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Extension cord for 110v outlet charging (long term)

Yes, the wire gauge is key, but I have yet to see a cheap cord with heavy gauge wire. Copper is far more expensive than plastic, and the good cords that are designed to carry current without dropping the voltage use heavier gauge wire and are more expensive. People get sticker shock and get the one next to it on the shelf that looks just as good but has half the copper.
By the way, for the OP, wiring gauge is actually backwards: the larger the number, the smaller the wire.

Thus, a 10-gauge wire is actually larger than 12-gauge wire. So you'll want an extension cord with the smaller number-gauge wire, which is actually larger wiring.

I have no idea why this is the case as it's quite counter-intuitive.
 

ATPMSD

Active Member
Mar 12, 2021
1,352
1,238
Atlanta, GA
By the way, for the OP, wiring gauge is actually backwards: the larger the number, the smaller the wire.

Thus, a 10-gauge wire is actually larger than 12-gauge wire. So you'll want an extension cord with the smaller number-gauge wire, which is actually larger wiring.

I have no idea why this is the case as it's quite counter-intuitive.

 

Rocky_H

Well-Known Member
Feb 19, 2015
7,977
10,105
Boise, ID
I have no idea why this is the case as it's quite counter-intuitive.
It seems backward until you realize what it represents. It relates to how many of those wires you can fit into a fixed size. So thinner wires, you can fit more of them in, so the bigger the number. It's like a quantity, not a diameter.
 
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I'm late to the conversation, but, got Experience.
First off: Agree with everybody to Watch Out for Home Depot extension cables. They look wonderful, nice and thick, and the labels say, "Ruggedized!"
But plastic is cheap, copper isn't.
Best place to buy decent extension cables that I've run across out this way is Harbor Freight. Their little display has a bunch of different extension cables and, importantly, How Much Current they can support. So, a 20' extension cable that's good for 20A has a lot thicker gauge wire in it (and, at HF, they actually tell you what gauge the wire is!) than, say, a 5' cable. It's the voltage drop that matters.
I also note that the Really High Power cables have the 120 VAC connector with one of the blades at right angles. See Wikipedia, and note the NEMA 5-20 connector. A 20A extension cord will have a plug with the blade at the right angle; the socket that one can plug into can accept the normal, straight up-and-down blade as well as the sideways one.
Code in NJ says that at least one socket in the garage has to be a NEMA 5-20. Dunno about other places.
But, a word of warning.. The OP is from Chicago. It can get cold up that way. And, before the car will charge, the battery will have to be warm enough to accept a charge. I drive around a 2018 M3; on days below 10F, plugging into a 120 VAC socket didn't provide enough power to heat the battery, so the rate of charge was 0 Miles of Charge per Hour. On warm days with that setup, one gets 5-6 MoCpH.
Which is why, if one can swing it, 240 VAC is so much better. 120 VAC @ 12A is 1440W; 240 at 12A is 2880W; but that NEMA 14-50 that can do 32A is 32x240 = 7.68 kW, more than enough to warm the battery up and get the car charged.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
7,977
10,105
Boise, ID
I drive around a 2018 M3; on days below 10F, plugging into a 120 VAC socket didn't provide enough power to heat the battery, so the rate of charge was 0 Miles of Charge per Hour. On warm days with that setup, one gets 5-6 MoCpH.
Well, let's fill in more information on that. It will eventually get there. It's just diverting all of the energy to heating at first. So you might have the first two or three hours with 0 mph charging, but it likely will gradually start to do some charging later on overnight. But of course that is part of the same problem if you are losing two or three hours of your overnight charging at an already slow speed, you aren't getting many miles back overnight.
 
I'm late to the conversation, but, got Experience.
First off: Agree with everybody to Watch Out for Home Depot extension cables. They look wonderful, nice and thick, and the labels say, "Ruggedized!"
But plastic is cheap, copper isn't.
Best place to buy decent extension cables that I've run across out this way is Harbor Freight. Their little display has a bunch of different extension cables and, importantly, How Much Current they can support. So, a 20' extension cable that's good for 20A has a lot thicker gauge wire in it (and, at HF, they actually tell you what gauge the wire is!) than, say, a 5' cable. It's the voltage drop that matters.
I also note that the Really High Power cables have the 120 VAC connector with one of the blades at right angles. See Wikipedia, and note the NEMA 5-20 connector. A 20A extension cord will have a plug with the blade at the right angle; the socket that one can plug into can accept the normal, straight up-and-down blade as well as the sideways one.
Code in NJ says that at least one socket in the garage has to be a NEMA 5-20. Dunno about other places.
But, a word of warning.. The OP is from Chicago. It can get cold up that way. And, before the car will charge, the battery will have to be warm enough to accept a charge. I drive around a 2018 M3; on days below 10F, plugging into a 120 VAC socket didn't provide enough power to heat the battery, so the rate of charge was 0 Miles of Charge per Hour. On warm days with that setup, one gets 5-6 MoCpH.
Which is why, if one can swing it, 240 VAC is so much better. 120 VAC @ 12A is 1440W; 240 at 12A is 2880W; but that NEMA 14-50 that can do 32A is 32x240 = 7.68 kW, more than enough to warm the battery up and get the car charged.
Home Depot cords tell you the gauge, too. the problem is you have to look for it. Ruggedized means nothing. 10 gauge copper does.
 
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