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Thread: Tapping per 240-21B

  1. #1
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    Tapping per 240-21B

    Hi ,
    for plan-A, can i tap my 400A / 400 MCM residential feeder that is off the main 400A service
    to two 40 feet-away -located 200A sub panels thru 3/0 ????

    or, as plan-B, just install a 400A distribution panel with main on the exterior wall of the house than,.......

    (the 400A service is located at the corner of the property, stand alone, dettached)

    THANK YOU

  2. #2
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    225.30 Number of Supplies limits you to one feeder, except for special conditions and scenarios thereunder. Using the 'tap rules' to supply more than one subpanel from a remote location would be a compliant loophole IMO.

    However, nothing is gained as I believe the 'grouped' requirement of 225.33 still applies. The two subpanels are not permitted to be installed at a location remote to each other without additional disconnecting means in the picture.
    I'll never get there. No matter where I go, I'm always here.

  3. #3
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    Quote Originally Posted by Smart $ View Post
    225.30 Number of Supplies limits you to one feeder, except for special conditions and scenarios thereunder. Using the 'tap rules' to supply more than one subpanel from a remote location would be a compliant loophole IMO.

    However, nothing is gained as I believe the 'grouped' requirement of 225.33 still applies. The two subpanels are not permitted to be installed at a location remote to each other without additional disconnecting means in the picture.
    In my opinion what you 'gain' is not having to purchase a 400 amp panel for the house. Two-200 amp main breaker panels are almost always less money than a single 400.

  4. #4
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    Quote Originally Posted by iwire View Post
    In my opinion what you 'gain' is not having to purchase a 400 amp panel for the house. Two-200 amp main breaker panels are almost always less money than a single 400.
    In that respect, yes... but just looking at the wire, a dual run of tap wire sets versus a single run of full 400A feeder, there's no gain. Running a full 400A feeder qualifies for the reduced wire sizing of 310.15(B)(7)... whereas two runs of taps the whole distance would not. Running a 400A feeder as parallel sets would require 2 sets #2/0 copper. Taps would require 2 sets of #3/0 copper.
    I'll never get there. No matter where I go, I'm always here.

  5. #5
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    Quote Originally Posted by Smart $ View Post
    In that respect, yes... but just looking at the wire, a dual run of tap wire sets versus a single run of full 400A feeder, there's no gain. Running a full 400A feeder qualifies for the reduced wire sizing of 310.15(B)(7)... whereas two runs of taps the whole distance would not. Running a 400A feeder as parallel sets would require 2 sets #2/0 copper. Taps would require 2 sets of #3/0 copper.
    You are not getting what I am suggesting.

    And I think you can forget about copper when dealing with home feeders.

    Run a single 400 amp feeder from service point to house, hit a j-box, split that 400 amp feeder into two 200 amp taps with a 200 amp MB panel on each side of the j-box.

  6. #6
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    Quote Originally Posted by iwire View Post
    You are not getting what I am suggesting.

    And I think you can forget about copper when dealing with home feeders.

    Run a single 400 amp feeder from service point to house, hit a j-box, split that 400 amp feeder into two 200 amp taps with a 200 amp MB panel on each side of the j-box.
    I have no idea why you say that. I wasn't suggesting anything different. I'm just saying 400A feeder for as much of the run as possible. J-box or trough to tap off to the two subpanels. Two sets #4/0 aluminum in parallel for full 400A feeder. 250kcmil aluminum for taps. Four-port Polaris connectors or equivalent.
    I'll never get there. No matter where I go, I'm always here.

  7. #7
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    Quote Originally Posted by Smart $ View Post
    I have no idea why you say that. I wasn't suggesting anything different.
    Given what you said it seemed you wanted to start the tap right at the service point which is doable but means you cannot used any reduced wire sizing for 'main power feeders' that way.

    If you did mean split them at the house like I did then I don't see what your taking about regarding wire sizing.

    I am going to walk away from this one, in my experience once you and I misunderstand each other there is no turning back and we will wreak the thread.

  8. #8
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    Quote Originally Posted by Smart $ View Post
    225.30 Number of Supplies limits you to one feeder, except for special conditions and scenarios thereunder. Using the 'tap rules' to supply more than one subpanel from a remote location would be a compliant loophole IMO.
    Interesting, never though of that. I love loopholes. Its like getting one up on the man and his rules
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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