Tesla owner's garage fire highlights EV charging safety and cost
A fire in Irvine California this past month highlights the fact that electric cars use more electricity than any other household appliance. The outlet in your garage was not intended to provide high amperage over a long period of time to charge a car. Like all appliances that draw a lot of current, any outlet that is used to charge an EV should be specifically designed and installed to accommodate that service.
EV Home Charger Wiring Basics
When an air conditioner or other large appliance is added to a home electricians do not tap into the existing wiring circuit closest to that appliance. Rather, they create what they call a “home run.” A home run is a circuit that goes from the single point of use directly back to the home’s main electrical panel. There are no other outlets on that wire. In addition, the circuit breaker that is between the appliance and the electrical supply (which is located in the electrical panel) will be added specifically for the service it will provide and it will be dedicated to just that one line.
A Tesla Model S can come with a battery pack as large as 85 kWh. That is pronounced 85 kilo Watt hours. This unit is a measure of power x time (energy). Take a look at your electrical bill. Mine says that I used a total of 644 kWh in all of November. That means that if I charged a Tesla from empty to full about 8 times, which would be twice per week, I would literally double my total electrical usage in the home. Charging 8 times would result in a range of about 2,000 miles per month. That is a lot of miles, but well within the amount of miles many Tesla owners report driving on forums we participate in. The upshot is that adding a powerful EV like a Tesla can double the amount of power your home’s electrical system handles. We are not trying to play any games here. If you feel the math has a logical error please reply below and we will re-check it.
On its website Tesla says “Most outlets are either standard 110 volt outlets or higher powered 240 volt outlets. Higher powered outlets charge between four and six times faster than standard household outlets. If you plan to install an outlet in your garage, we recommend a NEMA 14-50 240 volt outlet.” That is the type of heavy duty connection that an RV might use. It should be noted that the current rating on that is 50 amps (40 amps continuous draw). In your home there is nothing else that draws that much power. In fact, most New England homes built before the 1980s had only 60 amp service to the entire house. Now 100 amp or 200 amp is the norm. If your house has only 60 amp service you may need to change the entire electrical box. I did that on my home when I added a generator and AC system to my house. I paid about $1500 at the time, 15 years ago.
So far we have discussed the electrical service needs (not 60 amp), electrical panel needs (dedicated circuit breaker), and the wiring (home run to the point of use) for an EV. Tesla can help buyers with the proper in-car charging system (it offers both single and double) and also the type of home connector to use. Tesla also has a special High Power Wall Connector it can provide to owners who need fast, frequent charges. In its section on charging Tesla starts out noting that a “normal” 110 volt wall socket can only add 3 miles per hour of range to a Tesla Model S. Some quick math gives us a required charging time to add 240 miles of 80 hours! Clearly, that is not going to work for people who own these cars. It is just a nice option to have in emergency situations, or when one wishes to simply top off the battery on the road at a hotel.
Plan On an Electrician and Building Permit
If it has not yet become absolutely clear to the reader these electrical upgrades are not a homeowner project. In fact, they are not a handyman-service project either. Adding an EV charging point to a home should only be done by a licensed electrician who has pulled a building permit from the local town or municipality. Here in Massachusetts where I live, that would also result in the electrical building inspector visiting the jobsite after work is complete, inspecting the job to ensure it meets the code requirements for the town, and then the electrical inspector would sign the building permit if all was to his or her satisfaction. Anything less than this and your home-owner’s insurance policy is not required to cover problems like a garage fire that result from work done that was not to code. Here is what Tesla says about preparing your garage for your new Tesla:
“We recommend working with a trusted electrician to install your High Power Wall Connector or NEMA 14-50 outlet before your Model S arrives. All Model S include a Mobile Connector cable and an adapter for the NEMA 14-50 outlet. Depending on your home’s electrical system, installing a high Power Wall Connector at maximum amperage may be more difficult that installing a 240 volt outlet due to power availability. The High Power Wall Connector can be set to any amperage level. While you won’t charge at the rate of 58 miles per hour of charge, you will be able to enjoy the convenience of a sleek, permanently installed Connector.”
Home EV Charging Point Cost
The total cost to install a proper EV charging point in a home can start at about $750 for a home-run circuit and appropriate low current rating wall connector. The Tesla High Power Wall Connector requires a 100 amp circuit breaker to get the fastest charge rating. Most houses in New England cannot accommodate that. Adding 200 or 400 amp service, wiring the home run circuit and buying and installing the High Power Wall Connector could cost as much as $6,000.00. Our estimate is based on Tesla Forum discussions that say the electrical work including an upgrade to 200 or 400 amp service can range to as high as $3,000 and the Tesla website which lists the High Power Wall Charger and second on-board charger as a $2,700 adder to the car’s price tag. It should be noted that $6,000 will buy a lot of gas. In fact, it will buy 1,714 gallons of gasoline at today’s price of less than $3.50 per gallon. A 25 MPG car can travel about 43,000 miles on that amount of money. Again, we stress that these are the two bookends of the range one might pay.
The fire in Irvine California seems to have occurred at the connection between the Tesla’s cable and the wall. Here is what one news report summarized the Tesla response as being; "“The cable was fine on the vehicle side; the damage was on the wall side,” Tesla said of the garage fire. “Our inspection of the car and the battery made clear that neither were the source.”" We reached out to the Orange County Fire Authority for a comment and we asked if the job was recorded by a signed building permit, or their equivalent code requirements. They did not reply.
Evs are a part of the automotive present, not future. Those shopping for a new EV, particularly a Tesla, should include the cost to install the charger and make an installation plan including an electrician and building permit.