A circuit breaker utilizes a plurality of vacuum interrupters immersed in oil. A cross-bar with electrically conductive sections completes a series electrical circuit through the circuit breaker and actuates operating mechanisms, to close the contacts of the vacuum interrupters when in the raised position as the cross-bar is lowered, the contacts of the vacuum interrupters are opened by impact forces before isolation gaps which fill with oil are created in the series electrical circuit. Various arrangements of the vacuum interrupters are disclosed for uprating existing oil circuit breakers.