The 303 relay has 19 double break contacts in all N/O and N/C combinations.

The plug-in design offers secure locking feature for maximum ease of maintenance (no wires need to be disconnected or other hardware removed for relay inspection or replacement). The resistance to impact and vibration is conform to standards in force for Railway Transported Equipment.

Positive mechanical keying of relay to socket is built into relay and socket during manufacture and terminal identifications are clearly marked on identification plate that is permanently attached to the relay. Weld no transfer safety contacts are standard. If one N/O contact welds, no N/C contact can close and visa versa. All relays are factory tested to insure they meet this important safety requirement.

The 303 relay can be plugged in the COR NK or COR PA socket.