An E2-class circuit breaker is just a normal circuit breaker. However, it has a special design criterion to perform maintenance-free operations for interrupting fault currents. An E2 class circuit breaker is expected to interrupt fault currents for a prolonged period of 25 years without requiring any intermediate major maintenance of its interrupting mechanism. This E2 class is confirmed by a type test called the Extended Electrical Endurance Test.
E2 Class Confirmation Type Test
No Load Test before Wear Test
First, we need to perform the O, O-CO, and O-t-CO sequence of operations on the circuit breaker under no-load conditions. Then, we measure the opening time, closing time, travel time, and other related parameters of the circuit breaker as reference values.
Wear Test
T60 Operations
Then, we apply 60% of its rated short-circuit current to trip the circuit breaker. After that, we close the circuit breaker again and again apply 60% of the rated short-circuit current to trip the CB. In this way, we perform a specific number of operations according to the rated short-circuit current level of the circuit breaker.
These operations are called the T60 breaking operations. T60 means tripping at 60% of the rated short-circuit current of the circuit breaker. According to IEC 62271 Part 310, for a 25 kA rated circuit breaker, there are 15 such T60 breaking operations to be performed. For a 31.5 kA rated circuit breaker, there are 12 such T60 breaking operations to be performed. As the rated short-circuit current of the circuit breaker increases, the number of T60 breaking operations decreases accordingly.
The table below shows the number of T60 breaking operations to be performed on a circuit breaker based on its short-circuit current rating.
| Short Circuit Current Ratings | T60 Operations |
| 25 kA | 15 |
| 31.5 kA | 12 |
| 40 kA | 10 |
| 50 kA | 8 |
| 63 kA | 7 |
| 80 kA | 5 |
T10 Operations
After completion of these T60 operations, we perform the T10 operations. T10 operation means the circuit breaker is tripped with a short-circuit current equal to 10% of its rated short-circuit current. This sequence consists of only 9 such tripping operations, irrespective of its short-circuit current rating.
No Load Test after Wear Test
After that, we again perform the no-load test, which includes one O operation, then O-CO, followed by O-t-CO operation at no-load condition. We then record the travel time, opening time, closing time, arcing time, and all other related parameters of the circuit breaker.
Then, we compare these parameters with those recorded during the no-load test performed before the wear test. Here, the T60 breaking operations and the T10 breaking operations are referred to as the wear test.
If the parameters measured during no-load operations, before and after the wear test, are within the permissible tolerances, the first acceptance criterion of the E2 class is satisfied.
Acceptance Criteria Tests
Then, we perform the T10 operation with a single O operation. After that, we again perform a single open operation at 60% of the rated short-circuit current (T60).
Finally, we proceed to the line-charging breaking test, followed by the C2 class of operation test for the circuit breaker. C2 class is confirmed by opening the circuit breaker with a capacitive breaking current of 400 A for 48 operations and observing whether any recovery overvoltage is beyond the specified range or not. If it is not beyond the specified range, then the test is passed.
Alternatively, if we perform a total of 96 operations and find a maximum of only one restriking overvoltage, then the circuit breaker can also be accepted as a C2 class circuit breaker.
Then again, we perform one no-load test.
If all four tests after the E2 endurance test are passed, then overall the circuit breaker can be categorized as an E2 class circuit breaker.
Hope you got the basic overall idea. The entire procedure is explained on the basis of IEC 62271-310.