Automatic motor protection unit: what it is, features, application

The electric motor - the most expensive element of many types of household and industrial equipment. It needs protection to extend its service life. When motors are activated, overloading occurs most often at start-up. Motor overheating occurs if the device is jammed or it is running in excess. The motor protection automat detects the overload current or short circuit and shuts down the motor within a few milliseconds.

Features of the automatic motor protection

The automatic motor protection circuit breaker is mounted in the electrical circuit that supplies single-phase and three-phase equipment. It consists of several parts, which have their own purpose.Various elements of the automatic motor protection device react to possible malfunctions:

• electromagnetic release device triggers on a short circuit;
• The bimetal plate opens the circuit if the overheating of the motor is detected.

Automatic motor protection circuit breakers of the block type have the following features:

• robust housing, which does not get damaged for a long time;
• High class overload protection;
• Current adjustment option according to the motor rating;
• there is protection against dust, vibration and overheating;
• protection in case of voltage surges;
• Can be controlled remotely or manually.

The peculiarity of the automatic motor protection switch is that it not only blocks the current supply to the motor, but also serves as a starting device. In it, the contacts are protected by a special winding that extinguishes sparks. Therefore, the device can make several thousand starts. An ordinary circuit breaker would only be able to withstand a few dozen starts.

Automatic motor protection switches vary in design. There are models with pushbuttons or rotary levers. They have screw terminals or spring-loaded terminals. Some devices have a «test» button that allows you to check how the protection works.

Application of an electric motor protection circuit breaker

To choose the right automatic motor protection device, take into account that the value of the starting current should not be higher than the one that causes the instantaneous activation of the equipment. The permissible ratio of inrush current to rated current is given in the data sheet of the electrical appliance. The maximum value is 7/1. There are tables, according to which you can choose a suitable automatic unit for electric motor protection, which are provided by the manufacturers.

Automatic motor protection switch - one of the main elements that protect the motor and other elements of the equipment from breakdown. It works in conjunction with other sensors, soft starters, overload relays. You can also install a device status indicator, an emergency contact, etc. To protect all the devices and sensors in the electrical circuit, the automatic motor protection unit is installed before the other elements of the system. Such protection is necessary not only during intensive operation of the equipment, but also during power failures and sudden changes in voltage in the network.