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Thread: Garage feeder conversion to House feeder

  1. #1

    Default Garage feeder conversion to House feeder

    Hi All,

    Forgive my terminology, not my field, and I'm learning.

    My home has a detached garage, which has a subpanel fed by a direct burial single 15A circuit from the main house panel. I have a modest amount of shop equipment that I need to rewire for, so I plan to retrench a larger feeder circuit and rewire the garage.

    The home is fed overhead by service wires that run over the garage, so this is my plan:

    -Run/trench large cables undergound from the house panel to the back of the garage (trench to the garage, then conduit (?) through the garage attic)
    -Install a subpanel at the back of the garage that I will rewire the garage with.
    -At some future point, install a mast at the back of the garage, relocate the meter to the garage, and feed the garage panel directly, becoming the new main panel.
    -use the previously trenched cable to feed the house panel.

    Anything unusual about this? It seems logical to me, and I'm just unfamiliar with the exact panels and equipment that are necessary (doing my preliminary homework now).

    How do I run the two circuits - garage and home? meter to juntion box with disconnects individually for each? Or is there a panel that can be fed but has a feed through to the house? And can each have a 100A breaker?

    Any advice is most welcome.

  2. #2
    Join Date
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    Default

    Just noticed this was in the Canadian forum. I think most of my answer applies, but I don't know many of the differences between CEC -vs NEC code to know if the CEC has any issue with this.

    I guess the technical discriminator here is how much power you really need in the garage, and how far it is from the house. If you need 60A or less (which would cover most home shop needs), it will be easier and cheaper to just feed the garage from the house and not relocate your main service (the power company runs smaller wire than you're allowed to run, and they only run 3 wires whereas you must run 4). However, if there are other reasons pushing the service relocation, you can do it.

    To just have a feeder to the garage with no possibility of feeding the house from the garage:
    Install a 60A double pole breaker in the house panel. Use 6-3 UF cable, or a 1" PVC conduit with black-red-white #6 copper wires and a #10 green. NM or UF cable in the garage attic does not have to be in conduit if protected from damage (but if using individual wires, you'll need EMT, PVC, or flex conduit. ONly the EMT would not have to be protected from damage). Install a panel in the garage rated at 70A or higher (most will be 100A or 125A panels). Make sure to keep the neutrals and grounds on separate buses in the garage (neutral isolated from the chassis), and you'll need a ground electrode system in the garage (2 ground rods).

    To be able to feed the house from the garage, the first thing to assess is the house panel. Will you be replacing it? If not, you'll have to be able to separate all the neutrals from the grounds. A modern panel will have enough bus bar space to do this (old or new will most likely require an accessory grounding bar). Replacing the house panel when you feed from the garage makes this a non-issue.

    Next, you do what you did above except you must run wire rated for 100A (minimum size for a house) and conduit would need to be 1.5 to 2". That is enough if you have mostly gas appliances. If you'd like more power, then the wire will have to be even larger. You'll need #2 aluminum for 100A and #4/0 aluminum for 200A. Again, you need 4 wires with the neutral allowed to be a few sizes smaller and the grounding wire can be quite a bit smaller. For the panel, I'd get a 200A one with a main breaker. If the house feed is 100A, then use a 100A backfed main for now (label it main, the integral main won't be used right now). Later, that will be house feeder breaker when the garage becomes the main service. If the house is over 100A, you'll need a garage panel with feed through lugs, but for now put the wires on the main breaker. When the garage becomes the main, those wires would move to the feed throughs.

    When the garage becomes a main service, you'll need to connect the ground and neutral buses. So don't lose the green bonding screw -- lay it in the bottom of the panel. But for now (garage is fed from the house), you don't install that bonding screw.

    Hopefully, you can see reversing the feed from house side to garage side adds a lot of complication. I wouldn't do it unless you have good reason to, or you need more power in the garage than you do in the house.
    Last edited by suemarkp; May 16th, 2011 at 12:58 AM.
    Mark
    Kent, WA

  3. #3

    Default

    Since my house panel was just upgraded to 100A (cutler-hammer/bryant), I don't think I'll be replacing it. There's plenty of space as well.

    So, if I read correctly, the panel being fed needs to have neutral and ground busses seperated? In the main panel, are they normally connected?

    My reason for doing it would be just to get rid of the overhead line. I guess for some people that wouldn't be a good enough reason, but I'm stubborn I guess.

    Can you explain the bit about the backfed/integral breaker? Is the integral breaker the one that is bolted in to the panel, that feeds the busses?

    Thanks again,

  4. #4
    Join Date
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    Yes, a main panel is the only place where neutral and ground are connected. This is usually accomplished with a green bonding screw.

    A backfed breaker is like a normal breaker in a panel except power gets into the panel that way instead of out. You would use one of those is there was no built in main. These have a hold down clip, not certain if they are allowed in Canada since you tend to have the feed side completely isolated from the LOAD side.

    A larger panel usually has a separate breaker where the LINE wire land. Then there are bus bars or wires leaving that main which connect to the bars where all the branch/feeder breakers plug in.

    You'll have no problem finding what you need for a new CH/Bryant panel.
    Mark
    Kent, WA

  5. #5
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    Two option in Canada IF you are NOT keep animals in the detached structure.
    1. Three wire feeder with grounding electrode at structure and neutral bonded. (10-208(a))

    2. Four wire feeder and the neutrals and ground separate. (10-208(b)).

    You also need to verify your feeder size requirements. They are different in Canada than USA. I'm sorry I am not that up on exactly what you would require. There are some quirks between feeders for mains and feeders for subs that allow two different sizes for the same feed amps depending on if it is a main or sub.
    Last edited by joed; May 17th, 2011 at 09:46 AM.

  6. #6
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    That will certainly make his job easier, if a 3 wire feed is allowed to detached buildings, whether Service or Feeder. A 3 wire feed implies a bonded panel (neutral and ground bonded together with the green screw). This was allowed in the US prior to 2008.

    Like I said, I hated to erase my post of seeing that it was in the Canada forum, but perhaps I should have.
    Mark
    Kent, WA

  7. #7

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    Just a quick question regarding wire types.

    What is permissible by code for an underground conduit run between structures (I assume CEC and NEC agree here that any underground cable needs to be wet rated regardless of in conduit or direct burial).

    There's someone selling triplex 4/0 aluminum NSF-2, but this is an overhead wire, which I assume is not allowable underground in conduit, right?

    Also, how difficult is 4/0 aluminum to work with? I'm assuming very, and pulling it through conduit is not an option. If I was to bury in conduit, it would probably be better to be bent to shape in the conduit prior to being laid in the ground.

    also, am I to go 18" min depth for pvc conduit?

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