Every insulation system leaks a little. Apply AC voltage across ground-wall insulation and the current splits into two parts: a large capacitive current that leads the voltage by 90°, and a small resistive current in phase with it that turns into heat. The dissipation factor — tan δ — is the ratio of those two. It is the… Read More: Dissipation Factor (tan δ) Test for Stator Windings »
A bare CTI number can be read wrong. “CTI 400” looks like a clean result until you learn it was run with the aggressive contaminant, or that the 100-drop figure sat 50 V lower, or that erosion ate 3 mm off the specimen while it passed. All of that lives in the report — and a compliant report… Read More: How to Read a CTI and Tracking Test Report »
The letter stamped on a motor nameplate — usually F, sometimes B or H — controls how long that motor will last. Get the class wrong for the application and the motor either fails early or you paid for capability you’ll never use. Get it right and you have a motor engineered to run its full design life… Read More: Motor Insulation Class Explained: Class A, B, F, H —… »
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 »
The specimen decides the number almost as much as the material does. A tracking test measures how a surface behaves under a contaminated film, and nearly every rule about how you cut, clean, and condition that surface exists to stop the specimen itself from becoming the variable. Get the prep wrong and the result is not slightly off… Read More: CTI Test Specimen Preparation Guide (IEC 60112 & 60587) »
A datasheet quotes “CTI 400V, PLC 1, Material Group II” and an engineer new to the part assumes those are three separate properties. They are not. They are one measurement — surface tracking resistance — expressed in three different bookkeeping systems, because three different bodies standardized the same drop test. Knowing which system a number came from matters,… Read More: IEC 60112 vs ASTM D3638 vs UL 746A: CTI Standards »
The single most important thing to know before you use any CTI table: the number belongs to a grade, not a material family. Two compounds both labeled “PBT” can sit in different material groups because one has a flame-retardant package and a filler tuned for tracking and the other does not. Every value below is indicative — a… Read More: CTI Values of Common Insulating Plastics (with Table) »
IEC 60076-3 is the IEC standard that sets the insulation levels, dielectric tests, and minimum external air clearances for power transformers. It defines eleven dielectric tests, assigns each one as routine, type, or special based on the highest voltage for equipment (Um), and gives the test voltage tables. The current form is IEC 60076-3:2013 as amended by A1:2018.… Read More: IEC 60076-3 Explained: Dielectric Tests and Clearances »
The drop test tops out. IEC 60112 discriminates between poor, moderate and good tracking resistance for indoor equipment under moist conditions, and for that job it works. But it runs at hundreds of volts on 20 mm specimens for under an hour, and its own scope says the results do not qualify a material for outdoor service. Outdoor… Read More: IEC 60587 Inclined Plane Test: Tracking and Erosion »
Run an IEC 60112 test and the specimen can go bad in two completely different ways. One leaves a conductive path. The other leaves a hole. The headline number — the CTI or PTI — only tracks the first. The second gets measured separately, if at all, and it is the one people forget to ask for. Same… Read More: Tracking vs Erosion: Two Failure Modes in IEC 60112 »