I have a dust collector in a wood shop.
The motor has these specs: 1 1/2 hp, 115/230 V, 12/6 Amps, 60Hz
The original run capacitor has the markings SH-CAP, 30μF, 250V, 50/60Hz -- 1 3/8 dia, 2 3/8 length
I was able to bring the original cap to a local Grainger store to get a replacement (2MEC9, 370 VAC the correct one according to the rep). It seems to work OK but it is much larger than the original and does not fit in the protective cover.

I do not know enough about these capacitors to find an equivalent on the web, i.e. the significance of different VAC or μ values. Any suggestions are appreciated.

 

As far as substitutes go, the marked voltage and capacitance is quite important. The capacitance is necessary for proper motor operation, and the voltage rating to insure the capacitor does not fail due to insulation failure - the line voltage has a peak value of 1.4 times the RMS voltage, or about 175 peak volts for 120 VAC operation. You always want to have some voltage rating that gives some distance above normal peak voltage to keep stress off the insulation.

The cap you got is rated for 240 VAC operation, which has a peak of 336 volts. That is why the can is larger than your original one.

Since your first cap lasted some time, you must be running the motor on 120 VAC. So your substitute can have a voltage rating of 250 volts. That will probably mean it will fit the space for it. The capacitor should have the case dimensions included.