An X2Y capacitor is a four terminal device which is composed of 2 capacitors A and B connecting to a common pair of ground terminals. One example is Johanson Dielectrics’ X2Y® series capacitors. So how do you measure the actual capacitance value of X2Y capacitors as the datasheet mentioned?
In general, the capacitance value in the part numbers represents the nominal value of A (or of B). Therefore if X2Y is connected as in the below “Circuit 1”, you’ll get only one capacitor between each line and ‘ground’ (0 volt). If X2Y is connected as in the below “Circuit 2”, you’ll get the total capacitance to be twice of the A value.
The typical circuit to measure X2Y Capacitors is as below. The capacitance value is measured between A and G (i.e. G1 or G2 since they are connected) and/or between B and G. The measurement frequency is around 1 KHz if C > 1nF, and around 1 MHz if C ≤ 1nF.