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    1ELECTRIC MOTOR CONTROLSOnce the proper motor is selected, understanding the many various control devices available andtheir uses and limitations becomes an important part related to reliable operation and protection ofthe motor and the personnel using the motor.Motor Control TopicsThere are fou...

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    2MOTOR STARTINGAll motors must have a control device to start and stop the motor called a “motor controller”.Motor ControllerA motor controller is the actual device that energizes and de-energizes the circuit to the motor sothat it can start and stop.•Motor controllers may include some or a...

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    3Figure 26. Manual StarterThere are two different types of common “across the line” starters including1. Manual Motor Starters2. Magnetic Motor StartersManual Motor StartersA manual motor starter is package consisting of a horsepower rated switch with one set of contactsfor each phase and ...

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    4Figure 27. Magnetic Starterof contacts that energize and de-energize the circuit to the motor along with additional motoroverload protection equipment.CMagnetic starters are used with larger motors (required above 10 horsepower) or wheregreater motor control is desired. •The main element of ...

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    5•Reduced voltage starting may be required when:SThe current in-rush form the motor starting adversely affects the voltage drop on theelectrical system.Sneeded to reduce the mechanical “starting shock” on drive-lines and equipment whenthe motor starts.•Reducing the voltage reduces the cur...

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    6MOTOR PROTECTIONMotor protection safeguards the motor, the supply system and personnel from various operatingconditions of the driven load, the supply system or the motor itself.CMotor protection categories includeSOvercurrent ProtectionSOverload ProtectionSOther Types of Protection.•The Natio...

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    70 100 200 300 400 500 600 Full Load Amps (%)0 1 2 3 4 5 6 7 8 9 10 11 12 Time (Minutes)Motor Heating CurveMotor DamageAllowable Operation AreaAmperageTimeMotor Current DrawMotor Running CurrentStarting In-Rush CurrentOverload ProtectionOverload protection is installed in the motor circuit and/or...

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    8Other Motor Protection Devices Low Voltage ProtectionLow Voltage Disconnects - Protection device operates to disconnect the motor when the supplyvoltage drops below a preset value. The motor must be manually restarted upon resumption ofnormal supply voltage.Low Voltage Release - Protection devi...

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    9Circuit overcurrent protection devices must be sized to protect the branch-circuit conductors andalso allow the motor to start without the circuit opening due to the in-rush current of the motor.National Electrical Code ProceduresUse the NEC motor current tables to find the design Full Load Curr...

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    100.01 0.1 1 10 Time (seconds)0 500 1000 1500 2000 Amp Rating (%)Standard Fuse ResponseStandard (Non-Time Delay, Single Element) FusesStandard fuses protect against short circuits and ground faults using thermal features to sense a heatbuildup in the circuit. Once blown standard fuses are no lon...

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    110.1 1.0 10.0 100.0 1000.0 Time (seconds)0 500 1000 1500 2000 Amp Rating (%)Time Delay Fuse ResponseTime-Delay (Dual Element) FusesThese are generally dual element fuses with both thermal and instantaneous trip features that allowthe motor starting current to flow for a short time without blowin...

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    130.0 0.1 1.0 10.0 100.0 1000.0 10000.0 Time (seconds)0 100 200 300 400 500 600 Amp Rating (%)Inverse CB Trip CurveThermal ActionMagnetic ActionInverse Time Circuit BreakersInverse time circuit breakers have both thermal and instantaneous trip features and are preset to tripat standardized levels...

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    140.01 0.1 1 10 Time (seconds)0 500 1000 1500 2000 Amp Rating (%)Instantaneous Trip CB10 X Rating3 X RatingInstantaneous Trip Circuit BreakersInstantaneous trip circuit breakers respond to immediate (almost instantaneous) values of currentfrom a short circuit, ground fault, or locked rotor curren...

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    15prohibits settings above800% if the motor willstart and run up to speedat or below a setting of800%.

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    16Motor Overload ProtectionMotors larger than 1 horsepower must be provided separate motor overload protection devices.CThe most common devices typically used include:1) magnetic or thermal overload devices2) electronic overload relays3) fusesMagnetic & Thermal OverloadsOverload devices ar...

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    17Thermal Overload RelaysA thermal overload relay is an electro-mechanical relay that is operated by heat developed in therelay.CWhen the level of current in a circuit reaches a preset value, the increased temperature opensa set of contacts.CThe increased temperature opens the contacts through a ...

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    18Automatic Reset DevicesAutomatic reset is an advantage where the starter is inaccessible and the motor is provided threewire control from a magneticstarter.CThis control doesn’t allowthe motor to restart untilthe start push button ismanually pushed.CThis permits the overloadcondition to be re...

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    191 10 100 1000 Trip Time (Seconds)0 200 400 600 800 1000 1200 Rated Current (%)Heater Trip CharacteristicsOverload Trip TimeThe time it takes an overload to trip depends on the length of time the overload current exists.•A Heater TripCharacteristics chart showsthe relationship between thetime ...

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    20Sizing Motor Overload ProtectionThere are several types of devices that can be used to provide overload protection and the sizingprocedure can vary depending on the type of device used.CIt is important to keep differences in the procedures separate and understood well so as not toinstall overlo...

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    21The size overloads required to protect the windings of a motor can be determined by taking themotor’s full-load current rating and selecting the size overloads from the cover of a magnetic starter,a motor control center, or the manufacturer’s catalog.CThe following things should be kept in ...

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    2260 70 80 90 100 110 120 130 140 Rated Current (%)20 40 60 80 100 120 140 160 Ambient Temperature (F)Heater Ambient Temperature CorrectionStandard Rating, 40 C60 70 80 90 100 110 120 130 140 Rated Current (%)20 40 60 80 100 120 140 160 Ambient Temperature (F)Ambient Temperature CorrectionStandar...

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    23Sizing Motor Protection SystemsGiven the following motor, size the conductors, motor overcurrent and motor overloads toadequately protect the motor and conductors.Nameplate Info:FLA = 22Service Factor = 1.00Ambient = 40 CSTEP 1: Determine the motor’s FLA (full load amps)CGo to the appropriate...

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    24The maximum branch circuit overcurrent device size is calculated based on the type of protectivedevice selected (standard fuse, time-delay fuse, instantaneous breaker, inverse time breaker) andpercentage multiplier from NEC Table 430-152. CMultiply the motors design FLA by the appropriate perce...

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