Here's a basic guide on how to measure ground resistance and test the grounding system's proper functionality using a multimeter: According to NEC 250. 56, the maximum grounding resistance is 25 ohms. How to check if an area is grounded? Use a multimeter, receptacle tester, and visual inspection of bonding/earthing, ground rod, and service panel; verify ground resistance and continuity per NEC safety guidelines. How to Check If an Area Is Grounded? How to Check if an Area is Grounded: Proper. Static Power Converter: For devices such as rectifiers and inverters, the system grounding is determined by the grounding of the output stage of the converter. All categories fall under the NEC definition for a “separately-derived system”. If not dealt with in a timely manner, they pose.