Normally, all generators within an interconnected power system operate at like frequency with their magnetic poles coupled through interaction with the network. The interconnecting force is elastic, allowing some angular play between generators in response to system disturbances. A loss of synchronism occurs when the bonding force is insufficient to hold a generator or group of generators in step with the rest of the power system. This can occur when equipment outages or low voltage weaken the system or if the force is inadequate to restrain extreme rotor excursions following a system fault or switching.