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Thread: Shop electrical wiring - EMT vs MC cable

  1. #1

    Shop electrical wiring - EMT vs MC cable

    I am doing some planning and estimating for a possible 30x45x12 metal building shop, and have been doing some reading about EMT (metal conduit) vs MC cable in a surface mounted workshop setting.

    Having never worked with EMT before, a little bit with MC cable, and plenty with Romex in more residential / remodeling I’m trying to assess all options. Current plan is for everything to be surface mounted on wooden walls or open ceiling / bottom of the metal trusses. There will be a mix of 120v and 220v single phase circuits (receps, lights, etc) and also a rotary phase converter with 3 phase sub panel and likely 3 different 3 PH circuits (20 and 30 amp) going to various machines. The wiring needs will be fairly customized and substantial compared to a typical small shop with mostly 110/220v single phase, but nothing I haven’t done already in my basement shop (aside from the actual wire/conduit choice.)

    I am aware of the concept of running multiple circuits in a branch to a certain central location inside of larger conduit (as opposed to multiple different runs of MC back to the panel) Being able to fish more wire later inside the EMT seems to be a point of consideration but otherwise similar amounts of wire but visually less going on is the only difference I see in that.

    Can anyone more experienced speak to these choices in this application?

    What about cost of materials and labor differences at this scale?

    I would be doing most of the physical wiring after the initial inspection of minimal electrical from my electrician (panel and a couple of circuits with a few receps and lights to pass inspection.) I am comfortable with wiring and learning whatever I need to / asking for clarification from electrician friends to do the bulk of the physical wiring and planning the runs and then having one of them double check my work before hooking up.

    Any thoughts?
    Last edited by Phillip Mitchell; 05-03-2022 at 9:27 AM.
    Still waters run deep.

  2. #2
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    The advantage to MC is that you lay it in in one step and have just a slightly more difficult termination process to your boxes because of the need to cut the armor. It's also rated to be fully exposed which is why it's very popular in metal and other post frame structures. Conduit is certainly a valid method for exposed/surface mount electrical work. But you need to install the conduit and then pull the wire though it. Not "hard", but still a process. MC has a time advantage for sure. Whether it has a cost advantage or not has to be judged on actual costs in your area for either MC in the size(s) you need vs the cost for conduit + THHN conductors in the size(s) you need. In some situations, it might be cost effective to use both methods...MC for runs that are independent and conduit for those runs where you would benefit from more conductors through the tubing.

    If your wiring is going to be covered by insulation and walls, you do not have to go to the expense of MC or conduit...install in the wall normally and do whatever the necessary permit approval/inspections processes are for rough/finished electrical and then proceed with insulation and walls accordingly.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #3
    I've got both in my shop. The initial electrics were done by an electrician, all run with conduit.

    I have never tried to run an extra wire through conduit it seems to me it would be very difficult.

    But I have added/modified several circuits using metal flex. Yes, its much more expensive, but the time saving and lack of skill bending conduit made it a good choice.

  4. #4
    After building a new shop 5 years ago, I naturally did some re-arranging. Then some more machines came in. More re-arranging.
    In general, I find myself doing something inside that conduit at least once a year, so disregarding actual cost per foot, I would not dream of using the metal flex conduit, as it is "once and done".

    Use large enough conduit (3/4 seems to be the sweet spot for capacity and cost/availability) to allow for some expansion, addition and re-arranging of circuits, with junction boxes set at 6-8 ft maximum intervals. This allows a run or two of 220, and a run of 120. I keep 3phase runs in their own separate conduit.

    While the MC is physically flexible, I think the EMT has the kind of "flexibility" a shop truly needs.

    jeff

  5. #5
    When I built my shop, all my electrical was surface mounted EMT. Over the years, I have also moved and/or upgraded machines. With the EMT, any changes were doable. While EMT may be a little more labor intensive, I have never regretted using it.

  6. #6
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    There is a bit of a learning curve to bending conduit but probably some YouTube viewing can help. MC is a little harder to make look "neat" on the wall but can be done. Not sure what you are mounting to but you will need straps every 5' and within 12" of the box it is entering or leaving. If you have beams that form horizontal channels I think you find the MC is your friend as you can just lay it in there.

  7. #7
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    EMT hands down looks best for surface work. But you have to take some time to learn how to do the bending. Elbows are easy. It's the offsets, kicks and saddles that are a lot harder to have look good.

  8. #8
    With EMT, do you need to run a separate ground wire? If not, saves a lot of money on copper. I prefer the compression fittings instead of the single screw point ones. Have both types in my shop though.

  9. #9
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    I have a metal building also and I used regular 'ol romex house wire laid out horizontally on the center of the purlin and girts. For the interior walls I used 29ga prefinished Liner Panel (aka metal roofing). I cut the back off of plastic receptacle boxes and used rivets to fasten the modified boxes to the metal panels and I'd pull the wire through as I went. ....changes are pretty simple to do just back off some screws, do what ya gotta do and put it back together.
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  10. #10
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    My shop has EMT circling the walls near the ceiling with junction boxes every 8' or so. I then have drops out of the junction boxes for outlets down at a comfortable height. This keeps the conduit out of the way for cabinets etc. Bending is easy with a little info off the internet and I have added/changed my electrical layout multiple times. I did use MC above the ceiling for connecting the light fixtures.

  11. #11
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    Quote Originally Posted by Bruce Wrenn View Post
    With EMT, do you need to run a separate ground wire? If not, saves a lot of money on copper. I prefer the compression fittings instead of the single screw point ones. Have both types in my shop though.
    No, the conduit can serve as ground, but that's a practice that is often frowned upon by engineers (for good reason). If you do run a ground wire, it must be sized for the largest circuit in the pipe. Only one wire required per pipe. If you don't run a ground, be sure the lock nuts and set screws are securely tightened.

  12. #12
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    Quote Originally Posted by Lawrence Duckworth View Post
    I have a metal building also and I used regular 'ol romex house wire laid out horizontally on the center of the purlin and girts. For the interior walls I used 29ga prefinished Liner Panel (aka metal roofing). I cut the back off of plastic receptacle boxes and used rivets to fasten the modified boxes to the metal panels and I'd pull the wire through as I went. ....changes are pretty simple to do just back off some screws, do what ya gotta do and put it back together.
    You should check code on that. Here, you cannot run non-metallic cable on a metal surface without providing insulated spacers. And cutting the backs out of the boxes will certainly void the certification and not likely to pass inspection.

  13. #13
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    Quote Originally Posted by Frank Pratt View Post
    You should check code on that. Here, you cannot run non-metallic cable on a metal surface without providing insulated spacers. And cutting the backs out of the boxes will certainly void the certification and not likely to pass inspection.
    "You should check code on that"...I don't think so

  14. #14
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    I ran most of the wiring in the ceiling using plain romex then dropped the receptacles down using EMT. No bending involved, a significant cost/labor saving, and the wires are protected where they're likely to get hit by anything. It is fine to do the drops with romex for protection if the conduit is big enough (clear it with your inspector), but I mostly used THHN inside the conduit. I ran MWBCs to every outlet point so I could have either a mix of 120 and 240 circuits or two independent 20A 120V circuits in each quad box. Big machines that might run simultaneously (eg dust collector, compressor) got dedicated circuits.

    I've since installed a RPC, so how have a couple dedicated three phase runs as well. I'm sorry I didn't pull a bigger wire to feed the shop.

  15. #15
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    I did my old shop space with metal boxes and EMT. Ran most of the 3P to machines in conduit as well. Hate the crappy lock ring fittings and set screws. Told my BIL next time I'd run a cord across the floor to the machining center, order in a bunch of aluminum blocks, and make my own boxes with integral o-ring sealed spigots for stainless steel tubing. He smiled and said, 'yeah, that'd sure be nice. But it won't pass inspection because it's not 'approved'. :-(

    Oh well, it'll save me a bunch of work. But I'm planning on using the nice die cast waterproof boxes with fittings threaded in. Not cheap, but even with a ton of them it probably won't add up to more than an extra couple hundred bucks.

    I also pulled stranded wire. Much nicer, but a pain to connect to outlets and switches. May ... *will* use it again, but with terminal blocks. Will probably do the machines with cords. Easy to pull when a thunderstorm rolls thru. That wasn't generally an issue in the Bay Area ... other than those nasty little fires in Big Basin ... but not so uncommon here in TX.

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