The most common reason for blowing a start capacitor, especially repeatedly, is that the motor is starving for power at startup. The first thing you should be looking at is the circuit size for the compressor. Just because the voltage is fine does not mean the circuit is sized or wired correctly.


Whoaaa! I just realized that you never told us what type of 3-phase power you have in the shop. If this is a comercial-type building, then you likely have 120/208, but if it is light industrial, then it is likely 120/240 hybrid. This is important!

If your supply is 120/208, then all of your single-phase 240 tools are running at low voltage (208 volts). In this case, you need a buck/boost transformer to bring your supply voltage up to the 240 volts it wants to see. You don't do this for the entire shop, just the 240 volt single-phase tools.

On the other hand, if the shop is the hybrid 120/240 3-phase, then you need to check the size of the circuit feeding the compressor. If the circuit wire is undersized, then the voltage during startup will drop too low, the motor will start slower than normal, and the cap will blow.

I am running late and have to wrap this up. In the mean time, why don't you provide more specifics about the compressor and the wiring it is connected to.