Per @Harper-ReinstateMonica, asking a new question as a follow up to the previous question found here (What TYPE of wire should I install to future proof this install?).

Need help doing an electrical load calculation.

First, high res pictures of my panels:
Main panel: main panel with door open
Main panel inside: main panel inside
Main panel updated 2x label(s): enter image description here Sub panel: sub panel with door open
Sub panel label on inside of door: sub panel label on inside of door Sub panel inside: sub panel innards 1 and sub panel innards 2.
The wire from the main panel to the sub says: "Alcan S Stabiloy AA-8000 Series U Type XHHW CORS 600 Volts 2 CORS 2 AL 1 COR 4 AL (UL)".
Pool sub panel: pool sub panel

A/C units labels:
A/C unit #1: Bigger A/C unit - guessing 1st Fl
A/C unit #2: Smaller A/C unit - likely 2nd Fl

Double Oven label:
enter image description here

200A MAIN.
100A (bottom right - breaker #38-40) - feeder wire to sub-panel.
50A - 1st Floor A/C (bottom left - breaker #77-39).
40A - 2nd Floor A/C (breaker 30-32).
40A - Oven (breaker 26-28).
20A and another 20A (not dual pole breakers) - Cooktop (breakers #34 and 36).
20A - 1st Floor Heater (breaker #29).
20A - 2nd Floor Heater (breaker #22).
30A - Swimming pool (breaker #17-19).
20A - Office (breaker #21 - skinny dual pole 20A).
20A - Kitchen Countertop Outlets (dual-breaker #33, both breakers control different walls of outlets in the kitchen).
20A - MasterBathroom heated floor and one GFCI outlet, but not two other walls of outlets (breaker #24).
20A - (Breaker #35) - top is outside lights (4 front door walkway posts, 4 driveway posts, two spot lights on the ground); bottom is lights only, not outlets, for one side, roughly half or smaller, basement. Very likely it also covers an outside outlet right by front door and those front door walkway lights).

So above are all or almost all breakers 20A and above. Unfortunately not everything is labeled. House was built in 1987, we're second owners for 3 years now. Other things labeled on the main panel are:
15A - Kitchen (breaker #9).
15A - Master Bedroom lights (breaker #11).
15A - Garage (breaker #13) there are overhead lights - two florescent long tube fixtures, two garage door openers with their own two bulbs each, a regular outlet and another quad outlet; there's also a second fridge in the garage.
15A - "2nd Fl Bed Room" (breaker #6)

The rest is unlabeled unfortunately, but with the updates below, also reflected above, I think I covered all but possibly one 20A breakers. Everything else is 15A and is either described above or unlabeled. I count 20 separate 15A breakers, in total.

update 1:
Breaker #33 is kitchen countertop outlets, #35 surprisingly killed some of the lights, but not outlets in the basement, surprising because I thought the sub-panel solely controlled the basement.
@ ThreePhaseEel: I believe the basement is 1,664 sq ft, and I thought the sub-panel exclusively powered the basement, but see right above as breaker #35 killed lights, but not outlets, on one side of the basement.

update 2:
Breaker #33 - top and bottom - both cover kitchen outlets; top is one wall including the fridge; bottom is two other opposite walls.
Breaker #24 - one GFCI outlet in Master Bathroom and also appears to cover the heated floor in Master Bathroom. There are two other outlets in Master Bathroom, each on a different wall, and those are not powered by #24.

update 3:
Breaker #35 - top is outside lights (4 front door walkway posts, 4 driveway posts, two spot lights on the ground); bottom is lights only, not outlets, for one side, roughly half or smaller, basement.

updated 4:
Breaker #21 - top is 5 kitchen recessed lights (interestingly this is just one of three separate sets/switches of lights in the kitchen), also these florescent under cabinet lights in the kitchen, and another solo recessed light in the kitchen on its own switch; bottom is Office outlets.

Breaker #31 - seems like it's one outlet in the utility closet right next to the main panel, it used to have the security system plugged into it, and maybe cable modem; maybe it goes somewhere else, but can't find what.

Breaker #16 - this is the one with a weird red sticker, well I now think it says "pool outlet", which would explain why it would trip when I tried plugging a water removal pump into that outlet.
So the pool actually has another sub-panel, I'm adding a pic of it, but again it's all on the #17-19 30A breaker anyway, and the only things on there is the variable speed/efficient pool pump, a blower for the tub, and gas water heater - the pool pump is the only that the really gets used. I run an electric pool cleaner/robot off that outlet. I think back in the day there was a higher power vacuum being used here, and right 15A breaker is in the pool sub panel, but like I said, the one I use now I think is a lot lower power.

update 5:
Pool Pump motorPool Pump/motor
Hot tub blower Hot tub blower

update 6:
@ThreePhaseEel - regarding the two cooktop circuits, just tested and one controls the gas cooktop which has a kitchen exhaust-type fan built in; and the other controls the outlet (buried inside of the cabinet/space under the cooktop that has the microwave plugged into to it). CooktopCooktop
Connections for both (microwave plugged into the white face outlet, cooktop into the metal one): enter image description here

Added additional pictures.

SUB-PANEL: As noted, the 100A goes to a sub-panel, which is right next to the main panel. The feeder wire between the two panels says: "Alcan S Stabiloy AA-8000 Series U Type XHHW CORS 600 Volts 2 CORS 2 AL 1 COR 4 AL (UL)". The sub panel has 100A main, and contains 8 separate 15A breakers (4 and 4 on each side, see pictures). One of the 15A is labeled as Low Voltage Lts - I believe this is for on the ground lights outside in the front of the house, some of these have been removed, there are currently like 2 working lights not the ground under one tree, and then four light poles around the driveway, and four walk-way lights along the path to the front door (not sure if you need to know all that). The other 7x15A breakers are unlabeled but from testing appear to all be for lights and outlets in the basement, which is finished but almost entirely unused.

HOUSE: 3,700 sq ft, not including the finished but largely unused basement, which itself is 1,664 sq ft per plans. 2 A/C units and 2 Furnaces (gas), as well as 2 Water Heaters (gas). Pool heater is also gas and rarely used. Pool pump is a new efficient variable speed motor that typically is used on low power Stove is gas. Separate dual oven is electric. Washer is electric, Dryer is gas. If it helps, I've replaced almost all the lights around the house with LEDs.
As best as I can tell, heating/furnace and water heaters are gas, but here are pics of them just in case. https://www.dropbox.com/s/b1p8j201uyesbec/Furnace_WaterHeater1.jpg?dl=0 https://www.dropbox.com/s/53zdvy2kjhpwk8e/WaterHeater1.jpg?dl=0 https://www.dropbox.com/s/hhi3c97a9lf0ag8/Furnace1.jpg?dl=0

So the reason for the question, as from the prior question, is that it is being suggested that I run #2AL wire to the garage for an 80A EVSE circuit; do I have enough "capacity" (probably wrong term) in the house for that? Thanks in advance!!!

  • How many square feet is the house? Confirming that you've got gas air & water heat, not some sort of electric (resistive baseboard, heat pump, mini-split, etc), correct? Someone will ask...
    – FreeMan
    Commented Dec 13, 2021 at 15:19
  • Oops... just noticed the penultimate paragraph detailing the gas heat. May want to include the Sq/ft of the basement, too. Even if it's currently unused, I'm pretty sure it needs to be counted for sizing purposes. Also, please edit the info into your question - that helps people find it - things can get lost in the comments
    – FreeMan
    Commented Dec 13, 2021 at 15:39
  • 1
    Edited main question with additional info. Thanks. New to this site, figuring it out.
    – Alex
    Commented Dec 13, 2021 at 16:14
  • 1
    @ThreePhaseEel Please do not apologize, I very much appreciate the help you're providing to me. I just answered your questions by updating the main post, see the "updates" section.
    – Alex
    Commented Dec 14, 2021 at 4:03
  • 1
    @ThreePhaseEel Added pictures of labels of pool pump motor and the hot tub bubble blower. This has been a great exercise in getting all this info, although believe it or not I already had photos of a lot of these things without a need to go outside and take them. Hopefully this is enough info to do the electrical load calculation. Thanks
    – Alex
    Commented Dec 15, 2021 at 15:06

2 Answers 2


While your service isn't overloaded yet, that main panel is quite surely overstuffed!

Running a NEC Article 220 load calculation on your main panel, with 4 kitchen SABCs, the given square footage (including the basement), a 5kVA dryer, and the given oven and motor loads yields 38387VA, or just under 160A @ 240VAC. This is not yet an issue for your service; however, your main panel is badly overstuffed, with several double-stuff breakers present in a panel that does not accept any tandem/double-stuff breakers, never mind the several aliens that are present!

As a result, the first order of business is simple: replacing that main panel with a larger panel (you'd need to go up to a 54-space or 60-space loadcenter to do this), or alternatively fitting another subpanel next to the main panel and moving at least 4 circuits to it to evict the double-stuff breakers in spaces 21, 23, 33, and 35 from the panel. While this is done, the alien breakers in spaces 17-19 and 36 need to be evicted from the panel; the breaker in spaces 38-40 is also an alien, but we'll address it below as there are other things wrong with it as well.

That feeder, though, is overbreakered...

The other piece of bad news is that the feeder to the basement subpanel, while not at all overloaded, is overbreakered, as a 2AWG Al wire is only good for 90A at 75°C. This can be fixed by swapping the alien 100A breaker in spaces 38-40 for a Siemens Q290, or the correct type of 2-pole, 90A breaker for your new panel if you're going for a wholesale replacement.

And there's just not enough headroom for EV charging without upsizing the service as a whole

The final problem is that adding the 80A of EV charging isn't possible without a service upgrade, and would also overload the feeder to the basement subpanel as well were you to try to tap power from there. (The basement panel calculates out to about 15A right now, which is why the oversized breaker isn't currently a critical issue, but I wouldn't want to pull 95A on a 90A feeder on the regular, either!)

As to your options

You have two basic options: you can either scale your EV charging desires back to a single 32A charger on a 40A circuit, or upgrade your service. Unfortunately, in order to get a full 80A of EV charging, you'd need to go with a Class 320 service, which'd require a total overhaul of your service entrance hardware.

  • If I understand it correctly (which I might not) a Class 320 service normally ends up with 2 x 200A panels feeding from the meter (or meter main?). So while some work would be needed outside for that, wouldn't that go along with a second main panel next to the existing one, but instead of feeding A->B, the new panel would have its own feed and you would throw the subpanel feed (including EV) + a few other loads into it to relieve the pressure (alien breakers, double-stuff breakers and overall capacity) from the existing main panel. Commented Dec 17, 2021 at 4:24
  • 1
    @manassehkatz-Moving2Codidact -- yeah, that's what I mean by "complete rearrangement of the service entrance hardware" -- Rule of 6 being no more + the emergency disconnect requirements mean that NEC 2020 requires a somewhat different approach to Class 320 services than the traditional Commented Dec 17, 2021 at 4:34
  • @ThreePhaseEel Thank you! A couple of follow up questions helping me better understand everything: 1. 4 SABCs, not 2? I guess you're counting the ones that control lights, correct? Bc only two breakers control kitchen outlets. 2. Can you explain what this means, especially the bolded portions: "several double-stuff breakers present in a panel that does not accept any tandem/double-stuff breakers, never mind the several aliens that are present!" 3. Again, what are "alien breakers," and/or why are breakers #17-19, 36, and 38-40 "alien"?
    – Alex
    Commented Dec 17, 2021 at 14:42
  • As for my options? If I upgrade the feeder from the main panel to the subpanel to support 100A, since you say the sub/basement panel currently calculates to 15A, would I be able to run an 80A line from there to the EV charger? I understand you calculated the house to roughly 160A and the service is 200A hence Im asking? I guess the thought is that EV charging mostly happens at night, when most other equipment (other than maybe AC/furnace, and possibly pool (which I usually run at fraction of full power)) are not being utilized. What would happen would it trip the EV breaker if overloaded?
    – Alex
    Commented Dec 17, 2021 at 14:46
  • 1
    @Alex -- a Class 200 meter and socket are rated for 200A continuous/250A max. this is further limited by your current service entrance wiring and main breaker to 200A max. However, when PECO hands out new service, they require someone with 160A of load to upgrade to a "400A" (Class 320) service instead of coming close to maxing out a 200A service. Commented Dec 22, 2021 at 5:50

No discussion of EV charging is complete without viewing Technology Connections' very reasonable advice on circuit size.

Update: Power Limiting EVSE's make it possible

Since this was initially posted, a new type of EVSE has emerged which makes this problem "shooting fish in a barrel" :)

An average house averages 5 amps of power draw. It needs 200A service for all the loads that have a probability of peaking at once, that's true. But the rest of the time it draws only 1 or 2 amps - that's how it can hit an average of 5 amps. If only we knew WHEN that was!

This type of EVSE installs "current transformer" or CT clamps on the main service wires (typically via a separate module that communicates with the wall-unit EVSE). Now, it can watch for house nearing an overload condition, and simply turn down EV charge rate during peak periods. As such, the EVSE disappears entirely from the Load Calculation.

Examples of this in 2023 are the "Wallbox Pulsar" using its Power Boost feature with a specified module which attaches to clamp CTs... or the Myenergi Zappi's "Grid Limit" feature, with their Harvi module.

These units can also interact with solar generation, to divert solar energy into the car instead of selling it back to the grid. (useful for non-net-metering tariffs). If that is the intended use, safety is not at stake and antoher option becomes the Emporia EVSE paired with Emporia Vue, which unfortunately communicate via the cloud which makes it impossible to use for safety-rated applications like grid limiting.

How can that be?

This is due to how car charging actually works - it was designed by absolute geniuses, who understood "needing a service upgrade" would be a showstopper for 90% of prospective EV buyers. The car itself responds to a signal continuously sent by the wall unit, saying how many amps the car is allowed to take. You think "well that's hardwired down to 80 amps" - no, the wall unit can change the signal dynamically on the fly, and the car will obey in real time.

Remember that NEC requires a 125% derate for all EV charging equipment- 80A actual charge rate on the vehicle requires 100A circuit and feeder - so #1 aluminum to the disconnect (mandatory disconnect for >60A EVSEs) and #3 copper to the EVSE.

A 125% derate is also required for planned continuous loads on an electric service. When configuring grid-limit, you must choose 160A max not 200A max.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.