250A - 250A Series

Series: 250A Questions? Contact Littelfuse Support
Littelfuse Voltage Monitoring Relays
The 250A is a 3-phase, auto-ranging, dual-range voltage monitor that protects 190-480VAC, 50*/60Hz motors regardless of size from low and high voltage, unbalance/single-phase, and reverse-phase. The product provides a user selectable nominal voltage setpoint and the voltage monitor automatically selects between the 200V and 400V range. The 250A also features adjustable or manual restart delay.


This unique microcontroller-based voltage and phase-sensing device constantly monitors the 3-phase voltages to detect harmful power line conditions. When a harmful condition is detected, the Littelfuse’s output relay is deactivated after a specified trip delay. The output relay reactivates after power line conditions return to acceptable levels. The Model 250A includes advanced single LED diagnostics. Five different light patterns distinguish between faults and normal conditions.

Property (Mouseover for details) Value
Input Voltage (V) 190 to 480VAC
Maximum Input Power 5W
Input AC Line Frequency (Hz) 50/60Hz (50Hz will increase all delay timers by 20%.)
Output Form DPDT - 2 Form C
Output Load Rating (VA) Pilot Duty: 480VA @ 240VAC B300; General Purpose: 10A @ 240VAC
Restart Delay Range Manual 2 - 300s adjustable
Trip Delay Range Under/Over Voltage: 4s; Unbalance Phasing Faults: 2s
Trip Point Accuracy (%) ±1%
Overvoltage Trip Voltage (%) 110%
Overvoltage Reset Voltage (%) 107%
Undervoltage Trip Voltage 90%
Undervoltage Reset Voltage (%) 93%
Voltage Unbalance Trip Point (%) 6%
Voltage Unbalance Reset (%) 4.50%
Termination Type Torque: 7in-lbs; Wire: 12-18AWG
Mounting Method #8 screws
Operating Temperature -40° to 70°C (-40° to 158°F)
Humidity Up to 95% non-condensing per IEC 68-2-3
Dimensions 2.93 in H x 5.27 in W x 2.95 in D (94.4 x 133.9 x 74.9 mm)
Weight (lbs/g) 1.02 lb. (16.3 oz. 462.7 g)