China's electrical standard is the use of IEC (European standard), NEMA MG1 is the US standard. Basically, two are basically equivalent. Just different in different places. NEMA standard and IEC standard motor
The power use factor is slightly different from the rotor temperature rise. NEMA motor power use coefficient of 1.15, IEC (China) power use factor of 1. There are different ways of labeling other parameters, but the substance is consistent and basically equivalent.
IEC standard motor equipment is an average of 30% to 70% less than NEMA; smaller size and more accurate rating. Not just two switches to IEC standard motor control reasons.
The size of the most dramatic is equal to or less than 50 horsepower (HP), 80% of the world's rated motor.
Note that only 10% of the motor studies die due to age. Amazing 44% of the failures can be directly attributable to thermal overload or single phase conditions. IEC technology directly to solve these problems. IEC overload relay turns off the motor NEMA standard controls twice as fast. In addition, the IEC device detects single-phase conditions and quickly shuts down the event of the motor
First of all, IEC standard motor equipment using advanced arc technology to reduce the excess heat contact. NEMA equipment relies on greater quality to dissipate heat, resulting in greater physical size.
Second, IEC standard motor equipment is more accurately evaluated than NEMA controls.
The fact is that NEMA contacts tend to overestimate their own applications in the actual motor.
However, in fact NEMA controls their ability far less than conventional operations. This difference in cost users saves money and controls the panel space.
However, T-frame motors also have lower thermal overload tolerances because they build less copper and steel. Therefore, the overload relay of the T-frame motor must have a faster response time than using the U-frame. Most T-frame machines are manufactured by T-frame motors for 25 years of life. However, they will also tell you that each time more than 10 degrees Celsius motor insulation level increases, will reduce the life of half of the motor.
IEC standard motor overload relays are all 10 devices and they will trip under 10 seconds or less locked rotor conditions.
The standard NEMA device class, in 20 seconds or less locked rotor, they trip after. Although 20 seconds of response time, can prevent the fire, do not save the T frame motor.
A common misconception is that class 10 devices are unnecessarily tripping the motor; especially when starting and restarting. This phenomenon is called "nuisance trips."
While nuisance trips may occur in some specially designed motors, the IEC motor overload relay almost never trips unless there is a fault.
Almost all IEC standard motor have reached the speed at 10 seconds before the IEC device has reached the time.
The IEC standard motor overload relay detects the power supply single phase. The bimetallic strips in these devices monitor the current drawn through each of the three stages, bent in proportion to the distance.
If a phase is missing, the bimetallic sheet will be straightened and a double-calorie bar grab mechanism will be used to disconnect the motor immediately. Unless the timely disconnect, the motor was soon destroyed.