Voltage Drop

Won't you need a 240 v outlet if you convert the EVSE to 240v?

 

I'm no electrician, but I think You will need a least at a minimum of 12 Gauge wire and then a 240 volt outlet. Just my guess, getting a electrician is a great idea!

 

if you convert it to 240v, you can't use the supplied evse unless you have that converted as well. sorry, i think i'm confused.

 

Acceptable is not really a quantifiable term.

If you are dropping 17 volts at 11.5A, then your wiring is about 1.5 ohms. That's pretty high. When pulling 11.5A, you are dissipating almost 200W throughout the wiring in your house. So of the 1380W you are pulling from the grid, 200W is heating your walls meaning your charging is 85.5% efficient from panel to car plug. That's pretty bad in my opinion.

If instead you just ran an 8 gauge heavy duty extension cord from your panel to your car it is about 0.0006282 ohms per foot. A 500ft run is only 0.3141 ohms. The same 11.5A would only be 41.5W waste, making it about 97% efficient from panel to plug. That's just money in your pocket.

Someone should check my math, it was done quickly and at the end of a long day...

 

Depends on how long the run is. 200W is probably OK if it is on the opposite end of the house. It is definitely not ideal. Copper wire will gladly continue to deliver full current up until it melts if given the chance. With house wiring it will go until the insulation which is usually paper and then wrapped in plastic melts. When this happens with the heat of the fire, generally you will short the lines together, and this will trip the breaker. Temperature doesn't trip standard breakers though.

I am not sure what you are imagining when you say converted to 240v. It is not just some setting on the back of the switch. The outlet needs the other phase of wiring. In most homes they split the phases to different floors or sections of the house because that is easiest to manage. So best case scenario, 1 conductor has to be run from that outlet back to the panel. And all of the expense is in the actual running of the wire and the repair work that follows. You will have maybe a hundred little holes in your ceiling or walls that will need patching, texturing, priming, and painting for a moderately sized house.

So when you switch it to 240v, make it a dedicated 240v 60A breaker. Most electricians probably know nothing of electric vehicles. Tell them to install it as they would a high end hot tub. This will require 2 breaker spaces in your panel, so make sure you have at least 4 spaces available now.

And when running the new wire, DO NOT SKIMP ON MATERIALS. Buy the higher end low gauge wire, 8awg is what I used in my example. It may cost an extra $50 to $100 but in a project like this, do it right and do it once.

 

Isn't that per conductor? Multiply by 2 to cover both conductors.

At least, my mental rule of thumb is that 10 gauge copper wire is 1 milliohm per foot per conductor, and each 2-gauge step is a factor of 1.6 (10x for a 10-gauge step).

 

14 ga wire is to thin to carry your almost 12Amps/120VAC for several hours. Heating the walls by heat dissipation could be dangerous. To the point of initiating flash fire in connection points in the receptacles depending in the wire quality and age of the installation. Do you have nub and tube? Do you have aluminum wiring?
Do yourself a favor and start fresh with a new dedicated electrical outlet.

 

When I got my OEM Toyota EVSE upgraded to 240v I ran a new dedicated circuit for it using 12/2 copper.
My total run from the breakers is about 45 ft, so according to all the charts I read, 12 ga copper was sufficient for the load the Prius draws. I was very happy to find that the 12ga copper doesn't even get warm when the PIP is drawing full current for the first hour and a quarter. FWIW- if the run was longer than 50 ft I may have gone with 10 ga copper just to prevent voltage drop/heat...

 

You are correct, in my example the R should be double.

 

A 60A breaker will be overkill. The hardwired EVSE I had installed draws a max of 32A, and requires a 40A breaker. Even the Leviton 40A unit only requires a 50A breaker in the panel. It provides up to 10Kw. The Prius is only going to pull 2Kw.

 

If you have dual Superchargers in your Tesla however, you need the 60A. And if you are going to spend the money to pull a permit (yes you need to almost everywhere), and get it done, do it properly the first time. 10 years from now it might be really common to have 60A chargers and then you will be the fool who skimped on a couple of dollars 10 years ago.

The difference in cost between a 30A, a 40A, and a 60A is almost nothing. The limiting factor will probably be what your incoming house service is.

 

Mind you, I actually agree with what you are saying for the most part. I think if you can install the better wiring, it should be done, but I'd size the breaker to what the expected load is going to be. If you end up putting in a higher-capacity EVSE, then upgrade the breaker at that time, unless code requires that certain size wiring needs to have a certain size breaker on it in the first place.

Tesla doesn't make a twin Supercharger for home use. They don't even make a single Supercharger for home use. Supercharger is DC charging (like CHaDeMo). There is a twin charger option, which is what I think you are referring to, and it requires a single 100A feed.

When I first thought about putting in an EVSE at home, I contacted Leviton, had them come out to do a site evaluation, and give me a price quote. They were only going to be installing a 16A unit on a 20A breaker. I asked if they could upgrade the wiring and breaker to support a higher amperage unit in the future and they kinda hemmed and hawed about it. I eventually decided not to go with them (disagreement about the excessive fees they were charging for pulling the necessary permit) and instead got a AeroVironment EVSE-RS unit installed, which is a 30A unit on a 40A breaker (and yes, I pulled a permit for it and had my electrician do the install). Even though my car only pulls a third of what it can supply, I'm still glad I did that. It did come in handy when I rented a RAV4-EV for a week a while ago. If I do have to upgrade the EVSE at some point in the future, it's only a short direct 5 foot run to the panel.

 

I was referring to the "twin charger", not the super charger. My mistake, my bad. I didn't realize it was 100A though... I thought it was 2 30A's.

I just looked at Tesla's site, and it is 2 40A chargers, so a single 240V 80A connection is required. In that case I would put in the 80A or 100A right there if you can afford the panel space.

The breaker is not for protecting the car's charging but for protecting the wiring. If it is 60A wiring or 80A wiring, you should put the 60A or 80A breaker in there. The car itself should have fuses and controls to limit itself. In your case since the panel is right next to the car, then it probably doesn't matter.

In my case the panel is on the exact opposite end of the house from the garage, so I am going to be running it to a separate sub-panel in the garage fed from a high power feed then into the chargers. At that point I should have 2 EV's so it should work out well.

 

Yes.

The electrician may be able to just mark the ends of the neutral red, and switch the neutral line over to being the other hot. I can't tell from here.

 

It will also need a 2-pole breaker in the panel, in place of the existing 1-pole breaker.

 

The cod here lets us do that as long as both ends of the neutral are taped red. That's how you can use standard 12/2 for the 240v circuit.

 

Same here. When I relocated the water heater this spring, adding a new circuit (easier than moving the old wiring), I just used standard 10/2 and added red electrical tape on both ends of the white wire. No problem with the inspector.

The original WH and electric heater circuits also have regular 10/2, but predate the need for added red markings.