Trip Class Designation
Regardless of the product style (NEMA or IEC), overload relays respond to overload conditions according to trip curves. These trip curves are defined by the class of protection required (see the table Trip Classes).
The figure Typical Trip Curves shows the three types of trip curves.
IEC components are typically application rated: the controller is sized very close to its operational limit for a given application. IEC motors are also generally more application rated. For these reasons, Class 10 trip is most common on IEC applications.
Because NEMA products are applied with more built-in excess capacity, the Class 20 trip is most common.
Trip Classes
|
Class Designation |
Tripping Time |
|---|---|
|
Class 10 |
10 seconds or less |
|
Class 20 |
20 seconds or less |
|
Class 30 |
30 seconds or less |