A motor passes its insulation resistance test with a 500 MΩ reading and a PI of 3.2. Six weeks later it fails catastrophically in service. How? The IR test was measuring the bulk resistance of the insulation system, but somewhere inside the winding there was a tiny void in the epoxy-mica tape. That void had been producing partial… Read More »
The reading is 2 MΩ. The motor is supposed to be above 100 MΩ. You’re standing at the terminal box with a megger in one hand and a maintenance log in the other, trying to figure out what to do next. This guide walks through the actual troubleshooting sequence for low insulation resistance readings. Not theoretical — the… Read More »
Every time a motor starts across town, your power supply takes a hit. Every time a fault clears on the distribution grid, voltage drops for a few cycles. Every time the UPS swaps from mains to battery, there’s a transition. Most electronic equipment handles these disturbances without a hiccup. Some doesn’t. The difference is whether the equipment has… Read More »
A protection relay doesn’t work without its auxiliary supply. The CT and VT measurements feed the analog inputs, but the processor, the display, the communications, and the trip contacts all run off the auxiliary voltage. In most of the world, that auxiliary voltage is 220V — either 220V DC from a substation battery or 220V AC from a… Read More »
Switchgear sits at the center of every industrial power system. When it fails, an entire plant, building, or substation goes down. When it fails catastrophically, people can be injured or killed by arc flash. Testing switchgear insulation is one of the highest-leverage electrical maintenance activities you can perform — and one of the most commonly done badly. This… Read More »
A generator failure during an emergency is the worst possible time for a generator to fail. Data centers, hospitals, water treatment plants, and utility backup systems all depend on generators that sit idle for months and then must start and carry full load within seconds. Whether they do depends largely on the condition of their insulation — and… Read More »
The first time you pick up a megohmmeter, it looks familiar but behaves differently. It has probes and a display like a multimeter, but the numbers it produces are completely different. Why is 500 MΩ good on some equipment and 5 MΩ good on others? Why does the reading keep climbing after you apply voltage? Why does pressing… Read More »
A single insulation reading tells you the condition today. A thousand readings over a decade tell you when the equipment is going to fail. That’s the difference between preventive maintenance and predictive maintenance. Preventive says “test every 6 months.” Predictive says “this motor’s PI has dropped from 3.2 to 2.4 over the last four tests. At this rate… Read More »
Every megger review article online reads like a sponsored post. “Fluke is the best. Megger is also the best. Also here are five other brands that are the best.” That’s not useful when you’re trying to decide which instrument to actually buy. This guide takes a different approach. It matches megohmmeters to the kind of work you actually… Read More »
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 »