Rollie is right on. You need a set of normally open mechanical auxiliary contacts. These contacts mount on the 3 phase motor starter and have the "hot" leg of the circuit your dust collector is on wired to them. So, when the motor starter engages to run the 3 phase saw, the auxiliary contacts close and energizes the dust collector's power. This is really very easy to do, I have wired these sorts of circuits numerous times. It is easier than you think!

Quote Originally Posted by Rollie Meyers View Post
If the tool has a magnetic starter, use a aux. contact to control the DC. This only will work when parts & accessories are avail. for the mag starter,with off-breed Grizzly or the like garbage or obsolete starters problems will occur.