A switch assembly for mounting on a mounting rail, having a power supply unit and having a switchgear. The power supply unit has a housing and a power supply, arranged therein, which comprises a first connection and a second connection. A contact region having a first contact, which is in electrical contact with the first connection, and having a second contact, which is in electrical contact with the second connection, is introduced into the housing. The housing has a fastening apparatus for direct placement on the mounting rail, and the switchgear comprises an additional housing having an additional fastening apparatus for direct placement on the mounting rail. The switchgear has a lever which is pivotably mounted on the additional housing and which has a first counterpart contact and a second counterpart contact.