Cathodic Protection Tester Practice Exam

What is a common issue when measuring isolation resistance with ammeters?

1. High resistance values

2. Presence of corrosive environments

3. Inaccuracy due to parallel resistances

4. Dependence on temperature variations

The correct answer is: Inaccuracy due to parallel resistances

When measuring isolation resistance, a common issue arises from the presence of parallel resistances in the circuit. This situation can significantly affect the accuracy of the measurements taken with ammeters. Ammeters are designed to measure current flow within a circuit and can inadvertently draw some current themselves. If there are multiple parallel paths for current, such as through other resistive elements or components, the ammeter can provide a misleading reading. When other resistances are present in parallel with the isolation resistance being measured, the total current will divide among the available paths. This division means that the ammeter may indicate a lower resistance reading than what is actually present in the isolation resistance. As a result, it hampers the ability to accurately assess the isolation quality, which is crucial for ensuring effective cathodic protection systems. Understanding this issue highlights the importance of minimizing parallel paths when performing resistance measurements, allowing for more reliable readings and ensuring that the cathodic protection system's effectiveness is properly evaluated.