The Series LI emergency lighting inverter system is a single phase, continuous duty, seamless transfer inverter. The Series LI is designed to supply reliable, isolated, clean, regulated emergency power for emergency lighting and associated controls. An efficient ferroresonant transformer, microprocessor controlled solid-state PWM inverter and long lasting battery pack provide immunity to all line disturbances and power interruptions with no break in AC output power. Power factor correction and harmonic attenuation are provided. The synchronous inverter produces a true uninterrupted output in any mode of operation. A self-diagnostic monitoring alarm system continuously advises system status.