In safety system design process, they fail safety device is the necessity, that must choose to use the equipment are appropriate in the fail-safe circuit. Figure 4.6 has shown the comparison of a basic capacitor and the usability of a Fail-safe capacitor, when the open- fault occurred at a pole of a capacitor, but a pole of junction didn't separate with another part of a circuit. The current still can flow through a pole connection of junction to the other part, which might bring the circuit system to the dangerous failure situation, as shown in figure 4.6(a). In this propose circuit, a fail-safe capacitor will choose use in the circuit especially. Figure 4.6(b) illustrates the operation of a fail-safe capacitor in the open-circuit fault at a pole of the capacitor. In this case, the current cannot flow through to the other part of the circuit and cut off the capacitor circuit to load from the system.