IEC Electronic Overload Relays
The electronic overload relay is a basic, but very important component in motor protection. It protects electric motors against overloads, excessive heat, and phase loss. Electric overload relays are wired into the circuit that controls the motor and monitor the motor current. If the current exceeds safe tolerable amounts or if there's an abnormal condition present (such as two consecutive half-cycles of increasing current), the relay will trip. When it trips, it interrupts power to the motor, thus protecting both people and equipment from what could become a serious situation.
Electronic overload relays are adjustable and offer many types of protections. They can sense when a motor's phase currents and/or voltages are approaching or have exceeded certain thresholds. Adjustable settings let the relay be tailored to any given set of operating conditions or protected motor. Many different protection functions are built into EORs, including overload protection (OCP), phase imbalance protection (PICCO), ground fault protection (GFCI-like), and phase loss protection (VPC). So, depending on how you look at it, EORs address multiple simultaneous fault conditions for motor protection that is quite a bit more straightforward than designing a circuit that will work safely in all these half-dozen scenarios.
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