Electrical Installation33.11 Dynamic Braking Option, Motor ProtectionYASKAWA SIEPC71061753A GA500 Technical Manual 973.11 Dynamic Braking Option, Motor Protection◆ Install an Electromagnetic Contactor (MC) at the Input Side of the DriveYou can use an MC as an alternative to a molded case circuit breaker (MCCB) when:• The protective functions of the drive have been triggered• An emergency stop occurred, and the sequence de-energizes the drive.If an MC on the input side of the drive (primary side) stops the drive, regenerative braking will not operate, andthe drive will coast to stop.NOTICE: When you connect electromagnetic switches or magnetic contactors to the output motor circuits, make sure that yousequence them correctly. If the output motor circuit sequence is incorrect, it can cause damage to the drive.NOTICE: The drive can fail if users frequently turn the drive ON and OFF with the MC on the power source side to Run andStop the drive. Incorrect operation can decrease the service life of the relay contacts and electrolytic capacitors. If youfrequently use the magnetic contactor on the power source side to Run and Stop the drive, it can cause drive failure.Note:• When machinery must not restart after recovery from a momentary power loss that occurred during run, install an MC at the input sideof the drive and set a sequence that does not automatically set the Run command to ON after recovery of power.• When it is necessary to stop momentary power loss, for example to maintain a circuit that has momentary power loss, use a delayed-release MC.• Use an MC (magnetic contactor) to make sure that you can fully remove power to the drive when necessary. Wire the MC to openwhen a fault output terminal is triggered.■ Protect the Braking Resistor/Braking Resistor UnitUse an MC on the input side (primary side) to prevent damage to the braking resistor/braking resistor unit.WARNING! Fire Hazard. When you use a braking unit, use a thermal relay on the braking resistors and set a fault contactoutput for the braking resistor unit to disconnect drive main power through an input contactor. Incorrect braking circuit protectioncan cause the resistors to become too hot and cause serious injury or death.◆ Install a Thermal Overload Relay on the Drive OutputA thermal overload relay disconnects the power line to the motor during a motor overload condition to preventdamage to the motor.Install a thermal overload relay between the drive and motor in these conditions:• When operating more than one motor from one drive.• When operating the motor directly from the power line with a power line bypass.When operating one motor from one drive, it is not necessary to install a thermal overload relay. The drive haselectronic motor overload protection in the drive software.Note:• When you install a thermal overload relay, set parameter L1-01 = 0 [Motor Overload (oL1) Protection = Disabled].• Set up a sequence that will trip an external fault (coast to stop) for the contacts of the thermal overload relay.■ General Precautions When Using Thermal Overload RelaysWhen you use a motor thermal overload relay on the drive output to prevent nuisance trips and overheating of themotor at low speeds, be sure to think about these application precautions:• Operation of a low speed motor• When you operate more than one motor with one drive• Length of the motor cables• Nuisance tripping because of high drive carrier frequencyOperation of a Low Speed MotorUsually, you use thermal overload relays on general-purpose motors (standard motors). When a drive drives ageneral-purpose motor, the motor current is approximately 5% to 10% more than with a commercial powersupply. When a motor with a shaft-driven fan operates at low speeds, the cooling capacity decreases. This cancause the motor to overheat when the load current is in the motor rated value. Enable the electronic thermalprotection in the drive when possible to prevent this problem.The electronic thermal overload function uses the relation between the speed and heat characteristics in thevariable speed control range to simulate the cooling ability of general-purpose motors and forced-vented motors toprevent damage to the motor.
