Page 1 of 2 12 LastLast
Results 1 to 15 of 17

Thread: Workshop Sub-Panel

  1. #1
    Join Date
    May 2007
    Location
    Don't Mess With My Texas!
    Posts
    128

    Lightbulb Workshop Sub-Panel

    I finally am in the process of bringing electricity to my new workshop. So, my plans are as follows:

    1. Main panel is 200 amp.
    2. My home is separated with a 100 amp. breaker and is wired with #1 wire.
    3. My separated workshop is over 60 feet of wire away from that main panel.
    4. My sub-panel in my workshop has its own 100 amp breaker.
    5. The sub-panel has the neutral and ground bars separated.
    6. The plan was to run 3-3-3-5 wiring in a PVC conduit (1-1/2") to the workshop.
    7. The plan was also to ground to a ground rod at the sub-panel.


    Then I accidentally ran across this thread here on the forum. Confusing in some regards, but I can't see any disadvantage in having ground rods at both ends as well as the common (but separate) ground wire.

    I'd appreciate any comments on these plans, and I don't have any inspections to deal with although I do have a buddy that is looking over my results.
    Paul
    These words are my opinion, WYLION. Any resemblance to truth or fiction is accidental at best.
    "Truth lies dormant in our future history." ― Paul Lawrence LXXI


  2. #2
    If you are doing PVC conduit rather than direct burial, for a 100A subpanel you could do #4 copper for the hots and neutral and #6 bare copper for the ground. You are only going 60 feet and unless you intend on using way more power than the typical home shop user, you won't ever come close to drawing 100A, so you don't really need to worry about upsizing the wire for voltage drop. If you use aluminum wire, check the sizing charts for 100A (I think it is #2 for a 100A subpanel, but not sure), they are different than copper, and make sure you put the anti-oxidant stuff on the connections.

    Since it is a subpanel, you will need separated ground and neutral (white) wires. The ground bus and the neutral bus in the subpanel must be separated as well, so don't put in that green bonding screw on the neutral bus. Since the shop is detached, you need a grounding rod (possibly two) for subpanel.

    2" PVC is a lot easier to pull through than 1 1/2 and not much more expensive, so that is worth considering. The PVC needs to be a minimum of 18" below grade. Also, wire lubricant is your friend.

    When you are putting in the PVC for the electric lines, you might want to put in another 1" PVC conduit for phone, cable, LAN, etc. Much easier and cheaper to do it then.
    Last edited by Andrew Seemann; 12-02-2018 at 1:17 AM.

  3. #3
    Quote Originally Posted by Andrew Seemann View Post
    If you are doing PVC conduit rather than direct burial, for a 100A subpanel you could do #4 copper for the hots and neutral and #6 bare copper for the ground. You are only going 60 feet and unless you intend on using way more power than the typical home shop user, you won't ever come close to drawing 100A, so you don't really need to worry about upsizing the wire for voltage drop. If you use aluminum wire, check the sizing charts for 100A (I think it is #2 for a 100A subpanel, but not sure), they are different than copper, and make sure you put the anti-oxidant stuff on the connections.

    Since it is a subpanel, you will need separated ground and neutral (white) wires. The ground bus and the neutral bus in the subpanel must be separated as well, so don't put in that green bonding screw on the neutral bus. Since the shop is detached, you need a grounding rod (possibly two) for subpanel.

    2" PVC is a lot easier to pull through than 1 1/2 and not much more expensive, so that is worth considering. The PVC needs to be a minimum of 18" below grade. Also, wire lubricant is your friend.

    When you are putting in the PVC for the electric lines, you might want to put in another 1" PVC conduit for phone, cable, LAN, etc. Much easier and cheaper to do it then.
    Show me in the NEC where 4 AWG copper, or 2 AWG aluminum, is suitable for a 100A subpanel, you cannot use the 90 degree column to size the conductors, Table 310.15.(B)(6) has been removed from the NEC, load calculations are required to be able to reduce the conductor size where they carry the entire load of a dwelling, a feeder to a subpanel or outbuilding does not comply with that. 3 AWG copper, or 1 AWG aluminum, is minimum size for 100A. See Table 301.15(B)(16).


    To the OP, if shop is a detached structure then 2 rods at least 6 feet apart would have to be driven unless you can prove 25 Ohms of resistance or less, which requires expensive equipment & the expertise to use it, cheaper to just add the 2nd rod. If a new build, a concrete encased electrode "CEE", or UFER, is the best choice then no additional ground rods are required.

  4. #4
    Join Date
    Feb 2003
    Location
    Griswold Connecticut
    Posts
    6,927
    "but I can't see any disadvantage in having ground rods at both ends as well as the common (but separate) ground wire."

    There isn't. The ground rods(2) are supposed to be there.
    Exactly what kind of cable are you running? 3-3-3-5 is going to be a hard pull in 1-1/2" conduit. You might have to "put the conduit on the cable" prior to gluing and burial. Depending on the type of cable, it may also exceed the fill chart for circular mills. If you're running individual THWN wire, then the pull will be much easier, and you're well within the fill chart.

    I understand that you're not getting it inspected, but you really should install to code no matter what. Research your local code applications prior to doing the work.
    Last edited by Mike Cutler; 12-02-2018 at 8:37 AM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  5. #5
    Quote Originally Posted by Rollie Meyers View Post
    Show me in the NEC where 4 AWG copper, or 2 AWG aluminum, is suitable for a 100A subpanel, you cannot use the 90 degree column to size the conductors, Table 310.15.(B)(6) has been removed from the NEC, load calculations are required to be able to reduce the conductor size where they carry the entire load of a dwelling, a feeder to a subpanel or outbuilding does not comply with that. 3 AWG copper, or 1 AWG aluminum, is minimum size for 100A. See Table 301.15(B)(16).
    I did mine about 7 years ago, sounds like they changed it in the interim time.

  6. #6
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    9,889
    Since you are in Texas if any of this main run wire in the attic or even in conduit in the sun you will have to derate it for summer heat. Also if you cannot pull the wire into the conduit after it is installed it is not code. threading the conduit over the wire as you glue it up is not allowed for good reason.
    Bil lD

  7. #7
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    9,889
    Check ebay for used loaded panels with breakers included. If your existing panel is a good brand try to get the same brand subpanel so you can trade breakers around for testing etc.
    BILL D

  8. #8
    Quote Originally Posted by Andrew Seemann View Post
    I did mine about 7 years ago, sounds like they changed it in the interim time.
    It was never code compliant for subpanels or feeders to outbuildings, but it's been done when inspectors were ignorant. I am guilty of doing it once many years ago & it bugged me that I did it, it's not there anymore as the building burned last month with thousands of others in the Camp Fire that destroyed Paradise, CA, last month.

  9. #9
    Join Date
    May 2007
    Location
    Don't Mess With My Texas!
    Posts
    128
    Quote Originally Posted by Mike Cutler View Post
    ... Exactly what kind of cable are you running? 3-3-3-5 is going to be a hard pull in 1-1/2" conduit. You might have to "put the conduit on the cable" prior to gluing and burial. Depending on the type of cable, it may also exceed the fill chart for circular mills. If you're running individual THWN wire, then the pull will be much easier, and you're well within the fill chart....
    My use of the word "cable" was probably not accurate. I'll be using individual wires and threading them into the conduit as I go. The fill should be fine and loose as goose poop.

    Thank you for these comments!
    Paul
    These words are my opinion, WYLION. Any resemblance to truth or fiction is accidental at best.
    "Truth lies dormant in our future history." ― Paul Lawrence LXXI


  10. #10
    Join Date
    May 2007
    Location
    Don't Mess With My Texas!
    Posts
    128
    Quote Originally Posted by Rollie Meyers View Post
    ... if shop is a detached structure then 2 rods at least 6 feet apart would have to be driven ...
    That's new information for me, so I'll need to get another rod.

    Thank you for these comments!
    Paul
    These words are my opinion, WYLION. Any resemblance to truth or fiction is accidental at best.
    "Truth lies dormant in our future history." ― Paul Lawrence LXXI


  11. #11
    Join Date
    May 2007
    Location
    Don't Mess With My Texas!
    Posts
    128
    Quote Originally Posted by Andrew Seemann View Post
    ... Since it is a subpanel, you will need separated ground and neutral (white) wires. The ground bus and the neutral bus in the subpanel must be separated as well, so don't put in that green bonding screw on the neutral bus. Since the shop is detached, you need a grounding rod (possibly two) for subpanel.

    2" PVC is a lot easier to pull through than 1 1/2 and not much more expensive, so that is worth considering. The PVC needs to be a minimum of 18" below grade. Also, wire lubricant is your friend.

    When you are putting in the PVC for the electric lines, you might want to put in another 1" PVC conduit for phone, cable, LAN, etc. Much easier and cheaper to do it then.
    All good information, Andrew.

    My subpanel has ground and neutral separated.

    I am burying the PVC from the main panel around 24" to 30" deep, filling in approximately half of the trench, adding the 1" data conduit, covering that about half again more, adding a RED warning tape run the full length of the trench and filling in the rest of the trench.

    I would LIKE to add the 1" water line to the trench also, but that might be stretching reality a leetle bit!
    Paul
    These words are my opinion, WYLION. Any resemblance to truth or fiction is accidental at best.
    "Truth lies dormant in our future history." ― Paul Lawrence LXXI


  12. #12
    Join Date
    May 2007
    Location
    Don't Mess With My Texas!
    Posts
    128
    Thank you all for these comments! Please continue before I get beyond the dreaded point-of-no-return!
    Paul
    These words are my opinion, WYLION. Any resemblance to truth or fiction is accidental at best.
    "Truth lies dormant in our future history." ― Paul Lawrence LXXI


  13. #13
    Join Date
    Feb 2003
    Location
    Griswold Connecticut
    Posts
    6,927
    Quote Originally Posted by Paul Lawrence View Post
    All good information, Andrew.

    My subpanel has ground and neutral separated.

    I am burying the PVC from the main panel around 24" to 30" deep, filling in approximately half of the trench, adding the 1" data conduit, covering that about half again more, adding a RED warning tape run the full length of the trench and filling in the rest of the trench.

    I would LIKE to add the 1" water line to the trench also, but that might be stretching reality a leetle bit!
    "Generally", water and electrical aren't buried to the same depth, in the same trench . I've seen the water installed below the frost line, then the trench filled to the depth for the electrical. That's a deep trench in New England. Haven't a clue how deep it would be in Texas.

    Code requirement for PVC burial, as I know it, is 18" to the top of the conduit from grade. Here in CT, it is the norm to dig an ~ 26"- 30" deep trench, backfill with~ 6"-8" of screened material, drop the pipe in, and the top of the pipe should be about 18" to 20" deep from grade, depending on the size. It's also not uncommon to start digging the trench, hit rock and ledge, then shift to metal conduit.

    The 1" low voltage conduit can be buried right alongside the service conduit. In CT they like to see some "gap" between the two conduits in the trench.
    Last edited by Mike Cutler; 12-03-2018 at 8:42 AM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  14. #14
    Paul, my comment is do not to insult you are your abilities but consulting a forum on electric work is not really the best place, IMO. For one thing, often times the thread becomes a debate about codes, extraneous issues, etc which doesn't help you. Second, your local codes, such as burial depth, etc. may be different. For example, where I live its 3 feet, not 18" and direct burial service wires are no longer allowed but they were 25 years ago when I first wired my shop (BTW that wire failed after 23 years. Another example is you must have 2 ground rods 8' apart. I never knew that until I hired an electrician to install a new service to my shop.

    I say this because all you can do is read a post and what "sounds right" may not be right.

    That said, I can confidently tell you two things: 1) good choice using conduit, 2) copper is extremely expensive aluminum is used almost exclusively for service wires. ;-)

    3 things: put in that extra conduit. If you decide to run internet to your shop it will be very handy!!

  15. #15
    Quote Originally Posted by Paul Lawrence View Post
    I can't see any disadvantage in having ground rods at both ends as well as the common (but separate) ground wire.
    It's the grounding vs bonding discussion that clouds the issue. There should only be one point where the neutral is bonded (electrical connected) to ground and that is at the service entrance point - usually in the main panel. From there, there should be no other place within that system where the neutral is electrically connected to ground.

    In the case where you install a sub-panel, the wiring to that panel should be H-H-N-G, unless you have metallic conduit where the ground conductor can often be eliminated.

    The green ground screw that usually comes with the panel should not be used to bond the neutral to the sub-panel case. There should also be ground bus terminals installed in the panel so you aren't landing ground wires on the neutral bus, as is often done at the main panel where NM cable is installed. Neutral conductors are terminated on the neutral bus and ground conductors are terminated on the ground bus - never the twain shall meet - except, of course, at the service entrance where the neutral is bonded to ground.

    To protect your equipment from something like a lightning strike, you can install a grounding electrode (ground rod) at the sub-panel and bond that to the case of the panel and/or the ground bus installed in the panel. Again, DO NOT BOND to neutral at the sub-panel or at any other point outside the main panel.
    Last edited by Julie Moriarty; 12-04-2018 at 8:00 AM. Reason: further clarification
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •