I have a 240v/30a table saw and want to automatically start my dust collector, 240v/20a by means of a current sensing switch and relay. I have a 30a double pole relay w/ 24v coil. A 24v transformer 40va, and a Dwyer series ccs current switch, amprage sensing range 0 -200a ac, switch rating 1a @ 240 vac. My problem, in my very limited understanding, is the switch voltage in the sensing unit. Can i use these items. If not what do i need?
You can probably use them, but DON"T DO IT! You clearly know nothing about wiring practices, and your project has plenty of room for you to kill yourself or burn down your house.
If you must, this is the general approach
The motor current closes the switch output, which applies 24 VAC to the relay coil. The coil contacts switch 220 to the blower.
A few caveats. First, although you have a 24 volt relay, you do not specify that the coil is AC. If it's a DC input, you're out ouf luck (unless you rectify the transformer output). Second, you do not specify the coil current requirement. If you need 2 amps on the coil, the power needed from the transformer is 2 x 24, or 48 VA, and your transformer is too small. Third, I recommend you get a spark arrestor for your relay contacts. If you don't, sooner or later your relay will fail from the transients involved with switching the blower.