Do I need 400 amps breaker?!

I have a similar setup. 200 Amp service in the house, electric heat and installed an HPWC. It remains to be seen how this will work out when the electrons start flowing late December.

punkchip said:

Buying my first house on friday!.

Right now, it has 2 NEMA 14-50 outlets (one for my Tesla, one for another electric car when my parents or other friends come). I have 200 amps breaker.

If eventually I change one of the 15-50 outlet for a 100 amps circuit to plug the HPWC, so it charges at amps will it work? Everything else in the house is also electric (heat, in cold weathers of Canada), stove etc.

If not I guess the next step is to upgrade to 400 amps breaker? How does that cost?

Click to expand...

Another option might be to get a second 200A panel.

If you are planning on charging one car at 80A, and another at 45A, while running the heat -- you will probably have a problem.

I only have 125 amps at my house but I had an electrician install a 14-50 for my Tesla, and an 48 amp Clipper Creek for my Leaf (which only draws 13 amps). He was hesitant to do so since we have an electric range, dryer, hot tub, etc. (but natural gas for heat) and he warned me if we charged two Tesla's drawing 88 amps, that only leaves 37 amps and a potentially dangerous situation (although hopefully the main fuse would blow). I said I would never do that, and that it would only be the Leaf and Tesla taking 53 amps.

Do you really need to charge your car when your parents or friends are charging their car? If so, you can dial down the amps from 80 and both use 40 - that would leave you with 160 for the rest of the house. I have 200 amps at my cottage because there is no natural gas so the extra amps are needed for heat. I also have a hot tub there I run year round, dryer, range, etc. When I install my HPWC there, I doubt I will ever use the full 80 amps unless a fast charge is needed, and if so, I would make sure nothing else of high power use is running.

Electric heat in Canada? Wow how much does your heat draw?

I charge my Model S on a 60A breaker, and my FFE on a 40A breaker. And as long as I don't cook (using the oven and a couple of burners) and AC while both cars are charging my 150A feed is plenty.

In general I'm not preparing elaborate meals, or using much AC when my cars charge past 11pm. And I mostly stagger the car charging.

But if you are running full heat, charging the Model S at 80A and trying to charge another car at 40A you might need more than a 200A main feed.

Call an electrician, have him survey your equipment, and what you want to do. He will do a load analysis and tell you if your equipment and wiring is sufficient. There is no other way to tell if what you want to do is possible, or what upgrades you may need, and what it would cost.

If you are closing on this house Friday then its too late to fret about the 200A service. That should have been dealt with a long time ago. To up the service now will cost a lot, probably require a new transformer from the utility company, all new wires from the transformer to your distribution panel.

The issue isn't so much can your house handle it without the breaker tripping. It's the risk associated with constant draw appliances such as charging an EV or anything that pulls for more than 3 hours. Any loads that run for more than 3 hours need to be derated by 20%. Do not pull more than 160A @240 for more than 3 hours. I would install a monitoring system such as eGauge to keep an eye on your draw.

Unsure as to how utilities work in Canada but in the US the PUC has laws that vary. In my state the PUC requires utilities to stay within a certain voltage spec +/-5% of 240V. If I draw more than the transformer can provide while staying in that range they are responsible for the cost associated with upgrading the transformer. I have 400A service running to my house but they only had a 10kVa transformer on the pole. Bad news lol. Even my solar array overpowered the thing causing voltage runs up past 264V at the inverters. They were forced to replace it with a 50kVa at their expense.

We only had 50 A service to the garage and two EV's (Leaf and Tesla) for a couple of years, and were able to juggle charging both with few problems. It really depends on your daily commute--if you're at the 250 mile limit, then it's going to take about 12 hours to top off at 30 A. If your commute is less, then you can charge two cars at a lower rate even on 50 amps.