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Wall Charger Install - Help with load calculation 50a or 60a breaker?

Discussion in 'Model 3: Battery & Charging' started by paranoidroid, Aug 28, 2018.

  1. paranoidroid

    paranoidroid Member

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    I will hire or DIY a permitted wall charger install and want to make sure I'm doing my load calcs right (single family dwelling). I am calculating I can squeeze in a 60a breaker to replace my 30a breaker (unused wall dryer outlet that I will disconnect).

    Only 100a service but luckily I have gas dryer, gas stove, gas furnace and gas water heater.

    I attached a photo of my breaker box and my load calc says I am only using 35a therefore can possibly put in a 60a breaker (to replace the current unused 30a one).

    Even if I hire an electrician I want to make sure I know my options for this permitted install. IMG_1767 (1).jpg Screenshot 2018-08-28 15.27.52.png
    Can someone double check?
     
  2. TexasEV

    TexasEV Well-Known Member

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    I can’t double check that but I can double check your terminology. What you’re installing is a Wall Connector, not a Wall Charger. The charger is in the car.
     
  3. RandyS

    RandyS Fan of Elon

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    There are a lot of appliance spaces that are blank on the sheet. You have no microwave, no dishwasher, no electric cooktop, no electric oven? And what type of AC for a 2,000 sq foot home is just 1152 VA? Must not be central air. Mine is 4,000 watts for a 2,500 sq foot home....Otherwise, looks good.... :)
     
  4. ewoodrick

    ewoodrick Active Member

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    Aside from the things that RandyS suggest are missing, Gas dryers and gas furnaces require power too.
    Taking the panel all the way to 100% isn't something that I'm find of.
    Is your daily commute bad enough that you are going to need the full 60A? Are you on a time of use rate that will impact this?
     
  5. paranoidroid

    paranoidroid Member

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    The microwave is included in the kitchen appliance circuits category. No dishwasher and oven & cooktop is gas.
    I only have a furnace living in San Francisco, gas powered so only amperage is the fans.
     
  6. paranoidroid

    paranoidroid Member

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    The gas dryer is part of the included laundry circuit. I guess safe thing to do is go to 50A which gets me 40A continuous charge rate.
     
  7. Xenoilphobe

    Xenoilphobe Active Member

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    Switch out all lighting to LED and you will have some more headroom. Also keep in mind that you can set it up to charger after midnight when you aren't using the other appliances also.
     
  8. paranoidroid

    paranoidroid Member

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    I am pretty sure I have the headroom for 60a esp since charging is at night but what I need is someone familiar with doing the NEC Standard Load calc for typical city permitting purposes..
     
    • Informative x 1
  9. Xenoilphobe

    Xenoilphobe Active Member

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    #9 Xenoilphobe, Aug 28, 2018
    Last edited: Aug 28, 2018
    There has to be an app for that...

    ‎Electrical Load Calculator '17 on the App Store

    Description
    The Electrical Load Calculator is a convenient tool that can be used to determine the minimum electrical load demand for one-family and multifamily dwellings based on the Standard Calculation Method as defined by Article 220 of the 2017 National Electrical Code (NEC®). This app simplifies the steps of the Standard Calculation Method by breaking lengthy calculations into manageable parts and automating mathematical computations.

    The Electrical Load Calculator determines grounded and ungrounded loads for general lighting, fixed appliances, dryers, cooking equipment, heating and A/C units, and the largest motor. The calculated loads are compiled to determine the total service load for a one-family or multifamily dwelling. Each dwelling calculation can be uniquely named and saved for future access. Calculation results can be sent via email along with associated load values entered in the calculation.

    The calculated electrical load demand can be used in conjunction with the NEC® to determine the size of the service-entrance conductors required for the dwelling. Proper sizing of the conductors is required to ensure the safety and efficiency of the service.

    This app is designed to be an aid in electrical load calculations and is not intended to replace Article 220 of the NEC® or the NEC® as a whole. Specific procedures vary with each task and must be performed by a qualified person. For maximum safety, always refer to specific manufacturer recommendations, insurance regulations, specific job site and plant procedures, applicable federal, state, and local regulations, and any authority having jurisdiction. American Technical Publishers, Inc. assumes no responsibility or liability in connection with this material or its use by any individual or organization.

    National Electrical Code and NEC® are registered trademarks of the National Fire Protection Association, Inc.
     
  10. eprosenx

    eprosenx Active Member

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    Nice job! Where did you get that form btw? I like that version.

    So I am not sure you actually have three small appliance circuits. Generally most houses have the two required in the kitchen, plus one for the laundry.

    Correct me if I am wrong, but it appears you have a modern electrical service that is not all that old? Can you take a picture of the door panel label and post it? I want to read more aboit your panel.

    Are you going to run Romex or conduit to the wall connector?

    I concur that your load is extremely low.

    I would most likely double up some breakers with tandems (I see a number of options) and then install a new 60a circuit (leaving the dryer available for future).

    Then if further analysis (or an inspector) took issue with your wall connector being set to 60a (48a continuous) you could always crank it down a notch or two on the rotary dial and be back into compliance. Say you decided to get an electric dryer and you later decided the full 60a was overkill for charging, just remove the faceplate from the Wall Connector and crank it down a notch.

    Also, I likely would not go above 6awg (since it gets annoying to handle and your service is only 100a) so if you did decide to use Romex then you can only do a 50a breaker (40a charging). FWIW they also make tandems in 50a so you could just say tandem up the dryer and wall connector then (but really, doing two tandems for the 4x 20a circuits below the main would give you a spot for a non tandem 60a. This is what I did.

    Since this appears to be a modern service and appears well done chances are even if you do overload it, the penalty for failure is you blow the. 100a. If that happens then just crank down the wall connector dip switch a notch and reset.

    P.S. would be interesting to see pictures with the panel cover off as well if you can do it safely.
     
  11. eprosenx

    eprosenx Active Member

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    Also, line 8 is blank, and the total at the bottom I don’t get the same math to add up (it is not far off though). I still think you can do this.
     
  12. paranoidroid

    paranoidroid Member

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    Thanks for the feedback, first time doing this so I appreciate it. I found the form online: NEC Standard Electrical Load Calculation for Single Family ... - LADBS

    I am going to use 6awg THHN in EMT Conduit from the panel to the HPWC which will only be a two foot away. I was thinking of using tandems and adding a 50A breaker but I'm not sure that will pass inspection.

    I can add pictures later with the panel off but here are the pics of the panel door:
     

    Attached Files:

  13. gilscales

    gilscales Member

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    #13 gilscales, Aug 29, 2018
    Last edited: Aug 29, 2018
    Why not unhook the dryer outlet and replace the 30a with a 60a breaker in the same spot?

    Also many modern panels only allow a limited number of tandem breakers.
    How to know when tandem circuit breakers can be used (aka - cheater breakers)

    You may have large enough wire coming in to the panel that you could (if needed) upsize your main breaker to 125A, MAKE ABSOLUTELY SURE THAT THE WIRE IS OF ADEQUATE SIZE BEFORE DOING THIS!, your panel is rated is rated at 200A.

    I recently ran a sub panel in a detached garage (well my electrician did) He instructed me to get no#1 wire (rated for 130A in conduit) they were out so I ran 1/0 which has 150A rating.
    Ampacity Charts

    Even the NEC code allows for no#2 wire with 125A breaker and 75c rating is only 115A so there is a little leeway, unless you have no#3 wire or smaller then main breaker upsizing would be allowed per NEC code as long as there is no other circumstances preventing this (very long run is one possibility)
     
  14. paranoidroid

    paranoidroid Member

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    Yes, current plan is to replace 30a with 60a breaker and use that spot.

    I didn't know I could potentially use a 125A main breaker if the main wiring supports it. I most likely won't need to do this, but just so I know -the main house meter is right above this panel and if the wiring is sufficient would I need to verify the service from electrical company supports more than 100A?
     
  15. eprosenx

    eprosenx Active Member

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    You could unhook the dryer outlet, but I personally would want the option to use he dryer outlet in the future without having to do a bunch of work. That is why I suggested tandems. I don’t like leaving wires just hanging out in the breaker panel unterminated either if I can avoid it.

    Yes, most breaker panels have a limited number of breaker poles they are allowed to have. The NEC used to limit this to 40 (technically 42 but I think it includes the main). So most panels were/are rated this way. Since that panel is so small I can virtually guarantee all the bus stab locations are “notched” which is what indicates that they can accept tandems (or quads). Normally the sticker on the door indicates this, but strangely enough yours only seems to show a prototypical panel layout and not actual info on your bus unit.

    The wire coming into the panel is not the only limiting factor controlling if he can upgrade beyond 100a. It is very likely that his meter base or overall electrical service is only rated to 100a. It is a good thought though if it is an option. Though if this is an MDU with shared service feeds then the capacity of all the units has to be factored in to do load calculations.

    To the comment on having a 125a breaker on 115a wire: Yes, this is the “next size up” breaker rule, however: You still have to do all your load calculations to stay within the 115a limit.

    To the comment about derating the feeder due to distance requirements (voltage drop): This is actually not a code requirement. It is a recommendation not a requirement. (a good idea for sure, but not a code requirement)

    Can you send pictures of the main meter base and meter also? I am particularly interested in the rating of the meter base. Also, pictures of the panel cover removed from the breaker.

    Can we also get a single picture of the entire sticker on the door of the panel? I think some info may be chopped off between the two that were posted. Very odd that it does not specify which breaker positions accept tandems.

    Thanks!
     
  16. SpudLime

    SpudLime Active Member

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    Wall *Connector* We really need to get people on board to use the correct terminology.
     
    • Like x 1
  17. jdcollins5

    jdcollins5 Member

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    One thing you can do to see your highest load on the panel is to check your utility bill. Most electric utilities charge an On Peak KW which is the highest energy usage during an on peak 15 minute interval. This tells them the service rating they need to provide to your house.

    This KW rating can help you decide how much energy you are currently using and how much additional energy you can add to this panel without overloading the panel. Typically you do not want to exceed 80% of the rating of the panel for a continuous load.
     

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