Looking for advice on a sub-panel - 60 or 80 amp?

Discussion in 'Electrical Forum discussion & Blog' started by DTAZ, May 28, 2017.

  1. DTAZ

    DTAZ Member

    Joined:
    Feb 14, 2017
    Location:
    Arizona
    I am remodeling my home and am in the process calculating the load for a sub panel that will supply power to a portion of the house. The house was built in the late 1040s with an addition constructed in the early 70s. There is a contemporary 200amp load center with integrated service entrance on the exterior of the building. It supplies power to the addition through installed breakers and to the original portion of the house through a subpanel. When the addition was constructed an original service entrance was removed but the service lines were connected back to the new load center through number 4 aluminum SEC without a ground. The number 4 aluminum supplies an 8 breaker load center without a main. Consequently the older part of the house is not grounded. I am remodeling the kitchen and bath in the original house and need to modernize the electrical system. My plan is to run a new 3 wire copper feeder with ground from my 200 amp load center to a subpanel.

    The sub panel will supply the following circuits (with energy demand listed as per appliance manufacturer specs):

    • 20 amp gas range
    • 20 amp refrigerator
    • 12 amp dishwasher
    • 12 amp range hood
    • 20 amp counter top circuits x2
    • 15amp living room ( existing 6 outlets 1 ceiling light, 1 entry light)
    • 15amp bathroom/bedroom/hallway (existing 6 outlets, 2 ceiling lights, bathroom fan)
    • 15amp tv room, kitchen lights (existing 3 outlets 2 ceiling lights, 1 entry light)

    Total combined load is 155 amps across 2 legs of 120 volt

    With 77 amps total per leg, I hope I can reasonably use number 6 copper NM-B with ground fed by a 60 amp breaker back in my main panel. However, I am wondering if I should consider moving up to number 4 copper with 70 amp breaker to provide more capacity? Thanks in advance. My run from the load center to the subpanel is 55 ft.

    Thanks!
     
    Last edited: May 29, 2017
  2. Stuff

    Stuff Well-Known Member

    Joined:
    Mar 7, 2013
    Location:
    Pennsylvania
    The bathroom receptacles can no longer be shared with anything outside of the bathrooms so plan on another 20 amp circuit for that.

    Otherwise the proper thing to do is a load calculation. You don't just add everything up. Instead the assumption is that not everything runs at the same time and it gets based on square foot and large loads. Since you don't have any significant loads a 60 amp feed should be fine.
     
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  4. DTAZ

    DTAZ Member

    Joined:
    Feb 14, 2017
    Location:
    Arizona

    Thanks for the advice on the bathroom. I wasn't thinking about that since it's preexisting wiring. I believe that my legacy circuit has the bathroom in line with other devices right now. My plan was to connect that wiring to the new grounded subpanel. Based on my plans, I don't need to move any of lights, switches or receptacles in the bathroom. Though if redoing the bathroom makes a new circuit a requirement, then so be it.

    Regarding the load calculation, I know you are right. The person who I learned from taught me a basic rule of thumb that one can figure load at 1.5x supply capacity for simple residential applications while making sure the load is balanced across the two supply legs. So, 60 amp 220 feed for up to 180 amps of 120 volt load. My total is well within that margin. In my case the 200 amp main panel will carry HVAC, on demand WH (gas), W/D, water softener, and the remainder of the house lights and receptacles.
     
  5. Stuff

    Stuff Well-Known Member

    Joined:
    Mar 7, 2013
    Location:
    Pennsylvania
    It is up to your local Authority Having Jurisdiction / Inspector on if you need to fix wiring when doing a remodel. Old bathrooms had the electrical outlet in the wall sconce or medicine cabinet. so usually a remodel involves installing a new box and receptacle. Whatever you do make sure that you end up with a GFCI receptacle.
     
  6. DTAZ

    DTAZ Member

    Joined:
    Feb 14, 2017
    Location:
    Arizona
    The bathroom does have a stand alone outlet so GFI was in the plan. However, you have prompted me to just go ahead and run a new branch so I end up with a properly grounded circuit (I had planned to bond the GFI receptacle to the box). It means getting into a plaster wall but your comment convinced me since I'm going the extra mile on everything else. Might as well get a proper GFI device where it's most needed. Thanks.
     
  7. Brian M

    Brian M New Member

    Joined:
    Apr 11, 2021
    Location:
    Indiana US
    If it was me... I would run aluminum. They also have mobile home wire 2/2/2/4 IIRC. It probably will be cheaper than copper. Then run a 100 amp sub panel. It would give you more breakers, and may be more cheaper that a 60 or 80 amp box. BTW You need to run 3 wire with ground to a sub panel.

    Oops, Replied to an old thread... When the "other threads like this" pop up sometimes you miss the date.
     
    Last edited: Apr 11, 2021
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