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Thread: 100 amp service to 200 amp service ?

  1. #1

    Default 100 amp service to 200 amp service ?

    We have an older farm house that currently has 100 amp service with an old fuse box ! We recently put on an addition and ran all new wiring to the new rooms. In the cellar of the addition, we've installed a new breaker box and have 200 amp service ready to be hooked up. Is there a way to connect the wires from the "old" part of the house to the new box, or do we have to re-run all new wiring in the old part of the house ?? I've read other threads about a sub panel, but I'm not sure if that would work ???

  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
    Join Date
    Jun 2007
    North Carolina


    Coordinate with the inspector and power company for a time to pull meter and get inspection on new panel.
    Once this is done be prepared to remove interior of existing panel to connect new circuits ran to the new panel for the inspector and then have the inspector to release the new service to the utility. The existing panel enclosure becomes a junction box so be sure to secure the hinged door to the cover.

    If you prepare properly then it can all happen in less than an hour.

    You can leave the old panel but there can’t be any three wire dryers or ranges connected to the existing panel and the conductors from the new panel to the existing panel will have to be replaced with four conductor cable.

    The bonding will have to be removed along with any electrodes installed in the existing panel.

  3. #3
    DIY Senior Member Murphy625's Avatar
    Join Date
    Jul 2013


    If I understand your question, I believe you can switch the power feed to the home over to the new box and then use the current fuse box as a sub-panel that feeds the rest of the home. You'll probably also have to have the power company upgrade the 100amp service lines to the new 200 amp rating. You'd probably need to install a 100amp breaker in the new box and run the new 100amp wire to what is now a sub panel.

    But don't take my word for it.. you should talk to your local inspector to see what he wants. They all seem to be different..

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona


    Many houses have a large main breaker at the meter and the actual breaker panel elsewhere, which is what you would have if you connect the new service to the 200 amp panel, and then run to the existing panel as a sub panel being fed from a 100 amp breaker in the new panel.
    Licensed residential and commercial plumber

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    To convert a main power panel to a subpanel is possible. How easy it is in the one you have is the bigger question. A main panel has the neutral and system ground tied (bonded) together. A subpanel must have those separate, that's why they talk about using a 4-conductor cable to feed the old panel (two hot, neutral and ground). Separating the grounds and neutrals at the old panel may or may not be easy. And, as was pointed out, if you have something like a dryer or stove from the old panel that was connected using a 3-wire cable (two hots and a neutral), it would no longer be safe since the neutral does not count as a safety ground...those would need to be rewired. Could apply to other hard-wired devices as well (i.e., any 240vac equipment).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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