Power and Relay Connector You connect the DC power and alarm signals to the switch through two front panel connectors. One connector provides primary DC power (supply A) and the major alarm signal, and a second connector (supply B) provides secondary power and the minor alarm signal. The two connectors are physically identical and are in the upper left side of the front panel. The switch accessory pack includes the mating power and relay connectors. These connectors provide screw terminals for terminating the DC power and alarm wire and the connector plugs into the power and relay receptacles on the front panel. The positive DC power connection is labeled V, and the return connection is labeled RT The switch can operate with a single power source or with dual power sources. When both power sources are operational, the switch draws power from the DC source with the higher voltage. If one of the two power sources fail, the other continues to power the switch. The power and relay connectors also provide an interface for two independent alarm relays: the major and the minor alarms. The relays can be activated for environmental, power supply, and port status alarm conditions and can be configured to indicate an alarm with either open or closed contacts. The relay itself is normally open, so under power failure conditions, the contacts are open. From the CLI, you can associate any alarm condition with one or with both alarm relays. Alarm relays often control an external alarm device, such as a bell or a light. To connect an external alarm device to the relay, you must connect two relay contact wires to complete an electrical circuit. Both alarm terminals on the power and relay connector are labeled A, and you can connect them without regard to polarity.