The invention relates to a current transformer 1, comprising connection contacts 3 for contacting a secondary winding of the current transformer and a short-circuit device 105, 205, 305 for shorting the connection contacts 3, wherein the connection contacts 3 can be reached through a housing opening 4 of a housing 2 surrounding the current transformer 1, the current transformer also having a safety device 107, 207, 307 for blocking the access to the connection contacts 3 lying inside the housing, wherein the safety device 107, 207, 307 can be in a securing status or release status, and wherein the access to the connection contacts 3 is blocked by the safety device 107, 207, 307 in the securing status, such that the connection of a conductor to a connection contact 3 or the disconnection of a conductor from a connection contact 3 is not possible, and wherein the access to the connection contacts 3 is released by the safety device in the release status and the short-circuit device 105, 205, 305 shorts the connection contacts 3 in the release status, such that the connection of a conductor to a connection contact 3 or a disconnection of a conductor from a connection contact 3 is possible.