A reed relay consists of a reed switch, ie a sealed glass capsule containing two separated overlapping ferromagnetic reeds. A typical reed switch capsule. The capsule is surrounded by an electromagnetic coil. When the coil is energized, the contacts that are normally open are brought together. When the coil voltage is removed, the reeds separate by their own spring tension.
The reeds provide a magnetic operating gap and serve as a contact pair providing NO, NC and CO combinations.
Reed relays on ship electrical systems have the advantage of being hermetically sealed and as a result, are protected from atmospheric contaminants.
To make NC or CO contacts, reed switches will occasionally use permanent magnets for magnetic biasing. The current rating of the reed, normally up to one amp, depends on the size, type and amount of plating.
