Existing outdoor outlet more than 20' from parking, but we are not to use extension cords...

Existing outdoor outlet more than 20' from parking, but we are not to use extension cords...

I had an electrician out to the house to look over my setup. Here is my dilemma; he was telling me that the power company will be needing to move the junction box (or whatever it is called) to the front of the house because of adding poles and rewiring in the neighborhood. When that happens, he said that the power company would pay for the rewiring. I now have 100 amps coming in, but would like to upgrade to 200 amps, and, of course, would pay for the upgrade. Right now, it is a stretch to get the power I need, and adding on the charging of the Tesla would put undue stress on a system that is limping along to meet my needs: three breaker boxes all pretty much maxed out.
Most of my charging could be met with a 110 plug charging overnight as a temporary measure until the "spring rewire" is scheduled to happen. The problem is that the 20' cable that comes with the car is not long enough to reach my existing outdoor outlet. Also, the location of the plug is on my back porch but the cable would need to be woven through shrubs, bushes and all of the snow that falls of of the roof. All in all, a less than desirable set-up! It would be okay if I could leave whatever cord plugged in at one end and have the other brought back onto the porch each day, but it would need to be about 30'+ in length. Any thoughts? If I sign the paperwork, it's looking like the car could be delivered in February. Yikes!

Brian H | 15 décembre 2012

Not an electrician, but it sounds like you need a new outlet closer to the car. I think you can use an extension if it is VERY heavy duty. But maybe not.

ir | 15 décembre 2012

Have you looked into burying a power run to provide an outlet closer to your car?

Of course, you would have to dig-up your shrubs and otherwise be a big endeavor. The extension cord warning is mainly because your average orange cord can't deal with that much current over long hours every day. A licensed electrician can run the right kind if wire wherever you need it.

In a pinch, maybe you can have an electrician build you a temporary extension cord until the spring when digging will be easier.

bsimoes | 15 décembre 2012

Brian, that is the eventual plan, but as a stop-gap measure....Maybe I need to look around at work and see if there are any plugs within the 20' range of parking. One would think that this would be easy! I call my property "Barbieland," because things work or don't work completely differently than they do for my neighbors. For example, the rewire coming in from the street--the neighbors on either side of me have always been wired to the street. My house goes out back to a very remote and difficult location to reach. We had a storm; lightning struck said transformer, and 220 voltage was coming into my house, blowing numerous appliances and nearly causing a house fire. Another time, there was basically a tornado that stirred through. I had to have five mature maple trees taken down because of the damage. Not a leaf out of place for any of my neighbors--maybe I should take the hint! I go in to any venture expecting it not be straight-forward or easy. Any work done around here requires five other jobs done, too. Case in point!
Get an electric car and just plug it in; not in Barbieland!

Sudre_ | 15 décembre 2012

As a temporary thing a #10 gauge extension cord will be fine....

This cord at Home Depot is rated for 15amp at that distance.

bsimoes | 15 décembre 2012

Sudre--excellent! So then how does the cord that comes with the car come in to play? Would I need to plug it into the extention cord and then in to the charger or is there an adaptor that fits onto the extention cord and into the charger? Thanks!

Sudre_ | 15 décembre 2012

oh... FYI... many many many household plugs now days are not rated for continuous use... I don't mean plugged into several times. I mean used at rated load for more than 4 hours. I had a small window A/C 120 volt (10 amp full load) plug directly into a Leviton Decora 15 Amp Duplex Outlet and I had to replace it when I noticed it was starting melt.

Sudre_ | 15 décembre 2012

I think the car comes with a 120 volt tip that will plug into a standard plug... or that extension cord.

dborn | 15 décembre 2012

Perhaps. Your solution would be solar charging if you can get away with 120 volt. It sounds like your dail commute is short. A 3 kw system will average out at 10 kw per day.

jat | 16 décembre 2012

For charging continuously for more than 3 hours, you have to derate the capacity of the wiring/breaker/etc by 25%. So, if you want to charge at 15A, you need to have a cord capable of 19A, or you could charge at 12A instead.

Manta | 16 décembre 2012

What if you we're to decrease the charging rate to something excruciatingly slow like 6A? Could an extension cord handle that for extended periods?

petersv | 16 décembre 2012

My guess is that the existing wiring in your house isn't any better than that cord from Home Depot. The only problem might be the outlet. Limit the charge in your car the first few times and check for heat on all components, if OK you maybe can up it a few amps, but dont go over 80% of what that outlet delivers.

Be safe, don't gamble with these things.

Because of these things, I'm glad that we don't have 120V power in Europe...

DouglasR | 16 décembre 2012


I believe that when you use the NEMA 5-15 adapter, the car already defaults to 12 amps, not 15. However, I wonder whether attaching a 50' 15 amp-rated extension cord to your existing 20' mobile connector would exceed the rating. After all, the cord is rated at 15 amps for 50', not for 70'. Can someone enlighten?

Sudre_ | 16 décembre 2012

As mentioned above by petersv the #10 gauge wire is MORE than what the house is wired with (most likely #14 solid romex). So the extension cord should be irrelevant (#10 stranded SO). If the total distance from the panel to the car was closer to 100' then it would be something to think about because the voltage drop would start to have a significant effect. Electricity starts to damage things at the weakest point. That would most likely be the receptacle in this case. Inspect the plug and receptacle each time before and after use. It will be obvious if things are over heating.

DouglasR | 16 décembre 2012

I see that Home Depot has even has NEMA 14-50 extension cords in 25' and 50' lengths. In a pinch, could you use something like this:

to connect to someone's dryer outlet? You would need the NEMA 14-30 adapter, of course.

Sudre_ | 16 décembre 2012

Those cords are very dangerous in my opinion. They boast 30amps but only use #10 gauge wire. That would not work real well since you are extending the distance and plugging in for more the 3 hours.

In my opinion if you are using an extension cord on a continuous load charging you should increase the wire gauge by at least one. That would mean for 30amps you would go from a #10 to a #8. 50amp would go from a #6 to a #4.

DouglasR | 16 décembre 2012


bsimoes | 16 décembre 2012

Well...hell! I didn't think that the extension cord was probably a good idea. If I sign, and there is a time limit set upon us, then I won't be able to charge the car at home when I get it! The rewire from the street isn't going to happen until spring. The house is an old 1850's Vermont farmhouse, and I dare say, some of the wiring seems almost that old!

jat | 16 décembre 2012

@DouglasR - the distance matters because the voltage drop (the resistance of the wire is proportional to its length). However, my garage is 110' from the main panel as the wire runs, and the voltage drop over the #1 Al wire to the subpanel is negligible.

I'm no EE, but I don't think the total distance makes any difference to the performance of one component in the path.

You still have to derate by 25% for continuous load (which is why it only draws 12A from a 15A@120V outlet, and only 40A from a NEMA 14-50 outlet), and you may also have to derate it further if the ambient temperature is high.

nickjhowe | 17 décembre 2012

I just plugged a few numbers into this voltage drop calculator:

For a 100' run, 240v at 40A on #6 wire (NEMA 14-50) gives a 3.8v drop (1.6%)
120v at 12A on #10 wire gives a 2.9v drop (2.4%)

dtesla | 17 décembre 2012

I would suggest you diffidently consider upgrade to 200 amp service. If you use > 80% of the maximum for the circuit the breaker could trip for thermal reasons (Yes there is heat build up in a breaker). Since charging the car will use 50 amps for [potentially] an extended period of time, that will leave only 30 amps to guarantee the breaker doesn't trip for thermal reasons. So consider what other things you have that consumes electric before you make you decision. My electric water heater can consume 40 amps. NOTE: You may need to be consuming > 80% amps for a couple of hours for a thermal trip to occur.

krogers | 17 décembre 2012

Electrical code says a continuous load can only draw 80% of circuit capacity. So with the mobile connector (that comes with the car), plugged into a NEMA 14-50 outlet (50A circuit), will draw max of 40A. If you read the back of the mobile connector it it rated at 240V/40A max. In the car you can dial in the amps for charging. the car will take the lower value -- what max it can draw OR what you dialed in. If charging on 120V circuit you can dial in the Amps to be lower than the 80% rule...a good idea if there are other devices using the same circuit to avoid popping a breaker.

dtesla | 17 décembre 2012

I stand corrected. The NEMA outlet draws a max of 40 amps, with the circuit wire and breaker rated for 50 amps. This is done so you don't run into thermal breaker problems with the individual breaker. The house breaker however is 100 amps. So you should never plan to draw > 80 amps, for 100 amp service, for the entire house. If you expect to draw > 80 amps for the house you should upgrade the service to your home. The sum of all breaker amps can (and is almost always) > then the max amps supplied to the house since you don't have everything powered at the same time.

bsimoes | 18 décembre 2012

My plan is definitely to upgrade to 200 amps when I'm able to do so-rather, when the wiring from the street is scheduled to happen. My electrician is great, and is in contact with the powers that be. I appreciate everyone's efforts in offering suggestions and explanations. I am learning about things I never thought I would have to know about with this car! Tires, electricity, tech/phone/apps stuff...I suppose every project does this. We're always stretching ourselves; it's what keeps life interesting!