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Thread: 100 Amp Subpanel

  1. #1

    Default 100 Amp Subpanel

    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***
    Attached Images Attached Images   

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Your description sounds correct. The photos do absolutely nothing to clarify the description.
    Licensed residential and commercial plumber

  3. #3
    DIY Senior Member Chad Schloss's Avatar
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    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. #4
    Electrical Contractor/Instructor jwelectric's Avatar
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    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. #5
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by jwelectric View Post
    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
    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. #6
    Plumber jimbo's Avatar
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    Can a "black and white" wire be neutral?

  7. #7
    Moderator & Master Plumber hj's Avatar
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    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".
    Licensed residential and commercial plumber

  8. #8
    Electrician ActionDave's Avatar
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    Quote Originally Posted by jimbo View Post
    Can a "black and white" wire be neutral?
    Yes, as long as the stripes are continuous and there are three of them.

  9. #9
    DIY Senior Member Homeownerinburb's Avatar
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    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 by Homeownerinburb; 06-06-2012 at 12:22 AM.

  10. #10
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Homeownerinburb View Post
    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.
    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. #11
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by hj View Post
    He is assuming that your wires are #4, .
    You are correct I did misread the first post. He said 4 conductor cable not size 4, My bad

  12. #12

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    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. #13
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by tsingerjr View Post
    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?
    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. #14

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    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 by tsingerjr; 06-10-2012 at 08:06 AM.

  15. #15
    Electrical Contractor/Instructor jwelectric's Avatar
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    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.

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