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            Difference of smart motor protector and thermal relay

            Release time:2018-12-27 Times of browsing:

              The development of motor protection device is also integrative with the development of technology. Now, the widely used motor is developed from traditional thermal relay, and the thermal relay as the traditional protection device is still widely used.
              So, what is the difference between intelligent motor protector and thermal rely in application?
              The thermal relay has a single function, and it has the defects of poor repeatability and inability to be used again after the failure of large current. However, it is widely used due to its low price and simple structure.
              The intelligent motor protector has various functions compared with thermal relay, and can be used repeatedly, the action is sensitive and the measurement accuracy is high. However, the price of smart motor protector is relatively higher than other motor protection devices., and the initial purchase cost of adopting the smart motor protector to protect motor is higher too.
              However, in the long run, the overall cost that adopt smart motor protector is the lowest.

              Comprehensive comparison between intelligent motor protector and the thermal relay:



              Motor protector

              Thermal relay

              National policy

              Continuously promote and apply energy-saving product

              Eliminate outdated models


              Integrated circuit

              Machinery, heat principle

              Protect process

              Electrical signal transmission and electromagnetic action

              Heat transmission, Mechanical action

              Protect function

              Loss phase, stall, blocked, overload inverse time protection, start overtime, phase sequence protection, three phase unbalance, short circuit, heat accumulation overload, underpowered, overvoltage, leakage, temperature, analog input, external fault, contactor break overflow, TE time, etc.

              Loss phase, stall, blocked, overload inverse time protection

              Measurement function

              Measure the voltage, current, power, energy and frequency


              Control function

              On site, remote, bidirectional, start triangle, Self-coupling reducing voltage, anti-shaking start,

              no-voltage restart



              Electronic components. high repeatability, high accuracy, high reliability

              Dual-metal piece, easy aging, inferior repeatability, accuracy, reliability.

              Reflect time

              Fast, action in time, can be set according to the customer requirement.


              Slow, protection is not timely

              Recovery time

              Fast, can be set according to the customer requirement, can reach millisecond level

              Slow, manual two minutes, automatic five minutes.


              Relatively high

              Relatively low

              Annual cost

              Max. power 5W, annual electricity bills are about $7

              Min. Power 60W, annual electricity bills are about $90


              Serialize to circuit, low safety factor

              Parallel to circuit, high safety factor


              Modbus, Profibus, RS485


              Application occasion

              High protection requirements for industrial automatic occasion

              No need system integration, low protection accuracy for small power field.

              Overload requirement

              Solid, liquid and gas load

              Solid load, load flat

              Installation position

              No special requirement

              No vibration, no heat source,  dispose of the installation below.


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