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Use a contactor on light circuit to shut off the 220v tool lines? Brilliant or dumb?

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  • Use a contactor on light circuit to shut off the 220v tool lines? Brilliant or dumb?

    I'm adding one last VFD and dismantling my RPC, and since this frees up the RPC contactor, of course this leads me down the rabbit hole of rearranging the whole electric situation. For many years I've had most of the outlets on the same circuit as the lights, so they go off when the lights go off. No risk of soldering irons and such left on, and no wasted energy from wall warts etc. I have another circuit of always on, differentiated by receptacle color. But I've left my VFDs on 24/7, and when I forget to turn off the damn compressor, I have to jump up and turn it off in the middle of the night when it cycles from leakage.

    So I am wondering how viable an idea it is to use a 4 pole contactor to control two 220v single phase circuits, the VFDs and my compressor, off the light circuit? I've never blown the light circuit even though there's a bandsaw and 2hp sander on it, so I guess that can stay as is. Probably wouldn't do if there was ever anyone besides me working.

    I rummaged this one out of the archives (is anyone here NOT a packrat?) and am trying to figure it out. Seems to be a 4 pole contactor with a 3 pole thermal breaker. Ancient sticker in the cover say coil is 24v. I wonder what was the advantage? Low voltage control circuits like we have on the VFDs?

    Click image for larger version

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    Here's the one from the RPC, similar but no transformer and only 2 thermal breakers. The converter wasn't very well balanced and I could trip the thermals by hard pressure on the 2hp buffing wheel.

    Click image for larger version

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    Location: Jersey City NJ USA

  • #2
    Paranoid if you ask me.

    -D
    DZER

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    • #3
      Originally posted by Doozer View Post
      Paranoid if you ask me.

      -D
      It takes a good headshrinker to tell the difference between an OCD case unhealthily worried about leaving the iron on, and the space cadet who has done it many times and has good reason to worry. I can't tell you how many times I've left that damn compressor on!
      Location: Jersey City NJ USA

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      • #4
        It'll work. Are you worried about leaving the shop with something powered up? Or about somebody coming in and running your machines in the dark?!

        edit: I see you answered my question while I was typing. No reason not to do it if you want to, but it does seem like a lot of work for a small potential problem.
        Last edited by chipmaker4130; 01-22-2020, 07:48 PM.
        Southwest Utah

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        • #5
          Originally posted by chipmaker4130 View Post
          It'll work. Are you worried about leaving the shop with something powered up? Or about somebody coming in and running your machines in the dark?!

          edit: I see you answered my question while I was typing. No reason not to do it if you want to, but it does seem like a lot of work for a small potential problem.
          It's mostly about keeping the compressor off at night and saving the VFDs uptime. There was a discussion of the latter elsewhere. There's a bit of energy to be saved on the VFD standby also.The outlets on the lighting circuit has been working great for 22 years.
          Location: Jersey City NJ USA

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          • #6
            Originally posted by gellfex View Post

            It takes a good headshrinker to tell the difference between an OCD case unhealthily worried about leaving the iron on, and the space cadet who has done it many times and has good reason to worry. I can't tell you how many times I've left that damn compressor on!
            My compressor does not leak, so I never turn it off.
            I leave a bench top LED lamp on all the time
            and I leave the radio on all the time.
            Even when I am not around.
            I leave my VFDs on and I leave my DROs on.
            Never had an issue.

            -Doozer
            DZER

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            • #7
              My compressor is on a contactor powered by the light circuit. I did it that way shortly after installing the compressor and being startled by random top-ups occurring at any time of the day or night. My case is probably worse than the OP's, or anybody else's for that matter, in that I have 7 "loads" spread around the shop & garage, connected with rubber hose. I.e., I have leaks that aren't worth chasing down, but can cause the compressor to run at random times.

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              • #8
                Over kill. Why not just flip breakers on your way out. Beware the fourth contact - usually a low current auxillary for use with start/stop push buttons.

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                • #9
                  Originally posted by Bob Engelhardt View Post
                  My compressor is on a contactor powered by the light circuit. I did it that way shortly after installing the compressor and being startled by random top-ups occurring at any time of the day or night. My case is probably worse than the OP's, or anybody else's for that matter, in that I have 7 "loads" spread around the shop & garage, connected with rubber hose. I.e., I have leaks that aren't worth chasing down, but can cause the compressor to run at random times.
                  Same here. I've got seven quick-connects and a hose reel. I'm pretty sure the reel connection leaks.

                  So I power my compressor through a contactor controlled by the light circuit. Been that way for 25 years.

                  -js
                  There are no stupid questions. But there are lots of stupid answers. This is the internet.

                  Location: SF Bay Area

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                  • #10
                    I took a different path.My compressor has about 100' of air lines and hose reels attached to it. The compressor doesn't leak but probably the buried flexible line going to the shop does. So, I mounted an air shutoff solenoid at the compressor outlet to shutoff the leaks. The solenoid is powered by the light circuit in the shop.

                    Mike

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                    • #11
                      Thanks guys, interesting to hear that both Jim Stewart and Bob Engelhardt have followed this path. If I was disciplined enough to flip breakers on my way out I guess we wouldn't be having this discussion, but I'm not. Sometimes I shut off the 2 valves to the air distribution hoses, but that's a minority of the time, there's all sorts of leaks, mostly at quick disconnects.


                      Originally posted by deltap View Post
                      Beware the fourth contact - usually a low current auxillary for use with start/stop push buttons.
                      Can you elaborate? The contacts look exactly the same as the others. I need to look up how these are used, I know I rigged the RPC with momentaries and used the 4th contact to maintain closure, but it's been 22 years and those brain cells are long gone. But if I use the light circuit, I don't need the 4th contact for that, right? I think I'll try and use the line current solenoid one first, simpler is better. It might have issues though, in recent years I've had to hold down the OFF momentary button and give the contactor case a wack to get it to release. But the RPC has been used solely for the infrequently used pedestal buffer, so it wasn't worth addressing.

                      Curious: has anyone ever had a city inspector in their shop who looked at all the AC cable everywhere and go "WTF???". It's kinda my nightmare. One reason I want to get rid of the homebuilt RPC that is probably unidentifiable even if they looked inside the boxes. Then it's just VFDs and wiring everywhere.
                      Location: Jersey City NJ USA

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                      • #12
                        Your idea will work. Remove the overload block with the heaters though and just use the contactor.
                        There are theories that turning electronics on and off is what shortens their life but I dunno, you mileage may vary...
                        Cheers,
                        Jon

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                        • #13
                          Originally posted by Jon Heron View Post
                          Your idea will work. Remove the overload block with the heaters though and just use the contactor.
                          There are theories that turning electronics on and off is what shortens their life but I dunno, you mileage may vary...
                          Cheers,
                          Jon
                          Can you explain the reasoning for bypassing the overloads? I was never all that clear on why they're there to begin with, I'm not strong on electrical theory like many of you. As far as the on/off issue, you'd think that some industrial firm with thousands of VFDs would have studied this, no? I mean, they're in washing machines and air conditioning among so many other uses.
                          Location: Jersey City NJ USA

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                          • #14
                            Originally posted by gellfex View Post

                            Can you explain the reasoning for bypassing the overloads? I was never all that clear on why they're there to begin with
                            The OL's are for overload protection of 'fixed singular motor loads', so they would serve no purpose in the use you propose. Though they are another source of potential issues, get rid of them is my professional advice.
                            Your VFD's will have OL parameters that must be set at the FLA nameplate rating of the motor being fed by it.
                            Cheers,
                            Jon

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                            • #15
                              FWIW I just measured the standby load of 4 VFDs, it's 20w. Not a lot by 'bad old days' standards of 100w light bulbs, but if I can save it with zero cash investment using equipment I have, it seems the thing to do, besides the other benefits.
                              Location: Jersey City NJ USA

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