More Information about the Thermal Overload Relays

Thermal overload relay is considered protective devices. if the motor draws too much current for an extended period of time, they are designed to cut power. A normally closed (NC) relay is present in thermal overload relays to accomplish this. Due to sensed overload current, relay temperature, or increased motor temperature, the relay opens when excessive current flows through the motor circuit depending on the relay type.

in construction and use, Thermal overload relays are similar to circuit breakers but if overload occurs even for an instant, they interrupt the circuit. Most circuit breakers differ in this. To measure a motor’s heating profile, Thermal overload relays are designed conversely; therefore, before the circuit is interrupted, overload must occur for an extended period.

Type

Between several different kinds of relays, Buyers may choose including bimetallic temperature control, solid-state, or thermal types.

Bimetallic thermal relays use a bimetallic strip as their name implies to mechanically open the contacts. Expanded at different rates, bimetallic strips consist of two conjoined pieces of metal when exposed to heat. When heated, this difference makes the strip bend. The strip is attached by a spring to contact in a thermal relay. The circuit is broken and the contacts are pulled apart when excess heat from over current causes the strip to pull and bend the springs. It then returns to its original shape when the strip is cooled.

Having no moving or mechanical parts, Solid-state relays are electronic devices. As compared to electromechanical ones, Solid-state relays tend to be faster. Adjustable trip times and set points are also featured by these. They can be used in explosive environments as they are incapable of generating a spark.

A motor’s temperature is sensed directly by the Temperature control relays using a resistance thermal device (RTD) or thermistor probe embedded in the motor winding. Its resistance increases rapidly when the nominal temperature of the probe is reached.

A mechanical mechanism, a eutectic alloy, and a heater coil are present in a melting alloy overload relay that consists of breaking the circuit. By monitoring the amount of current drawn, the electronic thermal overload relay measures the motor’s temperature using the heater coil.

Electrical Rating

Control voltage, trip information, current range, and phase are included in Relay electrical specs.

To describe the circuit interrupting the action of circuit breakers and overload relays, Tripping is used.

A range of current values for a relay to be set is known as full load current range. A full load current rating for that particular motor will be included in a motor’s rating plate. To match the value on the rating plate, the relay’s full load current point must be set in order for the thermal overload relay to trip.

Relays designed to measure temperature instead of current, such as temperature control or solid-state relays have Temperature trip range used in them.

The maximum time, in seconds, is known as the Trip class. Before tripping, a fuji electronic thermal overload relay can withstand 6 times its current rating.