Shall withstand 60 Hz / 2500 V ac for 1 minute across without breakdown to the thinnest section before and after conditioning for 24 h in 85 ±5 %RH and 32 ±2°C (90 ±4°F).
Note: cover plate molded of a material that has been found to withstand a 60 Hz, sinusoidal potential of at least 2500 V ac, or a cover plate of phenolic or urea composition with a minimum thickness of 2.54 mm (0.1 inches), is not required to be tested.