Electric Motor Testing Tip: Keep Test Leads Clean for Precise Resistance Measurements

When assessing the health and reliability of electric motors, the condition of your test leads, clips, and connectors is just as critical as the measurement equipment itself. Neglected leads can introduce resistance errors that compromise your data.

During MCE calibration, PdMA technicians routinely encounter test leads whose clips are worn or whose connectors have accumulated grime from everyday industrial use. A simple alcohol‑based cleaner can restore their performance.

For phase‑to‑phase resistance measurements, the advanced 4‑wire bridge test performed by MCE mitigates the influence of lead resistance. However, when measuring resistance‑to‑ground under test voltages of 1,000–5,000 V—common in acceptance testing of new or refurbished motors—the integrity of the lead connectors becomes paramount. These motors often exhibit resistance‑to‑ground values in the thousands of megohms to gigohms, with some reaching millions of megohms or terahms. The MCE can measure these ranges, but only if the test leads and connectors are free of damage and contamination.

Before every measurement, visually inspect your leads and connectors for cracks, frayed insulation, or residue. Clean any fouling with an alcohol‑based solution and replace damaged components promptly.

For more guidance on electric motor maintenance, visit the PdMA Corporation website at www.pdma.com.