The majority of run capacitors will have a voltage rating of 370 or 440 VAC, a frequency of 50 or 60 Hz and a capacitance range of 2.5-100 uf.

If you are in the market to buy capacitor replacements, you should be aware that a run capacitor can, in some circumstances, be used as a start capacitor, as long as the capacitance and voltage ratings of the original start capacitor are the same as the replacement. A start capacitor can never be used as a run capacitor though, simply because it could not handle the continuous current and would burn out.

When you buy capacitor replacements, you should make sure the new capacitor has the same capacitance and frequency as the original. You can choose a new capacitor with a voltage that is in the range of the operational voltage of the motor; a capacitor will have a marked voltage indicating peak voltage acceptable. Starter capacitors will have either a black plastic or phenolic case, though this will not have any bearing on how well the capacitor will work.

Nearly all start capacitors will be round, but they may be oval shaped as well. An oval run capacitor could be used instead of a round capacitor, as there is no electrical difference between the two. As long as the replacement will fit within the space provided, the case shape makes no difference. If it does not fit, the mounting strap can be changed to better fit the oval shape.