |
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(209) What does the controller have that reacts to excess motor current? |
Overload device. |
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(209) The three-line terminals of a three-phase controller are labeled in what manner?
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L1, L2, L3 |
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(209) What is the purpose of a reduced voltage starter?
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To change the rotation of a motor. |
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(209) What type of reduced voltage starter uses taps?
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Autotransformer |
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(209) What type of starter uses a motor that has external motor connections? |
Star delta |
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(209) When are reversing starters used? |
When there is a need to change rotation frequently on three-phase motors. |
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(209) What should you do to change rotation on a three-phase motor? |
Change any two power leads. |
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(209) How many contactors are used with the reversing starters? |
2 |
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(209) What should you check first if you have a problem with the reversing starter?
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Check for power. |
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(209) What two meters do you use if you have a problem with the reversing starter?
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1. Voltmeter 2. Ohmmeter |
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(210) What are two main parts of an across-the-line magnetic starter? |
1. The contactor 2. The overload relay |
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(210) What part of the contractor attracts the armature? |
The operating coil. |
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(210) What is the purpose of the shaded ring on the stationary core of the armature? |
To prevent contract chatter. |
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(210) List the two basic types of overload relays. |
1. Thermal 2. Magnetic |
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(210) What are the two basic types of thermal overload relays? |
1. Bimetallic 2. Melting-alloy |
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(210) How can you find the full load current rating of a motor? |
By checking the motor data plate. |
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(211) List the two electrical circuits of the across-the-line magnetic starter. |
1. Load circuit 2. Control circuit |
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(211) What set of contacts keeps the holding coil energized after the start button has been released? |
Auxiliary contacts. |
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(211) How many overload relays must be installed on a three-phase magnetic starter? |
Three. Each ungrounded phase must have an overload device. |
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(211) List four automatic devices that control magnetic starters. |
1. Float switch 2. Pressure switch 3. Thermostat 4. Photoelectric cells. |
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(211) What is the function of the control circuit in a magnetic starter?
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It is the portion of the starter that starts, stops, controls, and protects the motor. |
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(212) To ensure trouble-free operation, list seven factors you should consider when selecting a motor.
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1. Physical location 2. Ambient temperature 3. Duty 4. Bearings 5. Voltage 6. Mechanical connection to load 7. Motor data plate. |
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(212) What type of motor enclosure is designed to prevent liquids or solids from entering it, except at indirect angles? |
Splash-roof |
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(212) What is the most commonly found ambient temperature rise of a motor?
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40 degree Celsius |
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(212) What type of bearings would you find on an electric motor mounted in a vertical position? |
Ball bearings or roller bearings
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(212) List six items found on the data plate of an electric motor. |
Any six of the following eight: 1. Marker's name 2. Rated volts and full load amperes 3. Rated frequency and number of phases 4. Rated temperature rise 5. Rated full load speed 6. Time rating 7. Code letter 8. Rated horsepower 9. Design letters |
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(212) A type 3 motor controller is used in what type of location? |
Outdoors (it can be exposed to the weather) |
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(213) List some of the items to look for when making a visual inspection. |
1. Excessive wear of gears, sprockets, and couplings, burned or overheated windings and bearings.
2. Frayed edges, or excessive wear of belts and pulleys. 3. Excessive temperature in the bearing area. |
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(213) What is the maximum air pressure that you can use to clean a motor? |
25 psi |
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(213) What could happen if a motor is lubricated improperly? |
Improper lubrication causes motor bearings to overheat and eventually causes bearing failure. Inadequate lubrication causes the bearings to wear excessively and, eventually, to cease operation. |
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(213) What wold you look for when checking the connections of a motor controller? |
Check all wiring for discoloration. Connections should be clean and tight. |
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(214) List five problems which many cause trouble in motors. |
1. Overload 2. Loss of power. 3. Driven machine blockage 4. Worn bearings 5. Bad connections |
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(214) What instrument should you use to determine current? |
An ammeter |
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(214) How can you repair openings in rotors caused by overheating? |
By using a soldering gun to restore the circuit. |
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(214) How can you determine if the drive of the machine is at fault? |
By disconnecting the motor from its load and rotating the rotor shaft of the motor by hand. |
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(214) How can you remove excessive end play in bearings? |
By adding fiber space washers. |
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(215) What are three common malfunctions of electrical circuits? |
1. Open circuits 2. Grounded circuits 3. Shorted circuits. |
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(215) Where may an open circuit exist in a three-phase motor? |
At any point between the power source and the rotor. |
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(215) Why is it sometimes necessary to disconnect the motor from the starter in a three-phase motor? |
To determine whether a ground exists in the motor or on the conduit. |
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(215) When must you check the motor windings for grounds? |
When the ground does not exist in the motor or on the conduit. |
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(215) How can you locate shorted circuits? |
By checking across conductors with the power off. |
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(215) What would indicate a short circuit between the main disconnect and the start?
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Continuity across any two conductors.
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(215) What would indicate a shorted stator in a wye-wound motor?
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Continuity between any combination of lead numbers other than those which form a winding.
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(215) How does an open circuit affect a single-phase motor with a squirrel-cage rotor?
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The motor slows down under a load; it will have low starting torque and signs of overheating.
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(216) Match the malfunctions. 1. Improper ventilation 2. Blown fuses 3. Power failure 4. Faulty relay 5. Open rotor 6. Deficient voltage supply 7. Dry motor bearings 8. Too frequent starting 9. Insecure mounting 10. Bad conductors 11. Faulty-driven machine 12. Voltage failure |
1. Motor will not start.
2. Motor will not start. 3. Motor stops running. 4. Motor stops running. 5. Motor runs slowly. 6. Motor runs hot. 7. Motor operates with excessive noise. 8. Motor runs hot. 9. Motor operates with excessive noise. 10. Motor will not start. 11. Motor runs slowly. 12. Motor runs slowly. |
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(217) What factor determines the class of a hazardous location? |
The use of the location |
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(217) Which class of hazardous location exists when large amounts of flammable gases are present in the air? |
Class I |
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(217) What class of hazardous location exists when ignitable fibers are present? |
Class III |
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(217) What does a Division 1 classification of a building denote? |
Danger is eminent at any or all times during the normal course of operation. |
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(217) What does a Division 2 classification of a building denote? |
Danger is not believed present under normal conditions, but is likely to arise from a reasonably foreseeable accidental occurrence. |
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(218) How can hazardous area electrical equipment be distinguishes from standard electrical equipment? |
Usually it is identified as explosion-proof, dustproof, or sparkproof; standard is not. |
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(218) Is equipment designed for Class 1 locations always recommend for other hazardous areas?
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No equipment designed for one class is not always designed for another hazardous class. |
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(218) What hazardous class requires the use of explosion-proof equipment?
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Class I |
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(218) Which class of hazardous equipment is designed to exclude ignitable amounts of dust from the enclosures?
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Class II |
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(218) Equipment used in Class III hazardous areas must have what sort of safety measure?
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It must be sparkproof. |
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(219) Why should most of a wiring system be located outside of a hazardous area? |
It saves labor and reduces the expense of electrical equipment located in the hazardous area. |
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(219) What type of conduit is needed in a Class I, division location installation?
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Rigid metal conduit, IMC, or type MI cable. |
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(219) Why must conduit in hazardous areas be wrench-tight?
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To minimize sparking when fault current flows. |
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(219) Where conduit enters hubs on boxes in Class 1 locations, at least how many full threads must be engaged?
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Five |
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(219) What fittings are installed to prevent the transfer of gases from one place to another in a hazardous area?
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Sealoffs |
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(219) What is the installation requirement for electrical equipment in Class II hazardous locations?
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It must be dust-ignition-proof. |
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(220) What must be done before servicing or disassembling equipment in a hazardous location?
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The supply circuit must be de-energized. |
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(220) What would happen to the system if you left a screw or bolt out of an explosion-proof box cover? |
It could render the equipment unsafe. |
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(220) Why should you take care when disassembling or assembling hazardous equipment? |
To keep from damaging the surfaces so they'll seal when put back together. |
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(220) How should you store covers and their mating bodies? |
Make sure covers are assembled to their mating bodies. |
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(220) What should you check when joining surface joints of enclosures together? |
Make sure foreign material has not accumulated on the surfaces. |
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(220) What should you use to remove corrosion products from threaded or flat-joint surfaces? |
Use solvents to remove the corrosion or discard |
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(220) What maintenance should you do if you find flexible cords mechanically damaged or deteriorating? |
Replace the flexible cords. |
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(220) When painting the exterior surfaces of equipment in hazardous locations, what should you avoid painting? |
The nameplate. |
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(220) If, during a preventive maintenance inspection, you find frayed or damaged insulation on conductors, what must you do to correct these problems? |
Tape, repair, replace or move the wires. |
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(220) Why should you correct loose connections when you find them in an inspection? |
To prevent excessive heat. |
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(220) What is usually a good indication of a poor connection? |
Corrosion around the connection. |
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(220) If a device fails to operate when an inspection maintenance check is being done, what should you do? |
Repair or replace it. |
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(221) How should you avoid spark hazards? |
Make every effort to eliminate hazardous conditions. When you must do work where you cannot eliminate spark hazards, make a safety engineering analysis. If the analysis shows unacceptable risk, develop and use precautions, procedures and tools to ensure a safe operation. |
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(221) What is a good lantern to use in a hazardous location?
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One that is powered by low-voltage, dry cell batteries and approved for use in the area. |
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(221) When should you use to treat equipment for troubleshooting in a hazardous location?
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Only when really necessary. Even then, it must be suitable for safe operation in that environment, especially considering ventilation requirements. |
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(221) Why should you remove hazardous material (when troubleshooting) in a hazardous location? |
To make repairs safely and because substances may be ignited. |
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(222) What happens when AC power is restored to emergency lighting systems? |
DC lights are turned off automatically. |
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(222) Name the four parts of the emergency light. |
1. Rechargeable battery. 2. Battery charger 3. Low-voltage incandescent floodlights 4. Test, monitoring, and control accessories |
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(222) Most emergency lights use a battery with how many volts? |
6 vdc |
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(223) In most cases, the battery in an emergency light can be recharged within how many hours? |
12 hours |
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(223) Each lamp of an emergency light sufficiently covers how many square feet? |
1,000 |
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(223) What purpose do exit lights serve? |
They provide a means of identifying the outside doors to a building. |
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(223) Why must exit lights be connected ahead of the main entrance switch? |
This allows the power to be shut off while the exit lights still work. |
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(223) If AC power fails, what is the requirement of the emergency power supply? |
It must be able to maintain at least 87 1/2 percent of the system voltage for at least 1.5 hours. |
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(223) What type of record must be kept on the test and maintenance of an emergency lighting system? |
Written |
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(223) How often should lead-acid batteries of the water-addition type be inspected? |
Monthly |
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(223) If, when inspecting a battery, you discover corroded battery terminals, what maintenance steps should you take? |
Wash battery terminals with a solution of baking soda and warm water. Apply a light coat of lubricant . |
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(223) How often should the battery in an emergency light be completely discharged and then recharged? |
About every 6 months. |
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(223) What should you do if the battery in an emergency light does not hold a charge? |
Replace it with the same type of battery. |
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(223) What should you do if the battery in an emergency light does not have a voltage output, what three items might be causing the problem? |
1. Bad fuse 2. Transformer 3. Diode or bridge rectifier |
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(223) A transfer relay is usually which type? What should you do if the relay stops operating? |
The plug-in type; insert a new one. |
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(224) What voltage(s) do commercial toasters use for operation? |
208, 220 or 240 volts. |
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(224) How is the temperature controlled on the heating element in the deep fat fryer? |
The thermostat controls the temperature of the element. |
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(224) What causes the heating element to heat up on an electric range? |
Electrical current passing thru the heating element. |
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(224) Elements on the electric range are supplied with what voltage? |
Either 120 or 240 volts. |
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(224) What type of heating element is often used on panel space heaters? |
Open coil type. |
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(225) What are the most common repairs of appliances? |
Burned out heating elements, motors, and switches.
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(225) What is the first check you should make to an inoperative appliance? |
Visual inspection |
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(225) What will you do to prevent unauthorized people from tampering with switches or fuses? |
Lock & tag switches, fuses, & other protective devices. |
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(225) What does a reading of "0" ohms indicate when you connect the ohmmeter leads to the element terminals of an electric range? |
A good element; continuity |
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(225) When replacing wire on an electric range, what type do you use? |
Heat resistance insulated wire. |
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(225) Using the Troubleshooting Guide for Electrical Ranges, what is the probable cause when a burner on an electric range gets too hot? |
Incorrect or reverse connections |
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(225) What troubles are usually found in panel heaters? |
Broken heating elements and faulty motors. |
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(225) What is the most common problem associated with water heaters? |
Open heating element |
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(225) What needs to be done after repairing the water heater and before you reenergize the appliance? |
Fill the tank with water |
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(225) What is used to quickly locate problems with the commercial dishwasher? |
Wiring diagrams |
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(226) What is a traffic signal controller? |
A complete timing mechanism that controls the sequence and duration of indications shown by traffic signals. |
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(226) What are the types of traffic signal controllers? |
Traffic adjusted and microprocessor controller. |
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(226) What are the basic parts of a microprocessor-based controller? |
Microprocessor chip, program memory, data memory, control and indication panel, input and output interfaces, and power supply. |
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(226) What is a traffic signal? |
A traffic signal is a complete installation including control mechanisms, signal head, and wiring. |
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(226) What is a cycle? |
The number of seconds for one complete sequence of signal indications (red-yellow-green). |
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(226) What is an interval? |
The portion of the signal cycle during which signal indications do not change. |
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(226) What is a traffic phase? |
A group of right-of-way and change intervals in a cycle assigned to any independent traffic movement. |
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(226) What are the two principles by which detectors operate? |
1. By detecting a mechanical force that causes the contacts on a switch to close. 2. By detecting a change in energy field caused by the motion of a vehicle. |
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(226) What are the most common types of detectors used for traffic control? |
Pressure and loop detectors. |
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(226) Loop detectors are made of what? |
A loop of wire buried beneath the surface of the road, attache to an electronic amplifier that is hooked to detector terminals in the controller. |
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(226) What type of systems does the controller operate? |
Loop and lead-in systems whose total inductance is between 20 and 70 microhenries. |
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(227) What reference materials and information should be available to reduce maintenance time? |
Wiring and equipment schematic diagrams, as-built drawings, manufacturer's technical data, system revision information, detailed information of controller settings, and a list of the major system parts with the manufacturers and model numbers. |
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(227) What type of checklist should you use to do preventive maintenance check on a traffic control system? |
One developed for your particular system. |
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(227) How often should you do a complete preventive maintenance check on a traffic control system? |
Every 6 months. |
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(227) What things should you check when doing preventive maintenance on installed traffic control systems? |
-Check to see that all detectors are operating -Make sure that the controller timing is correct -Check lamps for outages -Check the pavement around loop detectors -Check the fans on the controller cabinet |
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(227) How often should you do a complete preventive maintenance check on a traffic control system? |
Every month |
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(227) What type of repair is needed for faulty traffic control system detectors? |
Replacement with the same type of detector as removed. |
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(227) Most of the repair in the controller cabinet consists of what? |
Module or circuit board replacement. |
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(228) What are the four basic steps to troubleshooting any malfunction? |
1. Diagnosis 2. Sectionalization 3. Localization 4. Isolation |
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(228) What does the presence of output power at the power supply indicate? |
That input power is available and the power supply is working or good. |
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(228) How should you sectionalize a traffic control system problem? |
Check the outputs or returns of each section until you read an improper voltage. |
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(228) How should you localize a traffic control system problem? |
Divide the troubled section in half and determine which half of that section is in trouble. Then, split the troubled half of the section in half again and again until you reduce the point of the existing problem to a certain location or circuit. |
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(228) If needed, what is the procedure for isolation? |
Divide and redivide the circuit until only the bad component is left (divide and conquer). |
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(229) What are the two base warning systems found in the Air Force? |
1. 3-phase motor type 2. modulated, electronic siren types |
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(229) Explain the modulated, electronic siren system? |
An omnidirectional speaker system capable of producing a high-intensity warning signal covering a large area. |
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(229) Who activates the base warning system? |
The command post. |
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(230) How often do most installations test warning sirens? |
Once a month. |
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(230) Once sirens have primary power, what keeps them from sounding? |
The lack of a complete control circuit. |
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(230) What are general maintenance requirements with the modulated, electronic siren system? |
1. Speaker resistance test. 2. Defective component replacement. 3. Control module output. 4. Battery voltage test. |
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(230) What three areas should you look at when troubleshooting a base warning system?
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1. Control circuit 2. Primary circuit 3. Siren |
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(230) What are you looking for when you check the control circuit on the base warning system? |
Continuity |
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(230) What are some possible problems should you not have voltage on the load side of the controller?
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1. Contact point 2. Control circuit 3. Heater problems |
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(230) What are three common problems associated with the modulate, electronic siren system?
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1. No speaker output 2. Battery 3. Power problems or radio frequency problems. |
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(231) Define corrosion. |
Corrosion is the gradual destruction of a material by chemical or electromechanical means. |
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(231) List and explain the four components necessary for corrosion to occur. |
1. Anode- the metal or portion of metal that is corroded and from which the current leaves (enters electrolyte). 2. Cathode-the metal or portion of metal that the current enters. 3. Electrolyte-a solution capable of conducting electricity 4. Metal circuit-the circuit through metal or a conductor joining the two metals or areas of metal. |
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(231) Describe simple cell corrosion. |
Simple cell corrosion takes place where there is moist soil at one point of a substance and soil of a different moisture content at another point. |
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(232) The uniform corrosion of metal over the entire exposed surface is which kind of corrosion? |
General corrosion. |
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(232) Which type of corrosion occurs if two electrochemically dissimilar metal are metallically connected together? |
Galvanic corrosion. |
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(232) How many general types of soil have been characterized for corrosion properties? What is considered an "active" metal? |
50. One with a high negative potential. |
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(232) What type of corrosion occurs by electrochemical attack of a metal because of differences in the environment? |
Concentration-cell corrosion. |
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(232) What are some examples of corrosive soils?
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Merced (alkali) silt loam, Montezuma clay abobe, muck, and Fargo clay loam. |
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(232) What is caused when a surface is marred or scratched? |
It becomes anodic. |
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(232) What is the most severe form of corrosion? |
Stray current corrosion. |
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(233) How can corrosion be reduced and what is this process called? |
By reducing the anodic current leaving the structure. The process is called CP. |
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(233) Which type of current is used to control corrosion in CP? |
DC |
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(233) What are two basic methods of CP? |
1. Galvanic anode. 2. Impressed current. |
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(233) Why does the anode system require little maintenance? |
It has no power source and requires no regulation. |
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(233) How does an impressed current system provide CP? |
With an external DC power source. |
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(233) What is the power source for an impressed current system? |
Rectifier unit. |
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(233) What is the most commonly used anode material for the impressed current system? |
Graphite and high-silicone cast iron. |
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(233) How deep do you bury wiring when installing the anode? |
2 feet deep or deep enough to avoid damage from cultivation or erosion. |
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(233) How should the backfill be installed around the anode on an impressed current system? |
Extend at least 12 inches from each end of the anode and should surround it to a thickness of 3-4 inches. |
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(234) How should air-cooled rectifiers be maintained to permit free air circulation?
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Keep free of dust, brush, and grass. |
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(234) When should the oil-filled rectifiers be changed?
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When it becomes cloudy looking. |
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(234) What do heavily covered pits with a tight rust scale and dryness beneath the scale indicate? |
The pits have been sealed off and the corrosion has stopped or slowed down. |
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(234) What do pits, covered with moist tubercles or wet and showing bright metal when brushed out, indicate?
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The corrosion is active. |
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(234) How does protective coating aid in corrosion control?
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It physically separates a metal structure from the electrolytes. |
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(234) Where might the corrosion process be accelerated and for what reason on coated surfaces?
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Corrosion accelerates at bare, damaged spots in coated surfaces because current concentrates at small areas of bare metal. |
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(235) What information is provided on CP system records? |
A history of the system, including what, when and where it was installed, maintenance, and operability of the system. |
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(235) Where are changes in system design kept? |
TAB G-8 of the master plan. |
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(235) Where are the technical records on each installed CP system kept?
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In the corrosion engineer's posession. |
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(235) How are leaks causes by corrosion in a base pipeline system recorded?
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By placing a colored head pin at each point where there is a leak on a base map installed in the corrosion engineer's office. |
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(235) What does a visual inspection for corrosion of a metal structure reveal?
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The effectiveness of the CP system. |
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(235) How are potential surveys supplemented?
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With pipeline current tests. |
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(236) How can you determine if your protection is adequate? |
You measure your various potentials against the engineer's criteria. |
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(236) What voltage is measured between the structure surface and a saturated copper-copper half-cell contacting the electrolyte? |
Structure-to-electrolyte potential. |
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(236) In what position is the protective current when measuring for a minimum negative voltage criterion of 0.85 volt? |
The protective current is applied to the circuit. |
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(236) The protective current is in what position when measuring the 100-mV polarized voltage shift criterion? |
The protective current is turned off. |
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(236) When should corrosion activity cease on well-coated steel pipelines? |
When the entire structure is polarized to at least -0.85 volt. |
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(236) When is the 100-mV potential criterion commonly used? |
For uncoated and old pipelines. |
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(236) What are the maximums pipe-to-soil potential criteria for coated steel? |
-2.05 volts. |
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(237) What two purposes do electrical measurements serve in a CP system? |
1. How the system is functioning. 2. If it is providing adequate protection. |
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(237) When should a record of structure-to-soil measurements be initiated? |
When the structure CP system is first installed. |
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(237) Which is the most important measurement made in CP? |
Structure-to-electrolyte measurements. |
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(237) What two test instruments are use to measure CP? |
1. A high-resistance voltmeter. 2. A copper-copper sulfate half-cell. |
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(237) How is the equipment listed in the preceding question connected? |
The negative terminal of the voltmeter is connected to the structure and the positive terminal to the electrode of a copper-copper sulfate half-cell. |
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(237) What indicates whether or not the structure is adequately protected? |
The potential value from the voltmeter. |
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(237) What do sudden changes in potential indicate? |
Outside influences of failure of the CP system. |
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(237) What could give you an erroneous reading when taking structure-to-electrolyte potential readings? |
A high-resistance connection. |
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(237) What will an anode-to-electrolyte potential indicate? |
Which lead wire is attached to the anode. |
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(237) How is an anode-to-structure current measurement made? |
Insert an ammeter into the conductor between the anode and the structure. |
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(237) What is the most efficient method of measuring structure-to-electrolyte potentials under pavement? |
Install a permanent pavement insert. |
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(237) How can a leak in a pipeline system be detected without excavating the pipe? |
Structure-to-electrolyte measurements. |
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(237) What is provided in the CP system to make the electrical measurements more convenient?
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Test stations. |
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(237) What are the two methods of attaching conductors to the structure? |
1. Bolted welded. 2. Thermite welded. |
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(238) What does soil resistivity have to do with corrosion?
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The soil's ability to conduct or resist electricity is related to the rate of buried or immerses structure corrosion. |
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(238) How are most soil resistivity measurements taken? |
With a vibroground instrument. |
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(238) How can polarization and galvanic effects be overcome?
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By reversing the DC current or using an AC meter. |
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(238) How is water resistivity determined? |
By its inverse characteristic, conductivity. |
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(238) How is the soil box method used to measure soil resistivity?
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It measures the resistivity of a small sample of electrolyte. |
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(238) How are soil resistivity measurements used for new systems?
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In galvanic anode systems, soil resistivity measurements are used to determine how many and where anodes are needed; in impressed current systems, measurements are used to calculate the resistance of the groundbed. |
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(239) How often are electrical measurements made on galvanic anode systems the first year of use? After the first year?
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Quarterly; annually |
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(239) What is the primary measurement to be made on galvanic anode systems?
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Structure-to-electrolyte potential. |
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(239) The records from structure-to-electrolyte measurements can be used what? |
To determine the level of protection and trend of changes in protection. |
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(239) What is the purpose of anode-to-electrolyte measurements?
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To check lead continuity, anode condition, and location. |
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(239) In anode-to-electrolyte potential measurements, where is the peak potential measured?
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Over the anode. |
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(239) When are structure-to-anode measurements taken?
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At the same time structure-to-electrolyte measurements are taken (annually). |
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(239) How often are the rectifiers in impressed current systems inspected?
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Bimonthly (60 days) |
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(239) What potentials must be selected each year in the rectifier system?
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The point of maximum potential and three points of minimum potential. |
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(239) Where is the location of these points recorded?
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In section 9 of AF Form 491. |
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(239) How often are the meters in the rectifier units calibrated?
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Annually. |
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(240) What will the potential value read if the protection is good in a galvanic anode system?
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-0.85 volt. |
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(240) What does a value nearer zero indicate in a galvanic anode systems?
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Partial protection and may indicate that the leads to one or more anodes are broken, or the anodes are used up. |
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(240) What does a sharp drop in potential at a particular point on the structure indicate in galvanic anode systems?
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There is a leak on the structure. |
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(240) What is the simplest way to troubleshoot the rectifier unit in the impressed current system?
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Follow the flow of electricity through the unit. |
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(240) What should be done to the rectifier unit before checking internal components for heat and loose connections? |
Turn off the rectifier by throwing the AC circuit breaker and the outside disconnect switch. |
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(240) If not output voltage is shown on the rectifier meter and there is input voltage but no output voltage and all terminal connections are tight, what is the problem? |
The stacks may be defective and should be checked for opens or shorts. |
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(240) What would cause the anode bed resistance to increase slowly over a long period of time? |
Gas blockage or dry soil; or the anodes may need to be replaced. |
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(240) List the most frequent impressed current system troubles.
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1. Blown fuses 2. Loose terminals 3. Lightning damage 4. Faulty meters 5. Open-circuit breakers |
