Would someone mind helping me understand this wall charger install quote?

[nvx1977]

I've had some discussions with electricians about the load feasibility of adding a NEMA 14-50 receptacle to support EV charging. They've all said most houses with 100A service should be able to handle the addition of a 50A circuit. It still takes a lot of coincidences of major appliances + HVAC running at the same time to trigger the 100A breaker under typical use.

That said, they also universally recommended to utilize reduced draw from the car as well as to schedule charging at times where usage is low (middle of the night).

In the OP's case, it sounds like the electrician feels a 36A max draw is safe for existing load. I actually have two 50A circuits off a subpanel that's behind a 100A breaker. That panel also contains various small circuits (no major appliances). To be safe, I have both cars charging around 24A. No problem replenishing the battery overnight; plus I have less resistance thru the wire which translates into lower charging losses.

 

[aydyn]

That is not how a load calculation works. (Though some panels do limit total breaker ampacity per bus).

I'm aware, but still 100A household service does have limits, and many electricians will not install that much excess power regardless of the live load.

And it is usually relatively inexpensive to upgrade the home service, going from 100A to 200A for me cost $900

 

[SageBrush]

Thanks.

A little playing seems to show total possible VA load divided by 240 v.
Does that make any sense ?

This was posted on the MNL forum (happy coincidence):

Then you add up 3 * the square footage from (1), 1500 * the number from (2), and all of the nameplate ratings from (3). The first 8000 VA counts at 100%, the rest counts at 40%. For a 100A, 240V service, you have 24000 VA available. So your straight sum (ignoring the 40%) can be up to 8000 + 16000 / 0.4 = 48,0000.

 

[mongo]

I'm aware, but still 100A household service does have limits, and many electricians will not install that much excess power regardless of the live load.

And it is usually relatively inexpensive to upgrade the home service, going from 100A to 200A for me cost $900

Yah, there are limits. My point is that you could put every general purpose outlet and lighting circuit on it's own 15 Amp breaker and it wouldn't change the load calc, so we don't know what the real utilization is. Esp if there were things like electric and gas range/ dryer options where gas is being used.

 

[psykobunny83]

Hi everyone thanks again for the additional comments. So our usage is pretty low, something like 27kwH a day on average, as we are hardly home and every single bulb we have is LED and so on. Stove is gas as is heating and hot water. I'm fine getting a new panel if necessary, I just was curious what difference it made in charging speed, which from the Tesla website doesn't seem like a lot. I really drive very little and any long distance would be on a road trip with Superchargers. I will ask them for a second quote with the cost of a new panel just to compare and see if it's worth it, but one question:

I'd like to eventually get the PowerWall and go solar + grid, ideally maybe 1-2 years in the future, but all depends. Would I need a new panel for that anyway, making replacing it right now not worth it? Or would it make any difference replacing it now?

 

[mongo]

Hi everyone thanks again for the additional comments. So our usage is pretty low, something like 27kwH a day on average, as we are hardly home and every single bulb we have is LED and so on. Stove is gas as is heating and hot water. I'm fine getting a new panel if necessary, I just was curious what difference it made in charging speed, which from the Tesla website doesn't seem like a lot. I really drive very little and any long distance would be on a road trip with Superchargers. I will ask them for a second quote with the cost of a new panel just to compare and see if it's worth it, but one question:

I'd like to eventually get the PowerWall and go solar + grid, ideally maybe 1-2 years in the future, but all depends. Would I need a new panel for that anyway, making replacing it right now not worth it? Or would it make any difference replacing it now?

Your setup would probably add a backed up loads + solar + powerwall panel connect by the gateway to your existing panel. Depending on the particulars of your current panel, it might be fine. The concern is if the grid plus solar/PW can provide more current than the main panel's bus bars can handle. If it needed replaced, you could still keep the 100A service you have now since your loads would not be increasing and the PWs can adjust their charge rate.