The 777 is a fully programmable electronic overload relay designed to protect any motor drawing 2-800 full load amps (external CTs are required above 90 amps). The 777 (family of products) is for 3-phase 200-480VAC applications, with several specialized units for other voltage ranges and unique applications. Common applications include conveyor systems, HVAC equipment, saws and grinders, fan motors, and almost any pumping application.
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Mounting Options
Littelfuse enhanced overload relays can be surface mounted or DIN rail mounted, providing flexibility in limited-space environments.
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Built-in Current Transformers
Littelfuse enhanced overload relays feature built-in current transformers (CTs), providing protection for motors drawing 2-90 Amps. If external CTs are added, the overload relay will provide protection for motors drawing up to 800 Amps.
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Finger Safe Terminals
Littelfuse enhanced overload relays feature finger-safe terminals, protecting you from dangerous high voltages.
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Communications Port
Littelfuse enhanced overload relays come equipped with a communications port for use with remote monitors, software, and I/O modules.
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MODE SELECT Dial
The MODE SELECT dial points at the overload relay setting to program. To view an overview of each setting, simply click on the desired setting.
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DISPLAY/PROGRAM Dial
The DISPLAY/PROGRAM dial is used for dual purposes. When the MODE SELECT dial is not pointed at RUN, the DISPLAY/PROGRAM dial can be used in conjunction with the RESET/PROGRAM button to program setting. When the MODE SELECT dial is pointed at run, the DISPLAY/PROGRAM dial is used to display real-time operating parameters. Click on each parameter for a detailed description.
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RESET/PROGRAM Button
The RESET/PROGRAM button serves many useful purposes. If the MODE SELECT dial is not pointed at the RUN position, the RESET/PROGRAM button is used in conjunction with the DISPLAY/PROGRAM dial to program the overload relay. Otherwise, the RESET/PROGRAM buton is used to reset the overload relay (when running) or display the last fault.
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#RU/ADDR Setting
The #RU/ADDR is a dual function setting. #RU is the number of restarts allowed after an undercurrent trip condition before the overload relay requires a manual restart. ADDR is the RS-485 address of the overload relay.
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RD3 Setting
The RD3 setting is the restart delay (in minutes) used after an undercurrent trip. It is typically used as a dry-well recovery timer in pumping applications. This setting varies widely from application to application.
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RD2 Setting
The RD2 setting is the restart delay (in minutes) used when the unit has shut off due to a current unbalance, current single phasing, or an overload condition. This timer known as a motor cool-down timer and is usually set to 5-10 minutes.
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RD1 Setting
The RD1 setting is the rapid-cycle timer in seconds. This timer is initiated when power is first applied to the overload relay. Often this is set to 20-30 seconds to provide protection for successive power outafes or short cycling caused by other motor controls. The RD1 timer is also engaged when the motor shuts off.
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Trip Class Setting
The trip class is the parameter used to determine when the overload relay will trip when an overload condition is detected. For standard motors, the trip class is typically set at 20. Please reference the installation instructions for more details.
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Current Unbalance Setting
The current unbalance setting determines the maximum current unbalance the overload relay will allow. The current unbalance setting is factory set at 7%. Littelfuse recommends contacting the motor manufacturer be contacted for an exact setting.
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Undercurrent Setting
The undercurrent setting determines the minimum current the overload relay must see before initiating a trip delay timer. An undercurrent setting of 80% of the motor's full-load amperage is usually sufficient for most applications.
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Overcurrent Setting
The overcurrent setting determines the maxium phase current the overload relay will allow before initiating its trip delay timer. The overcurrent setting is typically set at the service factor amperage of the motor.
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#RF/COM Setting
The #RF/COM setting is a dual function setting. #RF is the number of restarts allowed after a current unbalance, current single phasing, or an overload condition before the overload relay requires a manual restart. The COM setting are RS-485 communication settings.
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Undercurrent Trip Delay
The undercurrent trip delay setting determines the amount of time (in seconds) the overload relay will allow the motor to run in an undercurrent situation before de-energizing its relay.
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Ground Fault Setting
The ground fault setting determines the maximum allowable current which can flow to ground before the overload relay de-energizes its relay.
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Run Mode
While in run mode, the LED display will show the value of the parameter determined by the display/program dial. For example, if the display/program dial is pointed at VUB, the LED display will show the real-time voltage unbalance.
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Low Voltage Setting
The low voltage setting is the minimum voltage the overload relay must see before it closes its normally open contacts. The low voltage setting is often set to 90% of the motor's nameplate voltage.
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High Voltage Setting
The high voltage setting is the overload relay's maximum allowable voltage at which it will close its normally open contacts. The high voltage setting is often set to 110% of the motor's nameplate voltage.
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Voltage Unbalance Setting
The voltage unbalance setting determines the maximum voltage unbalance the overload relay will allow. The voltage unbalance setting is factory set at 6%.
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Multiplier Setting
Littelfuse overload relays can support currents 2 - 800 Amps (external CT's may be required). The multiplier setting is determined by the current the unit will be monitoring and affects the UC, OC, and GF settings.
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L1 - L2 Voltage
Displays the line-to-line voltage between L1 and L2.
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L2 - L3 Voltage
Displays the line-to-line voltage between L2 and L3.
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L3 - L1 Voltage
Displays the line-to-line voltage between L3 and L1.
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VUB
Displays the voltage unbalance.
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A Current
Displays the phase A current.
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B Current
Displays the phase B current.
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C Current
Displays the phase C current.
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CUB
Displays the current unbalance.
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Ground Fault Current
Displays the ground fault current.