The S 4455 is a DIN rail mountable relay box with 2 sets of voltage free changeover contacts. Each set of contact terminals have a N/O (normally open), N/C (normally closed) and a common connection. The N/O and common terminals become a closed connection when the relay is activated. When the relay is not active the N/C and common terminals are a closed connection. The relay contacts are rated at 10 amps. The DC input voltage can be either 12V, 24V or 48V DC selectable via a three way jumper on board. A led illuminates when the relay is activated. Below is a typical example of how to use the relay box. The Altronics A 1707A timer is used to trigger a 24VDC school bell, which requires more current than the output of the timer can provide. The 24V switched output out of the timer is used to power the relay box, which in turn connects the +24V of the external 24V DC supply, to activate the school bell. Note: The jumper on the relay box is in the 24V position.