Current transformers must be specified according to the load to be connected to their secondary. In this way, NBR 6586/92 standardizes secondary loads.

For a current transformer, the secondary load represents the ohmic value of the impedances constituted by the different apparatus connected to its secondary, therein including the interconnecting conductors.

By definition, nominal secondary load is the impedance connected to the secondary terminals of the TC, whose value corresponds to the power for the guaranteed accuracy, under rated current.

It should be noted that when the nominal secondary current is different from 5A, the values of the loads shall be multiplied by the square of the relation between 5A and the corresponding nominal secondary current in order to obtain the desired values of said parameters.

The load of the devices to be connected to the current transformers must be carefully dimensioned to choose the compatible standardized load current transformer. However, since the devices are connected to the CTs by means of wires, usually of great length, it is necessary to calculate the power dissipated in these conductors and to add it to the power of the corresponding apparatuses.

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