What are the materials made of thermal overload relay? How OLR are selected?

What are the materials made of thermal overload relay? How OLR are selected?
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Answer :

The bimetallic materials are Invar and brass. These materials having the differential coefficient of expansion. All bimetallic relays incorporate additional built in single phasing protection. The range of the relay provided for the feeders are such that the full load rating of the feeders is comfortably within the range of the relay (range will be at Centre) except in very minimum loads ranging from 0.1 – 0.16 A. 
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Related questions

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 : 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

Last Answer : Answer: D

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 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

Last Answer : Answer: D

A circuit is protected from overheating by a/an ___________. A. pyrometer B. thermal overload relay C. magnetic contactor D. overload transformer

Description : A circuit is protected from overheating by a/an ___________. A. pyrometer B. thermal overload relay C. magnetic contactor D. overload transformer

Last Answer : Answer: B

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

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

Last Answer : Answer: B

Protection against sustained overloads occurring in molded-case circuit breakers is provided by a/an __________. A. overvoltage release B. thermal acting trip C. thermal overload relay D. current overload relay

Description : Protection against sustained overloads occurring in molded-case circuit breakers is provided by a/an __________. A. overvoltage release B. thermal acting trip C. thermal overload relay D. current overload relay

Last Answer : Answer: B

How does a thermal overload relay work?

Description : How does a thermal overload relay work?

Last Answer : The bi-metallic strip in the relay heats up by the over load current and the movement in the bi-metallic strip causes the breaker to trip. The breaker has to be reset (turn off) before turning on ... delay for the bi-metallic strip to cool down after which the breaker can be reset and switched on.

Why OLR time set high for belt driven fans?

Description : Why OLR time set high for belt driven fans?

Last Answer : Because acceleration time is high.  

What are the characteristics of CB, OLR and HRC Fuse?

Description : What are the characteristics of CB, OLR and HRC Fuse?

Last Answer : When CB is used the CB characteristics should be below the fuse, because the CB should operate first and then fuse. Not vice-versa. Because CB is the main protection or main breaking device.  

A loss of field excitation to an AC generator while operating in parallel will cause it to ____________. A. absorb more and more load due to decreased armature reaction B. lose its load due to the inherent speed droop built into the governor C. smoke and overload due to field flashover as residual field flux changes polarity D. lose its load, begin to motorize, trip out on reverse power relay, and possibly overspeed

Description : A loss of field excitation to an AC generator while operating in parallel will cause it to ____________. A. absorb more and more load due to decreased armature reaction B. lose its load due to ... polarity D. lose its load, begin to motorize, trip out on reverse power relay, and possibly overspeed

Last Answer : Answer: D

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Description : The purpose of the reverse power relay, provided on a ship's service alternator panel, is to trip the circuit in the event of ______________. A. main circuit overload B. high power transfer C. generator overspeeding D. alternator motorization

Last Answer : Answer: D

'A-1', as shown in the illustration, is/are ____________. EL-0017 A. normally-closed overload relay contacts B. a double pole knife switch C. normally-open overload relay contacts D. a single pole knife switch

Description : 'A-1', as shown in the illustration, is/are ____________. EL-0017 A. normally-closed overload relay contacts B. a double pole knife switch C. normally-open overload relay contacts D. a single pole knife switch

Last Answer : Answer: A

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 : 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

Last Answer : Answer: C

The purpose of a magnetic relay is to _____________. A. open a circuit only in the event of overload B. remotely open and close contacts C. provide overcurrent protection during starting D. relay voltages at increased power

Description : The purpose of a magnetic relay is to _____________. A. open a circuit only in the event of overload B. remotely open and close contacts C. provide overcurrent protection during starting D. relay voltages at increased power

Last Answer : Answer: B

Which of the motors for the devices listed below is fitted with an instantaneous overload relay? A. Fan B. Pump C. Winch D. Machine tool

Description : Which of the motors for the devices listed below is fitted with an instantaneous overload relay? A. Fan B. Pump C. Winch D. Machine tool

Last Answer : Answer: C

What is the difference between an auto reset and manual reset overload relay?

Description : What is the difference between an auto reset and manual reset overload relay?

Last Answer : a. Auto reset relay closes its contacts when the bimetallic strip gets cooled. In manual reset relay we have to manually reset the relay because even though bimetallic strip cools its contacts are not ... . Manual over load relay is reseted by pushing the reset button provided on the MCC cell. 

If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of wood C. inject small amounts of CO2 into the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents

Description : If overloading a DC machine becomes necessary in an emergency, you should ____________. A. cool the machine with portable blowers and fans B. hold thermal overload relays open with blocks of ... the windings for cooling D. increase the residual magnetism value of windings to reduce eddy currents

Last Answer : Answer: A

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 switch so the start windings will be energized B. push the stop button to deenergize the 'M' coil C. reset the thermal overload D. hold the 'M' contactor closed by hand while wearing electrical safety gloves to get motor started

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

Last Answer : Answer: B

In the illustration, 'D' is the symbol for a/an __________. EL-0005 A. thermal overload heater B. portable cable C. fuse D. indicating lamp

Description : In the illustration, 'D' is the symbol for a/an __________. EL-0005 A. thermal overload heater B. portable cable C. fuse D. indicating lamp

Last Answer : Answer: C

The arc resulting from the tripping of a circuit breaker is prevented from damaging the contacts by _____________. A. designing the contacts to open slowly B. directing the arc into an arc chute C. an inverse timed thermal trip for short circuit currents D. instantaneous magnetic trip for overload currents

Description : The arc resulting from the tripping of a circuit breaker is prevented from damaging the contacts by _____________. A. designing the contacts to open slowly B. directing the arc into an ... an inverse timed thermal trip for short circuit currents D. instantaneous magnetic trip for overload currents

Last Answer : Answer: B

Fuses placed in series with a thermal trip-type circuit breaker are used for _____________. A. time-delay protection B. short-circuit protection C. short duration surge protection D. sustained overload protection

Description : Fuses placed in series with a thermal trip-type circuit breaker are used for _____________. A. time-delay protection B. short-circuit protection C. short duration surge protection D. sustained overload protection

Last Answer : Answer: B

The main difference between a motor control circuit containing low voltage protection and low voltage release is that the latter contains _____________. A. a magnetic operating coil B. normally open line contacts C. thermal-overload protection D. a momentary-contact start button

Description : The main difference between a motor control circuit containing low voltage protection and low voltage release is that the latter contains _____________. A. a magnetic operating coil B. normally open line contacts C. thermal-overload protection D. a momentary-contact start button

Last Answer : Answer: D

What is an overload relay?*

Description : What is an overload relay?*

Last Answer : What is an overload relay?*

Explain the construction and working of electronic overload relay.

Description : Explain the construction and working of electronic overload relay.

Last Answer : Electronic overload relay consists of a solid state circuit that operates the electromagnetic switching device to protect the load from overload. The load current is sensed by using a current ... sections. The output of relay driver section sends trip signal to electromagnetic switching device.

A relay used for protection of motors against overload is :

Description : A relay used for protection of motors against overload is :  (A) Impedance relay (B) Electromagnetic attraction type (C) Thermal relay (D) Buchholz's relay

Last Answer : D

In Frame Relay, when. ______ is selected, it requires establishing andterminatingphases A) a PVC B) an SVC C) either (a) or (b) D) neither (a) nor (b)

Description : In Frame Relay, when. ______ is selected, it requires establishing andterminatingphases A) a PVC B) an SVC C) either (a) or (b) D) neither (a) nor (b)

Last Answer : an SVC

In Frame Relay, when a _____ is selected, the correspondingtable entry is recorded for all switches by the administrator A) PVC B) SVC C) either (a) or (b) D) neither (a) nor (b)

Description : In Frame Relay, when a _____ is selected, the correspondingtable entry is recorded for all switches by the administrator A) PVC B) SVC C) either (a) or (b) D) neither (a) nor (b)

Last Answer : PVC

Thermal overload relays are used to protect the motor against over current due to (a) short-circuits (b) heavy loads (c) grounds (d) all of the above

Description : Thermal overload relays are used to protect the motor against over current due to (a) short-circuits (b) heavy loads (c) grounds (d) all of the above

Last Answer : (b) heavy loads

Overload relays are of...... type. (a) induction (b) solid state (c) thermal (d) electromagnetic (e) all above

Description : Overload relays are of...... type. (a) induction (b) solid state (c) thermal (d) electromagnetic (e) all above

Last Answer : (e) all above

A thermal protection switch can protect against (a) short-circuit (b) temperature (c) overload (d) over voltage

Description : A thermal protection switch can protect against (a) short-circuit (b) temperature (c) overload (d) over voltage

Last Answer : (c) overload

Thermal overload relays are used to protect the motor against over current due to?

Last Answer : Thermal overload relays are used to protect the motor against overcurrent due to heavy loads.

Where automatic restart does not present a hazard after a power failure, Coast Guard Regulations (46 CFR) require motor controllers for auxiliaries vital to the propelling equipment to be provided with ________________. A. overload protection B. low voltage protection C. low voltage release D. reverse current protection

Description : Where automatic restart does not present a hazard after a power failure, Coast Guard Regulations (46 CFR) require motor controllers for auxiliaries vital to the propelling equipment to be provided ... overload protection B. low voltage protection C. low voltage release D. reverse current protection

Last Answer : Answer: C

Which of the following statements is true concerning the motor controller diagram shown in the illustration? EL-0023 A. Terminal 'T2' is hot only on high speed. B. Both indicating lights will be lit on both high and low speeds as they are connected to the common lead when the motor is running. C. Overload protection is provided for high speed operation only. D. 'L2' is always connected to 'T2' whenever the motor is running.

Description : Which of the following statements is true concerning the motor controller diagram shown in the illustration? EL-0023 A. Terminal 'T2' is hot only on high speed. B. Both indicating lights will be lit on ... high speed operation only. D. 'L2' is always connected to 'T2' whenever the motor is running.

Last Answer : Answer: D

If a DC motor runs faster than designed, with all other conditions being normal, the possible cause could be a/an ______________. A. shorted shunt field coil B. open armature coil C. reversed commutating pole D. overload

Description : If a DC motor runs faster than designed, with all other conditions being normal, the possible cause could be a/an ______________. A. shorted shunt field coil B. open armature coil C. reversed commutating pole D. overload

Last Answer : Answer: A

Component F in the illustrated device is for _________. EL-0033 A. short circut protection B. latching the trip unit closed after resetting the breaker C. overload protection D. providing a flexible connection between the input terminal G and the tripping unit E

Description : Component F in the illustrated device is for _________. EL-0033 A. short circut protection B. latching the trip unit closed after resetting the breaker C. overload protection D. providing a flexible connection between the input terminal G and the tripping unit E

Last Answer : Answer: C

In the illustrated motor controller, the motor fails to start. A voltmeter reading between 1 and 6 reads line voltage, while the voltmeter reading between 2 and 6 reads 0 VAC. The problem is __________. EL-0007 A. the control fuse is the wrong amperage not allowing full current to pass through B. the stop switch is open C. an open in the 'M' coil, 'Ma' contact/start switch or overload contacts D. fuse '10a' is blown

Description : In the illustrated motor controller, the motor fails to start. A voltmeter reading between 1 and 6 reads line voltage, while the voltmeter reading between 2 and 6 reads 0 VAC. The problem is __________. EL- ... in the 'M' coil, 'Ma' contact/start switch or overload contacts D. fuse '10a' is blown

Last Answer : Answer: B

In the illustration if the compressor fails to start but the condenser fan motor is running the problem is _______. EL-0042 A. no power between L1 and L2 B. the yellow wire is open at the freezer temperature control switch C. the overload is open D. the blue wire from the defrost heater is open

Description : In the illustration if the compressor fails to start but the condenser fan motor is running the problem is _______. EL-0042 A. no power between L1 and L2 B. the yellow wire is open at the freezer temperature control switch C. the overload is open D. the blue wire from the defrost heater is open

Last Answer : Answer: C

If a synchronous motor begins to vibrate severely and pull out of synchronism, the cause may be ____________. A. an overload B. an open in the field coils C. no exciter voltage D. all of the above

Description : If a synchronous motor begins to vibrate severely and pull out of synchronism, the cause may be ____________. A. an overload B. an open in the field coils C. no exciter voltage D. all of the above

Last Answer : Answer: D

An overload in which of the listed motors will result in the illumination of an indicating light at the propulsion control station alarm panel? A. Fuel pump motor B. Steering motor C. Condensate pump motor D. Forced draft blower motor

Description : An overload in which of the listed motors will result in the illumination of an indicating light at the propulsion control station alarm panel? A. Fuel pump motor B. Steering motor C. Condensate pump motor D. Forced draft blower motor

Last Answer : Answer: B

In the illustration if the compressor fails to start but the condenser fan motor is running the problem is _______. EL-0043 A. no power between L1 and L2 B. the yellow wire is open at the freezer temperature control switch C. the overload is open D. the blue wire from the defrost heater is open

Description : In the illustration if the compressor fails to start but the condenser fan motor is running the problem is _______. EL-0043 A. no power between L1 and L2 B. the yellow wire is open at the freezer temperature control switch C. the overload is open D. the blue wire from the defrost heater is open

Last Answer : Answer: C

In the illustration, the purpose of part B is to _________. EL-0033 A. increase resistance in series with the contacts as they close to prevent arcing B. create a magnetic field in the steel plates that interacts with the arc to cool and extinguish the arc C. cause the contacts to open in the event of an overload D. provide ventilation to the contact when the breaker is close to rated capacity

Description : In the illustration, the purpose of part B is to _________. EL-0033 A. increase resistance in series with the contacts as they close to prevent arcing B. create a magnetic field in the steel ... event of an overload D. provide ventilation to the contact when the breaker is close to rated capacity

Last Answer : Answer: B

During maintenance of circuit breakers, _______________. A. always smooth roughened contact surfaces with a file B. never pass more than rated breaker current through the overload heater element C. inspect for wear and misalignment of main contacts D. assume heater elements installed are of correct size

Description : During maintenance of circuit breakers, _______________. A. always smooth roughened contact surfaces with a file B. never pass more than rated breaker current through the overload heater element C. ... wear and misalignment of main contacts D. assume heater elements installed are of correct size

Last Answer : Answer: C

The 'reset' contacts of the master switch shown in the illustration provides the winch controller with ___________. EL-0102 A. low voltage release B. overload protection C. low voltage protection D. high power factor correction

Description : The 'reset' contacts of the master switch shown in the illustration provides the winch controller with ___________. EL-0102 A. low voltage release B. overload protection C. low voltage protection D. high power factor correction

Last Answer : Answer: C

If the motor fails to start and a voltmeter reading between 1 and 6, as illustrated, indicates line voltage, your next step should be to ________. EL-0007 A. replace fuse '10a' B. replace or repair contact 'Ma' C. reset and determine the cause of the overload D. check line voltage between L1 and L3

Description : If the motor fails to start and a voltmeter reading between 1 and 6, as illustrated, indicates line voltage, your next step should be to ________. EL-0007 A. replace fuse '10a' B. replace or repair contact 'Ma' C. reset and determine the cause of the overload D. check line voltage between L1 and L3

Last Answer : Answer: C

When power is restored after a complete power failure, a steering gear pump motor will ____________. A. have to be restarted B. have to be reset C. restart automatically D. trip its overload relays

Description : When power is restored after a complete power failure, a steering gear pump motor will ____________. A. have to be restarted B. have to be reset C. restart automatically D. trip its overload relays

Last Answer : Answer: C

As shown in the illustration, 'S' is the __________. EL-0017 A. safety switch B. overload trip C. start button D. stop button

Description : As shown in the illustration, 'S' is the __________. EL-0017 A. safety switch B. overload trip C. start button D. stop button

Last Answer : Answer: D