What does a thermal overload relay do?
Thermal overload relays are economic electromechanical protection devices for the main circuit. They offer reliable protection for motors in the event of overload or phase failure.
How do you reset a thermal overload relay?
When set in the H or HAND position the RESET button must be pressed manually to reset the overload relay after a tripping event. On the other hand, when set in A or AUTO position, the overload relay will reset automatically after a tripping event.
How often should a thermal overload be reset?
The automatic or manual reset function time varies but for general applications a 2 to 3 minute reset time can be expected. After this time period, the normally closed trip contact can be re-closed and starting of the motor contactor coil can be achieved by the control scheme used with the motor starter.
What are two types of thermal overload relay?
Thermal overload relays are classified into two types namely solder pot as well as a bimetal strip.
What causes a thermal overload to trip?
Short circuits can be caused by wires overheating and the insulation melting, or by accidents where the insulation is stripped away or the wire is cut by a metal object and shorted to ground. A short circuit will draw current above the overload and surge ratings and cause the relay to trip.
What are the two major types of thermal overload relays?
There are three types of thermal overload relays — bimetallic, eutectic, and electronic. Bimetallic thermal overload relays (sometimes referred to as heater elements) are made of two metals, with different coefficients of thermal expansion, that are fastened or bonded together.
What is 95 and 96 on a contactor?
The contact 95-96 is used to control the load contactor. The overload relays have a setting scale in Amperes, which allows the direct adjusting of the relay without any additional calculation.
What is the purpose of thermal overload protection at the motor?
The thermal protection is present to turn the motor off when excessive heat is generated within the motor circuitry. This safety feature halts the temperature climb before it can burn up the motor.
What is the principle of thermal relay?
The basic working principle of thermal relay is that, when a bimetallic strip is heated up by a heating coil carrying over current of the system, it bends and makes normally open contacts.
What are the two types of thermal overload relays?
What causes an overload relay to trip?
If the current rises above a certain limit over a certain period of time, then the overload relay will trip, operating an auxiliary contact which interrupts the motor control circuit, de-energizing the contactor. This leads to the removal of the power to the motor.