During miswiring to field power source, a large voltage can appear across the ADC inputs and burden resistor. Back to Back Zener diodes are used to protect the ADC inputs from high voltage. The Zener diode also limits the current through the burden resistor and limits the power dissipation in burden resistor in case of miswiring to field power supply. With Zeners, no overvoltage cut-off is provided and the voltage is clamped across the burden resistor. Due to this, there is still power dissipation in the PTC and burden resistor. This causes heating of the entire PLC module.