Power source switch for vac?

I plan to hook my shop vac into my IoT relay so it turns on and off with my router. But after a job is finished, I like to pop the hose out of the Suckit & clean up. So, I’d like to have a switch - the vac would either receive power from the IoT relay (during cutting), or from a constant power source (during cleanup). I feel like this should be simple, but I can’t find a switch meant for this. Maybe I’m not looking for the right thing? Has anybody done something like this?

you can also simply trigger the router on with manual code M7/M8, then M9 to shut off.
or unplug from the ‘switched on’ outlet to ‘always on’ - on the IoT. the IoT switch becomes your on/off.
i’ve done either way with my setup.

How to implement this depends on how complex you want to get. What IoT relay exactly are you using, and how is it controlled? Depending on the hardware you could either wire an inline bypass switch, use a low voltage manual switch to enable, use a microcontroller like NodeMCU to signal the IoT relay, etc. Knowing the exact setup you have will help in providing a recommendation.

In my case, I’m planning something similar. A relay will turn on dust collection when the router is powered up (and also open/close blast gates), but I plan on another NodeMCU micro with a low voltage button attached that will allow me to manually power on and off the dust collector.

I’m using the IoT from Amazon that’s pretty commonly used:

I found this:


Something like this. In one position it would be turned on and off by the IoT. The other position would always have power. So, flipping the switch would turn on the vac; flipping it back gives control back to the IoT.

This switch is expensive though & I’m guessing that it might be because having two power sources connected is dangerous, & this handles that properly. If this is what it costs it would be cheaper to just buy another vacuum, which I could then carry around the shop where the dust hose won’t reach.

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Have any 3-way switches in your house? Same thing.

Okay, I pulled out a meter and did some checks on my IoT Relay to be sure it worked the obvious way. The neutrals are indeed common. (Obviously, the grounds are. If you’re disconnecting the grounds… well.) So, basically, here’s the most straightforward way I can think to get an “I’m not done sucking!” switch. :grin:


  • Two-gang surface-mount box
  • Three-way “light” switch (splurge and get a 15/20 amp one, because why not)
  • Standard receptacle
  • Switch-and-receptacle cover
  • Two decent extension cords of appropriate length and capacity (if they’re feather light and from the dollar store, they’re probably not even actually copper, so don’t go there)
  • Wire nuts, Wago connectors, or whatever (based on your cord’s gauge)
  • Electrical tape, et cetera


  1. Cut and strip the non-plug side and feed it through knockouts (with whatever strain relief is appropriate for your box)
  2. Connect the white neutral wires (which come from the large blade of the polarized plug):
    • If the receptacle has two lugs for neutral, connect each white neutral wire to one lug.
    • If not, make a short pigtail to connect to the neutral lug, and wire nut (or Wago connect) the three wires together (two neutrals and the pigtail) – you can’t connect more than one wire to a lug.

    If the receptacle (or switch) has those little press-in connection holes on the back, don’t be tempted. Make pigtails if you need them, then strip the wire, bend it clockwise around the screw terminals (so it pulls toward the screw as you tighten), and screw down well. Theoretically, if you’re using the right type of solid copper wire, the press-in connections might work… for a while… before they go high-resistance and burn up.

  3. Connect the (bare or green) ground wires:
    • There will only be one ground terminal on the receptacle, so you’ll need to make a pigtail.
  4. For the hot black wires (which come from the small blade on the polarized plug, i.e. the one harder to stick something into), make a jumper wire to connect the common on the switch to the receptacle and connect that.
  5. Now connect one incoming hot black wire to each of the other terminals of the three-way switch.
  6. Using tape or whatever, bind the two cords together most of the way to the plug end.
    • Leave enough slack to not make life difficult to plug the ends into the IoT Relay, but not enough slack that you could plug one of them in somewhere else.

    Since you’re switching the hot and all unswitched neutrals/grounds should all be at ground-reference voltage, that shouldn’t matter, but if you plug one in to a receptacle that was cross-wired, you’d get to see how loud a dead short is (and get a free trip to your breaker panel). Other bad premises wiring issues could also be inconvenient. If you bind them so they can only reach the adjacent plugs on the IoT Relay, you can remain blissfully unaware even if your electrician was hungover.

  7. Mount the box somewhere convenient and close everything up.
  8. Plug one connection into a “Normally OFF” receptacle on the IOT Relay.
  9. Plug the other connection into the “Always ON” receptacle.

Note that I am not a licensed electrician. I gutted and rebuilt my house (to code), and I built my parents’ apartment (everything from the studs on up, including electrical, water, waste, and even everyone’s favorite mudding the drywall), so I’m not what you’d call completely inexperienced. Still, it’s electricity, and so on.


Why not just use a SPDT Break before Make switch to ground on the input signal? This would allow you to run the vac with the G Code sender with the switch in one position, change switch position to turn on vac.

This would require two of the IoT power blocks, one for vac, one for Spindle. Since you are only working on low voltage it would be low risk.

The break before make will help ensure the spindle does not turn on inadvertently when you flip the switch positions .

Maybe, there is a way to integrate a 3-way power switch into a holder for your vacuum hose?
In this way one could use the vacuum with the dust shoe, turn off the CNC, then by picking up the vacuum hose end pier is sent to the vacuum again. Placing the vacuum back in the holder would turn off the vacuum.
I just realized that I should do something like this with my CNC enclosure door.

@ClayJar, thanks a ton for the write-up. I though about a three-way switch but in my head couldn’t work it out. I just went back & reviewed how one works & yeah, that’ll do it.

Like you, I gutted and rebuilt my house, also to code, every bit of it EXCEPT mudding & sanding the drywall because I’m not great at it & I absolutely hate it. And although I know I didn’t cross-wire anything, joining the cords to only allow the IoT relay to be used is smart & what I’ll do.

Thank you all!

How could anyone hate mudding and sanding? :rofl:

When I built my parents’ apartment, I made a deal that I’d do the whole build but then hand it over for my sister’s family to tape, mud, sand, and paint. A fair price, hehe. Then three weeks after my parents moved in, we had our Great Flood of 2016 here in Louisiana (with some areas getting over three feet of rain in just over a day), and the apartment took on about 18 inches of water. Since my sister flooded, too, I got to gut and rebuild the apartment solo, and this time I got to tape and mud.

(For the record, when you’ve got an entire apartment’s worth of butt joints you need to disappear, you absolutely want to splurge on FibaFuse non-woven fiberglass tape, even if you have to order it online like I did. So much better than paper or the woven stuff at big orange/blue.)

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