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How feasible is installing a 100A breaker to provide 80A charging with an HPWC?

Discussion in 'North America' started by PoweredByRain, Jul 10, 2015.

  1. PoweredByRain

    PoweredByRain Member

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    Hello all.

    How does one determine whether it is feasible to install a 100A circuit breaker in a panel? I'd like to have 80A charging with an HPWC, but I don't know how to determine the biggest breaker that can be (is allowed to be) installed in the panel. The service here is 200A, and there's actually two panels. My understanding is that there is a big breaker on the input, so if the whole house exceeds the service limit it will trigger, and thus you can have circuit breakers whose capacity in total is much greater than the total available. This makes sense as it's highly unlikely that you'll be drawing the maximum, or anything close to it, on all circuits at the same time. But with 80A going to the car and the possibility of two ovens, two clothes washers, etc. I'm not sure 200A is enough.

    Or is this something that can only be answered by an electrician looking at the specific panel?


    (FWIW the HPWC could be installed just on the other side of the wall that the panel is on. i.e. the wire run would be very short.)
     
  2. Lloyd

    Lloyd Active Member

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    The rating for your panel should be on the inside cover. If not you will have to look up the model number and manufacturer. Make sure that the maximum load for your panel will not exceed your usage with an additional 80 amps while charging.
     
  3. FlasherZ

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

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    The panel's front cover should give you an indication, but almost any modern 200A panel will have the ability to carry a 100A breaker (and most will allow up to 125A before you have to use special 4-space bolt-ons).

    The bigger question is whether load calculations will allow you to do so. There are several different load calculators on the web, use one or two of them to determine whether your panel can safely support the load.

    My first EV subpanel was hosted from my grid-only service panel (one of 2 200A panels on 400A service) with a 100A breaker.
     
  4. PoweredByRain

    PoweredByRain Member

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    Thanks, guys!

    I didn't see any marking on the cover, but now that I look closer (doh!) it's right in the middle between the breakers - it says 225A (on the second, bigger panel). The service entry definitely goes through a breaker marked 200A at the top of the first panel, and there's a big (BIG!) wire from the first panel to the second, and the second also has a breaker marked 200. And tons of open spots too. So it seems likely a 100A breaker can be added.

    As for the load calculation - that's where much of the uncertainty lies for me. I mean, I don't think there's going to be an issue with remaining capacity with 80A going to the car, but are there rules that determine whether it's allowed or not?
     
  5. LetsGoFast

    LetsGoFast Active Member

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    I have a 100A breaker on a 200A panel and it works great. My only other heavy load is the AC and dryer, since I converted the oven to gas a few years back and I use gas heat. In my case, I'd never come close to 100A on the rest of the house.
     
  6. FlasherZ

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

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    Yes. Article 220 in the NEC has a few different methods that can be used. There are several web calculators to help you because it can get a bit complicated. The basic rules are 3 VA (.0125 amps) per sq ft until you reach 1000 sq ft, to which you can apply demand factors to reduce it, plus 3000 VA (12.5A) for small kitchen appliances, plus 1500 VA (6.25A) for laundry, plus nameplate ratings for dishwasher, disposer, water heater, and dryer, plus a calculation for electric heat and/or cooktop and/or ovens (complicated, see 220.55). Confused yet? Don't worry, I am too. :) Use a calculator on the web.

    The Tesla HPWC at 80A can be added as a fastened-in-place appliance at 19200 VA.

    Here's one:
    http://www.nojolt.com/load_calculations.shtml

    Or a spreadsheet - plenty of them around:
    http://www.inspectpa.com/wp-content/uploads/2014/08/DwellingLoadCalc.pdf
     
  7. dhrivnak

    dhrivnak Active Member

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    Yes it is possible but highly dependent on individual loads. But I have a 200 amp service and have charged at 70 amps many time with no issue. But I normally charge at 40 amps as I assume it is better on the car and grid.
     
  8. PoweredByRain

    PoweredByRain Member

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    Awesome, thanks! I appreciate all the pointers.
     
  9. N4HHE

    N4HHE Member

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    There is electrical code, and there is common sense. The two don't necessarily have to overlap everywhere.

    Its not really practical to size the service to meet the worst case load a homeowner may create. Say all burners going on electric oven and range, a load of clothes in the electric dryer, and electric heat strips defrosting one's heat pump.

    If one charges only at night then it would be pretty easy to assume the range/oven and clothes dryer will not be in use so their capacity is available for your EV. But then again why charge at 80A at night?

    The 200A master breaker is there because the distribution panel is "over subscribed" knowing the worst case all circuits at max is very unlikely. But possible.

    Don't know what a licensed electrician will do in your area but with a bit of thought before using your 100A circuit on an HPWC you can make it work. Or you can do what I do, set the switches to 40A because I only have a single charger in my Model S.
     
  10. DMC-Orangeville

    DMC-Orangeville 85D and John Deere 5100E

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    Just be careful as you are in Canada, and there are subtle differences between the NEC and CEC. Me - I'd ask the Electrical safety authority for guidance, and have it inspected (you can do your own work in Ontario, but it's mandatory to have an inspection). I suspect BC is the same
     
  11. FlasherZ

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

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    Oh yikes, I usually look but neglected to this time, and was bitten. Yes, CEC has similar load calcs but slightly different. Sorry about that - I was speaking US.

    - - - Updated - - -

    Right - this is why the Code allows for a demand factor to be used at various levels. When you use the optional, dwelling method (220.82), the first 10 kVA of non-A/C+heating is considered at 100%, the remainder at 40%, after adding up all the loads, then you add the A/C or heating.
     
  12. aesculus

    aesculus Still Trying to Figure this All Out

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    Since the OP lives in Canada, where electricity is cheap, this post may not apply:

    I am putting in a separate panel and meter mostly for a separate rate plan, although combined load is a secondary issue. My utility advised me that my 'normal' high load was only 150 amps but that it could be conceivable that I could hit the wall at 200 amps if the car was charging at full rate. Not likely, but possible.

    But my biggest reason to put a separate panel with a dedicated meter is to isolate my charges for the BEV onto another rate plan (a benefit of living in California:mad:). The BEV will not skew my usage into a higher charging tier for the rest of my load. The BEV will be on its on usage and charge schema where I can manage it independently. Without this it would be likely that my overall usage would push me into a much larger charging tier. I am struggling to stay at the lower tiers today and their is a huge difference between the upper and lower tiers.
     
  13. Ugliest1

    Ugliest1 S85: "Sparky"

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    I worked with an electrician to get the two EVSE's into the Regent Hotel (that is... I got the electrician to come and he did all the work). I was quite interested so I followed him around quite a bit. This was the first EVSE this electrician had installed, so he had to do a bunch of code reading etc to come up to speed with the rules. I was quickly out of my depth when he started using big words. Like Watt.

    I can't remember any details; what I do remember is he mentioned there were several code requirements that were a little difficult to manage through. E.g. for continuous load, there had to be not only the 100A breaker, but a separately-installed manual breaker away from the panel but within sight. Part of the problems were just how busy the condo's electrical room was and how he could route wires and use small empty wall spaces to mount the equipment. If you're in a house, it should be much easier (???). The Victoria inspector was quite nit-picky and forced certain small changes to the installation, thus requiring two more inspections.

    That's my take-away: the installation had it's own things to work through, but complying to every tiny code aspect and passing the inspection was the really complicated part.
     
  14. miimura

    miimura Active Member

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    If you are in PG&E territory, the EV rate has no tiers, it's just Time-of-Use. Unless you use a lot of A/C, I would not be so sure that you will recover the cost of installing a separate meter. You should see what your bill would be if you converted the house to the EV-A rate plan without the car. Calculating the cost of off-peak car charging on top of that is very easy.
     

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