3-22 C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUALWIRING CHAPTER 3: INSTALLATION3Figure 3-17: Typical contact input DC circuitThe presence of the impedance path (R1) across the contact output allows the stray (distributed) capacitance to charge asshown, thus developing a voltage across the contact input enough to momentarily operate the input while thecapacitance discharges in the presence of DC ground on the positive terminal of the battery.The duration of the discharge depends on the value of the distributed capacitance, the initial voltage of the distributedcapacitance, and the input impedance of the contact input. If the duration is greater than the debounce time setting, thenthe contact input operates.The application example that follows describes how to mitigate this problem by connecting a resistor across the contactinput, as shown in the next figure, or by adjusting the debounce time setting to a value greater than the discharge time toprevent spurious operation of the contact input only if the voltage (with output open) across the contact input due to tricklecurrent is less than the threshold voltage. This operation of contact inputs also can be prevented by using the Auto-Burnishcontact inputs.Figure 3-18: Contact input connected to a contact output with resistor (R2) across the inputApplication exampleThis example is for illustrative purposes only and the calculations present the worst-case scenario. In practice, the value ofdebounce time can be lower.Contact input ON state impedance used in the calculation of the discharge period is based on the following table.
