A Low-Voltage Continuous Insulation Monitoring Framework using Precision Isolation Amplification and Microcontroller Threshold Logic

Undetected insulation breakdown in energized low-voltage electrical networks 
poses severe risks of electric shock, equipment damage, and electrical fires. 
Standard overcurrent devices operate reactively, tripping only after a hard fault or 
short circuit occurs. This paper presents the design and simulation of a low-cost, 
continuous Insulation Monitoring Device (IMD) tailored for energized single
phase 220V AC systems. 
The hardware architecture interfaces directly with active line conductors and 
protective earth through a high-impedance resistor-capacitor coupling network to 
limit leakage currents to non-hazardous micro-ampere levels. To protect low
voltage processing electronics from mains potential, the design incorporates an 
ISO124 precision isolation amplifier, establishing a capacitive barrier capable of 
handling up to 1500Vrms common-mode potential. The isolated signal is 
conditioned using an AD620 instrumentation amplifier (G = 11) and processed by 
an Arduino Uno microcontroller running a threshold-evaluation algorithm. 
Mathematical modeling demonstrates a linear dynamic response, mapping 
insulation resistance breakdown (500kΩ down to 15kΩ) to amplified output 
feedback (0.105V to 3.158 V). The system successfully flags the international 
standard warning threshold (1kΩ/V, or 220kΩ for a 220V system) and executes 
near-instantaneous digital outputs to actuate visual LEDs and an active buzzer. 
The proposed design establishes a reliable, galvanically isolated framework for 
transitioning low-voltage facilities from reactive breaker tripping to proactive, 
continuous insulation health monitoring