[william_zion]

[tkrussell]

An Air Circuit Breaker has open contacts in open air, SF6 circuit breaker uses sulfur hexafluoride to surrounded the contacts to quench the arc.

[jcaron2]

Both breakers operate on the same principle, but the SF6 breaker is filled with compressed SF_6 (sulfur hexafluoride), whereas an air circuit breaker is filled with air. The advantage of the SF6 is that it has about 3 times the breakdown strength of air, which is very significant since the whole idea of these types of breakers is to minimize the effects of arcing.