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I've learned a lot of reading the questions/answers here, but I have one of my own.

I just purchased an EV and I'm looking to add a 50A circuit but my panel is full. I have 200A service and the panel (and service entry) is all the way on the opposite side of the house from the garage. There is no chance we are even close to 200A peak in this house. The main breaker is a CSR 25K, 200A.

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  1. So first problem is my panel has no empty spaces. There are a bunch of circuits labeled lighting, so I think I can either
  • combine those into double breakers or
  • put a junction box above the panel and combine the lighting circuits into one or two circuit breakers.

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I did purchase a current clamp so I can verify if this makes sense. What is the recommended course of action here?

  1. Next issue, should I just put a 100A sub panel in my garage in case in the future I get another EV? Other than cost, are there any other tradeoffs I should consider?

  2. I would like to get solar at some point. I think I understand the 20% rule for back feeding solar, so would I just back feed into the main panel or can I backfeed into the new 100A panel? If I backfeed into the new 100A, wouldn't I be limiting the size of the my solar system? Reading the label, I see my main panel has a 225A bus. When I deal with the full panel issue, I can make sure to leave space for a solar breaker.

  3. Also, on the label, I noticed a limitation of a max of 140A per stab. Looking at the panel, isn't position 39 (50A) and 40 (100A) violating that limitation? How is that limitation applied with double breakers?

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  • Sure are a bunch of beefy breakers in there already. You need a proper load calculation before doing anything.
    – Jon Custer
    Dec 29, 2023 at 4:08
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    I can do a load calc, but I'm pretty confident we are nowhere close to the limit. I think the previous electrician was lazy and just added circuits. This is a 3650 sq ft house with two condenser/gas furnace zones and a hot tub. Everything else is gas (water heater, stove, dryer). The 100A breaker is for a sub panel that has a bunch of circuits labeled "basement lighting"! Dec 29, 2023 at 4:14
  • Before you even think about provisioning full 50A circuits for EVSEs, you should do the math on the miles/kWh of your likely EVs, how far you typically drive, and how long you park overnight. A 3mi/kWh EV can replenish over 100 miles in 9 hours at 16A (20A circuit). Actually needing a 50A circuit for one EV would be pretty extreme.
    – nobody
    Dec 29, 2023 at 21:27
  • Is the "basement lighting" subpanel any closer to the garage and does it have some unused spaces?
    – jay613
    Dec 31, 2023 at 20:55

4 Answers 4

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I would recommend a Load Calculation for peace of mind. But assuming that works out OK, the easy solution is to replace a bunch of 15A breakers with half-size breakers:

Eaton 2x15A

just like you already have in space 27 (and similar to the 20A in 2, 4, 6).

The one thing you must watch out for is Multi-Wire Branch Circuits. You shouldn't find any because those breakers should be handle-tied. But if you start to replace breakers and find two (hopefully next to each other) that have black and red going into one cable then that's an MWBC and special rules apply.

As far as:

put a junction box above the panel and combine the lighting circuits into one or two circuit breakers.

Actually, if you were to do that I would join them together inside the panel. A lot less work and leaves the option of undoing it if needed. In fact, combining pairs of wires may be even easier than that! Some Eaton CH breakers, but you must check the specifications, can actually have two wires on each breaker at the smaller sizes. According to this page for the CH 15A on Home Depot - 1 wire 14 AWG to 8 AWG or 2 wires 14 AWG to 10 AWG. (A 15A circuit will almost always use either 14 AWG or 12 AWG wire.) So unless already paired up, you could pair a bunch of the 15A circuits on existing breakers without having to replace them with half-size breakers.

But keep in mind that while an entire house of lighting could probably run on a single 15A circuit, thanks to efficient LED bulbs/fixtures, "lighting" is often an electrician shortcut for "lighting/receptacles". Do you need 20 separate circuits for general lighting/receptacles, even in a big house? Probably not. But having more than just a few is a good thing to avoid overloading circuits.

There are three advantages to putting a subpanel in the garage instead of just running directly from the main panel to the EVSE:

  • Additional future 2nd EVSE is easy
  • You can use aluminum wire instead of copper wire, which is much cheaper and generally preferred at large sizes anyway. Many types of EVSE (including Tesla at last check) can only connect to copper wires. Running 50 feet or more of aluminum instead of copper between panels and then copper just from the subpanel to the EVSE can save a good bit of money.
  • Additional future anything else is easy - circuits for tools, HVAC, whatever.

If you do that, you can actually put in a larger panel than you need. The wire size determines the maximum feed breaker in the main panel - the main breaker (if you have one, and with large panels that's the norm these days) in the subpanel can be any larger size without a problem. For example, you could use 2 AWG aluminum for 90A maximum (and a 90A breaker or 70A or 80A, whatever) together with a 200A subpanel.

Why, you may ask (well, did ask in comments) would you use a larger panel than feed breaker/wire? Because larger main breaker panels are better! Most importantly, they have more breaker spaces. A 100A panel might have 20 spaces compared to 30 or 40 or 42 in a 200A panel, but for very little additional cost. It may not matter as much in a garage, but in a lot of cases those extra spaces come in handy for future expansion. The main space requirement for a panel is in front of it, and the width of most panels is the same, the only additional space required is a foot or two of space up or down on the wall, which is space you can't use for almost anything else anyway (because of code requirements). So the direct $ cost and the indirect (space) costs are minimal but the possible future benefit (not having to replace a panel due to limited capacity) is big. The main breaker in such a subpanel is only a disconnect so that doesn't matter. (Disconnect not required except in a main panel or in a subpanel that is in another building, but always useful.)

Note that if you have 2 50A max. EVSE (which would normally be 40A actual charge rate max., due to continuous derate, but that is still more than most people need), that can be just fine on a 90A (based on feed breaker) panel. That's because good EVSE work together to use a maximum total amount (based on your, ahem, Load Calculation, but also not to exceed feed breaker) and adjust charge rate of each vehicle based on user requirements, battery levels, etc.

I would stick with Eaton CH for consistency, but you could have a Square D or Siemens or GE subpanel - they don't have to match.

Solar gets complicated - ask a separate question when you are ready. But you can free up several spaces by replacing 15A breakers with half-size breakers. Not ideal but workable.

As far as bus stab limits, each pole of a breaker counts. So a 100A double-pole is 100A on one pole and 100A on the other pole, and yes it sounds like you already exceed (technically, fortunately your loads are low so it hasn't caused a real problem) some of those, which can be resolved by putting big breakers across from small breakers. One way to maintain a clean look (not that it matters) is instead of "all doubles at the bottom" make it "all doubles on one side".

But one thing to watch out for: 2 half-size 15A breakers is a 30A bus stab instead of a 15A bus stab. 2 half-size 20A breakers (like 2, 4, 6) is a 40A bus stab instead of a 20A bus stab. But since Eaton only offers half-size breakers in 15A and 20A sizes, with a 140A maximum stab you are OK with 100A across from 2x15A, 2x20A or any full-size breaker up to 40A. Just not 50A or above.

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    Wow thank you for the great response. I'm with you for the most part and I intend to do a load calc along with clamping some circuits under load to make sure they can be combined. I'm not following the idea of putting in a bigger breaker in the main panel. What would be the point of putting a 100A feed breaker and a 200A main in the sub panel? Would it be so I could say put 4 x 50A EVSEs on the sub panel and configure them to load share 100A? Dec 29, 2023 at 17:22
  • If you had 4 x 50A EVSE with load sharing of 100A, then the panel, feed, wire would all just need to be 100A, even though each EVSE would need a 50A circuit. Breaker handles can add up to more than total capacity (as they do in most big panels) as long as the actual load (in this case the EVSEs talking to each other to manage the load) is within the total limit. Dec 29, 2023 at 18:07
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The dealer, the lemmings, and the popular "travel chargers" (intended for this here use) tend to mislead novices into believing 50A circuits are the only alternative to level 1 charging. Pardon me if you're miles ahead of all this, but I want you to know that isn't true, and don't waste money on it.

Technology Connections has a first rate "how to charge at home" video that will set you straight if you aren't already.

https://www.youtube.com/watch?v=Iyp_X3mwE1w

There is no chance we are even close to 200A peak in this house ... I did purchase a current clamp so I can verify if this makes sense.

Really? I see a panel with seven 240V loads - 30A, 20A, 50A, 30A, 40A, 50A, and - concerningly - 100 amps! That 100A is a wildcard, and it can't just be ignored.

I know you just want to get this EV station installed as quickly as possible, and very badly want to believe that your project is blessed with great luck. One of the tropes we see a lot is "I can invent this alternative method of doing my Load Calculation which guarantees I get the answer I want!" Well, yeah, of course you can. But that does't mean the inspector or your insurer will accept it.

So no, we need to go one of two ways.

Ignore the Load Calculation and install an EVEMS system.

I've already done a lengthy Q&A on this, so here it is.

Yeah, we get to ignore the Load Calc because the EV charging simply backs off whenever the panel is anywhere near maxed out. If, as you say, the panel is never near max, then EV charge speed will never be affected!

Implementation is pretty simple: what's easier? A hard cat5 cable between main panel and EV station? Or guaranteeing always-up WiFi to the cloud at both panel and EV station?

  • If the cable is easier, then it's a Wallbox Pulsar Plus (the 9.6 kW model is $425 at CostCo right now) plus a $300 power monitor, and a cat 5E cable between the two. This is immune to internet nonsense and is guaranteed to work.
  • If the WiFi to the cloud is easier, then the Emporia Load management bundle. If contact with the Emporia servers has a problem, it will greatly slow EV charging. Upside: the power meter is actually the Emporia VUE, a full featured home energy monitor comparable to the Sense or Curb.
  • Elmac of Canada also has a solution, about which I know little.
  • The Myenergi Zappi is a European solution.
  • Tesla also has a solution here, but it seems to be only accessible by Tesla installers certified into that program.

In this scenario, I would size the subpanel feeder for the absolute worst case scenario of all your garage loads + 60A for the primary EV charging + 20A for a secondary EV charge station. Aluminum feeder is cheap. Run AWG 1/0 and you're good to 120A (anything larger than that gets really complicated).

60A? Yeah. Hard-wired wall units can actually use a 60A circuit instead of a 50A one. That means they are charging the car at 11.5 kW instead of 7.7 kW from a plug-in travel unit. That's half again the charging speed (because of an asterisk with 50A sockets on travel units).

Now on the Wallbox, the $425 Wallbox currently on sale at CostCo for $425 is the 50A unit which goes 9.6 kW (a hard-wired wall unit is immune to the asterisk). If you want the 60A Wallbox that goes 11.5 kW, you'll need to get it elsewhere, and not a CostCo deal either.

If you really, really want a socket, it's possible to do that with the "dumb load shed" devices mentioned in the Q&A. Market examples are the DCC, SimpleSwitch, BlackBox, PSP SAK-60MS, SWTCH - but these things are rubbish, cost much more than a proper EVEMS above, and require a dedicated circuit straight from main panel to socket.

Do a Load Calculation and size EV charging to what is possible.

The simple fact is you don't need 50 amps; like almost every EVer, you were misinformed by the dealer and the lemmings. The 50A myth came from travel charging; here's proper use of it.

A proper NEC Article 220 Load Calculation needs to be done, and here's an example of a good worksheet.

If the proper NEC 220.82 Load Calculation says you have 60A of headroom, then sure, you sold me. Go for it.

If it has less than 60A headroom but you can live with a lower charge rate (see the Technology Connections video at 32:55), then just do that. Most wall unit charge stations can be set to any amps that work for you.

If you are not satisfied with your panel's limits, then scroll down to the next - oh wait, I put it on top, scroll up for the previous EVEMS solution.

To answer your questions

So first problem is my panel has no empty spaces.

Trivial. I see tandems all over your panel, so clearly your panel is new enough to be post-CTL or is subject to the post-CTL waiver Eaton obtained from UL. So this is a 42/84 space panel and you can tandem to your heart's content.

Next issue, should I just put a 100A sub panel in my garage in case in the future I get another EV? Other than cost, are there any other tradeoffs I should consider?

No, you should get a subpanel with a separate bus rating from its feeder rating (the two are not the same). The bus rating must be >= feeder, and I strongly recommend 200-225A because panels are cheap. The feeder should be, as I suggested before, 1/0 aluminum (120A) since you can double-dip your Load Calculation using EVEMS. I want the feeder to be big enough that it has native ampacity for the max possible EV charge rate, so we don't need a second EVEMS to also protect the subpanel (since that is not technically feasible right now).

On a second EV, if you were able to allocate a fixed ampacity to one EV, you can simply do Power Sharing to dynamically split that capacity for two to six EVs. Power Sharing is much more effective than simply giving each car half. (when only one car is charging, it gets all). Wallbox and the Tesla Wall Connectors support Power Sharing. In Europe, Wallbox can double it up and do Power Sharing while also doing EVEMS. I expect Wallbox will export this to America once enough states adopt the latest NEC, which unambiguously permits it.

I would like to get solar at some point. I think I understand the 20% rule for back feeding solar, so would I just back feed into the main panel or can I backfeed into the new 100A panel?

Now do you see why I want you to have a very high amp subpanel and feeder? :) So you can put it either place. Note that if solar is in the subpanel, the subpanel breaker must be at the bottom of the panel per the 120% rule, meaning that 100A breaker must move.

Either way, you will be throttled to 70 amps of solar breaker, or 54 amps actual (about 13 kW). If you want to exceed that, you'll need to insert a "trailer panel" between your meter and your current main panel, and have that panel be solar-only... that would let you go to 200A.

Also, on the label, I noticed a limitation of a max of 140A per stab. Looking at the panel, isn't position 39 (50A) and 40 (100A) violating that limitation? How is that limitation applied with double breakers?

Absolutely, that is busting stab limits, and stab limits are serious business and should be optimized to minimize. So yes, move breakers so two 15s or 20s are across from the 100.

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Responding only to Question 1, creating space:

If you want to put a junction box above the panel to combine circuits rather than just do it in the breaker panel I recommend you buy a large metal enclosure for this, with lots of prepunched knockouts, run couple of 3/4" conduits between the enclosure and the breaker panel, and use loose wires through the conduits to run the combined circuits. It's easy and cheap to maintain. For example I recently bought an 8x6x4 box with 14 knockouts for $20 for a similar project. I have two main panels so it was better for me to use a box like this with conduits to both. For you, there is some sense to the other answer that says you don't need this, you should do the patching inside the breaker panel.

How to identify circuits for combining:

  • Look for circuits that were added just for one outlet or one light because that was the easiest way for the electrician installing that outlet or light to get the job done.
  • Look for circuits that fed window A/Cs before central A/C was installed, or that were installed for similar now-defunct purposes.
  • Look for circuits that do nothing at all. You know they are there, you always wanted to disconnect the cable and gain back the space. Well, disconnect the cable, cap it and move it out of the way, and go for it. You can always put it back.
  • Look for general lighting circuits (including outlets) that just don't have much demand any more. You used to have a bunch of 500W halogen lamps, and a couple of 36-inch CRT TVs and a few 300W desktop computers. Those are all gone, and you can combine almost anything you want.
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My solution was to admit that this wasn't going to get any easier -- and that it was starting to be hard to find breakers for my old panel -- and just have the whole thing replaced with a larger panel and new breakers at the same time I installed the heat pump which needed that additional heavy circuit. And while I was doing that, I upgraded to 200A service and put in the secondary panel I'd been wanting for workshop and future laundry room.

I already needed an electrician on site for the minisplit install; there was never going to be a better time. It completely eliminated the space problem. And per modern code, it gave me an outside main breaker, which I like because now I can work inside my master breaker box much more easily.

Yes, this required throwing a lot more money at the problem than cramming more half-breakers into the existing box would have. But it's a one-time investment for the next five decades (assuming I live that long), and the cost of the hardware was minor compared to the rest of that combined project.

Sometimes the right answer is a new car rather than repairing the junker, even if it does have some life left in it.

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    thank you for responding. I agree with you sometimes its worth just starting over, but in this case I'm pretty confident the Eaton CH will around for a long long time. The only thing I could do is upgrade to 400A service, but that is a bigger expense and makes adding a generator in the future more complicated. Dec 29, 2023 at 17:17
  • Granted. Just wanted to make sure the alternative was documented. A subpanel is still an alternative to overstuffing this panel. Some past answers have even suggested installing a subpanel panel adjacent to the existing one specifically for the circuits with generator backup.
    – keshlam
    Dec 29, 2023 at 20:11
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    This already is a 200a panel, it's pretty new and the best panel currently on the market, and 42 spaces is as large as panels come. Your logic makes sense if you had a 100A 16-space Pushmatic panel from 1974. Dec 31, 2023 at 3:27

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