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30 amp service

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  • 30 amp service

    Ive been running my shop with 30 amp service for years. At one time i had my mill boring on feed a hole the shaper running cutting a block of stainless and my lathe making a long turning pass. My friend rudy then walked in on me and kinda looked at me funny and said oh i guess youre busy ill come back later. I was laughing. Anyhow now i am trying to get a 250 amp welder and also picking up a 5 horsepower air compressor a devilbiss industrial 5 hp single phase. So far never power related problems. My lathe has a 3 horsepower motor my shaper a 2 horsepower and my bridgeport the original 2 horse i think three phase rewound to single phase power. Do i need to upgrade my wiring. PS I dont usually run three at once and certainly only start one at a time. I am currently running 3/3 wire to my shop from a hundred feet away from my home panel. thanx for any advice Mike

  • #2
    You need more capacity on your electric service, can't understand why you haven't been blowing breakers. Don't know what 3/3 service wire means. Did you mean 3/0? Need to know the wire size and number of wires.

    GUNS Don't kill people
    Drivers using cell phones do.


    • #3
      Volts x Amps = Watts and if I recall 745 watts = 1 HP. So lets see. 30 Amps x 220 volts = 6600 watts of available powere. That would be roughly 9 available HP. Just averaging here, don't have a calculator handy. So it looks like you could pull all of your machines but the welder may be a different animal. The first big draw is at startup, motors are like a short on start up and when you start to pull a higher load (i.e. big cut) you pull more amps. Not sure but there should be an electrician around who could tell you max amps for a #3 wire.


      • #4
        I would think at least 100 amps would be a good size to start with. The 3/3 wire you have now does it have 3 wires 2 hot legs and neutral covered and a bare ground? Is the service overhead or direct buried or in conduit? In any case you need #2 strand CU or 1/0 Al for 100 amps 100' away or at least that is what the power Co I work for would require # 2 Al or # 4 CU if it were overhead. I have been looking a 2 HP motors they require 15 amp service at 220 V single أ? 30 amps at 110. It sounds like you need to upgrade. Your welder will need at least a 50 amp ciruit. You will need a service with 2 hot legs a neutral and a separate ground. If it is going in conduit all conductors will be covered. You need to look into your local codes they vary from place to place.
        Last edited by gundog; 05-05-2006, 10:40 AM.


        • #5
          You say DeVilbiss 5 HP industrial compressor? If it's 5 HP for real, it will need that 30 amp service all to itself. A real 5 HP motor draws 22 Amps @ full load. When a compressor runs it starts into the empty discharge line. Pressure rapidly builds uitil the motor is running near full load, and if the compressor is set up correctly, shuts off at a slight overload. Since the compressor starts automatically there's no coordinating its starting surge with any other machine you have on the same circuit hence your compressor requires its own service or you're asking for a blown breaker.

          746 Watts = 1 HP only theoretically using a perfect motor. You have to look at motor name plate full load amps and consider induction motors as they exist when evolving electrical requirements for a proposed upgrade in an expanding shop. You also have to consider starting loads etc.

          I think your first plan is to list as you have the present and new machine motors, lighting loads, heat and A/C, fans, welders, phase converters, and all other electrical loads to be connected to your electrical upgrades. List their electical demand and probable duty cycle. Figure at least two 115 Volt wall outled circuits, a coffee maker, and one lighting circuit. Regard your heat and A/C and your compressor as automatic loads that could kick in at any time, the lighting as on full time when you're in the shop, etc. The others are under manual control.

          Determine the size of your present service and how it's fed from the electrical panel. Take a reasonable guess on how much electrically powered equipment load (water heater, pressure washer, new machine tools, woodworking machinery) you will add to the new service You now have the basis for planning an electrical service upgrade.

          You do not have to sum all you loads and install a service capable of feeding it all at once. Not all loads will be on at once or if they are, running at full load. I have about 380 Amps of breakers in a 200 Amp panel. Each breaker is sized to protect the branch circuit conductors connected to it. The panel breaker protects the sub feed panel, the sub-feed breaker in the main penel protects the sub feed consuctors.

          Go find a local electrician savvy on the local elctrical code. Ask him to walk you through your requirements and reccommend a service panel sized for your shop. Don't be surprized if he reccommends a 100 Amp service or maybe higher. If your electrical panel is adequate and you have space you can add a 100 Amp breaker and run #4 load conductors, a #6 neutral and a #6 ground if your local code premits.

          Your electrical upgrade will have to be code compliant even if you sneak it in without inspection. Should there be a fire originating in a sub-standard electrical system your insurance carrier may not pay your claim.

          Forrest Addy, not a licenced electrican but an amateur with considerable full time industrial electrical experience working under the direction of a licenced electrician.


          • #6
            30 amp service?? Wow, I'm amazed.

            I'm going to assume that your 30 amp service comes from the house service panel. Is that house panel 100 amp? 200 amp?

            In my case, I have a 200 amp service to my home and am running a 125 amp sub-panel (or feeder) in the garage/shop. I did VERY conservative load calcs on the house and came out to about 100amps needed for the house lighting and all appliances. Given the conservative nature of the house calcs, the 125 amp for the garage, given it's expected usage shouldn't cause any problems.

            What you will find is that if you're looking for a new panel with a main disconnect at the panel, the easiest solution will be a 100 amp panel at the big box stores. Those normally come with (but best to double-check) the main breaker installed. The next size up at these stores is 125 amp, but this one doesn't normally have the main breaker in it. It just has "main lugs", so the overall 125A protection comes from a breaker upstream, most likely in your house service panel. Up from that is the 200 amp panel with a main breaker, but chances are this is too big, if you're feeding it from a 200 amp house service panel.

            What I'm doing, since I don't like to have a lot of stuff on one circuit, is I got a 200 amp panel on ebay that has a 125 amp main breaker. The logic there is that 200 amp panels tend to have more slots for circuit breakers.

            If your house is only 100 amp service, perhaps look into upgrading the house service to 200 amps. In my area, they can slip in another underground (or overhead obviously) service conductor into the existing conduit to get you up to 200 amp service without any digging. And my local area doesn't charge you for it. (I was going to try to go from 200 amp to 400 amp, but that would've required larger conduit = big long trench, new meter socket, new panel, etc). It's worth a phone call to the power company just to find out.



            • #7

              Another dream squashed. Low budget but proud. Thanx for the tips guys.


              • #8
                Remain proud my friend. You've done more with 30 amps than I ever thought possible How often did you trip your breaker??


                • #9
                  You truly are a madman. Yank that 30 amp breaker out of there and replace it with a 70 amp. Then add a helium cooling system to the conduit carrying the power wires into your shop. You might want to negotiate a shedule with the wife so your combined power use doesn't raise the temperature of the main panel beyond the flash point of the paint on it. That's not a particularly appetizing smell.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #10
                    Breakers Away

                    I have never had a breaker trip. I have run my bridgeport on a feed powered boring cycle stop set while its running im turning a [email protected] norton commando axle long cut. My shaper is running on some stainless steel facing away im squaring up s/s blocks. The lathe is 3 horse shaper s 2 horse mills two horse three phase rewound to one phase and cap tuned for hertz range (whatever that means) Recently i was nervous dragged in a 250 amp miller welder and sat in shop for three days weding non stop, Customers job lumngs got black ened had to make money unemployed family to feed. BUT NO BREAKER POPPING. No kidding. But i didnt run anything but the welder.


                    • #11
                      I run my shop on a 40 amp breaker. I have a jet 3hp cabinet saw, 2 hp jointer, 2hp pennstate cyclone vac, 3 hp 80 gallon air compressor, 1 hp delta woodshaper and a Millermatic 175. Been like this for the past 5 years and never blew a breaker. I find that I can physically, only run one machine at a time


                      • #12
                        Madman -
                        What the other guys said, especially Forrest.

                        Money + professional, licensed electrician = Less BS from insurance carrier should problem arise.

                        I'm amazed that you're running a shop on 30A service. Keep in mind that if you're gonna upgrade (and it sounds like you should) the additional cost of really fat wire is not very much. Nothing says you can't run 300 amp wire with 100 amp service, and upgrade the rest of the way later. If you haven't already, you might as well run phone and network wiring at the same time.

                        Stay proud, buddy, but stay safe, too.

                        The curse of having precise measuring tools is being able to actually see how imperfect everything is.


                        • #13
                          non tripping breakers

                          Do you have Federal Pacific breakers?

                          If you do, that may explain the breakers never tripping. They are a defective design and seldom if ever trip. Many fires have been started by them.


                          • #14
                            Wirecutter-- I certainly agree with your premise that heavier wire is not a bad general. It allows you to change uses of a particular run in the wall at a later date (where you do it for branch circuits etc). Service entrance wire is a place not to get carried away. This is both because the bigger wire may cost you *lots* more for say three hundred feet of the stuff...and more importantly because it can be like trying to wrestle a live alligator and cause other problems.

                            The huge conduit you have to use for three runs of 3/0, the giant weatherhead (for an overhead entrance), and the fact that he may end up with wire in say a 100 amp panel that will not have main lugs large enough for 3/0 wire are all reasons not to go overboard.

                            I went with 3/0 for the 200 amp service entrance when I re-wired my old house about 16 years ago and regretted it. The run from the weatherhead was short enough that 2/0 would have made code and I had a horrible time trying to wrestle three conductors of 3/0 through the entrance ell to the panel location.

                            That having been said, when I wired my new shop building here a couple of years ago, I ran #10 wire to several drops for 220v tools despite the fact that I had no more than 20 amp current needs. This came in handy as I later bought a true 5HP compressor that draws 22, now. Just swap a breaker, hard wire it in in place of the old outlet for the portable and I was all set. One thing I did that made this all easy to judge for safety was that I made a spreadsheet listing all the breakers/services as well as the wire size I ended up using for each run. Even before I opened a box or the service panel, I knew that I had wire on that circuit that allowed for that compressor.

                            Paul Carpenter
                            Mapleton, IL


                            • #15
                              Paul -
                              I like your spreadsheet idea, and I'm going to use it. Thanks.

                              You make a good point about wrestling with fat wire - it can be a pain. I'm just making the point that, once you go to the trouble of running the wire, do it as big as practical so you only do it once. Usually, the additional cost of fatter wire is small compared to the cost and difficulty of the installation. YMMV, especially with really big wire. Point taken.

                              The curse of having precise measuring tools is being able to actually see how imperfect everything is.