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I own a Ford Charge Station Pro which requires 80A 240AC service to maximize the charging speed to my vehicle. This is a lot of current and I need some advice considering my current sub-panel configuration.

I have a main 200A service panel which is full. I had a secondary panel added by a contractor during the addition of a basement kitchen. He wired the secondary panel as follows.

Main 200A -> 50A jumper breaker -> 2AWG Aluminum jumper cables -> Secondary Panel 100A -> Plenty of space for 100A EV breaker.

As I inspected the setup I was suspicious of the 50A breaker feeding the secondary sub-panel which is headed by a 100A breaker. I feel like that was a cost saving measure by the contractor and ultimately needs to be upped to support an additional 100A breaker in the secondary panel. The other issue I noted is the 2AWG aluminum jumper cable due to the EV charger explicitly stating 3AWG copper is required for the thermal load, is one gauge higher aluminum going to be adequate?

I haven't done a load analysis but was considering the sense current monitor, or just buying a harbor freight current monitor to take some spot measurements.

Thanks! enter image description hereenter image description hereenter image description here

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    Most people who do not use their vehicle as a taxi/delivery service do not need 80 amp chargers, they can be quite happy at 20 or 30 amps. I would read up on that charger and see if that the only amperage it takes or the maximum. Quite a few chargers will limit charging to what is available.
    – crip659
    Apr 30, 2023 at 13:10
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    Can you post photos of both the main and the subpanels please, as well as the square footage of your house? Apr 30, 2023 at 15:23
  • I posted pictures for completeness. The house is 4500 sqft with three fully finished floors.
    – MikeR
    Apr 30, 2023 at 22:42

3 Answers 3

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It's astounding what is possible. EV charging tech is smarter than you could imagine.

"Don't I need 100A though?"

TLDR: No. The Ford Connected Charge Station Pro can work on any breaker from 15A to 100A. See below. This won't affect powering your house during an outage.

Here's an interesting fact: The J1772 charging standard has been improved for 30 years. Was it designed by the electrician's union to sell service upgrades? No! It was designed by the auto industry to sell cars!

They knew nobody would buy an electric car if you needed a service upgrade to charge. So EV charging has key technology built into it, that assures so level-2 charging can happen at ANY home with simple home-side equipment. All the complicated tech is onboard the car. This is not your father's battery charger.

So yeah, you don't need 100A. This can be dialed in so you get full battery every morning with no service upgrade, one way or the other. And this can be affordable.

If you want to wire it like your father's battery charger, then yes, you WILL need a service upgrade and that's that... like manassehkatz says. But SAE (Society for Automotive Engineers) put a whole lotta love into making you not need one, so let's stand on the shoulders of giants :)

Now that you realize 100A isn't necessary...

I advise Technology Connections' superb video on home EV charging. The first 20 minutes drags a bit, with too much about "what a watt is", but 28:15 gets into being sensible about charging sizes. Those figures are for crossover-sized EVs (or smaller EVs during winter) so figure 2/3 to 3/4 of the numbers you see. Unless you're trailering, then probably half lol*.

* Assuming you possess a brain and aren't deliberately trying to fail for the clicks, like most Youtubers who do "watch me trailer with an F150" videos.

That NEC Article 220 Load Calculation

I haven't done a load analysis but was considering the sense current monitor, or just buying a harbor freight current monitor to take some spot measurements.

That is not how Load Calculations are done. You need to use the procedure in NEC Article 220 with the 3 VA per square foot and weird 220.55 math relating to the range.

As manassehkatz discusses, that is your first stop. Because that will tell us the cheapest path to get this done. Multiple Load Calc's must be done: first on the whole house (subpanels included), and then on each subpanel to determine its capacity limits.

If we get a happy number there, boom we're done, just like that!

And by "happy number" I mean e.g. say you have 40A (9600 VA) to spare on the Load Calc. Configure the Ford Charge Station Pro for 40A and you're done. And your big truck regains nearly 200 miles in a 10 hour charging period, and you never realize you don't actually have a full 100A because it never comes up. This doesn't impede the grid-down house backfeed either, if you're doing that.

But if the Load Calculation number is awful, and/or you want to go faster than the number allows.... don't worry. There's kit for that. We'll come back 'round to that option.

Was that subpanel incompetently done?

Main 200A -> 50A feed breaker -> 2AWG Aluminum feeder cables -> Secondary Panel 100A...

As I inspected the setup I was suspicious of the 50A breaker feeding the secondary sub-panel which is headed by a 100A breaker. I feel like that was a cost saving measure by the contractor

No, that's perfect. If you asked here "how do I do this subpanel for this addition" we'd tell you exactly that.

The 100A subpanel is because we strongly recommend subpanels with plenty of spaces - loads of spaces. Spaces are cheap. If it has a 100A breaker, who cares? It's not even acting as a breaker, just a disconnect switch. They might have used a main-lug panel there, but economies of scale are weird, and sometimes the main breaker panel3 is cheaper.

The 2-2-2-4 aluminum is because it's a double win: It's cheap, at these large sizes aluminum is fine, and it's 90A wire, with plenty of headroom for expansion. It's so cheap we recommend it for all feeders from 30-90A. Why limit yourself to 30A when you can have 90 for the same price?

The 60A breaker is cheaper. All breakers 15-60A are the same price ($12-ish), and then rises exponentially after that. So yeah, we would say "just grab a 60A breaker, pay for the 90A later if you ever need it". I suspect 60A because #2 won't fit on most 50A breakers.

So no, I think the subpanel was well-chosen for the addition.

"But I want the FASTEST CHARGE POSSIBLE".

cracks knuckles okay. The subpanel isn't big enough, so it will need to be upgraded to a 200A panel. Upgrading the feeder larger than #2 is pointless since the main panel can't supply it! That means a servce upgrade must happen. The next size up is 400A service, and very happily, that is implemented as two (2) 200A panels. (because 400A breakers/panels are insanely priced). So that segues well with this plan. It'll still be very costly. You may think you need it, but a year into owning this car you'll realize it was a waste of money.

The other thing about dual 200A panels (that nobody ever thinks about on install day) is a generator can only serve one panel (unless it uses expensive and weird neutral-switching transfer switches). Which means if you want to use a generator or the Ford Home Backup feature, you need to put all your generator-supported loads in one panel. (or spend a lot more money on transfer equipment). And that won't be the same panel as the EVSE (which is fine; the Ford equipment supports that).

"I hear you. A slower charge rate will satisfy my needs."

You have the whole-house Load Calculation in VA. Your service has 48,000 VA, so subtract that from 48,000 and you have the "available VA for the house".

You also have the subpanel Load Calculation in VA. That has 21,600 VA assuming you up that breaker to 90A, so subtract the calculated load from 21,600 and you have "available VA in the subpanel".

Take the lesser of the 2 numbers, divide by 240V to get amps, and round down to one of

15, 20, 30, 40, 50, 60, 80, 100

(If 25, 35 or 45 would work, other EVSEs can do that; just not the Ford unit.)

If that number is less than 40, we may have a possible problem depending on how much driving you do. We should talk about that or pursue another option.

Anyway, that number is your breaker. Now see your Ford Charge Station Pro installation guide on page 15 and set the "maximum current setting" switch according to your breaker - oh good grief, they listed it in electrician-only crypto-speak... let me make that accessible. Actual charge rate is 20% less than breaker due to code; don't worry about that.

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"I want a compromise: max charging without an upgrade".

Unfortunately nobody makes a "100A breaker" charge station which knows this trick, so we'll have to settle for the "60A breaker" Emporia EVSE. But that's still A LOT. And the subpanel probably won't support over 60A anyway.

The Emporia (and over in Europe, the Myenergi Zappi) knows a neat trick: you can put "clamp meters" or current transformers on your service wires. Thus, the EVSE can dynamically slow down EV charge on those infrequent times when house load is nearing maximum. This only slows charging a short time per day and never at night when sleeping - but it makes the charging safe.

You install the Emporia VUE home energy monitor typically in the main panel, and set a grid limit in the Emporia EVSE to less than 80% of your service limit. Then they talk to each other, and the EVSE slows EV charging when the charging would otherwise overload your panel. This happens on the fly and is immediately adjusted back in your favor once the load is removed.

Because of this superpower, the Emporia ignores the house Load Calculation. (but not the subpanel Load Calc).

I told you SAE knew what they were doing when they designed EV charging!

"But I want to be able to backfeed my house during power outages! Don't I need the Ford charge station pro and a big breaker on it?"

The Home Backup feature uses the huge DC pins on the fat CCS connector - not the little pins on the J1772 connector. The Charge Station Pro is only needed for its connector and the high voltage DC wires that go through it. Those are wired via a different route to other equipment which actually provides the whole house backup. That means the circuit breaker feeding the Charge Station Pro is not involved at all in whole house backup. It can be 15A and the house can still get 40A or whatever from the EV.

But you are not chained to the Charge Station Pro, except when using it to power your house obviously. If you are constrained (suppose the Charge Station Pro can only get a 15A breaker), simply install the Emporia unit also. Then, you could simply use either EVSE at any time. Use the Ford when you can live with the charge limit, and the Emporia when you need the fastest.

It's just that if power failed, you would need to go in the dark and unplug the car from the Emporia and plug it into the Charge Station Pro.

In fact, if the Emporia was fed from the main panel instead of the sub, it could be used simultaneously with the Ford unit, since the Ford would be within the house's Load Calc and the Emporia would "do its magic".

Like I say, SAE knew what they were doing.

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    Thank you for the complete response - I think this is valuable to many F-150 Lightning owners who have been faced with or will soon be faced with do I match my electrical to my charger or vice-versa. I've got some homework to do.
    – MikeR
    Apr 30, 2023 at 22:43
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Seeing that you have already had to add a subpanel I'm guessing that after you perform a NEC 220 load calculation that your 200 amp service may not be enough for an additional 80 amp load. I have a Tesla Model 3 which can support 48 amp charging on a 60 amp breaker. Due to constraints I had to settle on 32 amp charging on a 40 amp breaker. I have no issue with topping of my car at night. Granted the F150 Lightning battery is bigger. I did look at the specs and your charger is adjustable to accommodate 20-100 amp breaker sizes.

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    Your setup (40A breaker/7.7kW charge rate) charging for 10 hours will restore almost 200 miles to an F150 Lightning. We have an endless revolving door of new EVers who arrive with no clue how EV charging works, and hopefully leave here smarter than most of the people on the EV forums (who unfortunately will shout down our advice). Apr 30, 2023 at 19:26
  • @Harper-ReinstateMonica Also if my neighbors and I are all charging at 19.2kw the 50kva tub by my house isn't going to be happy.
    – JD74
    Apr 30, 2023 at 20:06
  • Yup... and actually, that is why my winter cottage is 120V/30A (no room on the transformer), and why our power company requires their approval to install level 2 charging. Of course our city has an electrification initiative, and they own the power company, so something will give lol. And yes, I can level-2 at 120V/24A, using Grid Limit feature in certain EVSEs.) Apr 30, 2023 at 20:12
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I still have checks in my checkbook, so I can write a check for any amount.

Obviously it doesn't work that way. Similarly, just because you have spaces in your subpanel doesn't mean that you can draw as much current as you would like.

The key is Load Calculation. There are a few ways to do that.

The official way is to do basically add up all the fixed loads (e.g., HVAC, water heating, etc.) + a prescribed amount for certain other loads (e.g., cooking equipment - some special rules which often result in a significantly lower load than the absolute nameplate maximum) + prescribed amounts for certain circuits (e.g., kitchen countertop circuits) and for the house as a whole based on size.

An alternative is to figure out your real-world maximum. A monitor can do that. You may also be able to go online to your utility web site and download hourly (or ideally 15-minute) usage for a year.

I suspect the electrician who installed the 100A subpanel actually did some form of load calculation. 2 AWG aluminum is generally suitable for up to 90A. Connecting it to a 50A breaker makes sense if the main 200A panel really only has 50A to spare based on a load calculation. 50A and 60A breakers generally cost the same, often even a few sizes larger than 60A. So this would not be a cost-saving for the contractor, but it could be to satisfy code by not going over the load calculation for the main panel.

So for the moment we'll assume that 50A is the realistic available current for your subpanel. Why does the subpanel have a 100A main breaker? Because it is often cheaper to get a "main" panel, which includes a main breaker, than to get a smaller subpanel without a main breaker. Or if it isn't cheaper, it doesn't cost very much extra. But that does mean you don't have 100A to play with, only 50A. If you do a proper load calculation on the main panel and find you actually can spare more than 50A then you can replace that breaker with any appropriate size up to 90A (based on the 2 AWG aluminum cable).

The next step is a load calculation on the subpanel. With 50A feed does it have any spare capacity? Obviously not 80A, but you don't need 80A. You need at least 20A @ 240V for a realistic charge rate. More is better, but not required. If you have at least 20A available, install the largest breaker you can based on the available capacity (i.e., 20A, 25A or 30A - unlikely you'll get more than 30A). Install the EVSE (a.k.a., charger) and configure it based on the breaker size.

If you don't have at least 20A available then it gets more complicated. The options are either to upgrade the service or get EVSE that will automatically adjust based on the total current load of everything else in the house. Most of the time a 200A service isn't using anything close to 200A (or to the normal real limit of 160A = 80%), and the balance (which could be 80A or more!) can be used to charge your EV. But at the moment that means something different from your standard EVSE.

As far as the aluminum wire, that is irrelevant. The wire in question is from the subpanel to the EVSE. If they say use copper, you must use copper. The size will depend on your configured EVSE charge rate, and in turn that will determine the breaker. Typical is 20A 12 AWG, 30A 10 AWG, 40A 8 AWG. At loads greater than 40A, the wire size will depend on the wire/cable type. See an ampacity chart for details. Note that there are really two different numbers involved - 100% and 80%. Read the manual carefully to make sure you get it right. For example, a 30A circuit and 10 AWG wire can actually only charge at 24A (30A x 0.8).

Why is 20A or 30A OK? The rate will vary by vehicle. For example, the Ford Charge Station Pro specs say it can be configured for 20A - 100A with a maximum charge rate of 80A (which is 80% of 100A, so that makes sense). I am having trouble finding a chart similar to what Tesla provides, but I have found a reference to 30A (which would be 24A continuous, actual charging rate) providing 14 miles per charging hour for an F-150 Lightning. Extrapolating a bit, that means a 30A 240V circuit will get you about 112 miles in an 8-hours charging session or 140 miles in 10 hours. 20A (16A) would get you 2/3 of that, so 75 miles in 8 hours or 93 miles in 10 hours. So if you drive less than 100 miles per day (on an average day, there are exceptions, which is why there are Superchargers and similar) and are not usually doing extra stuff (towing or using the truck to power lots of other stuff on-site) then 30A is certainly fine and 20A is probably OK too.

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