100 Amp Subpanel

Discussion in 'Electrical Forum discussion & Blog' started by tsingerjr, Jun 5, 2012.

  1. tsingerjr

    tsingerjr New Member

    Messages:
    13
    I've added a 100 amp Sq D subpanel off of a Seimens 200 amp service. The cable I used has 4 wires (1 black - hot, 1 red & black - hot, 1 black & white - neutrel and a ground). My question is where these wires go into the 200 amp service. I'm assuming the following:

    1) The 2 hots get connected to the 100 amp breaker in the main panel.
    2) The black & white gets connected to the left side of the panel on the neutral side
    3) The ground gets connected to the ground bar on the right side


    *** I've attached pics of both the sub and main panels***

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  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,270
    Location:
    Cave Creek, Arizona
    Your description sounds correct. The photos do absolutely nothing to clarify the description.
  3. Chad Schloss

    Chad Schloss Member

    Messages:
    328
    Location:
    USA
    remember to keep neutral wires on the neutral bar, and keep grounds on the ground bar. they need to be separated in the subpanel. you should also 'recode' that neutral wire with white tape, like they did in your main panel, just so everyone who may look at that panel knows that it is neutral.
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Let’s hope that if that #4 is copper the breaker is not larger than 70 amps and if it is aluminum the breaker is no larger than 50 amps
  5. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    Can you explain this a little better?
    SE cable is excluded from 334.80, so why the restriction to the 60 deg C column? Are you assuming that it is installed in insulated spaces?
    And also why the round down for AL to 50A?
  6. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Can a "black and white" wire be neutral?
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,270
    Location:
    Cave Creek, Arizona
    He is assuming that your wires are #4, although I have not seen anything to indicate that that is the case. In fact, although we have nothing to compare sizes with, the wires in the right hand panel do NOT seem to be thich enough for #4. Aluminum wire has less capacity than copper wires of the same gauge . Three wires in a "cable" also have reduced capacity compared to single wires in "open air".
  8. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    Yes, as long as the stripes are continuous and there are three of them.
  9. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    The fact that the panel is rated to 100 amps does not necessitate protecting it at that level. Certainly it could be protected at no more than 60 amp. Obviously the wire between the two panels drives the size of the breaker protecting it in the main panel.

    The sub panel also needs to either have no more than six breakers or it needs a main breaker. Classically at the same size as the breaker in the main panel.
    Last edited: Jun 6, 2012
  10. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    Since this is fed with SER cable I can only assume it is within the same building as the main. The "six throws" or service disconnect rule does not apply.
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    You are correct I did misread the first post. He said 4 conductor cable not size 4, My bad
  12. tsingerjr

    tsingerjr New Member

    Messages:
    13
    So I have the subpanel connected to the main panel. I wanted to use the interlock and connect my generator to the subpanel and use that as the transfer switch Is this possible?
  13. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Are you planning on putting the generator on the main lug remote panel?

    If so how do you plan on turning off the main lug panel?
  14. tsingerjr

    tsingerjr New Member

    Messages:
    13
    I guess thats the part that Im struggling with. If I put it in the remote panel, would i have to add a breaker to shut off the feed to the main panel?
    Last edited: Jun 10, 2012
  15. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    When installing a generator the switching MUST be done in a way that the utility and the generator cannot be on at the same time.

    In the event of a power failure and the generator is in use and then the power comes back on if the utility is able to energize the same circuits as the generator all hell will break loose and the generator is destroyed as well as any damage to the panels.

    If the utility power is not shut off and the generator is started the voltage will be back fed to the transformer and a lineman could be hurt or even killed. Should this happen you can bet your bottom dollar that trouble is in store for whoever wired the generator to the panel as well as the one who started it up.

    If what you are connecting is one of the standalone generators there is a lot more to it than connecting it to the panel. In the event something goes wrong the damage could be catastrophic as well as the financial cost should you be sued.

    On this type of installation I suggest you hire a well-established electrical contractor.
  16. tsingerjr

    tsingerjr New Member

    Messages:
    13
    Thats what I plan on doing! Thanks
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