(1) The terminal of the primary winding of the current transformer should be connected in series with the load in the circuit under test, and the ammeter should be connected in series with the terminal of the secondary winding.
(2) The appropriate ratio should be selected according to the magnitude of the current to be measured, otherwise the error will increase.
(3) The secondary winding is absolutely not allowed to open the circuit, otherwise the core will heat up and burn the coil due to excessive saturation magnetization of the core. At the same time, the magnetic circuit is excessively magnetized, which increases the error. When the secondary winding is open, it will also generate a high induced electromotive force (up to several hundred volts), which is likely to cause an electric shock. Therefore, the secondary winding end of the current transformer is equipped with a short-circuit switch to prevent an open circuit.
(4) The secondary winding end must be grounded.
(5) The load impedance of the secondary winding end should not exceed the specified value to reduce the error. Usually the rated capacity is given on the nameplate of the current transformer, then the formula can be 
The allowable impedance value of the secondary side is obtained.
