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enter image description hereI’m calculating the loads in my 100 amp panel to determine the maximum amperage I can set my EVSE to. My understanding is that my total loads shouldn’t exceed 19200w.

It is hardwired with 6AWG THHN in conduit, so can be configured to work with either a 40, 50, or 60amp circuit, drawing 32, 40, or 48amps respectively.

With a gas furnace, hot water tank, range, and dryer, the following are potential simultaneous significant loads (not included are LED lights, phone chargers, etc.):

  • HVAC: 4324-5520w
  • Additional window AC: 450w
  • Dishwasher: 1176w
  • TV/cable: 203w
  • Refrigerator: 160w

Total: 7509w

Adding this total to the options below, should I stick with a 50amp to allow an adequate cushion, or could I safely add a 60amp breaker without concern for tripping the main?

  • EVSE@40amp: 7680w = 15189w
  • EVSE@50amp: 9600w = 17109w
  • EVSE@60amp: 11520w = 19029w

I believe that covers everything, unless I’ve unwittingly omitted something!

Photo is from the central AC condenser. enter image description here

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  • Yes, can you get us the number of kitchen receptacle circuits, the square footage of the house, and a photo of your air conditioner's nameplate please? Oct 6, 2021 at 11:37
  • The square footage is 2000. We have 2 baths, each with a single receptacle. The kitchen has 5 receptacles, which includes one for the garbage disposal. The laundry is adjacent to the panel in the basement, with a single 120v receptacle for the washer and gas dryer. I've added a photo of the AC condenser label.
    – oadesign
    Oct 6, 2021 at 14:12
  • If you'll note, in both of the comments, the question was the number of circuits, not the number of receptacles. Are both bathrooms on one circuit, or do they each have their own? Are the 5 kitchen receptacles on one circuit, two, or possibly more?
    – FreeMan
    Oct 6, 2021 at 14:24
  • I've added a diagram of my panel, but do not yet have all of the assignments mapped. Does this provide sufficient information?
    – oadesign
    Oct 6, 2021 at 19:27
  • @oadesign -- all we need now is the square footage of your house Oct 7, 2021 at 2:04

2 Answers 2

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Let me refer you to NEC Article 220.87 Determining Existing Loads. You need to be able to determine the maximum demand load (peak load) for 12 months year. This information usually can be provided to you by your utility provider and may already be shown on your utility bill. You need to look at your largest winter peak and summer peak and select the largest. You may need to go through last years bills to find the peak.

Then take that peak and add 25% to the total load.

This should help you determine your EVSE setting Or if you need to upgrade your service to maintain your new equipment.

Keep in mind this is the roughest of calculations and you need to use discretion while using it. In other words if it looks close or borderline don't use it, but if it appears you use say 55% of your 100A service main breaker then you can use your lowest setting.

Personally, if possible, I would upgrade to a 200A service, install a second Main, and set your equipment off of it. That way you could run it on it's highest setting,, and you will have available power for expansion. (Value Added).

Hope this helps.

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  • It does help, thanks. I’ll check my bills and see what actual usage has been. Unless I can budget for an upgrade to 200amp service and/or my actual usage is less than anticipated, I’ll temporarily install a 40amp breaker. Thanks to all who replied!
    – oadesign
    Oct 7, 2021 at 2:22
  • FWIW, to confirm, I checked my utility bills over the past year, and the highest month was 6/21, with a consumption of 692kWh (@1.25=865kWh). The next closest month was December, at 646kWh (@1.25=807.5kWh).
    – oadesign
    Oct 18, 2021 at 19:58
  • @oadesign - You need to dig a little bit deeper. Note that your meter is reading KW hours. That is the amount of energy you have used in one month not peak. You need to contact your provider and see if they can give you the Peak for the month of 6/21. That would be the largest KW load maintained for over 15 minutes. Oct 20, 2021 at 12:14
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You'll want to stick with a 50A breaker

Running a quick Article 220 load calculation, we get 3000VA of baseline unfactored load (two kitchen circuits), 3150VA of factored load (9000VA from the 2000ft²*3 for lighting + the third effective kitchen circuit (dish, disposal, fridge) and the laundry), and 5405VA of load for the air conditioner (18.8A * 230V nameplate * 1.25 for being the largest motor in the house). This together yields 11555VA, or 48A @ 240V. Given that the EVSE is a continuous load with a 1.25 factor for that, we are limited to a 40A (9600VA) load with a 50A breaker to stay under the 100A rating of your service.

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  • Thank you! Short term I’ll go with a 50AMP until I upgrade my service to 200AMPS.
    – oadesign
    Oct 10, 2021 at 18:07

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