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  • Jet Mill-Drill, wire question.

    Okay, so I am putting a Jet Mill-Drill in my garage. I have one 220 plug that is shared with my lathe and welding machine (I just plug in the machine I am using, one item at a time). I thought it was a 40 amp circuit but I now believe it is a 20 amp. (on my way to check.)

    Anyway, I went to the store to get parts to go from the three prong twist lock that is in the wall the the three prong flat plug on the mill-drill. The guy behind the counter had a ... fit... saying that it was not legal to put a 15 amp motor onto a 40 amp breaker (that is what I thought it was when I was there) circuit because it would cause a fire and that I could not make a adapter like I want because that was not legal either.

    Does any of that make reasonable sense to anyone here? I mean, who the heck has a 3.5 amp breaker to allow them to run their vacuum?

    So, what is the best way to put this thing in? (my lathe is a 1.5 hp motor and the mill is a 2 hp. I have one spot left on the top of my box but I may need that for the welder that is coming.)

  • #2
    The breakers are there to see that the wiring in the circuit can't get overloaded. Individual devices plugged in really should have their own over current protection.

    Not sure about rules for adaptors, but can't you just put another box next to the existing one with the new recepticle in it? You could leave both machines plugged in then.
    For just a little more, you can do it yourself!

    Comment


    • #3
      Originally posted by huntinguy View Post
      So, what is the best way to put this thing in?
      Short version is cut off the "wrong" plug on the new cord and attach a Properly Wired Up to Local Electrical Code plug to the mill-drill.

      The long answer of why the dude behind the counter freaked out was you probably walked up to him with a L21-30 plug in one hand (maybe smaller?) and a NEMA 14-50 receptacle in the other hand (maybe larger?) or something kinda like that. You and I know to never draw more than 30 amps (actually only 2 HP as you claim) outta that 50 amp receptacle, but the next lunatic might use your adapter to plug in a 50 amp compressor or whatever (hey, the plug fits the receptacle and it kinda works sometimes, so it "must" be OK right?)

      WRT grounded neutrals and stuff there is something weird about slapping a 4prong on an ancient 3prong appliance with a grounded neutral in the appliance that makes it non-trivial to rewire something about violating the rule about connecting neutral and ground at only one point in the system because you need strong enough wiring to handle full fault current thru that low wiring if the main neutral-ground bond ever opened up or something and a different device failed and shorted to ground or ... something. I know just enough about this to know I'd need to provide my local electrician buddy with some case of beer and it would only take him 10 minutes to do it the right way. So he might or might not have blown up if you walked up with a 3prong in one hand and a 4prong in the other knowing that whole area is sorcerers apprentice time if you don't actually know what you're doing.

      An alternative explanation is there is no consistency in local electrical codes BUT I've worked in a couple data centers and in the general area where I live, at least at a commercial or industrial setting, any kind of homemade adapter like you're trying to make, means inspection automatic insta-fail. Also permanently installed machinery needs permanent not temporary wiring in at least some inspectors minds, which also might relate to the freak-out. Your local inspector probably does vary.

      Comment


      • #4
        First of all, it's none of his business what you do. If you were a contractor or doing work for someone else, there would be a liability. But doing it for yourself, if you want to plug a toaster into a 100 amp welding receptacle, it's your gig. Maybe not brilliant, but it's your call.

        I wouldn't hesitate for one minute to run the mill drill from your 40 amp circuit. This is not an installation that you walk away from. Also, the circuit breaker is there to protect the wire to the receptacle, not the appliance. If that were the case, you couldn't plug your coffee pot into a 15 amp circuit because it only draws 3 amps.

        During a catastrophic motor failure, the circuit breaker will protect the circuit wiring. It is unlikely that ANY circuit breaker would help save the motor. If you want to do that, install motor overload blocks sized specifically for the load.

        Make all three machines identical and have at it.

        Comment


        • #5
          Originally posted by ed_h View Post
          can't you just put another box next to the existing one with the new recepticle in it?
          Sometimes.

          I can think of a couple electrical inspector failure modes for this, most of which probably won't apply, but if at least one does, then outta luck.

          One is wire fill. If it passes, cool. I don't think it will without modification. Why would they have installed grossly oversize boxes initially? Or maybe no junction/splice boxes at all. Which might lead to old wiring no longer being grandfathered in, leading to more expense.

          The next is possible 3 vs 4 prong issues. Adding a 4 prong to a 3 prong usually exceeds the tolerance of grandfathering provisions so now you get to upgrade the whole works to 4 prong which might be more expensive than just adding a new run of 4 prong and leaving the old 3 alone.

          Another bone of contention is going to be shared neutrals, some places will demand individual GFCI receptacles if you have multiple receptacles per branch something about a failure in one device with a human touching both chassis at the same time or something, and it gets really weird with 3-prongs and bonded neutrals and you are NOT going to like the price comparison of GFCI protection at 220 high current vs a couple feet of cable unless this run is like 200 feet or something. Or maybe your locale doesn't care about GFCIs and you're "lucky"

          Also 40 amp splices are possible but a pain. Its not like 15 amp 110. You're not going to like that cost or labor. You can do it I'm just saying the number of swearwords per receptacle increases much faster than linearily. High current 220 receptacles and junction boxes are just a PITA compared to 110 and frankly I would find it much less painful just to homerun each to a panel or subpanel.

          Something that does get electricians / inspectors all fired up is multiple sizes of receptacle on a circuit. Multiple 30 amp receptacles on 30 amp wire and 30 amp breaker, OK. A mixture of 20 and 40 amp receptacles seems to get them all fired up. Something about 20 amp hardware expects the circuit breaker to protect the hardware itself from overload, and they do that, if installed on a 20 amp ckt, but not so well on a 40 amp ckt. The literal receptable itself is only rated to pass 20 amps so putting it on a 40 amp ckt is "wrong" because the 20 amp receptacle could fail (well probably not, but in theory...).

          If you got way more ambitious about outlets than just two, you could run into that 180 watts minimum per yoke rule but you need a ridiculous number of receptacles before this is an issue. Still if you have a data center and advertise that every four rack U you get a receptacle if you try really hard you can annoy the inspector. Or if you had a full shop with ALL the machines every made and insist on running the whole works off one branch... Ham radio contest station or restoration/collector dude with like 10 legal limit linears all on the same branch will piss off the inspector. Maybe not a fail but there's no point in getting him worked up before he starts to critique the rest of your work.

          Multiple hardwired motors on a 220 branch involves some complicated flowcart in the NEC that I gave up on. Something about if both motors kicked on simultaneously in the olden days before VFDs the startup current would drag the voltage so low they'd both catch on fire from over current before the starter windings disengaged or ... something. Thats why you can't just tap into an air conditioner compressor or a furnace blower run, at least in most places.

          Installing a subpanel might end up being the cheapest way to do it and if done right certainly future proofs any additions. I would never put lighting ckts on the same subpanel as machines for safety reasons.

          Comment


          • #6
            Your example of a 3 Amp device plugged into a 20 Amp circuit is faulty. The low Amperage 15 and 20 Amp circuits are a kinda exception to the general rule because having circuits for every value between 0 and 20 Amps would just be too much and would drive the average user crazy trying to find the correct socket. The wiring and the outlets are rated for either 15 or 20 Amps to match the breaker. The line cords on most home appliances and lights ARE rated for at least 15 Amps, probably 20. So a 15 or 20 Amp breaker WILL provide safety ALL the way from the breaker to the enclosure of the device that is plugged in. Any fire from excessive current could only be inside the device itself and there are rules for that also.

            But if you put a 20 or 30 Amp outlet on a 40 Amp circuit and it or the 20 Amp device that is plugged into it fails at a current that is less than 40 Amps, then the breaker will NOT provide protection. A 35 Amp current could start a fire while the breaker sits there completely dumb and happy. This 35 Amp fault current could be in the outlet itself, in the cord, or in the device (your mill).

            I would suggest adding a sub box at the location of the present 40 Amp outlet. Then add breakers there for the individual currents needed by the machines. And use the correct sized outlets.

            You could check the wire size on that 40 Amp circuit. If it will take it, you could upgrade the 40 Amp breaker to 50 or more and that, with the added sub box and outlets, would give you the ability to run two machines at once.
            Last edited by Paul Alciatore; 05-06-2013, 01:56 PM.
            Paul A.

            Make it fit.
            You can't win and there is a penalty for trying!

            Comment


            • #7
              I looked today. It is a 20 amp circuit with the appropriate 20 amp female on the wall. The mill states 15 amps and has an overload protector right on the motor (okay, the electrical connection box on the motor.)

              I use only the one plug because... well, there is just one of me in the garage and I don't run two machines at the same time. I thought about putting in a sub box off the the main box but that opens a whole can of worms.

              I gave serious thought about cutting the end of the cord and putting on a 20 amp plug... Just seems to make more sense to put a short adapter in line, the twist 20 male and a flat plug 15 female. I would wire the line for 20 amps, wire to match the feed to the box.

              I wonder if anyone makes a 15 amp 220v GFI? I would just put that box on the back of my mill stand and plug into that from both ends. Heck, I have seen that done enough on 110v drop cords around the shop.

              (I am getting another welder and I think I need my last open 220 slot for that, I think it will be a 30 or 40 amp machine. I don't recall off hand.)

              Comment


              • #8
                Originally posted by Paul Alciatore View Post
                Your example of a 3 Amp device plugged into a 20 Amp circuit is faulty. The low Amperage 15 and 20 Amp circuits are a kinda exception to the general rule because having circuits for every value between 0 and 20 Amps would just be too much and would drive the average user crazy trying to find the correct socket. The wiring and the outlets are rated for either 15 or 20 Amps to match the breaker. The line cords on most home appliances and lights ARE rated for at least 15 Amps, probably 20. So a 15 or 20 Amp breaker WILL provide safety ALL the way from the breaker to the enclosure of the device that is plugged in. Any fire from excessive current could only be inside the device itself and there are rules for that also.
                Not so much. There is no "toaster" wiring that is rated for 15-20 amps. I have seen more than one of my own toasters burn a nasty death BEFORE any breaker decided trip (in fact, it happened twice). If you want motor protection, install motor overload protection. A branch circuit is not designed to be motor protection. It is designed to deliver power for a device or devices. Send however much power you want out there. If you want to do it right, protect each and every motor EXACTLY to it's nameplate with the correct overloads. If you don't, then simply plug it in and change the motor when it smokes.

                You aren't likely to burn the house down while standing there watching the tool explode. And 40 amps @240 volts is quite a small load. I wouldn't think twice about making all three tool the same and RUNNING them (one at a time of course).

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