Current transformers, also called CTs, are devices used in electrical installations to convert the magnitude of an alternate electric current, typically stepping down the current present in its primary circuit, which may of the order of tens, hundreds or thousands of amperes (A), to values in the order of 5 A in its secondary circuit. For such, the current transformer is connected in series with a load, so that the current consumed by said load crosses its primary circuit, while in the secondary circuit devices are connected for the functions of load current measurement, load protection against overcurrents, etc.
Constructively speaking, current transformers can be independent equipment or they can be associated with other power equipment, installed on transformer bushings, circuit breakers, etc. In this case, the wiring coming from the current transformer secondaries is directed to a crossover panel located on the equipment body, together with cables coming from other auxiliary devices. All the auxiliary devices' wiring is connected on this panel by means of crossover terminals; these devices include:                CT secondaries;        Contacts for signaling;        Contacts for alarms;        Contacts for equipment disconnection;        Amongst others.        
Current transformers are equipped with a set of coils between their primary and secondary circuits; this set of coils, while stepping down the value of the electric current, increases the voltage present in the secondary if it is not connected to a low impedance circuit. In fact, when the current transformer secondary is kept open and a current is applied to its primary circuit, the voltage produced between its two secondary terminals can reach values large enough to break the isolation of the circuits connected to the secondary, with a safety risk to operators and possible damage to the equipment. To reduce this risk, the crossover terminals used to connect the current transformer secondaries allow these secondaries to be short-circuited when necessary to disconnect the load associated to them, avoiding the development of elevated voltages.