# X1/X2/Y1/Y2/Y4 impulse withstand rating voltage calculator (IEC 60384-14)

IEC 60384-14 specifies that X1/X2-rated capacitors shall be tested to withstand an impulse voltage of 4 kV (X1), 2.5 kV (X2, Y4), 8 kV (Y1) or 5 kV (Y2).

However these values only apply for a capacitance $\leq 1 μF$ (except for Y1/Y4 capacitors). Use this calculator for X1/X2/Y2 capacitances $> 1 μF$!

F

#### Formula:

$$Up = \frac{Up_{\leq 1 μF}}{\Large\sqrt{\frac{C}{1\,000\,000\frac{μF}{F}}}}$$

where:

• $Up$ is the impulse withstand voltage rating
• $C$ is the capacitance in Farads
• $Up_{\leq 1 μF}$ is the voltage rating for that capacitor class with a capacitance of $\leq 1 μF$:
• For X1-class: 4 kV
• For X2-class: 2.5 kV
• Y1-class impulse withstand voltage is always 8 kV no matter what capacitance
• For Y2-class: 5 kV
• Y4-class impulse withstand voltage is always 2.5 kV no matter what capacitance

#### Why is the impulse withstand voltage lower for larger capacitors?

The rationale behind the derating of the impulse withstand voltage is that larger capacitances will have sufficient capacitance so that a given overvoltage doesn’t cause a large voltage spike in the capacitor.

The formula (see above) is chosen so that the energy in the capacitor:

$$E = \frac{1}{2}\cdot{}C\cdot{}U_p^2$$

is kept constant (i.e. at the same value as for a equivalent capacitor of 1 μF).