Q&A Q: Why does the start capacitor have a wide range of numbers? A: Needs, Space & Cost A run capacitor is used the entire time the motor is running, it needs to be precise for proper operation and a way to dissipate heat of the electrons flowing in and out. This is what they have metal casings, oil filled cans and precise machines foil and insulators. A start capacitor is only used temporarily so it doesn't need the cooling. It needs to store and move more electrons, more amp to provide more t