I bought and installed a new 1.5kw water-cooled spindle with an inverter to run it. Inverter is https://www.valinonline.com/products/esv152n02yxb . Now whenever I switch the spindle on it triggers my limit switches (in Mach3) and I can only reset it when the spindle is not running. Would adding a line reactor to the inverter help? Spindle and limit switch wiring is all shielded and properly grounded.

I'm virtually at a standstill. Any help?

Test to see if the noise pickup is in the switch wiring by disconnecting the limit switch wiring and shorting at the breakout board inputs. You should be using normally closed switches. If this enables the spindle to run you need to improve your wiring. More separation between the spindle motor cable and other wiring may be needed.

Noise in the DC power supply coupled through the AC mains is another possibility.

Are you using shielded, and properly grounded wire from the VFD to the spindle?

Yes I'm pretty sure it's shielded. I did a continuity check and that was okay. It just seems odd that it quit with no warning. I re programmed the VFD to eliminate that as a cause. I don't know too much about the electrical side of the issue, I just wish there were some way I could introduce power to the spindle, even for a second. Just so I could eliminate the VFD.