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  1. #1
    Ryan Slaback is offline Aluminum
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    Default Exterior 220v 1ph outlets

    I teach metals among other things in a high school. We are desperately running out of floor space in the shop itself. I have 5 220v single phase machines on rollers (1 plasma, 1 Tig, 3 mig) and only room enough inside to operate maybe 3 of them at once.

    Last summer I had a 16' x 40' pad of concrete poured adjacent to the shop on which my auto class can work allowing us room for more vehicles. I want to utilize this space to also allow some of the students to work on the metals fabrication projects (everything from speaker stands to trailer frames) as well. Ideally the kids would roll whatever machine they need outside, use it for the hour then roll it back.

    The plan is to run 2 lines out the side of the building, each one with a disconnect switch inside. The switches will be deenergized at all times other than during use. They will be locked off and the kids will have to check out a key to use them.

    I am looking for any advice anyone has on weatherproof 220v 30 amp enclosures. Has anyone done this before? Also, the plan is for the metals students and I to run the conduit and possibly pull the wire, having the electrician only come in to make the connections on both sides. I am thinking that #8 wire should be fine for a 220v 30 amp circuit (each one is about 100' from the box). If I need to run a ground (which I think I do) how big of conduit would I need for 4 #8's?

    Any advice would be appreciated. I know that advice item #1 is talk to the electrician and that is in the plan, however I would like to be as educated on the subject as possible before hand. He's not exactly the easiest guy to work with.

  2. #2
    Mike C. is offline Diamond
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    Should be the same as an outdoor RV hookup?

  3. #3
    Andrew_D is offline Cast Iron
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    I'm no electrician, but I think #8 wire is over-kill. Check with an electrician, but I would think #12 is probably OK.

    Since this is in a high school, I'd make sure that you have all the permits in place to cover your you-know-what. The inspector should be able to tell you what size wire to run and the minimum size of conduit. Don't use the minimum size, especially if you have any curves in the conduit. It will be harder to pull the wires.

    Andrew

  4. #4
    Wyoming is offline Cast Iron
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    Quote Originally Posted by Ryan Slaback View Post
    I am looking for any advice anyone has on weatherproof 220v 30 amp enclosures. Has anyone done this before? Also, the plan is for the metals students and I to run the conduit and possibly pull the wire, having the electrician only come in to make the connections on both sides. I am thinking that #8 wire should be fine for a 220v 30 amp circuit (each one is about 100' from the box). If I need to run a ground (which I think I do) how big of conduit would I need for 4 #8's?
    Ryan,
    First off, you don't need to run four #8 wires for a single phase 230v circuit. All that is needed are two hots and a ground. There is no neutral in a 230v circuit. Secondly, unless you feel the need, the ground wire need not be a #8, per code, so you can go with a smaller ground wire. My copy of Ugly's Elec. Reference give an allowable maximum of 3 #8 wires in 1/2" EMT using stranded THHN wire. I'd have to head to the shop to get my copy of the National Code, but #8 sounds heavy for a 30 amp welder circuit. Welders are allowed a more liberal rating due to their duty cycles.

    As far as hook up by an electrician goes, it would probably keep the school administrators and the insurance people happy. Still, aside from hooking the two hots to the circuit breaker and the ground to the buss bar on one end and the two hots to the labeled hot terminals and ground to the labeled ground terminal in the receptacle that is the sum total of the job you would be calling an electrician out on.

    You will need an outdoor rated NEMA enclosure for the receptacles. I've given away all that I had to friends, but I'll look in the scrap yard tomorrow or the next day to see if any are available.

    EDIT: I may have a couple of disconnects rated for 30 amps. I'll take a look around the shop in the morning. They won't be outdoor rated if I do have them, but that shouldn't be a problem as long as they are located indoors. They should have the hasp lugs to be lockable.

  5. #5
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    Thumbs up All standard stuff

    Quote Originally Posted by Ryan Slaback View Post
    I am looking for any advice anyone has on weatherproof 220v 30 amp enclosures. Has anyone done this before? Also, the plan is for the metals students and I to run the conduit and possibly pull the wire, having the electrician only come in to make the connections on both sides. I am thinking that #8 wire should be fine for a 220v 30 amp circuit (each one is about 100' from the box). If I need to run a ground (which I think I do) how big of conduit would I need for 4 #8's?
    This is all standard stuff. You can get twist-lock connectors and weather-proof housings for them at any commercial electrical supply house, and probably at Lowe'$ or Home De$pot.

    There are lots of different twist-lock connectors, having different voltage and current ratings. You want the NEMA L6-30 type, which is a three-wire connector rated 30 amps at 250 volts. That number should be printed on the face of all plugs and sockets. Parts bearing this number are intermatable across all manufacturers.

    The connector voltage rating is important. Connectors of the same current rating but different voltages are not intermatable due to polarization. This ensures that equipment can only be connected to the proper supply.

    Suitable devices from Hubbell would be the HBL2620 receptacle and the HBL2621 plug. Comparable products from other manufacturers would also work.

    Type THHN wire #8 AWG is rated up to 55 amps in conduit. Your electrician may say you can use #10 AWG (rated 40 amps) for your 30-amp service. But for the length of your run the #8 will have lower voltage drop, run cooler at full load, and give overall better performance.

    You can run three #8 THHN wires in 1/2" EMT. As WY said, you only need three, and one can be smaller than #8.

    Edit: However, I would recommend 3/4" EMT as a minimum considering the difficulty in pulling the wire, as others have noted.

    - Leigh
    Last edited by The real Leigh; 09-23-2009 at 11:13 AM. Reason: Added 3/4" recommendation

  6. #6
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    First of all, Its great to hear that you have a metals and auto mechanics class as it seems like most have ben discontinued. as far as your question I'd 2nd what Leigh said.

  7. #7
    wippin' boy is offline Diamond
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    Should be the same as an outdoor RV hookup?
    yup
    easiest way in my eyes
    nothing wrong with #8 in this ap

  8. #8
    mark thomas is offline Titanium
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    Quote Originally Posted by The real Leigh View Post
    Type THHN wire #8 AWG is rated up to 55 amps in conduit. Your electrician may say you can use #10 AWG (rated 40 amps) for your 30-amp service. But for the length of your run the #8 will have lower voltage drop, run cooler at full load, and give overall better performance.
    The cited amp ratings suggest a common misunderstanding of NEC ampacity tables. While it's true that #8 copper THHN is listed at 55 amp (for 90 degrees), and #10 listed at 40 amps, this does not mean you can run at those amperages. In fact, you most certainly cannot (and be NEC compliant)

    These ampacities are ratings for wire alone, not the circuit. And it is the circuit rating that defines how much ampacity you are allowed to run through the wire. The rating for the circuit has to take into consideration factors other than the wire alone, including the things connected on each end (circuit breakers, enclosures, switches, etc). The things you connect have a temperature rating, which will be either 60 or 75 degrees -- not 90 degrees. That defines the temp column you have to use in the ampacity table.

    So, for example, if you have a recent breaker panel and circuit breaker, it will be rated at 75 degrees (older stuff will be 60 degree). If we ignore what's on the other end for the moment, that means to find the maximum wire ampacity for your circuit you look to the 75 degree column of NEC table 310-16. For #8 copper, it is 50 amp. For #10 it is 40 amp.

    However, there is another wrinkle for #10. The 310-16 has a footnote for #10 that says you can never run it at more than 35 amp.

    Voltage drop is not as cut and dry from NEC point of view, but in general the recommendations are to limit voltage drop to 3%. #10 copper at 100 feet, 30 amp, 240v is about 3%. #8 is about 2%.

    In summary, NEC allows #10 for a max 30 amp 100' 240v circuit assuming THHN copper and 75 degree rated endpoints. Ampacity-wise, you can max out the #10 at 35 amps, but you'll be at 3.5% voltage drop.

    As others noted, you only need two current carrying conductors, plus equipment grounding conductor. The conduit can be the grounding, if properly done, but running a separate grounding conductor is a better idea and may be required by local codes. The size of the grounding conductor is also specified by NEC, and contrary to some suggestions here, it cannot simply be "smaller" than the current carrying conductors. There is a NEC table that defines it specifically, and it is based on ampacity of circuit, not current carrying conductor size. For 30 thru 50 amp circuits, it's #10.

    Although code allows 3 #8 THHN in 1/2" EMT, you won't enjoy pulling that unless it's mostly straight. If you have more than about 90 degrees total bend, you'd probably be happier using 3/4.

    If I were in your shoes, I'd run #8 THHN to be slightly conservative on voltage drop with #10 green grounding conductor, in 3/4" conduit unless it's a really straight run. Depending on the run and location, I'd also consider using PVC rather than EMT. Cheaper, simpler to install. Has to be Schedule 80 outdoors however, and some localities frown on it in exposed locations.

  9. #9
    mark thomas is offline Titanium
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    Quote Originally Posted by Ryan Slaback View Post
    The plan is to run 2 lines out the side of the building, each one with a disconnect switch inside. The switches will be deenergized at all times other than during use. They will be locked off and the kids will have to check out a key to use them.

    I am looking for any advice anyone has on weatherproof 220v 30 amp enclosures. Has anyone done this before? Also, the plan is for the metals students and I to run the conduit and possibly pull the wire, having the electrician only come in to make the connections on both sides. I am thinking that #8 wire should be fine for a 220v 30 amp circuit (each one is about 100' from the box). If I need to run a ground (which I think I do) how big of conduit would I need for 4 #8's?
    Upon re-reading this, I wonder if by two "lines" you meant running two conduit runs, each with separate wire, or one conduit with two circuits in it? Maybe that's why you assumed 4 wires?

    One conduit makes sense, however, note that this affects the wire size. If you have more than three current carrying conductors (so you don't count ground) in a conduit, you have to de-rate the ampacity of the conductor.

    For 4 conductors, you de-rate to 80%. So to find the allowable ampacity of the conductor, you take the 90 degree column from 310-16 and multiply by .8. So #10 is rated at 40, but 80% is 32, so the max ampacity of #10 wire if you have four in a conduit is 32 amps, not 35 amps per previous reply (using the special footnote). For #8, it's 44 amps, versus the 50 amps allowed with less than 4 conductors.

    In other words, #10 is NEC compliant for one circuit per conduit, but for two circuits, you MUST go to #8.

    As you can see, the NEC is a lot more complicated than it first appears. It is rarely as simple as just reading a value in a table. There are many rules and factors that vary how the table values are used.

    My last thought it this: consider a subpanel. 100' is a long way from the disconnect. You could run a single #8 circuit at 50 amp to a small subpanel with two 30 amp circuits. Or better yet probably bump up the subpanel circuit a bit to allow for future expansion. Once you start welding out there, you'll probably be grinding, and running other power tools, need more receptacles, etc.

  10. #10
    Wyoming is offline Cast Iron
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    Quote Originally Posted by mark thomas View Post
    In summary, NEC allows #10 for a max 30 amp 100' 240v circuit assuming THHN copper and 75 degree rated endpoints. Ampacity-wise, you can max out the #10 at 35 amps, but you'll be at 3.5% voltage drop.

    If I were in your shoes, I'd run #8 THHN to be slightly conservative on voltage drop with #10 green grounding conductor, in 3/4" conduit unless it's a really straight run. Depending on the run and location, I'd also consider using PVC rather than EMT. Cheaper, simpler to install. Has to be Schedule 80 outdoors however, and some localities frown on it in exposed locations.
    Mark,
    I wouldn't dream of disagreeing with you as your post is well written and concise. This is just a question on figuring the wiring gauge size. Was the NEC 630.11 (A) rating table involved in your computation of the wire gauge size? If I were in Ryan's shoes, I'd follow your recommendations.

    EDIT: Maybe I should ask whether it would even make a difference factoring in NEC 630.11 (A) in this instance?

  11. #11
    Carl Darnell is offline Titanium
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    Ryan, you may have to run a neutral depending on what kind of welder your using. If it's just a buzz box then two hots and a ground will work but if it has some control circuits that use one leg for the 110v controls, etc. then you will need a neutral. It also may use a transformer in it and not need a neutral.

    In the long run it may be a good idea to run a neutral to the control switch and then in the future if you need a neutral at the receptacle it's easy to do.

  12. #12
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    Quote Originally Posted by mark thomas View Post
    The cited amp ratings suggest a common misunderstanding of NEC ampacity tables.
    These ampacities are ratings for wire alone, not the circuit.
    That's correct.

    And it reflects a common mis-understanding of the NEC ampacity tables.

    The tables relate ONLY to the conductor current capacity in conduit, as the title states.

    Circuit and system considerations are also relevant, but not to the tabulated data.

    - Leigh

  13. #13
    Sea Farmer is offline Titanium
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    Installed several external outlets last year on my new barn. The electrician came up with the RV weatherproof enclosures for both a 220v, 30 amp outlet and a duplex 120v , 20 amp outlet. The inspector passed both. This however was under the residential code.

    Can't remember the wire sizes, sorry.

  14. #14
    mark thomas is offline Titanium
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    Quote Originally Posted by Wyoming View Post
    Mark,
    I wouldn't dream of disagreeing with you as your post is well written and concise. This is just a question on figuring the wiring gauge size. Was the NEC 630.11 (A) rating table involved in your computation of the wire gauge size?
    No. I was just applying normal branch circuit rules. 630.11 (A) does allow possibly reducing the conductor size, in recognition of the <100% duty cycle of a welder. While this could be done, and might get you to one smaller wire, I think it's ill-advised because it sort of limits you to using that circuit for that welder. At this scale (100' of small wire) the savings are trivial and not worth the hassle of limiting the flexibility of the circuit.

  15. #15
    Wyoming is offline Cast Iron
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    Quote Originally Posted by mark thomas View Post
    No. I was just applying normal branch circuit rules. 630.11 (A) does allow possibly reducing the conductor size, in recognition of the <100% duty cycle of a welder. While this could be done, and might get you to one smaller wire, I think it's ill-advised because it sort of limits you to using that circuit for that welder. At this scale (100' of small wire) the savings are trivial and not worth the hassle of limiting the flexibility of the circuit.
    Mark, thanks for taking the time to reply. Your reasoning seems rock solid on the issue. I asked since I'm used to dealing with much higher amp draws, 90-100 amps, from my two transformer based welders and a plasma cutter. I was assuming that a 35 amp load like Ryan's wasn't driving much in the way of duty cycle.

  16. #16
    mark thomas is offline Titanium
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    Quote Originally Posted by Wyoming View Post
    Mark, thanks for taking the time to reply. Your reasoning seems rock solid on the issue. I asked since I'm used to dealing with much higher amp draws, 90-100 amps, from my two transformer based welders and a plasma cutter. I was assuming that a 35 amp load like Ryan's wasn't driving much in the way of duty cycle.
    Probably not high duty cycle. Most welders in this size have 20% or 30% duty cycles. 630.11 (A) lets you derate the conductor using a duty-cycle-based factor. For 20%, it's .45. So if the welder is listed at 30 amps input, 30 * .45 = 13.5. Round up to 15 amp for next conductor rating, and this means you can run #14 wire. You can run 200% breaker on this (and you need to run the welder.)

    But note if you want to limit voltage drop it drives your size back up.

    The problem is that this is really intended for a dedicated welder. The OP said he was installing receptacles. If you follow 630.11 (A), you've got a 30A receptacle that isn't really rated for 30A in a general sense, but rather for a specific welder. If you or the next guy later comes along and plugs in some device with continuous 30A load into that receptacle, you're going to be out of code, and overheat that #14 wire.

  17. #17
    surplusjohn is offline Diamond
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    I would put the twist loc outlets inside the building and either run extensions or put extra long leads on the machines. Both color code and if you are running multiple voltages , make sure the plugs are non-compatable. I know Pass + Seymore has a line of color coded twist locs for use in fast food kitchens, yellow for the fryer,red for the fridge, etc

  18. #18
    mark thomas is offline Titanium
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    Quote Originally Posted by surplusjohn View Post
    I would put the twist loc outlets inside the building and either run extensions or put extra long leads on the machines.
    A good simple strategy, though one downside is that 100' foot cord can be a pain. If you felt limiting voltage drop was important, you'd need #10 wire. For reasonable durability you'd want something like SJO cord. 100' of #10 SJO is a big extension cord. Might weigh more than the welder. I have a 50' #10 SJO extension on something, and it's some exercise just coiling it up and carrying it around! The risk of cord damage, trips, etc. is also a consideration. And two of those cords will set you back more than wire and conduit, though the OP didn't say cost was a major issue.

    We don't know the layout of the building and electrical supply, and it's not clear why it's 100' to reach a 16' x 40' slab. You'd only need a 25' cord to reach the farthest point of that slab starting at the center of a long edge.

    I'd repeat the suggestion that OP consider running conduit to a small subpanel on the outside edge of the building at the new exterior slab. Then run from subpanel to to a couple receptacles, maybe each 10' in opposite directions from the panel. From there, the existing cords on the welder might be adeqaute, and if not, replace the lead on the welder with something about 25' long.

  19. #19
    Carl Darnell is offline Titanium
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    If you use 100' of cable you had better check the voltage drop on that. #10 would not be a good choice for a 100' cable for a welder supply line. Perhaps #8 may work.

    You have to be very careful of voltage drop and amp capacity when dealing with extension cords. It's best to go overkill than underkill. Buy it once, not twice.

    If you use outside outlets be SURE to use waterproof boxes. You may even have to have a ground fault circuit depending on code for outside.

    Remember this is a school and you don't know what the dummies will do and if they electrocute themselves you'll have hell to pay.

  20. #20
    chuckey is offline Stainless
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    Default Provide protection for the pupils

    I would include an earth leakage breaker on the supply. I think you call them GLFIs(?). If a student cuts a lead with a grinder, I would like to think that they are not relying on a 30 A fuse to save their skin.
    Frank

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