Can I add a 240v/50A circuit to one of my two 200A panels?

Question

I'm following up regarding adding 50 amps to provide service to an EV charger. Crazily, I have two 200 amp service panels and both are full. As suggested in responses to an earlier post, I am attaching pictures of the panel and my recent work to map the breakers on the panel (what was labeled by the previous owner was vague/inaccurate).

Please ask any questions as I'm trying to figure a lot of this stuff out myself. For what it is worth, a lot of these things are rarely or almost never used but since they could be used in the future I don't want to terminate them.

Note, I intend to hire an electrician to do this work, with me possibly (depending on cost) pulling the 6/2 cable since I have a large conduit from the panel to an unfinished utility room that goes directly into my garage (about a 75 to 100-foot run). I just want to get a sense of what I can expect, what I should ask for, and whether I'll need yet another panel!

Thanks in advance.

EDIT TO ANSWER QUESTIONS: House is very large and has tons of gadgets added by the original owner. There is an addition that has an Endless Pool in it. This is rarely used, maybe a handful of times per year. This has the pool, pool pumps, swim resistance motor, its own AC unit, a huge dehumidifier (not needed with sealed cover and little use). Otherwise, we have gas heat for the basement/lower level and electric/heat pump on the top level. On the steam shower, again this is just used a handful of times each year. On the cooktop, it is a gas cooktop that has a blower that raises and lowers. Not sure why, but it won't work without both breakers on.

Answer 1

Reading between the above lines and doing a lot of guessing, you probably have a large house so should factor at least 100A for lighting and general power (it's a sq ft calc you can do). Your heat and A/C seem to each require about 90A (guessing their actual load), your pool/hot tub complex seems to need about 150A. And all your special loads (steam shower, dryer, washers, sump pump, etc etc etc) also guessing their actual loads could potentially together draw another 190A.

IMO you are WAY oversubscribed already, and you cannot add an EV charger without either bringing in another service drop or installing some kind of load sharing device to share power between the EV and certain existing fixtures, eg "pool room furnace", "steam shower", etc.

I don't think your "full" panels are the main issue, you could move some stuff into a sub panel eg a bunch of lighting circuits. I think the issue is you can't add another 12kW fixed load to your service, you'll be blowing your 200A breakers.

I infer that natural gas is not available at your location, right? You might find that converting your entire pool complex to propane would be more economical than upgrading your electric service even further. Worth looking into.

Answer 2

As already noted, a load calculation is key here. But really 3 load calculations:

• Total Service - 320A
• Panel 1 - 200A
• Panel 2 - 200A

With a typical 200A or smaller service, there is an alternative method. Not sanctioned by code but often very practical: Check your utility usage reports. Many utilities provide free downloads showing 15-minute, 30-minute or hourly usage for a year or more. For example, my hourly usage for November 2020 - November 2021 shows a maximum of 9.98 kWh. At 240V (of course, not all loads are balanced, but the large ones are) that's 42A, so that tells me the near-peak (true peak would need peak demand kW in each interval rather than kWh usage) value. That's effectively your maximum load for the year, whether the load calculation comes up lower (you run more stuff at a time than the average homeowner) or higher (you run less stuff at a time). It is also helpful for figuring out generator capacity - 98% of my intervals are under 6 kWh, so I know a 7,500W generator is a reasonable match as long as I don't hit the absolute peak, which can easily be done by not putting the oven and clothes dryer on the generator.

The problem is that with a house/service this large, it is unlikely that your real peak usage is below 140A. If your peak usage is 200A then adding 50A to your service is OK, because it will only max. out at 250A. (Leaving aside the issue of whether a future owner might use the pool or other equipment more and run into trouble.) But since the utility can't tell you the split between the panels, you won't know which panel can handle an extra 50A. The real usage by be 160A on one and 40A on the other. Or flipped. Or even worse, balanced to one side in the winter (heat) and to the other side in the summer (air conditioning, pool), etc. Which is why load calculation is a very useful tool.

The other issue is whether you need 50A of charging capacity. Since you indicated you will do night-time charging, that typically means 8 - 10 hours of uninterrupted charging. 30A (possibly even 20A) of 240V charging is more than enough for most people using their cars for typical commuting and errands. But given your current (pun intended) situation, even adding 20A may be problematic.