We recently got an EV, and would like to connect it to a standard outdoor 110V outlet for level 1 overnight charging. It seems like many EV manufacturers and chargers recommend against using an extension cord, but I’m not sure why…
Is it safe enough if we just oversize the extension cord, opting for something like a heavy-duty 10 or 12 AWG cord? Does it need to have its own GFCI?
Or is there something more to it that makes EV charging, as opposed to any other load, more dangerous with an extension cord? Is there anything electrically different between a properly-sized extension cord vs a charger with a longer built-in cable?
That’s what I figured, but I’m also not an electrician so thought I should make sure before trying
So theoretically, if I get a properly-sized and UL-listed and outdoor-safe cord and prevent water intrusion, it should be the same? No different from a longer built-in charging cable? It’s just bundles of copper inside a sheathe…?
Speaking as someone who does Level 1 charging, but has no professional or amateur experience in the field, I do wonder if using the extension cord would prevent the charger from properly working with the on-board systems.
Apparently there’s a good bit of anecdotal examples that they don’t properly confirm there’s a connection - so scheduled charging doesn’t happen (on or off). I (again, non professional) doubt that there would be a electrical/fire risk from using an over-rated cord, but the charging may not be optimal/efficive.
Extension cords are common in some areas fo Canada for block heaters and interior heaters, which would have the same draw - basically as much as the outlet will handle, up to a 1200W interior warmer. No guarantee in a cold snap these aren’t on for hours at a time. Same goes for other heaters You just need to be sure they are heavy-duty cables. For charging, I don’t imagine there is much voltage loss in a heavy-duty power cord _ i’ve never felt one get warm to the touch. .
But even if you buy an extension cord with the “right” gauge of wire, you still have to contend with the pitiful quality of the receptacle. It’s a molded assembly put together by a machine, and the innards are not the same quality as a regular wall receptacle. As a result, the contact resistance can increase over time, resulting in excessive heating (and even arcing) at the plug-receptacle interface when used with a heavy load.
The best and safest extension cords utilizes a box that contains one or two duplex outlets. (The latter is often called a “quad box.”) These are hand-built and not cheap. This and this are what I’m talking about.
I’ve done it before, and you should be able to do it safely. I’ve even used an extension cord while level 2 charging.
The main thing is to get a cord that can handle 12 amps of continuous current, so a cord rated for 15 amps. Most extension cords are only rated for 12 amps (10 amps continuous). Expect to pay more.
The car charger (EVSE) should have a GFCI built in, so adding one to the extension cord is redundant. The EVSE should also be monitoring the temperature of the plug, so if it is arcing to the extension cord, it should turn off.
I’d be more concerned about the outlet the extension cord plugs into, if it is someplace out of the way and easy to overlook. The cord can get pulled and bent. It’s worth putting in some strain relief for the plug, even if that’s just a few loops of cord on the ground.
All of that is assuming that your EVSE is well designed and safe. If it’s some random thing you found on Amazon, then it might not be much more complex than a few resistors and LEDs. My Mom has one that pulls 15 amps from a 15 amp outlet. Fortunately it is plugged into a 20 amp outlet.
Also, if I remember my Ohm’s law right, you will experience some voltage drop across the extension cord, so use the shortest one practical for your needs.
I’ve changed the ends of high quality extension cords with good quality plugs and sockets (or in some cases a waterproof junction box to make a quad box). Usually to customize length rather than concern about the quality of the molded connectors. Extension cords are a good source of SO/SOOW wire, much cheaper than buying it by the foot.
Yea, if you’re the least bit handy, you can build your own extension cord that will be better and safer that anything you can buy. Just buy some SOW cable, hospital-grade plug, two hospital-grade duplex receptacles, quad box, cable clamp, and strain relief. The only drawback when compared to “molded” receptacles is that it’s not waterproof, so I wouldn’t use it outdoors if there’s a risk of rain.
Short term: Use a quality extension cord rated for 15 amps, prevent water intrusion, and you’ll be fine. I would not say this should be your long term plan if it’s avoidable.
I used a quality extension cord connected to a 240V 20a NEMA 6-60P outlet outside my house over the past winter in order to charge my EV at around 4KW.
It’s important to note that charging is less efficient the lower the charge rate you have, because there is a residual drain for powering the car’s electronics as well as the batteries needing to be above or below a certain temp.
On 1.2KW, which is the max a standard 120v outdoor outlet is likely to provide, you may be using as much as 50% of the charger (600W) keeping batteries warm in winter, or the battery cooling fan running in the summer. It will increase the time required to charge the car, and reduce the cost efficiency of using an EV.
On 4KW, which is what I got with my 240v 20amp setup, that same 600W load is only ~15% of the charging capacity, meaning I am getting much more charge per dollar spent on electricity.
PS Once the ground was soft enough, I trenched to my garage and had an electrician install a 240v 50 amp service so I could use a full 11KW charger and keep the car in the garage.
So apparently the reason it’s so hard to find longer charging cords is that they’re not actually code-legal… the NEC limits their max length to 25 ft: Article 625 |
Article 625.10 Electric Vehicle Coupler
Part C, Section 3.3:
Overall Cord and Cable Length. The overall usable length shall not exceed 7.5 m (25 ft) unless equipped with a cable management system that is part of the listed electric vehi‐ cle supply equipment.
Not Fastened in Place. Where the electric vehicle supply equipment or charging system is not fastened in place, the cord-exposed usable length shall be measured from the face of the attachment plug to the face of the electric vehicle connec‐ tor.
Fastened in Place. Where the electric vehicle supply equipment or charging system is fastened in place, the usable length of the output cable shall be measured from the cable exit of the electric vehicle supply equipment or charging system to the face of the electric vehicle connector.
Well, I guess extension cord is the way to go, then… no telling if the longer chargers you can find online are safe and real =/ (I think longer lengths are legal in Europe and you can find some ETL listed ones, but I don’t really trust the random Amazon listings…)
Is there a reliable source for “hospital grade” electrical stuff? I don’t necessarily want to build my own cable, both out of laziness and because it would be a huge hassle to explain to insurance, etc. if anything ever happened…
It’s a 25’ 12/3 SJTW 15A cord rated for 1875W (unclear if peak or continuous). I’ll set the EV to only pull 8A (on a 15A circuit reserved for the garage). At under a kilowatt, I think that should be enough of a safety buffer.
I also found a GFCI outlet in the garage, and we’ll use that instead, so most of the assembly will be indoors and out of the weather. Only the end of the charging cable and the J1772 connector will be outdoors while charging (because the car is in the driveway).
It feels a bit overkill — we take less precautions for space heaters and electric cooktops that draw more power — but better safe than sorry, I suppose.
Long-term, if she keeps the vehicle (it’s currently leased), we’ll definitely look into getting a hardwired and properly installed level 2 charger if we can. For now, though, this will hopefully suffice…
Just to add a bit: use the shortest cord that works for you (but not so short that causes problems like having to stretch out at an angle or dangle in space). Also, if there is extra cable, try to spread it out a bit instead of leaving it in a pile, where it could build up heat. Aside from that, just get something high quality and you should be fine.
Reducing to 8 A seems like overkill, though if the outlet is questionable I might reduce to 10. 12 A is the rated max (80% of 15 A).
Ideally I’d like something 10’ to 15’, but where is a reliable place to buy this stuff? Amazon is full of fake products, and so is our local Home Depot (I’ve had to return several items that were not what the box said… people apparently have been buying things and returning other things in their boxes… sigh). Our local ACE doesn’t have anything with a big enough gauge, and they’re all 25’+ anyway.
So I’m left with electrical supply stores, of which Platt is the only one I know of in the area. They also don’t sell shorter cables at this gauge or bigger. Maybe there’s not enough demand for it…?
I sadly don’t have that option, at least not from the car It goes from 8A to 15A to “MAX”. If I set it to 15A, maybe the charger itself will only pull 12A (that’s what it’s rated for), but it isn’t explicit about that…
Given that she doesn’t drive more than 5 mi or so on an average day, even this pitiful rate should be able to charge that back up overnight… I think. 8A * 120V * 0.8 (assuming some losses along the way) ~= 768 W. At the car’s rated 320 Wh/mi, it should only take, eh, a couple hours even at that rate…? I think the car will slow down charging once it gets near 100%, but we plan to limit to 80% charge anyway. We’ll see…
I don’t really have a solution for the fake products, unfortunately. Mostly I’ve had good luck at Amazon, but there is a risk. A 10 AWG should feel noticeably heavier than one of thinner gauge, and certainly have a thick cord, but it’s impossible to be sure of this stuff without disassembling the cord.
Sometimes you can get an idea from the negative reviews. Positive reviews are useless, and there will always be some negative reviews, but if they’re all some variant of “it shipped late”, “the box was damaged”, or “I’m too stupid to use this product”, it’s at least a reasonable sign.
Interesting that your car doesn’t have intermediate current limits. But yeah, 8 A will be fine for 5 mi/day. I don’t think there will be any noticeable slowdown when it hits 100%. The car needs the taper for L3 and to some extent L2 charging, but not for half-L1.
Couldn’t you tell a lot just by weighing it? I mean, yeah, the insulation adds some weight, too, but the weight will mostly be the copper, and there’s some minimum weight that 25’ of 10 AWG copper will have. And I doubt most fakes will go so far as to stick some other metal in there to artificially weight it.
You certainly could, but I think most people could just do it by feel. There’s 60% more copper in 10 AWG than 12 AWG, and 170% more than in 14 AWG. The insulation weighs almost nothing in comparison.
Anyway, there should be about 1 kg of copper in there. 0.36 kg per 10 AWG conductor, and maybe another 0.36 kg for the ground, but more likely they skimped on that (say to 12 AWG) since it doesn’t have the same requirements. So probably a tad under 1 kg total. Plus the other stuff.
I bought one of these a while back due to people “ice-ing” electric charging stations and also some of them have cords too short to reach the back of my vehicle (in a front-in angled parking spot). It works.
Huh, that’s a good idea… didn’t think about that. So it extends the J1772 end instead of the household plug end? Interesting, thanks for the suggestion. I’ll see if anything similar can be found nearby.
It goes from 8A to 15A to “MAX”. If I set it to 15A, maybe the charger itself will only pull 12A (that’s what it’s rated for), but it isn’t explicit about that…