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Looking for a "Warm and Fuzzy" on Sizing Shop Sub-Panel

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  • Looking for a "Warm and Fuzzy" on Sizing Shop Sub-Panel

    Life's been a bit bumpy the past few years but I am very slowly piecing together the shop I've always wanted. I've got a detached, insulated 1120 square foot building with 3 roll up doors that is dedicated to shop space. Right now, it has 30 amp service - obviously nowhere near enough!

    I basically have two options where the first option is the "best" but is going to be expensive and probably take me a much longer time with all the other projects I have going on (this house was a major fixer-upper). The second option is not quite as good but is much easier to implement. Conventional wisdom says to oversize everything and grow into it but I'm worried that I may end up waiting another several years before I'm able to do that...

    1) Replace 200 amp service with 325/400 service - Based on conversation with poco, it looks like they would keep the drop the same size but I would have to hire an electrician to install a new meter pan with dual lugs. Then I would run one branch to the 200 amp panel in the house and the second branch (4/0-4/0-4/0-2) would run to a 200 amp panel in the shop. This is both expensive and would have to be scheduled sometime in the indefinite future. The main complication here is the state of the house wiring. I'm slowly bringing it up to code. Each time I rennovate a section of the house, I run new electrical, all to code, to a new 200 amp panel that is being fed as a sub. Eventually, I'll have the poco pull the meter and I'll move the SE cable over to the new 200 amp panel and remove all the old stuff. But until I'm ready to move the SE cable, I don't really want to involve an electrician (FWIW, I am allowed to do my own electrical work past the meter as long as I get it inspected) only because I'm concerned about the project scope exploding.

    2) Run 150 amp sub-panel in shop - This is the easiest solution because I can pick away at it myself and at my own pace and then have it inspected when complete. It's also much cheaper. Basically, I'd be popping in a 150 amp breaker in the 200 amp house panel and running 2/0-2/0-1-4 to the shop. The material is cheaper, no need to hire anyone, schedule flexibility, etc. But now I've got 200 amps for both the house and shop. I don't want to blow the main breaker if my furnace kicks on or my dryer is running and I try to start an arc with my welder! And, of course, I have 150 amps instead of 200 in the shop.


    The equipment I want to run in the shop:
    Lights
    General purpose 20 amp outlets
    Window AC
    Furnace
    Syncrowave 350
    Phase converter (10 hp idler motor)
    Bridgeport (3/4 hp 3-ph motor)
    KT 2D (3/4 hp 3-ph motor)
    Cincinnati horizontal mill (2 hp? 3-ph motor)
    Bandsaw (1 hp 3-ph motor)
    Pacemaker #1 (5 hp 3-ph motor)
    Pacemaker #2 (7.5 hp 3-ph motor)
    Drill press (1.5 hp 3-ph motor)
    Shaper (5 hp 3-ph motor)
    Etc.

    Of course, this is a one man shop and it's unlikely I'll ever have my Syncrowave cranked up to its max setting. The most I can see myself doing is letting the bandsaw or shaper run while I'm also doing some TIG welding or machining on another machine. Most of the machines are less than 2 hp, with the exception of the lathes. But there again, it's unlikely I'll be hogging off enough to hit the FLA since I'm doing this mostly as a hobby now. Also, if I'm in the shop, the house is empty so it's not like there's a huge power draw there. No central AC, either.

    I just can't decide what to do. I hate to hobble myself with an undersized electrical system but I also don't want to wait forever... It's already been 3 years since I moved in and I haven't even started on the shop!

  • #2
    For a one man shop, I'd say a 100A sub panel should not limit you in any way. Even with the Syncrowave, it only draws max current when in Stick/SMAG mode and not in TIG mode. Do you have an air compressor? That's one of the items than can kick-on drawing 30A-50A while you're melting holes in your welding table and possibly trip your main breaker.

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    • #3
      Well, I run my shop on a 50 amp sub-panel. It IS small, but it was in place when I bought the house in 1995. I have a 7.5 hp rotary phase converter, it will run my 5hp lathe motor plus another machine. In fact, when I want the best finish from my surface grinder, i will often use the lathe as an additional idler. I don't weld in the shop, welder and air compressor are in the garage. I have no clue what your welder draws, but mine requires only a 50 amp circuit.

      The 150 amp sub panel would be my choice. Makes sense in many ways, and using a little common sense about electrical loading would be better than the complex and expensive alternatives
      I cut it off twice; it's still too short
      Oregon, USA

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      • #4
        My house and detached shop are all powered through a 200A service. There is a 100A sub-panel for the 5hp compressor, 7.5hp rotary and the heat-pump (30A). I used a 100A sub because I'd eventually like to get a larger compressor. Never had any issues. Note that the 50A welder outlets come from the main panel, not the sub.
        Southwest Utah

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        • #5
          Originally posted by 3 Phase Lightbulb View Post
          For a one man shop, I'd say a 100A sub panel should not limit you in any way. Even with the Syncrowave, it only draws max current when in Stick/SMAG mode and not in TIG mode. Do you have an air compressor? That's one of the items than can kick-on drawing 30A-50A while you're melting holes in your welding table and possibly trip your main breaker.
          I thought that and installed 100A panel in my shop... Then I got into CNC machining where I could (and do) use more than one machine at a time, and I wish I had run a 200 amp panel with appropriate size drop wire.
          *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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          • #6
            Originally posted by Bob La Londe View Post
            I thought that and installed 100A panel in my shop... Then I got into CNC machining where I could (and do) use more than one machine at a time, and I wish I had run a 200 amp panel with appropriate size drop wire.
            Must be a CNC welder and CNC plasma cutter? Why on earth would you need another 100A to run some CNC machines?

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            • #7
              Originally posted by 3 Phase Lightbulb View Post
              For a one man shop, I'd say a 100A sub panel should not limit you in any way. Even with the Syncrowave, it only draws max current when in Stick/SMAG mode and not in TIG mode. Do you have an air compressor? That's one of the items than can kick-on drawing 30A-50A while you're melting holes in your welding table and possibly trip your main breaker.
              Oops - forgot the air compressor. Yep, that's a good point. Re: the welder, I have a 350A TIG torch and associated cooler and, at 350A, 34V the welder pulls 128 amps on 240 VAC. But I've only used this once when I was working on huge machinery - something I won't be doing in this shop.

              Thanks all for the vote of confidence. Sounds like I can be pretty confident in a 150A sub panel for my needs.

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              • #8
                There are no 150 amp breakers to install in a 200 amp panel, 100 is the biggest. I would consider installing a 200 amp panel in the shop fed by the 100 amp breaker. If you ever needed more power you wouldn’t need to rip out the panel. You might even make it a service entrance in the future.

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                • #9
                  Here is a 125A:

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                  • #10
                    Originally posted by garyhlucas View Post
                    There are no 150 amp breakers to install in a 200 amp panel, 100 is the biggest. I would consider installing a 200 amp panel in the shop fed by the 100 amp breaker. If you ever needed more power you wouldn’t need to rip out the panel. You might even make it a service entrance in the future.
                    Probably depends on the panel manufacturer. Mine is a SD HomeLine (not the best, I know). Here is the 150A branch breaker I would use:



                    Or are you suggesting that a 150A breaker in a 200A panel is somehow a NEC violation? I can't imagine why it would be ...?

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                    • #11
                      I forgot that I installed two 100A sub-panels in my machine shop. A 100A panel on each end of the shop. But all of the big stuff (Welders, plasma, compressor) are run off one of the 100A panels. The machines (BP, lathe, grinder, saws, lights, etc.) run off the other 100A panel. I also have a 100A sub-panel in my woodshop in the basement. I do have a 400A service though. If you have a large shop, you might want two sub-panels and their location inside of your shop might make all of your tool placement/wiring much easier as it was in my case. It would have been a real PITA if I didn't locate the sub-panel right where I want them. Maybe installing two 100A or a 100A and a 50A or something might make more sense depending on where your tools are located in the shop and how much power you really need. EDIT: added pics



                      Last edited by ; 06-07-2018, 03:22 PM.

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                      • #12
                        Let me ask this question: If you pop a breaker due to overload once a year or so, is the inconvenience of resetting it worth the cost of upgrading to the larger service? If so, spend the money.

                        I'd probably just put in the smaller feed and be done with it. Sounds to me you've hit the level of "acceptable annoyance."

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                        • #13
                          Originally posted by Puckdropper View Post
                          Let me ask this question: If you pop a breaker due to overload once a year or so, is the inconvenience of resetting it worth the cost of upgrading to the larger service? If so, spend the money.

                          I'd probably just put in the smaller feed and be done with it. Sounds to me you've hit the level of "acceptable annoyance."
                          Yes ideally once a year. But when you're running very close to the limit, it might be once a week or daily which you want to address now rather than later. For my current setup, 100A is more than I need so I'm probably never going to trip a breaker. If anything, my needs will lower in the future as I swap out the transformer machine(s) for efficient Inverter technology like a Dynasty 400.

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                          • #14
                            Two Pacemakers? That ain't fair.!!!

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                            • #15
                              Originally posted by 3 Phase Lightbulb View Post
                              Must be a CNC welder and CNC plasma cutter? Why on earth would you need another 100A to run some CNC machines?
                              Why must it be that?

                              How about 4 CNC mills on 20 amp 220 circuits 1.5 hp each for spindles. 1 on a 30 amp circuit with a 5hp spindle. 3.7 hp 220V air compressor. 220V split air conditioner in office. 220V 3hp manual lathe. Firing up the 220V Miller 212 to do a quick weld. Its on a 50 amp circuit and if I try to use the peak current of the welder it can trip the breaker. (Spindles are not the only load from a CNC mill. One machine peaks at 30 amps and 90VDC on the servo motors (it has 3) for example.)


                              Of course there is a fridge, lots of misc tools, 110V and 220C horizontal bandsaws, computers (besides those controlling machines, enough lights to light up a 3000 sf shop, 700 sf of office inside the shop, and 3 pretty heavy overhead doors that can be opened at any time as needed. I'm not at 100% most of the time, but if peak loads time just wrong I could be. I also want to bring in another machine that has a 20HP spindle. The price is right, but I would have to shut off a lot of other things to really make use of it.


                              I really do wish I had a 200 amp sub to my shop for real reasons 100% valid reasons.

                              I never understood the just barely enough mentality. A larger service or a larger sub panel doesn't raise your electric bill, and the upfront cost difference is relatively low. Its only actually using more power that raises your electric bill. Atleast on a residential service.


                              To be fair I thought 100 amps was overkill when I built my shop. It was a small office and a warehouse for my contracting company. I ran very little equipment back then.
                              Last edited by Bob La Londe; 06-07-2018, 05:46 PM.
                              *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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