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2014 Tesla Charging at 120v - No Ground

sivakarthik06

Member
Feb 19, 2020
10
0
Pittsburgh
Hello everyone, so I recently moved into a shared home and was planning to use the regular 120v outlet to charge my car. The car charger was blinking red 4 times when i plug in and on inspection found that all the outlets in the house are two wires, and no ground. I would like to know my options on how to charge using this. Will installing a GFCI outlet rectify the issue and fool the charger that it has a ground? I cannot change the wiring in the receptacle as the place is a rental. Any input is much appreciated.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,252
7,300
Boise, ID
Will installing a GFCI outlet rectify the issue and fool the charger that it has a ground?
No, that doesn't do anything for a missing ground. What the GFCI is doing is comparing the current flow between the two sides of the circuit to make sure they are closely matched, showing that all is flowing through only the devices that are plugged into the outlet. If you have a big imbalance, it's showing that some of the current is finding an inappropriate and likely dangerous path out somewhere else.
I cannot change the wiring in the receptacle as the place is a rental.
In that case, no, there is nothing you can do.

The Tesla charging cord does a test for ground on that pin, and it has to see it. If it's completely missing, you will just get those red error blinks. If you want to get pretty hokey, you could drive a ground rod in the dirt somewhere and then run a wire to where that outlet is and attach it to the ground pin of the Tesla plug, and that might possibly work--not sure. But that's a mess, and I would never recommend something like that.
 

doghousePVD

My grandfather’s car
Dec 3, 2018
601
476
New England, USA
Get one of the 3 wire to 2 wire adapters. Connect a green ground line to the connector and attach it to a metal water pipe (NOT a gas pipe), some embedded metal in a concrete foundation, or drive a stake. Not kosher, and don't tell'em I suggested this. It probably would work. By the way, old houses often have metal junction boxes and metal conduit and are effectively grounded. If this is your case, use the 3 wire to 2 wire adapter and attach the green wire to the outlet box. Once upon a time that was code (pre-WW2?). Note that newish houses almost always have plastic boxes so this won't work.

Or cheat and connect the ground to the neutral. Make sure you identify the neutral at the outlet. Some old houses may be wired backwards. The neutral should be the larger flat pin. Some older outlets have both pins the same size, so use a multimeter to see which one is hot. We did this all the time in Brazil, but is definitely not up to code.
 
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ucmndd

Well-Known Member
Mar 10, 2016
6,522
12,211
California
Yeah, your only real choice is to connect a ground. @doghousePVD's first suggestion to run an external earth ground to a stake or water pipe is what I'd probably do in a pinch.

But I'd not consider this a permanent or even semi-long-term solution. Pulling 12 amps through obviously old wiring and a cheap externally grounded 3->2 adapter for hours and hours on end is a recipe for a house fire.
 

bo3bdar

Member
Feb 21, 2021
25
40
Silicon Valley
Or cheat and connect the ground to the neutral. Make sure you identify the neutral at the outlet. Some old houses may be wired backwards. The neutral should be the larger flat pin. Some older outlets have both pins the same size, so use a multimeter to see which one is hot. We did this all the time in Brazil, but is definitely not up to code.
This is what I would do. The ground wire is a safety feature to keep people from being killed by electrical appliances that have internally shorted. If you follow the ground wire back to the box, it will be connected to the same neutral/ground for the house. So by attaching the ground to the neutral at the socket, you are defeating the shock safety part, but it is not a large risk, especially for something like a Tesla that has smart charging and GFCI characteristics.

Just to be clear- this is not technically legal, and is definitely not up to code. But it works, and I personally put the risk very low. You can replace the outlet when you move, it's not a permanent change.

Yeah, your only real choice is to connect a ground. @doghousePVD's first suggestion to run an external earth ground to a stake or water pipe is what I'd probably do in a pinch.

But I'd not consider this a permanent or even semi-long-term solution. Pulling 12 amps through obviously old wiring and a cheap externally grounded 3->2 adapter for hours and hours on end is a recipe for a house fire.
I don't think that's a real concern. The only way you get a house fire with this would be if the breakers/fuses in the box are broken or the wrong rating. The entire point of fuses and breakers is to stop the current if it's too much for the house wiring. To clarify- there is ZERO current going through the ground wire. It's strictly a safety feature for scenarios where the neutral fails either in the wall or in the device.

Even if his house is knob and tube wiring, that wiring can easily handle and is specced for the 12 amp load for a Tesla. It doesn't match current code, but is not required to be replaced because it's not risky.


Another option might be to have an electrician add a 220V circuit for your charging. Even as it's a rental, this does not have to be a permanent installation, and would not necessarily cause any damage.

Depending upon your relationship with the landlord, they might allow this as a good perk for future renters, and actually encourage it, as long as they don't have to pay for it.

So my advice: Good relationship- add a 220V circuit. Bad relationship- rewire the ground on the 110.


As an aside- in my garage, I have a plug where the Tesla 110v charger worked in the top socket, but not the bottom one. Very odd. Same no-ground blinking red light. I just recently took it apart to inspect it, and, the ground for the bottom socket had been broken sometime in the past so that it no longer had the metal socket for the ground plug. Replaced outlet with a new one and now both sockets work.


Source: I'm an electrical engineer, so I've got a better than average background in electrical systems.
 

ucmndd

Well-Known Member
Mar 10, 2016
6,522
12,211
California
I don't think that's a real concern. The only way you get a house fire with this would be if the breakers/fuses in the box are broken or the wrong rating.
Or the 50+ year old outlet is worn and the connection is bad, and resistance causes it to heat up under continuous load until the receptacle or 99 cent cheater plug melts.

Or the same thing happens to any other 50 year old connection point at another outlet in the branch circuit. Or the breaker terminals.

Or or or.

I appreciate the engineer’s perspective but your analysis assumes everything is well maintained, in good working order, and hasn’t been mucked with by countless amateurs in the last half century.

Also, be sure to update your EE schematics and analysis to proper 120/240v nominal US voltages. 110/220 isn’t a thing in North America. ;)
 

bo3bdar

Member
Feb 21, 2021
25
40
Silicon Valley
Or the 50+ year old outlet is worn and the connection is bad, and resistance causes it to heat up under continuous load until the receptacle or 99 cent cheater plug melts.

Or the same thing happens to any other 50 year old connection point at another outlet in the branch circuit. Or the breaker terminals.

Or or or.

I appreciate the engineer’s perspective but your analysis assumes everything is well maintained, in good working order, and hasn’t been mucked with by countless amateurs in the last half century.
Sorry, wasn't trying to piss you off. If any of those things are actually a risk- then they are a risk whether you modify an outlet or not. If the house can't handle a 12 amp circuit, then no one should be living there. A vacuum cleaner can easily draw 12 amps. An electric stove can draw 40 or 50 amps.

Modifying a socket this way is negligible risk, I've done it before. I'm sorry, but talking about fire risk is just fear mongering and it set me off.

My house was built in 1966, so I've got 55 year old wiring, and nothing is even remotely that risky. A place built in the 1930s, maybe. Your point is well taken however- if the socket itself looks like crap, barely functional, or damaged in any way, I'd first replace it with a new one.

Also, be sure to update your EE schematics and analysis to proper 120/240v nominal US voltages. 110/220 isn’t a thing in North America. ;)
Cute, but the spec itself says all of those are the same. When I'm talking to electricians I try to use 110/220 as nearly everyone in the trades I've worked with uses that. You are correct that the nominal voltages are 120/240.
 
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ucmndd

Well-Known Member
Mar 10, 2016
6,522
12,211
California
Sorry, wasn't trying to piss you off. If any of those things are actually a risk- then they are a risk whether you modify an outlet or not.
Agreed. My point is that the NEED to modify the outlet in the first place is an indicator itself of age, potential problems, and other good reasons to thoroughly inspect the entire circuit before using it for a high continuous load. 3-prong grounded circuits have been required by code (for good reason) since ~1968.

If the house can't handle a 12 amp circuit, then no one should be living there. A vacuum cleaner can easily draw 12 amps.
My opinion would not change if someone asked about regularly running their vacuum cleaner for 12-24+ hours at a time on an old general purpose lights and plugs circuit through a 99 cent cheater adapter. It's a stupid thing to do and strikes me as a poor long-term solution with associated risks. Whether or not that's "fear mongering" I suppose we can leave as an exercise to the reader.
 
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Oct 10, 2019
310
151
So-Cal
damn its 2021 and there are houses with 2 prongs still? how TF old is this house you're renting?
Your best bet is to install a dedicated line to charge the car direct from the breaker box. if its close and there is amps to spare in there, install a 240v outlet of any kind based on the amount of amperage you have available 240v at 10 amps is a hell of a lot better than 120v at 12 amps. if its far away or you don't have the spare amperage in the box then just run a standard 120v 3 prong outlet.
I'd highly recommend you talk to the landlord and get it done, if you have skills and they are willing to let you DIY then rock on, if not ask if you can hire a pro and that you'll pay for it to be done.

As others have said you can jerry rig it but its not safe for all the reasons everyone has mentioned. if you charge the tesla you'll be drawing a constant 12 amps for 8-12 hours at a time and that gets hot which is dangerous. I currently charge my P85D off a 120v at home and it takes about 3-4 days to charge it 20% to 90%
 

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