Note that EVs are considered "continuous loads" under the US electrical code, so the circuit actually needs to be sized for 125% of the load (ie to charge at 80 A requires 100 A service, not 80 A service).
How would a normal homeowner even know if they were approaching 75% of their breaker rating, unless the breaker tripped at <75% of its stated limit? If someone has had 100A service installed with 100A breakers and it's not wired for at least 125A with #2, then they have been defrauded by their electrician and contracor.
If you think that inductive power factor doesn't matter for power efficiency, rating, and safety then I also recommend that you continue your education. I can't imagine a licensed electrician saying that.
> unless you're worried about the breaker box flipping, ruining at 90% of the fuse rating is reasonable (if it is a stable 'non-inductive' load).
A continuous load (usually) requires a breaker rated at 125% of the load, as calculated by the electrical load. A 90A continuous load on a normal 100A breaker is not okay, full stop. It doesn’t matter if that load is literally a giant resistor or is some real-world device.
> If someone has had 100A service installed with 100A breakers and it's not wired for at least 125A with #2, then they have been defrauded by their electrician and contracor.
In the infamous words of Wikipedia, citation needed. In standard US residential usage, a “200A service” is 200A for non-continuous loads and needs to be wired for 200 Amps. Same for 100A, etc. The only common exception I’ve heard of is “class 320” service, which is genuinely rated for 320A continuously, and that’ll have 400A wiring and perhaps a 400A main breaker or a pair of 200A breakers. The latter seems fairly common, since you can buy the hardware at Home Depot.
As a home owner how will I ever discover this in a non-catastrophic way? Will I put an ammeter clamp on at the breaker box with an alarm on it? Will I know the load of everything that is plugged into that service? The breaker won't blow, but the building will burn down... and it's not the fault of the electrician who installed it and code enforcement says it's fine?
As examples of non-continuous loads that are likely to be continuous for 8 hours or more: a double oven during Thanksgiving, halogen flood lamps at night, or an electric space heater during winter. Oops, you burned your house down for Christmas.
(edit) Discussing this with an electrician, he says that in fact the breaker will flip after extended/continuous load near the breaker limit. It would not be considered a hazard, because the home owner would experience the breaker flip each time before there was a problem. He also said that it's the difference between running at 75 vs 100% of rated current is about 15C of increased temp on the wires and also not a concern for copper.
Your 40A (or whatever) oven isn't a 40A continuous load even on Thanksgiving. It'll draw 40A (maybe) while heating up, but it'll use much less while maintaining temperature.
If you really want, you can probably melt your breaker box, though. You'll need some really nasty nonlinear loads. Off the top of my head, with standard single-phase service, you want lots of even harmonics so that you draw 200A from each phase but put more like 400A on the neutral. Since your breaker doesn't sense neutral current, you won't trip it. (I suspect you'll acutally fry your utility's transformer long before you melt your breaker box, though -- most utilities use a rather different formula for transformer sizing and can't actually supply your rated current for very long.)
Given the skin effect, the ampere rating of an AC cable should be the square root of the material used, more or less, but that's per cable.
Obviously you can't get around that by braiding cables, but does anyone ever try to save on material by running multiple independent cables? Or would that end up being more expensive overall?
72 amp loads would require 90 amp circuits.
And there's a good reason they do.
My custom house is almost complete and we only put a single 40 amp circuit in the garage. I've lived with an EV for a few years now. 40 amps is plenty. When we get two EVs, 40 amps will still be plenty. The garage is also close enough to the breaker box that we can run another 40 amp circuit if we need to.
You don't need both of your Teslas to go from 0 range to 300+ miles in two hours everyday. If you did that much driving you'd be running a taxi service.
In our case, the charger will be between both bays. Assuming that both EVs have 300 mile range, we won't need to charge both cars everyday. (Edit) I'm also assuming someone will come out with a 40-amp dual-car charger that will split the load between two cars when both are plugged in.
Anyway, I did ask about 400 amp service because I wanted to use tankless electric water heaters. What he told me is that he'd have to wire in a second panel and second meter.
At that point I decided that 200 amps was plenty.
Aren't these prohibitively expensive compared to natural gas?
(I've considered the same but I have gas service)
- An electric water heater is the only way to go truly "net zero"
- You can power it with solar panels
- Your gas company might have a high fixed charge (e.g. I pay $20/mo just for the hookup)
- Routing gas lines & exhaust can get expensive and quickly wipe out fuel savings
- Cutting gas service completely eliminates combustion concerns. No worries about combustion air, no carbon monoxide, etc.
- Electric might still be the service of the future; electric appliances are a bet on renewables
Now, a tankless electric can also get expensive if you wind up needing to upgrade your electric service. Which is why I ultimately went from tanked gas to tanked electric.
Typically electricity are the worst in places where this is a meaningful benefit to consumers because the state usually has policies about sourcing its electricity that take environmental impact into account in such a way that price is driven through the roof.
Paying a premium for green energy is the best thing states can do to discourage conversion from fossil fuels to electric power.
Actually, the whole water heating business seems to be like this. All kinds of way better tech than an old fashioned 82 AFUE open flue tanked, at really minor cost increases, but the cost of water heating in the first place just isn't that terribly high.
In the end the most significant cost savings on my water heater replacement project, turned out to be the space heating savings from closing the old atmospheric vent & combustion air vent.
I ended up going with an electric heat pump hot water tank.
I do have natural gas service, but I'd rather put my money into assets (solar panels) than consumables (utility services).
The electrician's time is the most expensive part; oversize for decisions such as these (load center, EV run to outlet, subpanels, etc).
The caveat is that your system must charge the battery from your panels, and cannot charge from the utility (trivial inverter setting). With that said, based on net metering laws in most locales, it behooves you to consume as much of your own production as possible. Exceptions abound.
https://www.reddit.com/r/energy/comments/82fchy/irs_letter_o...
However, when more and more people try to have fast chargers in their homes for EVs, then not only the residential installation poses a problem, but utilities would need to rebuild ~two layers of distribution to accomodate for a 100-200 % increase in residential power consumption.
[1] Not just because high currents are more difficult to handle properly, but also because you need a lot less copper.
Hell if the PowerWall 3 could dump 40 amps you could pull 20 from the wall at the same time and hit your 60 amp total.
This seems to be a common best practice, sort of like blowing in expandable foam insulation between the historic (unchangeable) facade and new inner walls to properly insulate a historic home.
Electrical Metallic Tubing (EMT) conduits are similar but more stringent (fire protection).
What people need in their garage is 20 amps for the trickle charge to replenish the 30 miles lost from their commute and some grocery shopping overnight.
It's also likely that future EVs won't have this battery limitation, just put in the heavier gauge wires and breakers while you're in there if the house is going to be around for the next century.
Or less gloomy: In between appointments, you drive home to charge. Do you want to come 15m late just because your pipe is too weak?
Big pipe = freedom.
You can run out of gas in an ICE car too, and then it's even worse because you need to go track down a gas can instead of plugging in. The simple solution, of course, is to never fly that close to the Sun.
The scenario of an empty EV battery is not that unlikely. Eg you forgot to charge when you returned.
My wife drove me to the emergency room on a 3am Sunday morning when I felt like someone was pushing a golf ball out through my ribs and I had my gall bladder out that week. $750 copay for ambulance service.
He thought I was crazy, and maybe I was. But articles like this make me wonder.