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Electrician needed! Circuit breaker panel load calculations...

Discussion in 'Technical' started by Frank Schwab, Aug 27, 2017.

  1. Frank Schwab

    Frank Schwab Member

    Joined:
    Apr 7, 2016
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    96
    Location:
    Arizona
    Background: Talented amateur electrician, not afraid to add/remove breakers, run new circuits, etc.

    Started looking into adding a 14-50 outlet to my garage. Phoenix will start cooling down in the near future to where that kind of work will be possible. My problem? A full breaker panel.

    I have 200A service, and a panel rated for 200A. As an all-electric home in Phoenix with a pool and jacuzzi, you can imagine that I inconvenience a lot of electrons. My panel has 20 spaces for breakers, and I currently have 30 in there using one tandem 240V and 5 tandem 120V breakers. As an amateur, swapping one of the existing 240V breakers for another tandem in order to add another 50A circuit is easy - but I don't know if it's a good idea.

    I used a couple of different online load calculation worksheets to see where I stand; they all give results in the range of 260 amps.
    Q: Is this a problem for an existing 200A panel?
    Q: 220 amp panels seem to be the largest residential panels that are easily acquired; 400 A are available, but price goes up from $150-$200 to $800. Ouch. Do such things as 300A panels exist?

    I don't have any problems with breakers tripping at this point because my loads are heavily timed due to a time-of-use electrical plan. My water heater is only allowed to run from 7:00PM to noon, my Jacuzzi runs at 9:00PM, my Pool runs at midnight. EV charging would be slotted in here also, probably running from 1:00 AM to 7:00 AM or so. This would keep me from hitting 200A in real-life, but I'm not sure that the NEC recognizes timed loads - certainly none of the online calculators allow that.

    Any help out there? I wasn't sure whether to post this here, or in "charging infrastructure" but that forum seems to mostly deal with public chargers...
     
  2. Tam

    Tam Active Member

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    Could you use a throw switch so either your pool got energized or your charger got it but not at the same time?

    It's a manual hassle when you want to use one or another but at least you don't have to upgrade your main 200 amp panel.

    [​IMG]
     
  3. boaterva

    boaterva Supporting Member

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    The load calc should tell you that you do or don't have capacity for the 40 Amp continuous load circuit (50 Amp breaker). I have a hot tub, 200 Amp service and had no problems. But you do need to take one of the load calc spreadsheets from the internet and do all the calculations.

    Edit: seeing how it's an all electric home, you may be over the limit, definitely. I don't know if an A-B switch is code for load switching or not. May depend on location.
     
  4. SageBrush

    SageBrush Active Member

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    I don't have an answer for OP but perhaps a related question:
    If PV is coming into the panel does that reduce the load ?
     
  5. Lloyd

    Lloyd Well-Known Member

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    Only during the time the PV is producing
     
  6. deonb

    deonb Supporting Member

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    He already has that on a timer.
     
  7. BrokerDon

    BrokerDon Member

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    Newport Coast, CA
    Our Tesla recommended electrician installed our 80A HPWC on a 100A breaker in a 100A subpanel connected to our 200A Main Service Panel. Electrician did this after completing and receiving approval of his a Load Calc worksheet and submitting it to our local Building Department with our permit application. We've used it for 2 years now (mostly at 50A to 60A to maximize HPWC and dual charger life expectancy) with no issues... but we RARELY run our 2 main HVAC units at night (cools off nightly near the ocean) when our Tesla is charging... and ALL of our other major amperage appliances are completely off or just cycling (1 SubZero + 2 under counter beverage refrigerators).

    I'd recommend either getting a Tesla recommended licensed electrician or getting a Load Calc worksheet from your Building Department and run the numbers. Hopefully your proposed 14-50 outlet will be fine.
     
    • Like x 1
  8. Tam

    Tam Active Member

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    Good point!

    However, timer is voluntary. My kids or I myself might play with it and alter the settings at any time. Thus, two loads can run simultaneous by altering the timer setting.

    On the hand, the throw switch is hardwired in order to only allow one load at a time. That's the way it is set and not user changeable.

    I am not familiar with electrical codes but I am only thinking out loud to ask that question to qualified people.
     
  9. Mishakim

    Mishakim Member

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    One issue is whether your 200A service can handle all your loads, which the worksheets are for. Assuming that's clear, there's also a question of overloading the panel itself - it sounds like it's already overcrowded (is it really supposed to have that many tandems? older panels don't support tandems in every slot), and may have too much wiring inside it. To address those issues, and just make it easier to work with, you could add a sub panel with six or eight slots, and move a bunch of those circuits over to it.
     
  10. BrokerDon

    BrokerDon Member

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    Great point. That's what the builder did at our 2006 constructed house: 200 main service panel + 100A subpanel to handle all the circuits. Works great and the most cost effective way to add breaker spaces.
     

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