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5-15 extension cord

Buderflie28

New Member
May 10, 2020
1
0
Keizer, OR
I have been researching extension cords to use for charging my Tesla Model 3 on a now and then basis when staying with family out of town. They only have a 5/15 plug so it is trickle charging (12 amp). I need to use at least a 25 ft. extension cord. Everything I have researched says I need at least a 12 AWG, or a 10 AWG. I have also read that the longer the cord the greater the resistance. What I don't know is if a higher gauge improves the charging in some way (other than just safety)? I did find a 12 AWG, 25 ft. cord, but I couldn't find a 10 AWG, 25 ft cord. The shortest extension cord I can find at 10 AWG is 50 ft. So my question is this: Which will charge faster/better: a 12 AWG, 25 ft cord, or a 10 AWG, 50 ft. cord? Thank you in advance.
 

Sophias_dad

Active Member
Supporting Member
Jul 29, 2018
1,905
2,113
Massachusetts
Amazon has a bunch of 10AWG 25' cords... I've linked one below. But I agree that you don't really need one. At 50 feet carrying 12 amps on 10AWG, you'll be seeing 1.05% voltage loss. At 25 feet carrying 12 amps on a 12 gauge, you'll be seeing 0.87% loss. If you were to upgrade to a 10AWG 25 foot cord, it would be 0.52% loss. (per https://www.southwire.com/calculator-vdrop)

The only upside to the 10awg is that they are likely to be better terminated and able to deal with hours-long charge sessions. I wouldn't worry much about it.

Amazon 10AWG 25'
 
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MXLRplus

Active Member
Mar 11, 2020
1,601
2,807
Eastvale, CA
In practical terms, there is a reason some extension cords are expensive and some are cheap.
I've had cheap 12 AWG cords trip a breaker while a quality 10 AWG works flawlessly.
I'd go with the 10, get a good one it will last you decades. Get one that has an LED in the receptacle end, it makes life simplier.
 
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eprosenx

Active Member
May 30, 2018
2,076
2,542
Beaverton, OR
I have been researching extension cords to use for charging my Tesla Model 3 on a now and then basis when staying with family out of town. They only have a 5/15 plug so it is trickle charging (12 amp). I need to use at least a 25 ft. extension cord. Everything I have researched says I need at least a 12 AWG, or a 10 AWG. I have also read that the longer the cord the greater the resistance. What I don't know is if a higher gauge improves the charging in some way (other than just safety)? I did find a 12 AWG, 25 ft. cord, but I couldn't find a 10 AWG, 25 ft cord. The shortest extension cord I can find at 10 AWG is 50 ft. So my question is this: Which will charge faster/better: a 12 AWG, 25 ft cord, or a 10 AWG, 50 ft. cord? Thank you in advance.

12 gauge will be fine for 12 amps of continuous draw on that short a cord. In the wall a 15 amp circuit only typically uses 14 gauge.

Of colors I recommend avoiding extension cords where possible, but temporary charging situations like this are the exception.

Any chance you could add a 240v receptacle right off the panel? Even a 6-20 receptacle would be vastly faster!
 

camalaio

Active Member
May 28, 2019
1,483
2,198
Vernon, BC, Canada
To somewhat answer your question more directly, the maybe ~0.25% difference in voltage drop only accounts for about the same difference in charge time. So no noticeable "improvement" to the charging. 12AWG will in theory get a little warmer, but nothing concerning or out of spec.

10AWG is nicer for things like air compressors or things with motors that briefly draw a lot of current on startup (>15A sometimes) to reduce the voltage drop. The car doesn't have this same behaviour. Actually, it's opposite - it slowly ramps up the current.

"Cheaper" 10AWG cords are also annoying and stiff in general due to their thickness. The more flexible ones are even more expensive. Just not worth it for charging.
 

electrongeek

Metrology Fanboy
Nov 1, 2019
69
75
Maine
In practical terms, there is a reason some extension cords are expensive and some are cheap.
I've had cheap 12 AWG cords trip a breaker while a quality 10 AWG works flawlessly.
I'd go with the 10, get a good one it will last you decades. Get one that has an LED in the receptacle end, it makes life simplier.

A 12 AWG cord would not cause a breaker to trip where a 10 AWG cord wouldn't. Yes the 12 AWG cord would run a bit warmer, but the breaker cannot sense this. The breaker only sees 12 Amps passing through it while Tesla charging, regardless of the size of the extension cord conductors. However, if your breaker is GFCI, and your 12 Amp cord was faulty and allowed current leak to ground, then that would trip the breaker.
 
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MXLRplus

Active Member
Mar 11, 2020
1,601
2,807
Eastvale, CA
A 12 AWG cord would not cause a breaker to trip where a 10 AWG cord wouldn't. Yes the 12 AWG cord would run a bit warmer, but the breaker cannot sense this. The breaker only sees 12 Amps passing through it while Tesla charging, regardless of the size of the extension cord conductors. However, if your breaker is GFCI, and your 12 Amp cord was faulty and allowed current leak to ground, then that would trip the breaker.

Last time was a small air compressor in an empty building. The 12ga tripped the non GFI circuit, and the 10ga pro did not even though it was twice as long (50 vs 100').
If the cord gets hot, that's more power pulled from the wall.

I blame it on the poor quality of dubious '12ga' which was showing signs of heat damage at the ends.
 

electrongeek

Metrology Fanboy
Nov 1, 2019
69
75
Maine
Last time was a small air compressor in an empty building. The 12ga tripped the non GFI circuit, and the 10ga pro did not even though it was twice as long (50 vs 100').
If the cord gets hot, that's more power pulled from the wall.

I blame it on the poor quality of dubious '12ga' which was showing signs of heat damage at the ends.

That explains your experience. An air compressor will behave differently than the Tesla charger. Because of the voltage drop along the smaller gauge extension cord, the compressor will probably draw more current to make up for it. So in that case, the breaker may trip with an inadequate extension cord. This is different from the Tesla charger, which will draw a constant 12 amps regardless of the extension cord gauge. The breaker will see 12 amps through it. The voltage will be the same at the breaker regardless of the extension cord, so power through the breaker will be the same with either cord. The smaller gauge cord will be warmer because of more voltage drop along the length of the cord. That voltage drop X 12 Amps is how much power is lost in the cord. The charger, still drawing 12 amps, will have less power to charge the battery because the voltage it is seeing is lower. All of this looks exactly the same to the breaker.

I.
 
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eprosenx

Active Member
May 30, 2018
2,076
2,542
Beaverton, OR
That explains your experience. An air compressor will behave differently than the Tesla charger. Because of the voltage drop along the smaller gauge extension cord, the compressor will probably draw more current to make up for it. So in that case, the breaker may trip with an inadequate extension cord. This is different from the Tesla charger, which will draw a constant 12 amps regardless of the extension cord gauge. The breaker will see 12 amps through it. The voltage will be the same at the breaker regardless of the extension cord, so power through the breaker will be the same with either cord. The smaller gauge cord will be warmer because of more voltage drop along the length of the cord. That voltage drop X 12 Amps is how much power is lost in the cord. The charger, still drawing 12 amps, will have less power to charge the battery because the voltage it is seeing is lower. All of this looks exactly the same to the breaker.

I.

^———— What they said.
 

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