The overload relay is wired in series with the motor, so the current that flows to the motor when the motor is operating also flows through the overload relay. It will trip at a certain level when there is excess current flowing through it. This causes the circuit between the motor and the power source to open.
How does an overload relay work?
Overload relays protect a motor by sensing the current going to the motor. … When current is too high for too long, heaters open the relay contacts carrying current to the coil of the contactor. When the contacts open, the contactor coil de-energizes, which results in an interruption of the main power to the motor.
How does the overload relay protect the motor?
Overload protection relays prevent motor damage by monitoring the current in the motor circuit and breaking the circuit when an electrical overload or a phase failure is detected. Since relays are much cheaper than motors, they provide an affordable way of protecting motors.
How is motor overload detected?
Overload Protection Test:
- Measure the normal motor running current (i motor).
- Turn off the motor and let it cool for about 10 minutes.
- Calculate the following ratio: i (motor) / i (overload min FLA). …
- Set the overload to its minimum FLA and turn on the motor.
- Wait for the overload to trip.
What must be done before a motor overload can be reset?
the overload relay cannot be reset until the overload heater has cooled. The overload relay is reset by first turning the starter all the way off and then turning it back on.
How do I know if my overload relay is bad?
Give the compressor a shake if the start relay isn’t plugged in. If you hear rattling on the inside of the start relay, it’s time to replace it. You may have a problem with the actual compressor if it’s not rattling and in good condition.
Do all motors need overload protection?
EVERY motor needs overload protection of some type. Some small motors are impedance protected by design. Some motors can be overload protected by breakers or fuses. Some motor have internal temp probes that shut down the motor starter.