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What is the capacity of my panel?

Discussion in 'Model S: Battery & Charging' started by Boourns, Apr 13, 2016.

  1. Boourns

    Boourns Member

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    I have no electrical know-how, so I apologize if this is a n00b question. In February we bought an older house (built in the 70s), and I need to install a NEMA 14-50 outlet in anticipation of my Model 3 and possibly a CPO Model S in the interim. I am not sure the amperage capacity of my panel. I thought the panel in my previous home just said so right on the panel, but that home was built in 2007.

    In the first pic below, the piece of paper that is older than me says the "Main Rating" is 125 amps, but the current breaker switches installed add up to more than 125 amps already. The panel passed inspection when we bought the house, so either (1) the panel has been upgraded at some point or (2) I am doing it wrong.

    If there is physical space for additional breaker switches does this mean there is additional amperage capacity necessary to support the 14-50? Or is the only way to know for sure to open it up and look? Obviously I'll have an electrician come out to do the work, but I would like to know if I'll need a new panel to support home charging so I can budget for that now.

     
  2. aesculus

    aesculus Still Trying to Figure this All Out

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    You will need an electrician. While you do have the space it depends on how the loads are used. Many panels have breakers that add up to far more than the panel load, but if they are for loads that often don't come on at the same time, its acceptable.

    Note for example if you were only going to charge your car during the overnight hours and you were not going to bake a turkey in your electric oven at the same time.
     
  3. SabrToothSqrl

    SabrToothSqrl Active Member

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    I don't see a large breaker at the top. All panels I've ever seen have a "100" or "200" at the top that kills all power below... Mine's 200 in the house.
     
  4. Boourns

    Boourns Member

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    Cool. I was kind of expecting to have to talk to an electrician to find out, but thought I would give it a shot here. Thanks!

    Yeah if I remember that's how my previous house was, too. That's why I am very confused now.
     
  5. Pando

    Pando Member

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    You should have a main breaker somewhere. This panel doesn't seem to have it - looks like this is a sub-panel? Is there another panel close to your electric meter?
     
  6. cdub

    cdub Future Model 3 owner

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    Just get an electrician. :)
     
  7. Lloyd

    Lloyd Active Member

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    The panel itself is labeled for 125 amps. This panel is a subpanel and is fed from another panel so you will have to see what the breaker is that feeds this panel and that will be your limitation.
     
  8. Boourns

    Boourns Member

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    Re subpanel: Eureka! That totally makes sense. I will take a look tonight when I get home. Thanks all.
     
  9. SabrToothSqrl

    SabrToothSqrl Active Member

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    My subpanel has a 100 at the top and a 100 at the main breaker.

    I guess I could have wired sub panel to the mains, but told them to do it off the primary. It's a seperate bulding, but if I flip that top one, i want everything dead.

    I can kill my subpanel from the main panel, or top switch in the subpanel.
     
  10. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    That is called a "split bus" panel.

    Your service rating is a maximum of 125A (panel's rating). Your "main" breaker is the group of breakers at the top of the panel above the "MAIN SECT" sticker.

    The NEC requires that you be able to disconnect all power to the premises with 6 breakers or less. The power is supplied from your meter to the top of this panel, feeding the top 4 slots on each side. One of the breakers in the top section of the panel (labeled "MAIN SECT") then feeds and protects the bottom part of the panel (all the half-height breakers you see here). Heavy loads go up top, lighting and receptacle loads down below. It's odd that you don't have handle-ties on the breakers at the top, because they all look like 240V loads.

    Most of the time, it's the lower right hand breaker (the one labeled "60") that feeds the bottom section of the panel, but with a piece of tape on it that says "AC", I'm guessing it's one of the 50A breakers above it that feeds the lower section of the panel - looks like the upper right if your label is correct (not much of a directory there!)

    You will need to free up either one of the double-50A breakers or the double-30A breaker to install charging for a Tesla - it will need to go in the top portion of the panel.

    Needless to say, they don't really install these style of panels anymore. :)
     
    • Informative x 2
  11. Boourns

    Boourns Member

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    Awesome reply. Thanks! When you say "free up" is that a matter of re-arranging things, re-wiring to add capacity, or just putting in a whole new panel? I would think the answer depends on what each breaker controls. I honestly have no idea-- the tape was there when we bought the house.

    Oh, the joys of owning an old home.
     
  12. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    You're right, it matters what's behind breaker #1 (and #2 and #3).

    The 30A breaker is likely to be an electric clothes dryer and/or its receptacle, or electric hot water heater. That's the most common breaker size for those appliances. Do you have one of those (or an unused receptacle behind the dryer)?

    The 50A breaker on the upper left may be an electric range and/or its receptacle. Do you have one of those?

    If some of those aren't in use, you can repurpose those breaker slots. An electrician can look in the panel and give you an idea if the 30A load can be moved down into the bottom of the panel (perhaps with a boost of the breaker feeding it) so that you can put another 50A breaker in the top for EV charging.

    If you want to experiment, I'm willing to bet a small amount that all of your lights and receptacles go out when you turn off the top two slots on the right (the ones marked "50"). That will be your split bus breaker if so. If not, I'd try the 60A at the bottom that's labeled AC.

    One of those breakers on the top controls all of the breakers at the bottom - the ones that are providing your power to receptacles and lights.
     
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  13. Boourns

    Boourns Member

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    I have an electric dryer and an electric range, which I want sometime to replace with a gas range, so it sounds like that could be a win-win option.

    Of course, upgrading the panel with a modern 200-amp unit would also do the trick I presume. That may be the route I investigate first, since at some point in the near future we are likely to have two EVs.

    Thanks very much for your insight. This board is awesome.
     
  14. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    No worries. My guess is that the 30A double-breaker is your dryer, the upper left is the stove, the upper right is the bottom of your panel, and the 60A is your A/C.

    Panel upgrade will solve it too. With a house that old, you might only have a 100A meter base - that might need an upgrade as well if you do upgrade to 200A. An electrician can help you there.
     
  15. tnt1971

    tnt1971 Member

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    My experience with my electrician was that he was overly cautious. I have 200 amp service and everything that can be is gas (dryer, stove, etc.) My only big draw was my central AC, which has two double breakers that combine to 50 amp. The rest of the breakers were all 110 outlets, lights, and other small draw items like the water pump for the boiler. He even admitted to me that if everything in my house was on I would not draw more than 60 amps (without the car charging). Seemed simple, and I asked him to run a 100 amp line and breaker for the car in case I upgraded to dual chargers later. He refused and said it would require a panel upgrade. I am no electrician but the math just did not add up to me.
     
  16. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    There are many spreadsheets, calculators, etc. available that will help you do the calculations from NEC article 220 that the electrician is supposed to do.

    The basic formula is that you start with is 3 VA (volt-amperes) per sq ft. 2,000 sq ft would be 6,000 VA. Then you have to add the required small-appliance circuits at 1500 VA each -- 2 in the kitchen, and 1 in the laundry - so 4500 VA there. That gives you a total of 10,500 VA. You then apply a demand factor to that - the first 3000 VA comes at 100%, the next 117,000 at 35%, and any remainder at 25%. So for our total of 10,500 VA, we'd have (3000*100%)+(7500*35%)=5,625 VA for general lighting and receptacles.

    Then you go to individual appliances that are fixed in place: dishwasher, disposer, dryer, electric range/oven, A/C & heat, etc. There are various fomulas used for some of these (dryers are 5,000 VA or the nameplate load, whichever is larger; cooking appliances typically come in at 8,000 to 14,000 VA, depending upon how many appliances you have). There's also a complex way to handle heating & A/C because they are typically noncoincident loads with multiple units - breaker size doesn't matter. Let's say for the sake of argument that you don't have emergency heat strips and you're talking about basic forced-air A/C; the compressor's RLA (rated load amps) is 27.1 and its accompanying fan is 1.9 (total of 29A) and the blower motor is 5A. 34A * 240V = 8,160 VA. Let's assume nameplate loads of 10A each @ 120V, that's 1200VA each or 2,400.

    So in our hypothetical 2,000 sq ft house with gas everything, we've got 10,500 VA for lighting & general purpose loads, 2,400 VA for dishwasher & disposal, and 8,160 VA for A/C. That's a total of 21,060 VA / 240 V = 87.75A. You could add 2 50-amp 14-50's for charging or a single 100A HPWC on this service and be under your 200A limit.

    (There are also "optional" methods of calculating load in 220.82, but they get pretty complex and I think you get the point.) It's very possible your electrician wanted to sell you something more.
     
  17. tnt1971

    tnt1971 Member

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    Thanks for this. You are right on. My house is a hair under 2,000 sq ft. The panel is quite full, because when we remodeled about a decade ago things were really separated, no more than 2 outlets on a circuit and single 20 amps for bathroom and kitchen outlets. All the lighting is also low power LEDs, so I know they are drawing virtually nothing. The appliances are all new too, so I know they are low draw.

    What also makes me suspicious of his statement is I have a portable generator for power outages rated at just under 6,000 watts. I can run everything off of it without issue (except the central AC and the car charger) and I have never seen the usage exceed 70%.
     
  18. Edmond

    Edmond Permanon

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    So it looks like 50A is the best I can get with a UMC. 2 legs and 2 25A breakers. What gauge of wire for 50'?
     
  19. Camera-Cruiser

    Camera-Cruiser Fully Charged

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    Since the OP has some time, I'd use Yelp, track down some highly rated electricians, call the, tell them what you want to do, and ask them what they would charge to come out and look at what you want.

    First, you're letting them know that you value their time and will compensate them for it. Tell them to write up a proposal (your paying them), and ask them if they will give you their proposal fee back if you go forward in 6 months or less, etc.

    You don't need 3 proposals, but two is smart.

    Then you will have your answers.
     
  20. Rocky_H

    Rocky_H Member

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    No, please don’t use that bad terminology. It is not 2 25A breakers. For a 240V circuit, that is a “2-pole 50A breaker”.

    Oh, and for your second question, that is specified in the 14-50 installation guide that Tesla provides:
    https://www.teslamotors.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf
    It says 6 gauge copper wire only.
     
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