Enclosed Low-voltage ``De-ion'' Air Circuit Breaker of High Interrupting Capacity

The demand for protection against fault currents up to 20,000 amperes at 250 volts d-c or 600 volts a-c has led to the development of air circuit breakers having the desirable features of the present line of enclosed air circuit breakers, but having higher interrupting capacity. Tests at 20,000 amperes on the circuit breaker of lower interrupting capacity showed that certain modifications were necessary. By increasing the gap between the contacts, by using contacts which resist welding, and by using a modified arc chamber and contact construction, it was found possible to make the breaker satisfactory for 20,000-ampere short circuits.