max number of branch circuits

Discussion in 'Electrical Forum discussion & Blog' started by lahabra, Dec 24, 2007.

  1. lahabra

    lahabra New Member

    Dec 21, 2007
    I am doing an old home re-wire, all new circuits. I am planning to add a 100A sub panel to give me more spaces to work with. I will feed the sub panel with a 50A breaker from the main panel.

    If I fill all the spaces on the 100A sub, the draw would likely be enough to cause nascence trips on the 50A breaker.

    How dose one go about calculating how many branch circuits can be added to a de-rated panel?
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Jun 14, 2007
    North Carolina
    See Article 220 of the NEC
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  4. 480sparky

    480sparky In the Trades

    Oct 8, 2007
    Electrical Contractor
    Can you increase the wire size feeding the panel so you can increase the breaker ampacity?
  5. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    The panel capacity is a maximum and is completely independent of how many slots are used. You have to calculate the actual, or estimated, load on the panel to see if its feed wire and breaker are adequate.
  6. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    You can get a 40-space panel for almost the same cost as a 100 Amp subpanel. They sell panels at HD that even include a bunch of breakers.

    I would put in a 200 Amp panel with main breaker and a new service. If you want to make the changeover easier with minimal outage of power you can feed the new panel as a subpanel off the old panel using lugs on the old panel, protected by the main of the old panel. When you are ready you can remove the old panel and put in the new service connection.

    The advantage is that you don't have to worry about managing the load of a lot of circuits on a 50 Amp breaker.

    The other solution is to get a piece of #2 aluminum SE R at HD and connect your subpanel as a 90 or 100 Amp panel.
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