350 Watt Pulse Start 21UF 400 Volt (Metal Oval)
Aerovox Z93S4021MN/3928-MF ,3210-MF, 21UF 400 Volt, 350 Watt Pulse Start Capacitor.
Commonly used for 350 Watt Pulse Start Metal Halide fixtures and works with M-131 bulbs with a pulse start-constant wattage autotransformer circuit type ballast. The case is oval in shape 1.75" x 3.1" tall with a maximum temperature rating of 100oC. This case has a resistor that dissipates charges to less than 50 Volts in 60 seconds when DE energized. This unit has a protective interrupter device to open the circuit at failure or the end of life (if you see the top bubbled and the capacitor is dead this is what happened).
All Aerovox lighting capacitors have resistors, some resistors are internal and others are external.
Capacitors do deteriorate; stop replacing ballast kits if the transformer is good. The average life of an Aerovox capacitor is 60,000 hours, most other brands of capacitors only average 10,000 hours. They can become weak, this is easy to check. See the Meters Section or Video Section on home page.