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Feed wire sizing to my garage

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by magu, Mar 7, 2017.

  1. magu

    magu United States Active Member Active Member

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    Hi all, I'm looking for some advice. I'm looking to add power to my detached garage so I can run my machines and do a bit of tinkering. My question is what size wire I need, the run will be 70', it will power some lights (>2amps), a little old radio, and 1 thing at a time (it's just me, I can't weld, run a mill and a sander all at once). I will be installing a 1 HP vfd to power both my mill and lathe (240 3ph, 3/4 and 1/2 Hp respectively) I will also install 8 outlets.

    Can I use 12/3g wire for this?

    My plan would be to put half the lights and half the outlets on each circuit breaker, that way if I blow a breaker I won't lose all my lighting. I would then use both legs to feed my vfd as well.
     
  2. uncle harry

    uncle harry United States Active User Active Member

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    Hi, Wire size might depend on the potential of additional needs such as an air compressor or any other needs or bargains that may come along in the future. I supplied my outbuildings with # 6 direct burial thinking that 60 amps continuous would all that I would need. Now I wish it was at least # 4.
     
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  3. ddickey

    ddickey United States H-M Supporter - Premium Content H-M Supporter-Premium

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    I used 6 gauge also.
     
  4. cathead

    cathead Active User Active Member

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    You only want to bury the wire once. I put in a 100 amp service and have no regrets. Wire is cheap compared
    to the time and expense of digging in another line. Also a breaker box is necessary so
    you can have various breakered lines to your equipment.
     
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  5. roadie33

    roadie33 Active User H-M Supporter-Premium

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    I used 3/0 for a 200 AMP Breaker box for my garage.
    Never know when you might have the lights on, AC, air compressor and welder running at the same time.
    Better to have more than needed than not enough and blow breakers all the time.
     
  6. jim18655

    jim18655 United States Active User H-M Supporter-Premium

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    Are you using direct bury cable or conduit? You could save on the expense now by installing a large (2") PVC conduit and up-size the wire later. It's more expensive overall but might help you out now. I wouldn't do less than 100 amps for the equipment you listed. The welder might have substantial draw and don't forget about running some type of heat in the winter.
     
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  7. Silverbullet

    Silverbullet Active Member Active Member

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    I wouldn't go with anything smaller then #6 for the distance at least . If you have to dig conduits nice but 2" black water pipe will work and 100' roll is pretty cheap . You should bury at minimum 18" , 36" would be better the straighter the run the better . You can tie string to a dense sponge and blow the line thru with a air tank or compressor. If you pull the wire add an extra string in case you need to had later lines. Be careful to keep the buried line safe from any digging. If you use #4 you should have plenty of current with no worries of melting and shorts. Wires get hot when there's to much draw. Temco a store on eBay has pretty good prices Ck them out . Good luck and keep safe
     
  8. magu

    magu United States Active Member Active Member

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    Thank you all for your replies, at the moment, I have 1/2" EMT running to the garage with 5 very old and crusty wires in it. I can either make use of that, or wait for a year or two, but an eventual new trench for bigger wires is very low on the family centric priority list. Hence my attempt to use 12g copper.

    I'm nearly never out there before the baby is asleep, the housework, the leftover office work is done, and the clock has struck midnight. As a result, in the short term at least, AC will be unnecessary, and an air compressor would not be well received by the neighbors.
     
  9. markba633csi

    markba633csi United States Active Member Active Member

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    If it was only 50 feet I'd say 10 gauge but I think you should use at least 8, maybe 6. 70 feet of 12 gauge will not be good enough at all if you want to weld.
    Mark S.
     
  10. jim18655

    jim18655 United States Active User H-M Supporter-Premium

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    Black water pipe isn't code compliant. I'd hate to see you get shot down by a building inspector, assuming you'd need an inspection in your area. I know in some places you can't plant a flower without someone sticking their nose in your business.
     
  11. Glenn Brooks

    Glenn Brooks H-M Supporter - Premium Content H-M Supporter-Premium

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    What Jim said. Check your local electrical code. Most all local codes are based on the national electric code. So mostly everywhere is similar. It will tell you what depth to bury, wire size for amperage, etc.

    I just did what you contemplate and dug a 36" deep trench 100' in two days with a rented trencher and a 4" trench shovels -these things are great! I used 3" grey plastic conduit - which was the cheapest part of the job- it is WAY easier to pull wire through the bigger the diameter.

    Regarding outlets and circuits. It only took me 1 year to want more outlets. And I installed plenty, with a big elaborate shop design plan. This spring, I get to open up last years some Sheetrock and put in more wiring... hint, hint.

    Also call before you dig...
     
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  12. CluelessNewB

    CluelessNewB Active Resistor H-M Supporter-Premium

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    I don't believe I have ever heard anyone saying something like "I wish I had run less power to my shop". I have a relatively small shop ~576 sq feet with 100 Amp sub panel and every breaker is used. Most of my stationary tools are wired for 220V.
     
  13. Uglydog

    Uglydog United States Active User H-M Supporter-Premium

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    My original plan was to run a buzz box and DP.
    Things grew from there.
    I ran 6. Should have run 4.
    I occasionally have to go to the main panel in the house to reset a breaker.
    Arrgh.

    Daryl
    MN
     
  14. ewkearns

    ewkearns United States Active Member Active Member

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    Personally? I'd go with 2-2-2-4 and a 100 amp sub panel. Just doing enough to get by for "today" will probably come back to bite you in the posterior "tomorrow."
     
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  15. mksj

    mksj Active User H-M Supporter-Premium

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    If you are using 240VAC for the VFD, the breaker would need to be ganged, both legs would trip. I would not run 120 and 240 off of the same breaker. You might be able to put in an electrical sub panel for future upgrade and have two single pole 120VAC breakers and a separate 240 VAC ganged breaker.

    Like the others have mentioned, if you are going through all the trouble to trench and put in a new sub panel, then I would pull a minimum of a 100A line. I ran #4 copper wire in 1.5" ABS electrical conduit to my garage (about 40') and put in a 100A sub-panel. I believe code would require #3 wire for 100A breaker at the main panel (I use an 80A breaker at the main breaker box). All the sub panel breaker slots are filled and I recently had to put in a quad pole circuit breaker for a compressor and two 120VAC circuits. The VFD will give you soft start, so you do not have the motor start current that needs a bigger breaker. I think you would have too much voltage drop using #12 wire running a machine and anything else. I would also go a bit bigger on the conduit, you need to review the electrical code with regard to the fill volume (wires size and number) that can be pulled through the conduit.

    I recently put in a Champion 5Hp compressor, they specify a 50A breaker. It is surprisingly quiet, it uses a low speed motor and air pump, and I can barely hear it outside of my garage. There is also the California Air compressors if you do not need higher volumes of air, they have about the same noise level as your mill when running.
     
    Last edited: Mar 8, 2017
  16. wawoodman

    wawoodman himself, himself H-M Supporter-Premium

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    More is better. When I set up the shop, I ran a 60 amp subpanel. I wish it had been 100.

    And while you're running the receptacles, use 12 ga. wire, and 20 amp breakers. 14 ga./15 amp just doesn't cut it. And make sure the receptacles are 20 amp, as well.
     
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  17. stupoty

    stupoty Active User Active Member

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    Not exactly on topic but ..

    I just changed out my workshop (cubby hole) lighting for led flurecesent fitting of 50w, it has a maintained live and a battery that will keep half the lights on for upto 3h if the power drops might be worth considering if your going to be working at night in the dark surrounded by spinny and sharp things :)

    They have got a lot cheeper, and you can get a small bulk head light as a very cheep one juat to give enough light to find your way out.

    Stuart
     
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  18. tweinke

    tweinke United States Active User H-M Supporter-Premium

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    I did a 100a panel and am tickled
     
  19. mzayd3

    mzayd3 Active User Active Member

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    I run my entire setup off of 240 volt, 20 amp. No issues at all.

    My vote says use what you have until there is a problem, then upgrade.


    Sent from my iPhone using Tapatalk
     
  20. mksj

    mksj Active User H-M Supporter-Premium

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    So to answer the original question, the recommended wire for a 240 VAC single phase input 1Hp (0.75 kW) VFD is 12-14AWG with a recommended breaker/fuse of 15A. Assuming a 15A draw at 240 VAC the voltage drop for 70 feet of 12 AWG wire is about 1.4%, at 120 VAC it is 2.8%. The The NEC maximum conductor voltage drop recommended for both the feeder and branch circuit is 5 percent of the voltage source. So with a 20A main panel breaker feeding your 12AWG branch circuit to your detached garage should be OK, I still would consider a sub panel and breaking out two 120VAC separate 15A single pole breaker socket circuits for each set of 4 outlets, and a 15A double breaker for a 240 VAC circuit. I also believe there is a requirement for all garage outlets to be on a GFI, the standard big box store GFI's usually trip when a VFD is attached to it.
     
  21. ewkearns

    ewkearns United States Active Member Active Member

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    Magnetic contractors are your friend in a power outage....
     
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  22. Keith Foor

    Keith Foor Active Member Active Member

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    Hate to point this out, but.... It's never a good idea to sit and think about how little you are going to do and then subtract from what you think you need for power in a shop. If you are not going to work in the shop, then forget about it. Put up a sky light to get some light in and start building shelves to store crap on. It's typically easier to begin building shelves in the middle of the floor so you can store as many things you will never use again on them. OR you can do it with the idea that you WILL be working out there. And buying equipment that will consume more power and build to accommodate it now.

    I am not saying to get a new 400 amp service put in, but running 3 12 gauge runs of Romex ain't gonna cut it either.

    First off, how big of a panel is in the house? You can't exceed that so don't bother trying to. If the main is 100 amp, then a 200 amp sub panel on it fed from a 200 amp breaker is pointless. You can go 100% of the main, but no more than that. and I wouldn't do that. 75% is where I would stop and 80% is a hard limit in my book. Code's in your area may vary, so don't think I am quoting regulation, I am not.
    So lets size the wire for 80 AMP.

    Book says that you are looking at 4 gauge copper but that is for 50 foot. I would go to 2 gauge and call it good for that distance.
    Cutting it in is easier that you might think.
    Use a rototiller and just go from one building to the other over and over again. Have a couple friends or kids walk behind you with shovels and clean out the trench until you are 2 foot or so down and lay the pipe. Cover it up, put in the wire and go to town.
    get a used panel and an ebay breaker to feed it power and you are off to the races.
    Wire garage to the sub panel you installed and you are golden.

    If there is at any point, any doubt as to your abilities to do this work, stop and call a professional.
     
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  23. tq60

    tq60 United States Active Member Active Member

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    Forget ebay for panels.

    We got our 200 amp capable subpanel with a good supply of breakers at home depot for 70 bucks.

    The box stores have different sizes from small to large with breakers for decent money.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk
     
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  24. ewkearns

    ewkearns United States Active Member Active Member

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    One might, also, consider wiring in a Main Breaker Load Panel, if there is any thought that over 100 Amps will be needed. When I re-wired my (soon to be) workshop, I did so, knowing that an addition of a phase converter to existing lights and whatnot might exceed the capacity. If I find 100 A won't cut it, all I'll need to do is change some wiring, add a meter base, and pay the utility to connect.

    NOTE: That wiring a subpanel and wiring a main breaker fed from the utility are two different animals. If you don't know the differences, you might want to get professional help...
     
  25. TORQUIN

    TORQUIN United States Active Member Active Member

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    My garage is about 50 ft from the house. I ran 2 #4 wires for each leg. I had a tiny panel in there until I got into the lathes and mills. I found a 100A panel on CL and upgraded and have been very happy since. I have almost 0 voltage drop from the house and have never been able to blow the 100A breaker in the house, even when welding 3/8" aluminum. I suggest you go bigger than you think you need. Overkill is good in this situation.

    Chris
     
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  26. jim18655

    jim18655 United States Active User H-M Supporter-Premium

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    If you ran 2-#4 per phase in parallel then it's a code violation. NEC prohibits conductors smaller than 1/0 in parallel (310.10 (H)(1)). Also, most lugs on breakers and panels are not rated for more than one wire per terminal so you would have to splice them to a larger wire to connect to the panel.
    I'd hate to see someone try it and get shot down in a building inspection.
     
  27. ewkearns

    ewkearns United States Active Member Active Member

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    You would probably spend about 1/3 more in wire cost (minimum) to run 2-#4 wires vs., say, a #1 wire, which is roughly (but not quite) equivalent. Check your local codes, one #2 would probably be sufficient and meet code....
     
  28. TORQUIN

    TORQUIN United States Active Member Active Member

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    Bummer. My buddy that wired it is a licensed electrician, so I thought he knew what he was doing. Maybe he just cut a corner to save bucks in my situation.

    Thanks for the info.
    Chris
     
  29. ewkearns

    ewkearns United States Active Member Active Member

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    Very likely so..... he may have had a surplus of #4 wire left from a particular job. It is unlikely that (after the fact) any inspector is going to be rummaging in your panel. If it works, enjoy what you have...... others, that may have an inspector driven solely by the black and white of the NEC may not be so forgiving..... IMHO, everything should be driven by common sense, an all to rare animal in this "Nation of Laws."
     
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  30. Bob Engelhardt

    Bob Engelhardt United States Iron Registered Member

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    You have a baby? Well, I can see why shop wiring is not a high priority budget item <G>.

    For my shop, I have a 15A 240v circuit that runs VFD's for a drill press, lathe, and mill. At 3.6KW, I could run 2 at once, but I'm not nimble enough to do that.

    All the outlets (12?) are on one 15A 120V circuit. A baby MIG is on that. Lights are on a shared house circuit.

    I know, "more is better", "better now than to have to upgrade later", yada yada. But if I were you, I would pull a 12-3 wG through the conduit you have & put in a sub panel large enough to hold a 15A 240 & 2 15A 120's. 15A is big enough and 14ga wire is so much easier to handle than 12ga. In other words: what you said.

    This could satisfy your needs for years, depending. Could probably even have a moderate (20 gal) compressor on it.

    Bob
     

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