Moving main panel to detached garage

Discussion in 'Electrical Forum discussion & Blog' started by Lakee911, Sep 28, 2009.

  1. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Can someone please confirm that my plan is up to code?

    Current 100A aerial service to house from pole. No electric in detached garage.

    Install new 200A panel in garage. Install new grounding rod at garage. Install meter base on exterior of garage. Install either 2-1/2" for Al or 2" for Cu rigid galvanized riser/mast from meter base through roof. Install 4/0 (Al) or 2/0 (Cu) in riser/mast and terminate on line side of meter base. Install 4/0 (Al) or 2/0 (Cu) from meter base to panel and terminate on load side of meter base and in main breaker.

    Install 2" rigid galvanized conduit between garage and house underground to a depth of at least 6" (per NEC 2008 Table 300.5 Column 2, Row 1). Stub up underneath attached deck. Transition to PVC. Attach conduit to bottom of deck every 32 inches (every other joist). Penetrate building envelope. Route conduit to existing panel.

    Install 2/0 Al or #2 Cu from garage main panel to existing panel in house. Terminate said wire on 100A breaker in garage.

    Call utility company for disconnect at house.

    Remove green screw bonding nuetral to ground in the house. Terminate wire from garage to 100A main breaker in house.

    Move meter.

    Get inspection from City.

    Call utility for reconnect at garage.

    What have I not covered?

    Thanks,
    Jason
  2. 3m

    3m New Member

    Messages:
    76
    Location:
    NY
    I would check with your local inspector and see what he or she says
  3. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    Not all panel types support a 100 amp breaker.

    >Remove green screw bonding neutral to ground in the house.

    yep. you need 4 wires (including ground)

    >Install 2" rigid galvanized conduit between garage and house underground

    Why use galvanized underground and then plastic above ground ?
    I would run plastic all the way to avoid corrosion.

    Also don't forget to use that gray puddy at both ends of the conduit so that moisture does not migrate into it over time.
  4. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Bill,
    If you look in the 2008 NEC, the underground portion needs to be a metal conduit to allow a depth of only 6". If I use plastic it needs to be 18". I've got some fairly large trees in my backyard and I do not want to disturb the roots more than necessary.

    Plastic is also easier to work with, it's cheaper and won't corrode so I'm using that elsewhere.

    What is this gray putty? Does it go in the conduit? I don't care if water gets in ... I'll be using THWN wire most likely. I don't want to plug up the conduit in case I need to get the wire out at some point and reuse the conduit.

    Jnass2,

    I do plan on contacting the AHJ, but I want to make sure that I know what I'm talking about here. When I do electrical design (of the little that I do), I do not get into these type of minute details.

    Thanks,
    Jason
  5. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    The gray puddy just goes on the ends where the wires go into the box. It's code here as part of the house vapor seal rules to seal up the ends to prevent moisture from getting into the meter socket as well.

    In your case it's to prevent water laying in the pipe and then freezing... then again I dont know if that's a problem in your area.
  6. 3m

    3m New Member

    Messages:
    76
    Location:
    NY
    Whats the distance from the garage to the house, you will need to do a voltage drop calculation to see what size wire you need.
  7. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Need more info: If you are referencing the 2008 NEC then I assume this is what governs your installation.

    Garage will need 2 rods, not 1.

    House will need 2 rods and bonding of metal water pipe if present.

    Four wires will be needed between the garage and house.

    Current house panel will need to be converted to a sub-feed. Separate grounds and neutrals, isolate neutrals from the enclosure.

    Slip risers needed a the garage to the meter base and the house if you are going directly to an enclosure.

    The wire for your lateral feed must be rated for a wet location even though it is in conduit.

    If any part of your trench is where you park or drive then you need an 18" depth.

    You must bond the RMC and now that you want to transition it to PVC that will make it difficult to do. Either stick with ridgid the entire length or go to schedule 80 pvc. The electrical continuity of the RMC must be kept.

    There is more but not enough information
  8. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Thanks for the responses.

    Actually, I think I might use PVC. Per the blue box store, 2" RGS is $34 and PVC SCH40 is $3.40. That will save me over $120!

    I'm planning on putting the new main panel directly behind the electric meter. Does anyone know if I can come out of the back of the meter and into the back of the panel? Do they make a nipple that small?

    I'm pretty sure you are correct, but what is the code ref on two ground rods?

    What are slip risers? Do you mean an expansion and deflection fitting? I have conduit stub ups 18" below grade into the garage foundation. I'll need one there.

    When I come out of the ground underneith the deck, will I need one there? I was planning on using a couple of 45degree fittings to come out of the ground. Deck is only 12" off of the ground where I will come out. By the way, I have 270 degrees of bends between the house and garage. One long sweep 90 (already in place in the foundation) and an assortment of 45 fittings around the deck to get into the house.

    If I use PVC and seal the joints, I'm not sure water will (easily) get in. If it did,freezing, though, is an issue.

    If I assume that my panel in the house (100A) will be loaded to 80% (which it won't, it will be less), then I am fine (3%) with the voltage drop with #2 Cu. If I use 2/0 Al, my voltage drop is even less (2.4%). Think that's fine?

    Thanks,
    Jason
    Last edited: Oct 1, 2009
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,641
    Location:
    Cave Creek, Arizona
    plan

    You left off the part where you submit your ideas to the city for evaluation, revision, and a permit, then the inspection should be BEFORE you have your existing power terminated. Otherwise you could be without power until your new wiring IS approved.
  10. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH

    I actually already have a call out to the city inspector w/ questions.

    I mentioned get inspection from City which would infere I am getting a permit.
  11. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Per NEC 310.15(B)(6) and inspector, I can run 3#2,1#4G to the house provided my load calculations show that 100A is sufficient (no problem).

    But, it turns out that SER can not be run underground, even in conduit. The USE cable (which can go underground) that I need is $1.83/ft at bLowes, but can not be run indoors. :( If I want to take advantage of this cheap cable, I'll have to splice it as it leaves the garage. Splice and JB might eat up savings.

    I'm having trouble determining how to size a junction box to make a straight (not angled) splice of 3#2 and 1#4. Can someone lend a hand?

    Thx,
    Jason
    Last edited: Oct 6, 2009
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