Description : When troubleshooting motor controllers, a shorted relay or contactor coil is often indicated by _______________. A. a resistance reading of 'infinity' on an ohmmeter B. charred insulation and/or a blown ... of the coil's leads to ground D. a higher-than-normal voltage reading across the winding
Last Answer : Answer: B
Description : The winch shown in the illustration operates in any of the positions with the master switch in the 'lower' direction, but will not 'hoist' in any of the master switch hoist positions. Which of the listed faults ... '2M' in the power circuit may be badly corroded. D. Series relay 'FR' may be open.
Last Answer : Answer: A
Description : During its operation, loud buzzing and resultant welding of contacts of a magnetic relay may be caused by __________. A. overheating of the contactor coil B. low voltage on the operating coil C. low insulation resistance to ground D. lubrication of the contact bearing points
Description : Which of the following statements represents the main difference between a relay and a contactor? A. Contactors control current and relays control voltage. B. A relay is series connected and a contactor ... loads than relays. D. Contactors are made from silver and relays are made from copper.
Last Answer : Answer: C
Description : A variable shunt, connected across the series field coils of a DC compound wound generator, to permit adjustment of the degree of compounding, is called a _____________. A. divider B. diverter C. converter D. rheostat
Description : Which component is responsible for energizing solenoid 'B1-B2' and releasing the brake for the winch motor shown in the illustration? EL-0102 A. Contactor '3M' B. A spring not shown in the schematic diagram C. Resistor 'B2-R1' D. Relay 'FR-B.O.'
Description : Magnet chatter or 'pumping' occurring in a magnetic contactor can be caused by ______________. A. dirt or grease on pole faces B. mechanical interference in the contacts C. chattering contacts on the control relay D. magnetic lock out of the contacts
Description : A circuit is protected from overheating by a/an ___________. A. pyrometer B. thermal overload relay C. magnetic contactor D. overload transformer
Description : The devices marked 'T' in the illustration are _____________. EL-0080 A. trouble alarm units whose contacts activate when problems arise either on starting or stopping of the motor B. topping ... contactor parts whose contacts start and stop the defrosting cycle of the compressor driven by the motor
Description : When an operating motor is connected to the controller shown in the illustration, the a path of current flow through the circuit is ____________. EL-0010 A. 'L1', stop button, start button, coil 'CR', 'L2' B. 'L1' ... L2' D. 'L1', stop button, start button, 'CR' contact, 'M' contact, 'CR' coil, 'L2'
Description : Regarding an AC generator connected to the main electrical bus; as the electric load and power factor vary, a corresponding change is reflected in the generator armature reaction. These changes in ... . governor speed droop setting B. voltage regulator C. balance coil D. phase-balance relay
Description : In the illustration shown, coil 'MR' is a ____________. EL-0012 A. running contactor coil B. rupture (blowout) coil C. resistance coil D. reversing coil
Description : The winch shown in the illustration will not operate in any speed in the lowering direction and at an abnormal speed in 'first point hoist'. The possible cause is that _______________. EL-0102 A. ... '1M' in the power circuit are badly corroded D. master switch contacts 'MS6' have weak springs
Description : The illustrated motor fails to start and gives a loud hum when the start button is depressed, your first action should be to __________. EL-0007 A. disassemble the motor to fix the centrifical ... D. hold the 'M' contactor closed by hand while wearing electrical safety gloves to get motor started
Description : If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. will continue to operate B. will probably burn out immediately C. will operate on reduced current D. temperature will drop
Description : The 'safe switch' of the winch controller shown in the illustration is operated _______________. EL-0102 A. through the master switch handle B. when heater circuit current is high C. by contactor coil 'FR' D. manually by the winch operator
Last Answer : Answer: D
Description : If a magnetic controller contactor fails to pick up when the coil voltage is applied to the contactor coil, the cause may be _____________. A. overload B. misalignment of the affected contactor contacts C. low spring pressure D. an open contactor coil
Description : If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. temperature will drop B. will probably burn out immediately C. will continue to operate D. will operate on reduced current
Description : A shading coil used in an AC magnetic controller, functions to _____________. A. reduce vibration and noise in the contactor B. prevent flux buildup in the operating coil C. eliminate arcing when the contacts close D. energize the operating coil and 'pull in' the contacts
Description : Why shading rings provided in armature core of ac contactor. Why not for dc contactor?
Last Answer : Because the force developed is not steady in ac therefore contacts will chatter but if shading ring is used force developed becomes steady due to splitting of phases of flux, therefore contacts becomes bounce free and humming sound reduces.
Description : Can we use AC contactor in DC circuit?
Last Answer : Yes, but with adequate de-rating.
Description : If a transformer is connected to a DC source, the transformer will overload at the ____________. A. contacts B. primary coil C. secondary coil D. core
Description : The simplest method of controlling the terminal voltage of compound-wound DC generator is with a _____________. A. hand-operated field rheostat connected in series with the shunt field circuit B. ... in series with the load D. balance coil diverting neutral current through the shunt field
Description : When the series field relay "FR" of the winch circuit shown in the illustration is energized during dynamic braking the _______________. EL-0102 A. shunt Field Relay "FR-B.O." is de-energized and contacts ... . shunt Field Relay "FR-B.O." opposes the series coil's flux and sets the mechanical brake
Description : Air gap readings should be taken periodicly on electrical generation equipment to __________. A. determine the amount of varnish that can be applied to correct insulation problems B. determine the ... field coil bolts and correct lateral adjustment of the field coils D. increase machine efficiency
Description : Excessive humming of AC contactors may be caused by ______________. A. burnt arc shields B. shorted armature coils C. a broken shading coil D. high voltage
Description : If coil 'R1-R2' on the transmitter in figure 'A' shown in the illustration is turned 30 degrees clockwise, corresponding coil 'R1-R2' on the receiver should ____________. EL-0092 A. make coils 'S1 ... a higher voltage depending on the turns ratio D. align itself to the same position if free to move
Description : Shading coils are installed on AC full-voltage starters to _____________. A. eliminate contact chatter B. dissipate opening contact arcs C. delay current build up in the holding coil D. protect the motor windings from momentary starting current overload
Description : A low voltage source is being used for testing armature coils. A coil short circuit will be indicated by a _______. A. high voltage reading, while the other coil readings will have an ... the other coil readings are steady D. steady voltmeter reading, while the other coil readings are fluctuating
Description : When using a megohmmeter to determine which shunt field coil is grounded in a DC machine, you must ____________. A. insulate the field frame from the ship's hull B. disconnect each shunt ... C. use a motor driven high capacity megohmmeter D. remove all main line lead connections before testing
Description : Which of the following statments is true of the illustrated motor controller? EL-0023 A. The low speed is used for starting the motor and when the controller automaticly shifts to High speed. B. The HOL relay ... D. If the overload relay opens for high speed the motor can still be run in low speed.
Description : What is a relay? How is it different from a magnetic contactor?
Last Answer : Contactor is a heavy duty switch whereas the relay is light duty switch. Relays can be as simple as 12 V DC solenoids with 12 V, 0.5 A rated contacts. They are used to detect faults on the power system and signal a local or remote switching device (breaker) to trip the circuit.
Description : What is the difference between relay and contactor?
Last Answer : Relay have smaller ratings. Contactor is a high rating relay.
Description : Coil of relay is connected to the A. input of op-amp B. output of op-amp C. midpoint of op-am D. anywhere in between input and ouput of op-amp
Last Answer : output of op-amp
Description : A synchronous motor maintains synchronism with the rotating field because _____________. A. field strength varies directly with rotor slip B. DC current applied to the rotor coils causes the rotor ... the flux created by the excitation current D. the stator flux rotates in the opposite direction
Description : Which of the following precautions should be taken when troubleshooting various power circuits using a common solenoid-type mechanical voltage tester (wiggins)? A. Never use this tester on circuits greater ... voltage expected in the circuit in order to prevent damage from an off-scale reading.
Description : Can we use ac coils in dc circuit?
Last Answer : Yes with economy resistor in series.
Description : The schematic diagram shown in the illustration uses symbol 'A' to represent a/an _________. EL-0011 A. non-renewable fuse link B. circuit breaker coil C. overload relay coil D. thermal overload heater
Description : Which of the listed procedures is the best way to tell if a motor has become overloaded? A. Measure the current flow and compare it with the motor full load current flow as shown on the nameplate. ... Watch for telltale signs of smoke coming from the motor. D. Periodic opening of the O/L relay coil
Description : The motor starts when the start button in the illustration is pushed, but stops when the button is released the trouble is _________. EL-0007 A. the incorrect thermal overload coil B. a faulty 'M' coil C. a dirty contact on the Disc.Sw. at 'L3' D. a faulty holding relay contact
Description : The contacts operated by the D.C. relay coil shown in the illustration are located in the schematic diagram prints at coordinates ____________. EL-0100 A. '41Y' on this page B. '52M52M' and '52H35M' C. '57R' on this page D. '52N' on page '57R'
Description : The vertical dotted line connecting the small circular symbols at coordinates '05L', '09L', '13L', '21L', '25L', etc., shown in the illustration, indicate that all _______________. EL-0100 A. contacts are ... board 'TB2' C. wires are grounded at both ends of the line D. wires have a common shield
Description : When troubleshooting a motor controller, all indications are that a relay coil should be energized. If there were no magnetic pull, with rated voltage measured across the coil, the most probable cause ... open C. auxiliary contact in series with the coil is defective D. relay armature is stuck
Description : The devices located at coordinates '49W' in the illustration represents a/an _________. EL-0100 A. A.C. motor B. A.C. relay coil C. D.C. motor D. D.C. buzzer
Description : The device at coordinates '63/1' in the illustration represents a/an _____________. EL-0100 A. A.C. buzzer B. A.C. motor C. D.C. motor D. D.C. relay coil
Description : Power necessary to operate the horn shown in the illustration _____________. EL-0093 A. comes from each station's magneto B. is supplied from a 115 volt source C. is conducted through a relay coil D. also lights lamps 'R' and 'T'
Description : A loud buzzing noise in an AC controller is probably caused by _____________. A. poor contact with the overload relay B. an incorrectly sized heater C. a broken shading coil D. abnormal starting current
Description : If a magnetic controller relay fails to drop out when the coil voltage is removed from the relay, the probable cause may be _____________. A. excessive spring tension B. overvoltage C. excessive current D. welded contacts
Description : Low voltage releases as used in some shipboard motor starter and control equipment will have which of the following characteristics? A. They trip circuit contactors when the motor starts to overspeed. B. ... coil of the starter. D. They allow the motor to restart upon restoration of normal voltage.
Description : 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? A. Overspeed trip B. Thermal overload relay C. Three-pole safety switch D. Magnetic blowout coil