A megohmmeter reading only means something once you know the winding temperature that went with it. The same motor can read 800 MΩ cold in the morning and 90 MΩ after a shift at full load, and nothing is wrong with it. Correcting to a fixed reference temperature is what makes today’s number comparable to last year’s number.… Read More: Insulation Resistance Temperature Correction Calculator »
You meggered a motor. The display says 12 MΩ. Now what? Almost everyone in the field carries the same number in their head: one megohm. Anything above 1 MΩ, energise it. That rule is older than most of the motors it gets applied to, and for a modern machine it is far too generous. IEEE 43-2013 — the… Read More: Motor Megger Value: What Reading Is Acceptable? »
If you’ve been doing motor insulation testing for any length of time, you’ve heard the standard cited a hundred times. “IEEE 43 says the PI minimum is 2.0.” “IEEE 43 requires correction to 40°C.” Most techs and engineers work from the rules without ever opening the document. That works fine until it doesn’t. Until an auditor asks where… Read More: IEEE 43-2013 Explained: A Clause-by-Clause Guide to Motor Insulation Testing… »
Most people who run a Polarization Index test can tell you the formula: 10-minute IR divided by 1-minute IR. Fewer can tell you why that ratio is meaningful, where it stops being meaningful, or what a result of 1.1 on a modern epoxy-mica winding actually implies — compared to the same reading on an asphaltic machine from 1965.… Read More: Polarization Index Testing of Motor Windings »
Insulation resistance testing is one of the most practical condition assessment tools in electrical maintenance. Apply DC voltage to a winding, measure the leakage current, divide one by the other — you get a number in megohms that tells you whether the insulation is clean and dry, wet and contaminated, or failing. IEEE 43-2013 is the standard that… Read More: Insulation Resistance Testing of Motors: A Complete Guide to IEEE… »
Motors fail. The question is whether you catch it during a scheduled outage or at 2 AM on a Sunday. Insulation testing is the tool that decides which one. This guide covers everything you need to run a complete motor insulation testing program — from a single 5 kW pump motor to a 2,000 kW medium-voltage drive. It’s… Read More: Motor Insulation Testing: The Complete Field Guide »
You test a motor at 20°C and read 200 MΩ. Looks good. You test the same motor three months later at 45°C and read 40 MΩ. Has the insulation degraded? Or is it just the temperature? Without correction, you can’t tell. A 200 MΩ reading at 20°C and a 40 MΩ reading at 45°C can represent exactly the… Read More: Temperature Correction for Insulation Resistance Tests: The Complete Guide »
The polarization index test is the most reliable way to assess insulation condition on motors, generators, and other rotating machinery. It goes deeper than a standard 60-second megger reading and gives you a result that’s independent of temperature and equipment size. If you only have time for one insulation test on a critical motor, make it the PI… Read More: Polarization Index Test: What It Is, How to Do It,… »
A megger test on a motor takes about five minutes. Reading the result correctly takes a bit more than that. The number on the display means nothing on its own. A 50 MΩ reading is fine on a 6.6 kV machine and a warning sign on a 400 V one. Temperature moves it. Humidity moves it. A dirty… Read More: How to Megger a Motor: Steps, Voltages, and Good Readings »