FI circuit breaker, 4-pole, Type A, selective, In: 40 A, 300 mA, Un AC: 400 V, with rated current adjustable for overload protection. The FI switch is the residual current protective device for touch protection. Siemens' patented residual current devices are an important component of the SENTRON protection systems for electrical installations, as they prevent life-threatening electrical accidents by safely disconnecting dangerous fault currents to ground. Electrically ignited fires can be prevented right from their inception. Whether through direct contact with live parts or indirect contact with operating equipment, protection is primarily achieved through rapid disconnection. The Siemens FI circuit breakers 5SV are characterized by: comprehensive protection for people and property against electric shock, as well as suitability for sinusoidal alternating fault currents or smooth direct fault currents.