An overcurrent relay cuts power to a circuit or machine if it detects an overload or fault. It consists of a switch and a current sensing relay, with a delay feature to handle high current draws. It prevents damage, explosions, and electric shocks. It can be standalone or integrated, with adjustable current settings and time delay functions. It should be investigated before resetting after tripping.
An overcurrent relay is an electrical protective device designed to cut power to a circuit, appliance, or machine in the event of an overload or fault. These devices typically consist of a manual switch or contactor and a current sensing relay that interlocks with it. If the appliance or circuit is damaged or overloaded, it will begin to draw current in excess of its normal operating parameters. This causes the current sensing relay to trip the circuit breaker or trip the contactor and cut the power. Because many machines draw a very high current when they start up, most overcurrent relays have a built-in “delay” feature to handle a high current draw for a set period before activating.
An overloaded or damaged electrical appliance or machine draws current which gradually begins to increase until it exceeds the design parameters of the device. If left unchecked, this causes further damage and eventual destruction of the machine. It can also cause an explosion or fire and poses a serious risk of electric shock to operators. One of the most effective ways to prevent this is an overcurrent relay in the primary power circuit. This device is designed to interface with a power switch or contactor, thereby shutting off the power if excessive current draw is detected.
These relays can be stand-alone units or integral parts of the primary power switching devices they work with. Some features set current ratings while others have a user-adjustable range of current settings. Self-contained relays may have removable current sensing coils on each phase or line which can be replaced with units of different current ratings. In the case of circuit breakers protected by overcurrent relays, a trip requires the circuit breaker to be switched back on when power is restored. Contactor relays typically cut power to the contactor tripping coil in the event of an overcurrent and must be reset before the machine or appliance can be restarted.
Many variants of overcurrent relays include time delay functions that allow excessive current consumption for a predetermined time before the power trips. This feature is designed to suit machines with high starting current ratings. Delay settings allow the machine to start and its current consumption to return to normal without activating the relay. When an overcurrent relay trips, it is always advisable to investigate the cause before resetting the system and restarting it to prevent possible damage or injury to the operator.
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