A lineman is about to work an energized 7,200 V line, phase-to-ground. The glove bin holds four pairs marked Class 0, 1, 2, and 3. Before you read on, decide: which is the lowest class you can put on and still be protected? Guess wrong on the low side and the rubber breaks down with your hand inside it.
Rubber gloves and sleeves are graded by class, and each class carries a fixed maximum use voltage from ASTM D120. Class 0 tops out at 1,000 V, Class 1 at 7,500 V, Class 2 at 17,000 V, Class 3 at 26,500 V, and Class 4 at 36,000 V (Class 00 covers 500 V at the low end). For 7,200 V work the math is simple: Class 0 is far too low, and Class 1 at 7,500 V is the lowest class that clears the line. You can always go heavier, but you can never go below the line voltage.
Picking the right class is only half the job. The rubber degrades, and a glove that passed last spring can hide a cut, an embedded sliver, ozone cracking, or swelling today. That is why every glove gets a field air test before every single use: roll the cuff to trap air, squeeze, and watch and listen for it to leak down. If it loses air, or you find any cut, crack, or embedded object, the glove comes out of service on the spot.
The field air test catches the obvious failures, but it does not measure dielectric strength. That is what the lab retest is for, and it runs on a fixed clock. In-service rubber gloves must be electrically retested at least every 6 months; sleeves go on a 12-month interval. Track the date, not the wear. A glove that looks fine but is past its retest date is not in service until it is back from the lab.
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