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Thread: Yet another shop electrical question

  1. #1
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    Yet another shop electrical question

    I’ve been lurking here for some time and have picked up lots of useful information, but this is my first post. We recently moved into a new house where I plan on turning the garage into a shop. The space is ideal for a shop with 980 sq feet of space and 11 ½ foot ceilings. The garage already has all the 110V circuits and outlets I could need along with ample lighting (12 four foot, four bulb, fluorescent fixtures). The only thing I need to add is 220V power to feed a variety of machines. The garage is already insulated and the walls are covered with sheet rock and painted. My plan is to add a surface mounted 125AMP subpanel and run all the new 220 circuits off of it. I will run the cable through either flexible metal conduit or EMT. I would like to run separate circuits for each 220V outlet so I can run several machines simultaneously. I plan on running a mixture of 12/2 and 10/2 wire depending on the expected load (20amps and lower will be run with 12 gauge anything higher will be run with 10 gauge). I would like to do the wiring myself then pay an electrician to come in and inspect my work prior to connecting the subpanel to the main panel. I’ve done minor wiring throughout the house, but nothing on this scale.

    I have a couple of couple of questions that I’m hoping my fellow creekers can help me with so I can complete the first draft of the electrical design. This isn’t all the questions I have, but it is what I need to know to get started. Once the basic design is completed, I’ll post it for review along with what I’m sure will be more questions.

    1.Can multiple 220 circuits be run through the same piece of conduit (up to the NEC limit for the number of wires in a certain size conduit) or does each circuit need to be run in its own conduit?
    2.If multiple circuits can be run through a single conduit, can they share the same ground wire?
    3.Does the conduit need to be grounded?
    4.I know all the machines just need two hot wires and a ground, is the same true for the dust collector and compressor?
    5.If multiple circuits can be run through the same conduit, can I mix 10 and 12 gauge wires in the same conduit provided I don’t exceed the NEC limit on number and size of wires for the size of the conduit?

    Here is a list of the 220V circuits I plan to run.

    Table Saw
    10" Unisaw
    1.5HP 230V 9.6A

    Clearvue Cyclone Dust Collector
    5HP 230V 20.8A

    15” Planer
    3HP 220V 18A

    8” Jointer
    3HP 220V 15A

    Ingersoll Rand Compressor
    (not sure about the HP) 230V 15A

    18” Bandsaw
    4.5HP 220V 30A

    For future Use
    3HP 220V 18A

    Also included is a copy of the shop layout.
    Attached Images Attached Images

  2. #2
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    I would run separate 20 amp circuits to all the machines listed with the exception of the dust collector and band saw. They will reqire 30 amp circuits. Rule of thumb: mulitply full load amps by 1.25 and that is the size of circuit you need. I never run circuits smaller than 20 amp or 12ga copper. 10 gauge is good for 30 amp circuits. You may run all your wire in the same conduit reguardless of size or number of circuits etc. You will need a green ground wire for each circuit. I don't know if code alows you to share this ground between circuits. The problem with sharing the ground is in the event that you experience a short in 2 circuits at the same time (unlikely but not impossible) the total load could equal the sum of the two breakers that protect the two circuits. This current would be returning to ground via a single conductor 1/2 the size it needs to be. All this said, I share grounds in my shop. I would call your local building inspector (anonymously of course) and ask what the requirements are. I ran my circuits with THHN stranded in schedule 40 PVC. This is a lot cheaper than EMT and is easy to work with. I think it keeps the dust out better as well. A word to the wise, run LARGE conduit so you can add circuits later. No need to run extra circuits until you need them. If you use LARGE conduit, you can always fish more wires. I ran 2 1/2" (after running 1" the first time) with 6x6 boxes every so often.

    Jon, who needs to do everything twice in order to perfect the proccess

  3. #3
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    electrical service to garage.

    i am assuming that this garage is attached to the house. you should NOT run common grounds. could come back to bite you. also check the code book (condensed) at your local big box store. go to the conduit fill table for pvc. do not over fill as this will not allow for heat dissipation, which could cause the coating on the wire to break down. THHN wire is the best way to go. you can go 1 size smaller for the ground wire. in my opinion you would be better running several smaller conduits. hope this helps

  4. #4
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    Jon & Paul,

    Thanks for the responses thus far. I kind of figured that separate circuits would need their own ground wires.

    So it sounds like I can run multiple circuits through the same conduit as long as I stay within the NEC limits for conduit fill. This will dictate the number of conduit runs I will need.

    Quote Originally Posted by Jon Dieterlen View Post
    I would run separate 20 amp circuits to all the machines listed with the exception of the dust collector and band saw. They will reqire 30 amp circuits.
    Yes, that is what I was planning, sorry if I wasn't clear. The amps you see listed are the actual amps of the devices in question, not the size of the breaker.

  5. #5
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    1. yes
    2. I Wouldn't
    3. depends on the conduit. PVC no, EMT via the metal boxes they are connected to.
    4. Almost all your tools should need only the 2 hots and the ground. The neutral is only required when the machine such as a dryer operates some controls on 120V in addition to 240V.
    5.You can mix wires and circuits in the same conduits.

    Depnding on how set your shop is I would standardize on the same outlet. I have 2 240V tool circuits with 3 - 30A outlets each and a seperate 20A 240V circuit run to my cyclone. I did it that way because I didn't want to have to change the wiring if I upgraded my machines from what I currently have. My 5HP TS is the only machine I have that requires 30A.

    Mike

  6. #6
    How many people will be working in the shop at once? If it's just yourself, you likely won't be running more than one of the jointer/planer/tablesaw at the same time, so they could theoretically all share a circuit. The compressor and dust collector should each get their own circuit.

    You may have a hard time finding an electrician to sign off on something that they haven't done since they don't really know what's in the conduit. Around here you can pull a permit as a homeowner and get the electrical utility to inspect it after you're done.

    1) Multiple circuits can be run through the same conduit, but watch the conduit size. Also, multiple circuits mean that the ampacity of the conductors must be derated based on how many conductors are in the conduit. (But for the purposes of derating the ampacity starts with the full amount the conductor can carry, not the artificially limited amount.)

    2) I think you could use a single ground conductor. If you use EMT, the conduit itself will be a better ground than the ground conductor, and in some places may be used as the ground conductor itself (but it's better to have a separate ground conductor as well, if only for added security).

    3) If it's metal, yes.

    4) Yes.

    5) Yes.
    Last edited by Chris Friesen; 10-26-2007 at 1:31 AM.

  7. #7
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    I just wired my entire 2000 sq ft home and attached 35’ x 24’ shop with a 100 amp sub panel.

    Everything in ½ emt.

    You are limited to a max of three 20 amp circuit insofar as wire file (6 current carrying conductors),,, and a total I believe of 11 conductors total. 6 number 12’s fit fine so long as you don’t pull them all at once. Equipment grounding wires are non conducting.

    Larger conduit will not change the conductive wire fill maxim. The code refers to bundled conductors… ie, there is no less heat being generated just because the bundle is in a larger conduit.

    I pulled 40 amp # 8 in one ½ run of emt (two hot, one neutral)

    The emt is in itself the EGC . Perfectly within code… but for added safety you could pull a few greens through in case there was a break in one of your emt runs… but very unlikely if it were you who tightened the connectors and used channel locks to tighten your couplers to the boxes and you yourself tighten the set screws on each coupler/connector. That means, hold the threaded ring with your left hand inside the box and tighten the coupler itself with channel locks till that ring pulls up tight. Give it a good, firm crank. It’s not coming loose then.

    Seriously, I have no greens running through the house at all… just bonded emt from the main panel forward on out to my respective runs. Very safe.

    There was no issue with my inspector over this because it is in fact per NEC,

    Because you have a separate panel, assuming it is attached to the garage and feeding from your mail panel in the house, DO NOT use the Neutral bus on the sub panel as a grounding source. If you don’t have one, apply a grounding bus to the boxe’s metal and ground there. If you want, you can pull a green from there back to the main panel (the only place you can connect neutral and ground on the same bus.)

    Run #12 for 20 amp and #10 for 30 amp. You can use 15 or 20 amp outlets on your 20 amp circuits, but you must use a 30 amp outlet on your 30 am circuit.

    Buy a reamer for after your saws-all cuts.

  8. #8
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    Quote Originally Posted by Paul Simmel View Post
    You are limited to a max of three 20 amp circuit insofar as wire file (6 current carrying conductors),,, and a total I believe of 11 conductors total. 6 number 12’s fit fine so long as you don’t pull them all at once. Equipment grounding wires are non conducting.

    Larger conduit will not change the conductive wire fill maxim. The code refers to bundled conductors… ie, there is no less heat being generated just because the bundle is in a larger conduit.
    If I understand you correctly, you are saying that for 220V I can only have a maximum of 6 hot wires in a conduit regardless of the wire gauge or the size of the conduit and any conduit fill calculations, correct?

    Quote Originally Posted by Paul Simmel View Post
    The emt is in itself the EGC . Perfectly within code… but for added safety you could pull a few greens through in case there was a break in one of your emt runs… but very unlikely if it were you who tightened the connectors and used channel locks to tighten your couplers to the boxes and you yourself tighten the set screws on each coupler/connector. That means, hold the threaded ring with your left hand inside the box and tighten the coupler itself with channel locks till that ring pulls up tight. Give it a good, firm crank. It’s not coming loose then.
    Interesting idea, but since my runs are relatively short, I will probably pull a green wire for each circuit just to be on the safe side.

    Thanks for the information.

  9. #9
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    Paul, one thing I see in your shop diagram that "Might Not be Legal", is the location of the subpanel. I see it on the wall "Over" the table for your mitresaw, and IIRC, you cannot have ANYTHING in front of the panel. There are dimensions (that I cannot recall with accuracy) but something like a space 30" wide and 30" or 36" in front of the panel must be clear space. It looks like you might have enough room though if you just moved the subpanel location to the left of your mitresaw table. Anyhow, check it out with someone more "UP" on the NEC than I am. Nice drawing and layout.
    "Some Mistakes provide Too many Learning Opportunities to Make only Once".

  10. #10
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    I’ve got some comments I’d like to add to this thread.

    1) For the circuits being discussed here, there is nothing in the NEC that requires separate Equipment Grounding Conductors (EGCs) for each circuit. In fact, if you ran all of the wiring in metal raceway (EMT is one form of raceway), you can use the raceway itself as the EGC with no additional EGC conductors. Paul talked about this in his post and is absolutely correct. My personal preference would be to run EMT with an EGC anyway, just because it guarantees the continuity of the grounding path and that path isn’t dependent on the conduit connections. You would want to bond the EGC in each box. I would only run the 1 EGC. A separate EGC per circuit is overkill and just adding wires into the raceway that you don’t need.

    2) When thinking about sizing conduit, the number of conductors that will fit in the conduit based on the conduit fill tables is NOT the only factor that determines how many conductors, and what size conductors, you can pull. You also need to take derating into consideration. Derating occurs when you have more than 3 Current-Carrying Conductors (CCC’s) in a raceway or cable. The NEC table is 310.15(B)(2)(a) if you want to look it up.

    • From 4 to 6 CCC’s means a derating factor of 80%
    • From 7 to 9 CCC’s means a derating factor of 70%.
    If you’re talking about 20 amp circuits and are pulling #12 THHN/THWN, the 100% ampacity is 25 amps. This means you can pull (3) 240v 20 amp circuits with #12 THHN/THWN through a conduit and you’re still OK. 25 amps * 80% = 20 amps. If you try to pull (4) 240v circuits, that’s 8 conductors and means a 70% derating factor, so the ampacity drops to 17.5 amps for the #12.

    Another way to look at this is that running an absurdly large conduit won’t buy you anything other than making it easier to pull the conductors. If you start running a lot of circuits through that conduit, you’ll have to upsize ALL of the CCC’s. Given the cost of copper today, I’d guess it’d be cheaper to run a second run of conduit.

    I will say that upsizing conduit 1 size (for example from 1/2" to 3/4") just makes it a lot easier to pull the conductors. Remember that you must have a pull point at least every 360 degrees of turns. In other words, at the 4th 90-degree bend, you must have a way to pull the conductors - you can't just fish line through bends forever and ever without some sort of junction box or pull point.

    3) Norm’s correct about the “Working Space” requirement. You can’t obstruct the area where your panelboard will be – 30” wide, 36” deep, floor to ceiling.

    4) In terms of feeding your subpanel, you MUST have a 4-wire feed from your main panel. The subpanel MUST have an isolated Neutral bus. You do NOT install the green bonding screw that bonds the Neutral buss to the subpanel enclosure. Installing the subpanel and running the conductors for that is the same as any other circuit – it’s just 4 conductors instead of 3 and the conductors are terminating on a buss instead of a device. If you can run all of the other circuits, you can run your subpanel too.

    5) Definitely call your local building department – but be upfront about this and pull a building permit. The vast majority of code enforcement officials are very happy to work with you. It’s when you try to do things without permits that things can get ugly. Now, there is the rare inspector who is too big for his/her britches. If that’s the one you get, just say Yessir and live with it.

    6) If you have any wall penetrations that go through firewalls or floors, you need to caulk the holes with FireStop. It’s a flame retardant caulk that’s designed to slow down flame spread through holes in floors or firewalls.

    7) If you really want to do things properly, get a torque screwdriver and pay attention to the torque requirements for the screws on your circuit breakers and devices (receptacles). You can get them on eBay for reasonable prices. It’s actually not good to crank down too hard on those terminating screws – you get something called “cold flow” in the conductor metal and the connection can loosen up over time.

    Rob
    (not a licensed electrician, just an anal retentive homeowner electrician who happens to like to read the NEC).

  11. #11
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    Paul,

    >>> If I understand you correctly, you are saying that for 220V I can only have a maximum of 6 hot wires in a conduit regardless of the wire gauge or the size of the conduit and any conduit fill calculations, correct?

    3, 20 amp circuits, 120v or 240v. On 120v the neutrals are current conducting too.

    I haven’t read Rob’s response yet, but if he is who I think he is, he was a huge help to me before I wired my house/shop. I’m sure you are in good hands.

  12. #12
    Quote Originally Posted by Rob Russell View Post
    If you’re talking about 20 amp circuits and are pulling #12 THHN/THWN, the 100% ampacity is 25 amps.
    Looking at table 310.16, the full ampacity of #12 wire with 90 degree insulation is 30A, not 25. This means you can have up to 9 current-carrying conductors and still use #12 for a 20A circuit.

  13. #13
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    Quote Originally Posted by Chris Friesen View Post
    Looking at table 310.16, the full ampacity of #12 wire with 90 degree insulation is 30A, not 25. This means you can have up to 9 current-carrying conductors and still use #12 for a 20A circuit.
    Yeah, but I don't think that you can use the 90-degree column in that table. The terminals on any of our residential devices will be 75-degree C rated. Take a magnifying glass (if you're like me where you're wearing bifocals already) and read the really fine print on the side of a circuit breaker. That 75-degree rating limits the ampacity of the wiring in another manner, but I didn't want to get into that earlier.

    Rob

  14. #14
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    Quote Originally Posted by Paul Simmel View Post
    Paul,

    >>> If I understand you correctly, you are saying that for 220V I can only have a maximum of 6 hot wires in a conduit regardless of the wire gauge or the size of the conduit and any conduit fill calculations, correct?

    3, 20 amp circuits, 120v or 240v. On 120v the neutrals are current conducting too.
    You can have more than 3 circuits in a raceway, but you may need to upsize your conductors.

  15. #15
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    Man I love this place. You guys are really helpful.

    Quote Originally Posted by Norman Hitt View Post
    Paul, one thing I see in your shop diagram that "Might Not be Legal", is the location of the subpanel. I see it on the wall "Over" the table for your mitresaw, and IIRC, you cannot have ANYTHING in front of the panel.
    Good catch. I will either move the miter saw or the subpanel to make sure there is enough space in front.

    Quote Originally Posted by Rob Russell View Post
    I would only run the 1 EGC. A separate EGC per circuit is overkill and just adding wires into the raceway that you don’t need.
    This is good news, this means I should only have to pull one grounding wire for each conduit run. I will definitely bond the ECG to each box in the conduit run.

    Quote Originally Posted by Rob Russell View Post
    In terms of feeding your subpanel, you MUST have a 4-wire feed from your main panel. The subpanel MUST have an isolated Neutral bus. You do NOT install the green bonding screw that bonds the Neutral buss to the subpanel enclosure. Installing the subpanel and running the conductors for that is the same as any other circuit – it’s just 4 conductors instead of 3 and the conductors are terminating on a buss instead of a device. If you can run all of the other circuits, you can run your subpanel too.
    I was aware of this, but it's alway nice to be reminded

    OK so here's my preliminary plan based on the input I have received thus far. Please let me know if you spot any potential problems.

    I will end up with three different conduit runs:

    Run #1
    3/4" EMT with the following circuits
    Dust Collector - 5HP 230V 20.8A - 30AMP Breaker - 10 gauge wire
    Future Use - 3HP 220V 18A - 20AMP Breaker - 12 gauge wire
    15" Planer - 3HP 220V 18A - 20AMP Breaker - 12 gauge wire

    Run #2
    1/2" EMT with the following circuits
    8" Jointer - 3HP 220V 15A - 20AMP Breaker - 12 gauge wire
    10" Unisaw 1.5HP 230V 9.6A - 15AMP Breaker - 12 gauge wire

    Run #3
    3/4" EMT with the following circuits
    Compressor 230V 15A - 20AMP Breaker - 12 gauge wire
    18" Bandsaw 4.5HP 220V 30A - 30AMP Breaker - 10 gauge wire

    Below is the actual wiring diagram
    Attached Images Attached Images

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