FUNCTION -5 (ELECTRICAL)

180. Regarding battery charging rooms, ventilation should be provided
     1. at the lowest point of the room
     2. horizontally near the batteries
     3. at the highest point of the room
     4. only when charging is in progress

ANS.: C

181. The main difference between an electron tube and a transistor is the
     1. type of function they can perform
     2. reaction of electron flow through a gas or vacuum in a transistor
     3. reaction of electron flow through a semiconductor when placed in a tube
     4. reaction of electron flow through a semiconductor used to form a transistor

ANS.: D

182. A generator has been exposed to water and is being checked for its safe operation. Therefore, it is necessary to
     1. check for shorted coils with a growler
     2. take moisture readings with a hydrometer
     3. test insulation values with a megger
     4. ground the commutator, or slip rings and run it at half load for 12 hours

ANS.: C

183. Before testing insulation with a meg ohmmeter, the windings of large machines should be grounded for about 15 minutes just prior to test, because the
     1. static charge of the machine may give a false reading
     2. armature will have a greater number of leakage paths
     3. insulation may be damaged
     4. insulation may be covered with moisture

ANS.: A

184. In a DC series circuit, all the conductors have the same
     1. power expended in them
     2. voltage drop across them
     3. resistance to current flow
     4. current passing through them

ANS.: D

185. A three-phase induction-type motor experiences an open in one phase. Which of the listed automatic protective devices will prevent the machine from being damaged?
     1. overspeed trip
     2. thermal overload relay
     3. three-pole safety switch
     4. magnetic blowout coil

ANS.: B

186. Most three-phase induction motors used for driving engine room auxiliaries are started by
     1. resistor starters
     2. across-the-line starters
     3. impedance starters
     4. reactor starters

ANS.: B

187. When electrical cables penetrate watertight bulkheads,
     1. they should be grounded on either side of the bulkhead
     2. they must be bent to a radius of six diameters
     3. a watertight stuffing tube capable of accepting packing should be employed
     4. they should be secured by a clamp

ANS.: C

188. Across-the-line starters are used with AC motors to provide
     1. reduced starting current
     2. regulated starting current
     3. high starting torque
     4. controlled starting acceleration

ANS.: C

189. Most conductive materials such as copper, aluminum, iron, nickel
     1. increase in resistance with increased temperature
     2. increase in resistance with decreased temperature
     3. decrease in resistance with increased temperature
     4. decrease in resistance with decreased temperature

ANS.: A

190. The electrician reports to you that he has obtained low (but above 1 megohm) megger readings on the windings of a deck winch motor. Upon checking the records of that motor, you find the readings have consistently been at the same level the last six years. You should, therefore, recommend that the
     1. motor be replaced
     2. windings be dried
     3. windings be cleaned
     4. readings are acceptable

ANS.: D

191. Line losses in a distribution circuit are kept to a minimum by
     1. adding rubber insulation conductors to the circuit
     2. using higher current and lower voltage
     3. increasing the number of thermal relays in the circuit
     4. using higher voltage and lower current

ANS.: D

192. Adding resistance in series with the field winding of a DC shunt motor without a load, will cause the motor speed to
     1. increase
     2. decrease
     3. remain the same
     4. fluctuate rapidly

ANS.: A

193. The function of the compensating windings used in a DC generator is to
     1. prevent cross-commutation
     2. increase armature coil strength
     3. increase field strength
     4. neutralize armature reaction

ANS.: D

194. Capacitors are used on the output of the power supply in today’s consoles to
     1. filter out “ripple”
     2. prevent overloads
     3. act as a permanent load
     4. decrease the average value of the output voltage

ANS.: A

195. The purpose of a motor under voltage protection device is to
     1. prevent high armature current when power is restored
     2. start the motor at a very low voltage
     3. trip the load off the motor in case of fire
     4. protect personnel from low voltage shocks

ANS.: A

196. In testing a three-phase delta winding for an open circuit using a meg ohmmeter, you must
     1. test each phase with all connections intact
     2. measure the voltage across the open connections while testing
     3. test the windings as parallel groups to avoid short circuiting
     4. open the delta-connections to avoid shunting the phase being tested

ANS.: D

197. The direction of rotation of an induction motor is
     1. opposite to the rotating field
     2. the same as the direction of the rotating field
     3. determined by the number of poles
     4. determined by the staggering of the brushes

ANS.: B

198. mercury filled thermometers should never be used to determine the temperature of the battery electrolyte because accidental breakage of the thermometer can cause
     1. severe sparking and explosions
     2. rapid oxidation of battery plates
     3. contamination of the electrolyte
     4. corrosion on the battery terminals

ANS.: A

199. The purpose of a main switchboard circuit breaker’s revers-power trip is to
     1. prevent main circuit overload
     2. protect the circuit breaker blowout coil
     3. prevent alternator motorization
     4. prevent low voltage trip out

ANS.: C

200. When charging lead-acid batteries, the charging rate should be reduced as the battery nears its full charge to
     1. prevent damaging battery plates
     2. allow equalization of cell voltages
     3. reduce lead sulfate deposits
     4. increase lead peroxide formation

ANS.: A

201. Regarding an induction motor, the power developed by the rotor automatically adjusts itself to
     1. power required to drive the load
     2. speed required to drive the load
     3. current flow in the motor stator
     4. torque developed by the rotating field

ANS.: A

202. The purpose of a magnetic relay is to
     1. open a circuit only in the event of overload
     2. remotely open and close contacts
     3. provide overcurrent protection during starting
     4. relay voltages at increased power

ANS.: B

203. A semiconductor is a material with a
     1. conductivity higher than a normal conductor
     2. conductivity higher than a normal insulator
     3. high conductivity at low temperatures
     4. low conductivity at high temperatures

ANS.: B

204. The winding resistance of a coil can be increased by _______ the number of turns or using a ______ wire.
     1. increasing, thicker
     2. decreasing, thicker
     3. increasing, thinner
     4. decreasing, thinner

ANS.: C

205. The most common source of excitation for synchronous motors is a/an _____________.
     1. low voltage battery
     2. motor attenuator set
     3. DC exciter generator
     4. AC supply

ANS.: C

206. On an engine throttle control system, the aux control circuits are provided with devices to prevent excessive over travel of the pilot valve by the synchronous motor these devices are called.
     1. overlap sensor
     2. limit switch
     3. over travel relay
     4. proximity switch

ANS.: B

207. The speed of the squirrel cage induction motor is determined by
     1. Dia of stator
     2. No of stator poles
     3. Rotor winding resistance
     4. Bar resistance of conducting rotor

ANS.: B

208. The method used to produce electron emission in most vacuum tubes is known as
     1. Photo electric emission
     2. Secondary electric emission
     3. Cold cathodic electric emission
     4. Thermionic emission

ANS.: D

209. A reverse current relay prevents dc generator motorization automatically by option
     1. Redirecting up prime mover,
     2. Securing the exciter generator,
     3. Tripping the circuit breaker.

ANS.: C

210. Di-electric constant of ____ is 3.6
     1. Water
     2. Paper
     3. Electrolyte
     4. Air

ANS.:B

211. RMS value of a sine wave current is expressed as
     1. Average value,
     2. Max value
     3. Effective value
     4. Instantaneous value

ANS.: C

212. Which of the following statements comparing transistors and vacuum tubes is correct?
     1. Both transistors and vacuum tubes have a cathode that must be heated to give off electrons.
     2. A vacuum tube must have a heated cathode, where transistors do not.
     3. Neither transistors nor vacuum tubes require heat for electrons to flow.
     4. The anode of both transistors and vacuum tubes must be heated to give off electrons.

ANS.: B

213. Electric and electro-hydraulic steering gear motors are required by Coast Guard Regulations (46 CFR) to be _________.
     1. protected by a circuit breaker set at 125% and a thermal overload device
     2. provided with a running motor overcurrent protection device
     3. served by a single two conductor cable
     4. served by two feeder circuits

ANS.: D