In the wire electrical discharge machining (WEDM) process, wire breakage (tool failure) reduces the machining productivity and also damages the machined surface. Most of the state-of-the-art WED machines attempt to prevent wire rupture by selecting a safe (longer) pulse off-time which limits the discharge frequency and slows down the machining speed. However, even with lower discharge frequency, wire rupture can not be completely avoided. This paper introduces a recently developed WEDM monitor to detect the sparking frequency for on-line control to avoid wire rupture and improvement of the machining productivity. With this new monitoring system, a large amount of sparking frequency data in the wire rupture process has been collected and analyzed, and vital characteristics have been identified. The factors affecting the wire rupture phenomena have been investigated. This paper also process an algorithm to predict wire rupture caused by high sparking frequency and unstable gap conditions.