9

here is what I have.

On the corner of my house, I have the main breaker box. I also have a 2nd sub panel that was installed later on the other side of the house which has 240V ac running to it. This panel has one breaker for a 120V ac light. That is it. Nothing else is connected.

I have a undeveloped area (about 140 feet away from the sub panel) that I would like to run 240V ac service to via underground conduit so I can use a 240V ac electric stove for outdoor kitchen.

My question is: Can I install a new sub panel from the undeveloped area utilizing the existing sub panel or do I need to go directly from the main panel? If I can then can I just run 2 wires from the panel and install a ground rod at the new area?

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[additional pictures from OP's link added in:]

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  • 1
    Are you asking if you can feed a sub-panel, from a sub-panel? What is the main breaker rating in the existing sub-panel? What is the breaker rating in the main panel feeding the sub-panel (not the main breaker, though that might be worth mentioning too)? What size wire is used to feed the existing sub panel?
    – Tester101
    Mar 4, 2013 at 12:33
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    Without the details requested by Tester the answer is a definitive Maybe. Mar 4, 2013 at 12:46
  • 2
    Running 220VAC in the US would involve 4 wires: 2 hot, a neutral and a ground.
    – HerrBag
    Mar 4, 2013 at 13:21
  • Ok here is are a couple of pics of the existing sub panel. Still haven't gone under the house to trace the 220 wire. stevenleespage.com/Images/220subpanel.jpg stevenleespage.com/Images/220subpanelA.jpg plz tell me what you think. Thanks, Steve
    – user11883
    Mar 7, 2013 at 10:45
  • You said the original sub panel was 8 or 6 guage wire you have to be sure it is ok to run 6 gauge wire to the new sub panel as long as the existing subpanel is six gauge it is easy go to original subpanel go inside it and check what gauge feeder wire was used and match it to new sub do not go over it's not good Dec 7, 2019 at 13:22

2 Answers 2

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Yes, you can. The systematic computer programmer in me even thinks it's a good idea, allowing a "star" topology for electrical distribution.

  1. You will need 4 wires, as others have mentioned.

  2. Keep the ground and neutral separate in the subpanels. The only place they should be bonded is in the main panel.

  3. You will need ground rods at the new location. Yes, it's redundant, but it's still required.

  4. The wire feeding the new subpanel must be protected from overcurrent by an appropriately-sized breaker. It can be at either end - in the old subpanel or in the new subpanel - or at both ends. It's up to you, but if only using one, I slightly prefer the upstream location, so that I can easily kill power to the feeder wire. If using both, 1 must be sized for the conductor, and the other can be that size or larger -- convenient if you buy a panel with a 100A breaker preinstalled.

  5. While there are wires rated for direct burial, it's good that you're planning to use conduit. Oversize the conduit for ease of pulling wires, and minimize bends. While you have the trench open, run a second conduit for future expansion (ethernet? gas? macerator?). May as well run a water line, too, so you can have a sink.

  6. Most electric kitchen stoves are installed on 240V/50A circuits. If you're installing something like that, then I suggest a 60A subpanel. That gives you plenty of headroom to install lighting, a small point-of-use electric hot water heater, and some convenience receptacles. Those will come in handy when doing maintenance in the area.

  7. Aluminum wire is usually much cheaper than copper, but harder to work with. It's stiffer. You must use 1 size larger than with copper. The ends must be protected from corrosion with anitoxidant goop. The lugs must be torqued correctly. Some people think you should retorque the lugs on some schedule. Last time I bought wire, I wanted 8ga copper, but 2ga aluminum was 1/2 the price, so going with Al was worth it.

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    +1 for point 5 alone... if you have the trench already dug out then run all the lines you may ever need just in case, that way getting water or sewer is as simple as just connecting at the primary building at your liesure. Point 7 though... working with alumininum is hard enough and it is easy to create a dangerous situation if you don't know what you are doing. Mar 4, 2013 at 20:28
  • Yeah, that's why I usually only use Aluminum for long feeders. Maybe also for range/dryer/RV circuits, but would consider having a pro install those just to be on the safe side.
    – Jay Bazuzi
    Mar 4, 2013 at 23:01
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    For regular 15A / 20A circuits in a house, I'd stick with copper. One trick, though: if you run a subpanel to a couple key spots in your house, especially the kitchen, you can dramatically reduce the amount of copper required, increase ampacity for longer motor life, and make future expansion easier. I'm a subpanel nut. :-)
    – Jay Bazuzi
    Mar 4, 2013 at 23:06
  • Hi All sorry for the late reply. Here is a link to an image I created that shows what i am trying to do. Thanks to all for the help. Please correct my plan. stevenleespage.com/Images/220plan.bmp
    – user11883
    Mar 6, 2013 at 4:20
  • 1
    Feeding a sub-panel from a sub-panel is not a "star topology", it's a daisy-chained toplogy, which is less desirable. A star topology would have all sub panels fed from the main panel. By daisy chaining, any problem in either panel will result in loss of power to the sub-sub panel so the chance of failure is doubled (not a big deal with a stove, maybe a big deal if it were a sump pump or freezer).
    – Johnny
    Feb 14, 2015 at 0:02
4

You can connect a sub panel to a sub panel, if the allowable capacities are observed(# devices, wire current capacities) and you keep neutral and ground separate all the way through both sub panels. You must add a separate ground rod at the separate structure/area Check with your inspector, as a second rod, spaced 7' apart, might be required.

If the sub box utilizes 6 or fewer breakers, you can omit a main breaker in that box but its a handy way to disconnect everything at once. A disconnect switch is another way to cut all power to the new building/area.

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    The 6-circuit rule is something different: if you have a panel on one structure (e.g. the house) and want to add circuits on another structure (e.g. detached garage), you can skip a subpanel entirely, and just run a circuit from the main panel to the garage. The limit is 6 circuits, over which a subpanel is required. Still, I usually recommend a subpanel even if only running 1 circuit, for future flexibility.
    – Jay Bazuzi
    Mar 4, 2013 at 19:26
  • The point is to have a means of disconnect at the remote structure. Your 6 branch circuits will still need a disconnect locally. A sub panel is a better way to disconnect outlet circuits than to have special outlet snap switches.
    – HerrBag
    Mar 5, 2013 at 17:46
  • Hi All sorry for the late reply. Here is a link to an image I created that shows what i am trying to do. Thanks to all for the help. Please correct my plan. stevenleespage.com/Images/220plan.bmp
    – user11883
    Mar 6, 2013 at 4:21

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