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Thread: Is there a 200 amp breaker box with 100 amp main

  1. #16
    DIY Member rayh78's Avatar
    Join Date
    Sep 2008


    Quote Originally Posted by TWEAK View Post
    Does the guest house have its own independant service entrance? Or is it a sub panel fed off the main house panel?
    has own seperate service entrance.

  2. #17
    DIY Junior Member Bob_of_Maine's Avatar
    Join Date
    Oct 2010


    You could buy a separate 100 amp main for the new panel but it would cost almost as much as the panel.

    If you go to HDepot you can buy a 200 Amp Homeline panel with a number of breakers. Additional breakers are as cheap as any you can get.

    Run some appropriate size wire for 100 Amps (2 hots, neutral, and ground) from the existing 100 Amp panel to the new panel, connecting to the lugs of the 100 Amp panel AFTER the main breaker. Connect to the standard input of the new panel. If there are no lugs you can probably buy a cheap 100 amp branch circuit breaker for the old panel on the famous auction site.

    The new Homeline panel will have separate terminal strips for neutral and grounds, which you must use. The neutral should not be grounded at the new panel. Leave out the big green screw that they will furnish.

    You can leave existing circuits in the old box or move them to the new panel. You can use the old panel as a splice box if necessary.

    If there is adequate space you can connect the two panels through a short conduit, or multiple conduits. For the 15, 20, and 30 amp circuits with THHN wire you can run as many as 9 current carrying conductors in a single conduit. You can run more if it is a very short run.

    If you ever upgrade to 200 Amps (such as if you need it for "grow lights" for yourpot plants) you can eliminate the 100 amp panel and connect the new service to the 200 amp panel. If you are going to do it to code you will need to provide grounding adequate for the 200 Amp service.

  3. #18
    DIY Junior Member cswilson's Avatar
    Join Date
    Nov 2010
    North Bay, ontario, canada


    I don't know about it where you are. But I just recently replaced my main panel as well as the separate service I had for my garage. I bought 2 new panels. one is a 100 A the other a 200A on looking up the specs of the panels. the 100a is rated higher then they are breakered for.

    . the 100A is rated as a 200, but came with a 100a breaker (both panels are identical except for this)

  4. #19
    DIY Member TWEAK's Avatar
    Join Date
    May 2009
    Bay Area CA


    Quote Originally Posted by rayh78 View Post
    has own seperate service entrance.
    That being the case....

    In San Jose CA, where I live, you can't do that. PG&E, the poco here, won't let you install a 200A box with 100A main breaker. I know this for a fact because I tried. I wanted to replace an old 100A Zinsco panel that was scaring me - I had a couple of instances where breakers didn't trip and branch wiring became the fuse. Zinsco is nearly as bad as Federal Pacific. Anyway, I wasn't ready to spend the bucks to upgrade the underground service quite yet. So I wanted to put in a 200A box fitted with 100A main breaker, and upgrade to 200A later. PG&E, would not approve it. I had to either put in another 100A panelboard or if I wanted a 200A panel I had to upgrade the underground service. Ended up upgrading.

  5. #20
    DIY Member jetlag's Avatar
    Join Date
    Dec 2009


    This might be hard to believe but the code allows you to install 2 -100 amp panels on the same service entrance , even though the meter , service entrance cable and every thing else is only 100 amp . All you have to do is show that the calculated load for install is less that 100 amp . The NEC code that allows this is NEC 230.90 A exception 3 . There is a debate going on right now at www.mikeholt.com , look under forums, NEC, post entitled, "hypothetical-table" . My user name is jetlag and I am argueing agaist this kind of install being allowed .
    Last edited by jetlag; 11-29-2010 at 06:22 PM. Reason: mistake

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