Is there a 200 amp breaker box with 100 amp main

Discussion in 'Electrical Forum discussion & Blog' started by rayh78, Oct 7, 2010.

  1. rayh78

    rayh78 Member

    Messages:
    79
    Location:
    Virginia
    Have a remodel to do and will sub out electrical.
    Electrician I have used in the past said I cant do this.
    Years ago I had the same situation. Small house with 100 amp service and customer does not want to pay for upgrade now but wants breakers. Instead of putting in just a 100 amp breaker box, I had a 200 amp Murray box put in and install a 100 amp main breaker instead of a 200 amp main. The box was still 200 amp to make a future upgrade easier. A murray 100 amp breaker fit in the same space as a 200 amp for the Murray brand. Which was not the same with square D. Since then if ever I contracted out any electrical we have used square D brand. But have this situation again and they dont make murray anymore. Is there another brand out there?
    Electrician does not want to do this either. Use just a square D 200 amp box with a 100 amp square D line feed breaker because he saids maybe a problem with inspector.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    I'm by no means a pro, but it is my understanding that as long as the supply line capacity is not exceeded by the protection circuit, it is okay to use a smaller cb. Now, with more available slots, you are more likely to be able to trip the main breaker, but that's another issue. Logically, but maybe not by code, it should be in the same idea as using 12g wire on a 15A service, which could also use 14g. The wire size determines the maximum current that can be drawn.
  3. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    You need to convince the customer that they are mad.

    When I tried to do the opposite (upgrade the service but not the panel) the extra cost of calling out an electrician just to do the panel in the future would have been much more than the modest increment I ended up paying to get it all done in one go.

    Not to mention the requirement for another inspection.

    Refuse.
  4. rayh78

    rayh78 Member

    Messages:
    79
    Location:
    Virginia
    Alittle more info.
    This is a small 600 sq.ft. guest house on a seperate meter and has gas heat.
    So it is questionable if an upgrade would ever be needed but they would like the option. And it would save some work. And the price difference between a 100 amp or 200 amp box is not that great.
    Would save morethan that if ever an upgrade
  5. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    I can see no logical reason to think about installing any more than a 100 amp panel for a 500 square foot house.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,230
    Location:
    Cave Creek, Arizona
    What is feeding this panel? If it is a subpanel, just install the 200 amp unit with a 100 amp breaker at the main panel. if it is being metered, the electric company can install new cables and meter, or just a 200 amp meter if their wires are adequate.
  7. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    600 sq feet with gas and 200 amps? Going to smelt aluminum?

    60 amps is plenty like every three bedroom house had until 1970...

    You can use a 100 amp panel and feed it with a 50 amp breaker, and I'll bet it NEVER trips.

    200 amps is absurd unless they plan to add 4 more 600' units to this one.
    Last edited: Oct 10, 2010
  8. rayh78

    rayh78 Member

    Messages:
    79
    Location:
    Virginia
    still has electric hot water and stove and the long term possiablity was to switch to a heatpump
  9. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    If you switch to a heat pump stay with the gas for the backup heat.
  10. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    You could feed 200 amp sub panel with a 100 amp breaker but should size wire for the 200 amps.
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,230
    Location:
    Cave Creek, Arizona
    Goes without saying if this is for a future upgrade, otherwise the whole discussion is irrelevent.
  12. rayh78

    rayh78 Member

    Messages:
    79
    Location:
    Virginia
    Would use the same wire for now. Just so I understand options.
    It would be against code to use 200 amp box. Blank off cover space for the factory main breaker and then use 100 amp line feed breaker.
    thanks
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,230
    Location:
    Cave Creek, Arizona
    You can use any panel you want, with or without the main breaker, as long as the breaker feeding it is appropriate for the wire to the panel. Although you might have a bit of difficulty attaching the wires to the buses without going through a main breaker.
  14. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    If you decide to backfeed the breaker you will need to install a breaker hold-down kit.
  15. TWEAK

    TWEAK New Member

    Messages:
    86
    Location:
    Bay Area CA
    Does the guest house have its own independant service entrance? Or is it a sub panel fed off the main house panel?
    Last edited: Oct 16, 2010
  16. rayh78

    rayh78 Member

    Messages:
    79
    Location:
    Virginia
    has own seperate service entrance.
  17. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    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.
  18. cswilson

    cswilson New Member

    Messages:
    2
    Location:
    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)
  19. TWEAK

    TWEAK New Member

    Messages:
    86
    Location:
    Bay Area CA
    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.
  20. jetlag

    jetlag New Member

    Messages:
    84
    Location:
    Ga.
    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: Nov 29, 2010
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