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  • Contactor

    Hey everyone,

    I am looking for contactor to install in my mom's new wood shop. I want it to cut off the power to all of her tools if the need arises. You know those big red buttons you see. "In case of emergency press button".

    The machines are 110v with a 15a max. (table saw). I will most likely have 2 different breakers for all the machines. So the table saw and sawdust vaccum aren't on the same breaker, for example.

    So i was thinking a 3 wire contactor with a 24v or 110v coil. A 110 would eliminate a transformer. I also want to wire in a start switch. This way, the worker would have to arm the contactor so everytime they go into the shop. Just in case a kid wonders in, they can't turn on any of the equipment.


  • #2
    If I understand correctly, you want to put this contactor between the circuit breaker panel and the outlets that the machines are connected to. The hot wires from two (20-amp?) breakers would be connected to the input side of the contactor, and the output side of the contactor would be connected to the receptacles.

    That sounds like a good idea, but I doubt it meets the electrical code. Two breakers in the service panel would be connected to the same device (the contactor) in a separate enclosure. You'd need some sort of physical interlock between the two breakers to make sure you couldn't leave one on when working on the contactor.

    You could use a double-pole breaker (like you'd use for a 220V circuit) to run power to the contactor, and then split the circuits on the output side to run the two sets of 110V outlets. I'm still not sure about that meeting code requirements, though.

    Last edited by winchman; 02-02-2007, 01:56 AM.
    Any products mentioned in my posts have been endorsed by their manufacturer.


    • #3
      What about using a remote-trip breaker?
      "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill


      • #4

        I see what you mean. The proper way would to be to put a disconect between the contactor and the breakers. Hmmm. I could also wire in warning lights that tell people there is power coming from the breaker.

        I was going to use 2 15a breakersin the fuse pannel. That way i would not have to use the amperage attachment (forgot the name) that usually goes on the bottom of the contactor.

        I was thinking of using a contactor for a 3hp motor on 1 phase. That should be big enough?



        • #5
          A remote trip breaker? What do they look like?



          • #6
            Single phase amps add up fast.

            A large contactor for 3phase, unless you find a deal on a used one? Last one I bought and installed at a local mill was $3600.00 Seems it was 20hp.

            Why not install a e-stop type switch on each machine? You have to have a button on each anyways.

            I got a bunch of old electrical junk here and there. When you figure out WHAT you want to do I can look to see what I got laying around. I had 3 bushels of 10hp contactors.. I think I have whittled that down to nothing thou helping people out.

            We put a cable through in front of a carpet roll up once, it had a vari-speed drive to roll the carpet up, a elderly gentleman would "walk" the carpet while it was rolling up and look for defects and get some exercise.. One day he fell.. got back there and rolled for about sixty feet before the guy hit the button and stopped the rollup. I installed the trip wire the next day..

            Ain't nothing to laugh about sixty to 300 feet per minute when you are old and frail.

            Anyways, a cable ran through the ceiling about "reach" high is a good mechanical way to operate a single control.
            Excuse me, I farted.


            • #7
              Originally posted by spkrman15
              A remote trip breaker? What do they look like?

              Back when I worked for Square D, that was one of the optional accessories on some of the lines of breakers. I presume other mfgs have competing products. It didn't change the appearance of the breaker IIRC, but it had an additional wire pair from the breaker that would trigger the magnetic trip and an immediate break. This would be on the main, not the branch circuits. For other purposes you could get a set of make contacts so when the breaker tripped that could operate a bell or light remotely.
              "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill


              • #8

                A remote trip breaker is a electrical "magnetic" trip breaker that has external buttons and contacts to make it drop out. THEY are not made for continuous use thou and using them often will quickly wear them out.

                The oil filled breakers at some TVA hydro plants, well the oil leaked out long ago.. and you can weld with the small wires and it will "NEVER" trip.. a house style breaker is a thermal type unit that has a flex-bimetal joint inside that springs and causes the breaker to loose contact.. why you have to let them cool before resetting.. and the more they trip, the longer it takes to cool.. and also, they wear out too..

                Fuses are the best, but alas, one shot only. There are numerous types of fuses too. Time delay, instant trip, motor rated.
                Excuse me, I farted.


                • #9
                  Because of the aforementioned cost of a contactor big enough to disconnect the entire supply for the shop, you may want to think more modularly. If you truly are only talking about disconnecting a few circuits, that is fairly managable. Smaller relays are available surplus much more reasonably. You could use one for each circuit you wish to disconnect. Holding current is typically minimal, so you can just use the lighting circuit to energize the coil providing an easy way to insure power is off when you leave.

                  I don't have everything disconnected, but do have a contactor that disconnects power to my air compressor when I shut off the shop lights. This prevents a burnt up compressor even if I would forget to leave the shutoff valve open and a line would burst. It took several months to get used to the "bang!" every time I went to leave the shop and shut off the lights. Its a substantial relay and in a fairly empty metal enclosure/disconnect mounted by the compressor and so it echoes a bit.

                  Paul Carpenter
                  Mapleton, IL


                  • #10
                    That is exactly what i want to do. We had contacts at my old job where a 24v system would control higher current. 600v, 347, or 220. All 3 phase. I saw on Ebay some 3hp 3 phase contactors, with 110 or 24 volt coils for about 20 bucks.

                    I want the stop buttons on the wall so ANYONE can hit them. 3600.00 for a 20hp 3 phase Contactor? Why so expensive? I have bought 60hp 3 ph contactors for around 700.00 that includes the coil and amperage trip.



                    • #11
                      An E-Stop Switch?:
                      "The men the American people admire most extravagantly are the greatest liars; the men they detest most violently are those who try to tell them the truth." H. L. Mencken

                      "All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."

                      "When fear rules, reason and logic are ruled out."


                      • #12
                        Not speaking as an authority on code or anything, but I don't see why a double pole relay wired to a dual breaker would violate code. Put it in a separate box, run four leads from the breaker panel to the relay box (two hots, a neutral, and a ground) then carry on the wiring to the outlets from the second box. You would be tripping the breaker anyway if you were to work on the wiring or the relay, just as you normally would ( or wouldn't in some cases). I would find a relay that has three sets of contacts, at least two of which are rated for minimum 15 amps. The third contact is wired as a 'hold', and is wired in series with normally closed safety switches and the coil. If any one of these switches is pressed momentarily, the relay drops out and can't be clicked back on unless a momentary 'master on' switch is pressed. This switch is placed where kids can't reach it, probably near to or on the relay box.

                        Wiring it to the lights is a good idea. You will always have to hit the master on switch to enable power- merely turning on the lights won't do it. But the lights will have to be on before the relay can come on.

                        A power failure will also kick out the relay (of course), but when power comes back on, the relay won't come on until you hit the master on switch.

                        Seems like a good system to me. If all wiring is done according to code, meaning proper boxes, et al, it should be perfectly legal. You'll be outputting one 220 circuit, or two 110 circuits from the relay box.

                        As suggested, if the relay coil is 110 vac, you won't need a transformer. If you find a suitable relay but it has a 24 vdc coil, then a doorbell transformer would probably suffice to run it. You'll need a bridge rectifier and a capacitor. Most doorbell transformers I've seen are 16 vac output. Rectified, this makes about 24 vdc, which will operate the coil. Using dc for the coil can eliminate the annoying buzz that ac coil relays can give off.

                        Doorbell transformers can be bought with a mounting stub which fits a standard opening in an electrical box. It shouldn't be hard to find an electrical box which is big enough for the relay and some wires going in and out. It might be a challenge finding a relay with three sets of contacts, without paying for the fort.

                        Off the top, all I can think of that would affect code is if your dual breaker was rated higher than 15 amps, unless the associated outlets and wiring were also properly sized, with the outlet being the proper one for the higher current. I think you can go to a 20 amp for 110vac with #12 wire and the special outlet. Of course the machinery would have to follow suit by having the matching plug end on it.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                        • #13
                          I'm not trying to be a smartarse here but why the need for such a circuit unless she is working in a flooded basement and you want to power down from the stairway?

                          It might make more sense to me if someone was going to stand there by the switch all the while she is working but electricity only needs a second to do it's damage.

                          If she is going to work on cumberson sized pieces of plywood or rip thinner pieces on the table saw then a manualy operated "off " switch would be very helpful for her. It is simply a board that hangs done from a hinge in front of the on/off switch. It has dowel on the side that faces the "off" button so that you can turn the saw off when hit the board with your knee. It has a large hole drilled in it just in front of the "ON" button so you can reach your finger in the hole to power up the saw. This is an extremely popular safety mod with woodworkers.

                          Something has gone over my head as I've missed the point. Hope this doesn't sound too sophomoric and I realize I might be missing something here.
                          Last edited by Your Old Dog; 02-03-2007, 07:33 AM.
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                          • #14

                            i was thinking about it and i beleive there is suposed to be a disconnect box within visual range of the contactor. This way you can make sure there is no power going to the contactor. I do however think the light switch is a good idea but over kill. If the layout allows for it, i will see how easy it will be to do that as well.

                            Yeah it is overkill, maybe. All industriel places have Emergendy stops. Having a switch or several switches on various locations in the building could save someone. Running to the switch on the machine just might be to late.

                            Ok all this doesn't help me with my original question. How big of a contactor, amp rating, do i need to handle 110v 15a. For example would a contactor rated for 30a at 220v. be strong enough?



                            • #15
                              Put a knife switch on the wall. Equip it with a padlock. Any power tool emergency that happens slowly enough to allow time to reach a distant e-stop also allows time for someone to reach the knife switch. Most power tool accidents hurt you before you realize anything is wrong. I one time ripped open my leg with a chain saw and didn't know about it until we stopped for a break.
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