# Extension Cords



## mrkazoo

Hi all,

I'm new to the forums and have a MY on order for delivery sometime in September. I've been collecting tidbits of what to get for the car and was trying to understand the reasoning from people in grabbing extension cords that are 10awg.

Can you enlighten me on whether that is actually needed versus a normal 14-16 awg variety? From my calculations, you are only drawing 5amps on a 110v plug. A 10awg extension cord is rated to 15amps. A 16 awg cord is rated to 10amps, which is more than sufficient at 2x the amperage.

Am I missing something? Or people just want to be extra safe? 

The price difference between 10awg and 16awg extension cords is 2x-3x so I just want to understand is it really worth the extra money + weight?


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## JasonF

mrkazoo said:


> The price difference between 10awg and 16awg extension cords is 2x-3x so I just want to understand is it really worth the extra money + weight?


Yes. Larger conductors will heat up less, and live longer.


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## FRC

Are you absolutely certain that you are going to need to haul an extension cord around? In nearly 90K miles(2/3s road trips) I have never been in a situation that the suppiied mobile connector would not solve. Unless you're absolutely sure of your need, wait til after you've had the car a while to buy the cord, and then only haul it when you must.


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## shareef777

mrkazoo said:


> Hi all,
> 
> I'm new to the forums and have a MY on order for delivery sometime in September. I've been collecting tidbits of what to get for the car and was trying to understand the reasoning from people in grabbing extension cords that are 10awg.
> 
> Can you enlighten me on whether that is actually needed versus a normal 14-16 awg variety? From my calculations, you are only drawing 5amps on a 110v plug. A 10awg extension cord is rated to 15amps. A 16 awg cord is rated to 10amps, which is more than sufficient at 2x the amperage.
> 
> Am I missing something? Or people just want to be extra safe?
> 
> The price difference between 10awg and 16awg extension cords is 2x-3x so I just want to understand is it really worth the extra money + weight?


I haven't plugged into a 110V outlet in a long while, but when I did I recall the vehicle drawing over 10A.


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## D. J.

If I recall correctly, the continuous draw is 12A with the standard 110V plug, around 1.5 mi/hr. With the 20A plug adapter, you can get up to 16A continuous (80%) from a 110V 20A plug, somewhere around 4 mi/hr.

(edit: corrected 20A per FRC)


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## FRC

D. J. said:


> If I recall correctly, the continuous draw is 12A with the standard 110V plug, around 1 mi/hr. With the 20A plug adapter, you can get up to 16A continuous (80%) from a 110V 20A plug, somewhere over 2 mi/hr.


I get about 4 mph from a 20a plug.


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## Ed Woodrick

mrkazoo said:


> Hi all,
> 
> I'm new to the forums and have a MY on order for delivery sometime in September. I've been collecting tidbits of what to get for the car and was trying to understand the reasoning from people in grabbing extension cords that are 10awg.
> 
> Can you enlighten me on whether that is actually needed versus a normal 14-16 awg variety? From my calculations, you are only drawing 5amps on a 110v plug. A 10awg extension cord is rated to 15amps. A 16 awg cord is rated to 10amps, which is more than sufficient at 2x the amperage.
> 
> Am I missing something? Or people just want to be extra safe?
> 
> The price difference between 10awg and 16awg extension cords is 2x-3x so I just want to understand is it really worth the extra money + weight?


It is definitely not 5A, more like 12A continuous which requires a circuit that can support 15A. A "circuit" is everything back to the power station and would include the extension cord.

Get the biggest cord that you can and I wouldn't recommend going over 50 ft. A cord that would support 20A would be better, and you could even charge on 20A circuits when available. 
If you get the cheaper cord, your charging will be reduced and you'll notice the cord getting hot. Any time a cord gets hot, that means that a chance of a fire increases and wear and tear on the cord occurs. The car will notice the voltage drop and drop your charging current.

A warm cord is okay, not the best, but expected when you are pulling 80% of the circuit load on a continuous basis.

Don't skimp on the cord.

And I hope that this is only for incidental charging and not regular charging.


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## JWardell

Unless you dial down the current, the car will pull as much as it can, 12A from a standard 5-15 outlet. Absolutely make sure you use only high quality extension cords. That's enough to not only make some cords run hot, but poor connections from weak and dirty plugs will heat up even more. Often the car will sense this and dial down the current to protect thins, charging at an insanely slow rate.
You also battle voltage drop with longer wires which will also slow charging, so if you have a long cord it IS worth it to overcompensate.

I do keep this 75ft 10 gauge LifeSupply cord in my frunk. I've reliably charged a continuous 16A over it, and it has saved my hide when I've stayed a few places where parking is a distance away, or the only outlet is around the back of the building!


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## DocScott

I charge at home from a 120 V outlet. The standard charging cable draws 12 A. On my RWD M3 that's 5 mi/hr. 5 mi/hr is actually fine for my purposes, as I can easily recharge 60 miles in one night. It's not that I never drive more than 60 miles in a day, but my total range is around 300 miles, so as long as I don't _average_ more than 60 miles in a day, I'm fine.

Incidentally, in 2018, when I first got the car, I swear the standard cable did _not_ limit the current draw to 12 A. It would try to draw 15 A, and usually the circuit couldn't quite handle that, and the Tesla charger would then refuse to charge. I had to set the limit down to 12 A so it would work consistently. Since I'd set the limit I was surprised to later find that I couldn't raise it back up--there must have been a (very sensible) firmware update at some point to make the limit 12 A.

Just a few weeks ago I upgraded the circuit to 20 A (still 120 V). I had to get a 5-20 adapter for the charging cable so that it knew it could go past 12 A, and it now draws 16 A. With that rate, I add 7 miles per hour, which is more than enough for my purposes.

So why did I upgrade, if 5 miles per hour was enough for me? Two (related) reasons. First, my car is outside, and I'm in suburban New York. On the very coldest nights in winter, it takes 12 A just to keep the battery heated enough to accept charge, meaning that my charging rate was zero! Related to that is what happens on cold but not very cold nights--a good portion of the current is just going to heating the battery, and my energy efficiency is low. So 16 A will allow me to charge on very cold nights, and will save me money on garden-variety cold nights.


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## JasonF

Ed Woodrick said:


> A warm cord is okay, not the best, but expected when you are pulling 80% of the circuit load on a continuous basis.


A 16ga extension cord is designed for something like 12 amps - and it will definitely heat up at its maximum. It's likely the Tesla mobile adapter will sense the heat conducted into the plug head, and limit you to something like 8 or 9 amps, which is not ideal.

At 14ga, it will take 15 amps, but it will get warm. That won't limit your charging, but the warmer the cord gets, the more current loss you have, meaning the car will take longer to charge. A 12ga will heat up less, but only if you use exclusively 15 amp outlets - if you find a 20 amp somewhere, you're going to have the same heating and resistance issues, and possible charging slowdowns.

So I would recommend 10ga like @JWardell is using, simply because it's not likely to heat up even charging on a 20 amp circuit (at 16 amps), which means lower resistance, and _more kWh going into the car battery_.

Of course sometimes you have to borrow someone else's extension cord, and then any will do in a pinch. But if it looks a little thin (less than 12ga), keep an eye on it for a while when the car is first charging. The last thing you need is a worn or excessively cheap extension cord catching fire and burning your Tesla to the ground!


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## Doug Johnson

FRC said:


> I get about 4 mph from a 20a plug.


That's the amperage and charge rate shown in the display when I connect to a 15-Amp receptacle in my garage, although the app reports 5mi./hr.

I use a 16 AWG extension cord, and there is no discernible warmth in the insulation on the cord. (Note: Because of their minimal resistance, moderate heat does not degrade copper conductors.)

If you do choose to utilize an extension cord, I'd recommend one rated for cold-weather use (Search for SJTW Extension Cord, or SJTOW if you want one rated for outdoor use. Woods is a highly-rated brand, and are reasonably-priced at Walmart.), as their jacket is much more flexible; hence they are easier to coil.


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## mrkazoo

Thanks for all the insight. To answer some of the questions- I live in NYC so will be completely dependent on superchargers and destination plugs. So that's why I figured I will need an extension cord because who knows where I would need to plug into in a pinch.

So I guess the consensus is to just be safe and grab the 10AWG cord then even though it may work fine with thinner cords.


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## MachV

I tested an extension cable with 14awg, 50 foot cable and it very quickly reduced the amperage down because of heat. when I removed the extension cord and plugged in using the Tesla 120vac plug direct, i got maximum amperage. i believe the max was 12amps, which gave a maximum 5miles per hour charge. ambient temp was 80F

So I would recommend 12AWG or bigger. and 10AWG if you go with 20amp circuit getting 16 amps.


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## Long Ranger

mrkazoo said:


> So I guess the consensus is to just be safe and grab the 10AWG cord then even though it may work fine with thinner cords.


Yes. You'll also save yourself potential headaches if you're going to be plugging into various outlets. Besides heat issues, you also want to minimize the voltage drop that your extension cord is adding to the circuit. The car will slow down the charging if it detects too much voltage drop. You can't control the drop due to a given building's wiring, but you want to minimize what you add to that. A given length of 10AWG wire will have 1/4 of the voltage drop of 16AWG. Also, this means the longer your extension cord, the more important it is to use heavy gauge.


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