All electric motors have a lifespan, and to keep them running efficiently and safely they must be protected. One of the main causes of failure is electrical overload, sometimes called overcurrent. When a motor draws more current than it is designed to handle it causes the temperature to build-up resulting in overheating. This damages motor windings and coils. It is important to protect the motor and its circuit, and this is where the use of contactor overload relays can help.RS offer an extensive range of high-quality contactor overload relays from leading industry brands including Schneider Electric, Siemens, ABB, Eaton, Lovato, and Rockwell Automation.
Overload is where a motor draws a high current above its rated value for an extended amount of time. Overload causes overheating of the motor causing damage. To prevent this from happening devices such as contactor relays are specifically designed for industrial control motor protection. They are used with contactors as part of a motor starter or in a control panel or centre.
The motor protection devices can be classified into two main types which are thermal types and electronic types.Thermal overload relaysUtilise a bi-metallic plate located near a heating element. When excessive current is passed through the heating element N/C (Normally Closed) contacts switch over and opens contacts. This interrupts power from flowing to the contactor's control circuit. Thermal overloads usually offer an adjustable current range as well as a manual or automatic reset option.Electronic RelaysElectronic overload relays don't have a bi-metallic mechanism, Instead, they work by using components such as temperature sensors to measure the load current. They are generally more accurate than thermal devices and they usually have a wider current range, a selectable trip class provides enhanced trip protection against single phasing against the motor.