WARNING: Extension Cords

It's a Duosaida. I've been using it for at least three years.

 

I just came across this YouTube video and thought that a number of people in this forum would find it of interest:

The video is somewhat long, but it does a good job of explaining many of the issues with extension cords and why their wire-size is so important.

One take-away is that because the Prime's OEM charging cable (EVSE) is designed to run on a 15-amp household circuit, if you're using an extension cord rated at 15-amps you're reasonably protected by the 15-amp circuit-breaker when you plug into a 15-amp circuit. But if you plug into a 20-amp circuit, and there is a fault in the charging unit or elsewhere along the length of the cord, don't expect the 20-amp circuit breaker to protect the extension cord from overheating, melting, or igniting something.

Also noted in the video is that 20-amp circuits should have outlets with T-slots but that is not always the case. So you can never be sure whether an ordinary-looking 120-volt outlet is protected by a 15-amp circuit breaker or a 20-amp circuit breaker.

 

Well, you can, once you know what breaker it's on; then you just look. I've usually made it a point right when moving into a place to figure out what circuits all the outlets are on: it's easy to spot them all before furniture is in place, and there might even be some helpers around to watch in different rooms while the breakers are tried.

 

Thank you so much for writing this informative thread.

I’ve been able to locate some 10/3 50 foot extension cord from a local industrial supplier. Unfortunately the website doesn’t say what kind of material it’s made from so I will need to go in and hopefully it lists the materials and it’s pure copper as suggested.

I’m trying to take every single precaution.

The outlet I will be plugging into is 15 amp and contains a GFCI on the breaker. I’m thinking of changing the outlet. The house is only 13 years old but I’d rather start with something fresh. I heard someone mentioning hospital grade outlets. I found one with a GFCI built into it. I know I already have one on the breaker but the redundancy should make things safer, right?

Here’s a link to it:

Anyone know if this is safe for outdoor use?

I also have a box around the receptacle. Only problem is it stays open when a cord is plugged in. Thinking of replacing it with a box I can run the cords from underneath so the box remains close.

Finally, as a precaution I plan on changing the car to 8-amp charging rather than 12. Is this overkill for safety? Given everything I said above, am I pretty safe at 12amps? I figure most of my charging will be done overnight when my car is not in use for
10+ hours.

Any other suggested precautions? I’m hoping this is just temporary and that I will be able to run a 15 amp plugin to the back shed before winter. Also plan on moving in the next 2 years and will definitely be looking for a garage with power running to it.

 

A 10/3 cord probably more than you need for your Prius Prime. A 20-amp outlet usually would be wired with only 12/3 romex so you'd be a whole wire size larger than the house wiring. The 50-foot length is moderately long, but still should not be a worry.

Actually, cascaded GFCI devices are not recommended. They can interact with one another. I don't think this is dangerous, but it can result in many false alarms when one or the other GFCI trips because of their interaction.

The cord itself is OK outdoors for reasonably long periods of time, but eventually the jacket and insulation will break down from exposure to sunlight (ultraviolet) and temperatures. If you don't leave it lying on the lawn 24/7, it will most likely outlast the next 2 years until you move.

If it looks like it's becoming stiff, brittle or cracked, you should take it out of service. But I doubt that will happen unless your conditions are really extreme. Also, be aware of any physical damage like someone driving over the cord with studded snow tires or standing on the cord while wearing hockey skates.

And, I keep reminding people that in addition to electrical safety, extension cords can be a serious tripping hazard, especially if they are laid across a side walk or even a grassy area where people walk.

Yes. The most vulnerable points are the connections at each end. You should protect them from the weather.

I don't think you'd be any better off at the lower charging current. The 10/3 cord will handle 12-amps easily.

The Prime's ability to charge at a lower current is a useful feature if you're plugging it into a circuit shared with other devices that may total over the 15-amp or 20-amp capacity of the circuit. If charging at 12-amps is not tripping your house's circuit breaker, I don't think that cutting back to lower current charging offers any advantage.

If you're planning to move in the next few years, it's probably not worth the effort to install a dedicated exterior outlet on a post near where you park your Prime.

There is a type of romex cable designated UF or UF-B for exterior use. It's outside jacket is made of an ultra-violet resistant plastic. In some jurisdictions it can be buried. Depending upon your local electrical code, it may need to be buried in a conduit at depth sufficient to protect it from things like roto-tillers and garden tools.

You also can run overhead wiring from your house to your garage or to an appropriate pole with an outlet. It depends upon your individual situation and local building official.

I can't speak to your situation in Canada, but in the U.S., there are great differences between what might be considered acceptable at a remote ranch in Montana compared with an urban neighborhood in Los Angeles.

Hope this helps and resolves some of your concerns. It sounds like you're being ultra-cautious and that's not all bad.

 

I've been using a 50' 10/3 copper extension on and off for about 10 years now, with no issues.

 

Outlets installed outside (wet locations) need to use Weather Resistant receptacles (stamped WR). They are made with corrosion resistant materials. You also need a waterproof-while-in-use cover. I found that the "extra deep" cover at home Depot is necessary for stiff cords even though it costs more than 2x as much as the standard depth despite being only slightly deeper.

Do you have a reputable source for this? My understanding is that there is a GFCI inside the EVSE, and in commercial settings extension cords with built in GFCI may be required. And that weird plug on hairdryers is probably a GFCI. So there's plenty of precedent for cascading them. I don't think you need a third one, but I'm not convinced it would cause any issues.

 

One of the electricians who frequent Prius Chat may have a better understanding of this. I've certainly seen GFCI outlets cascaded with no problems. But I've also had to deal with cascaded outlets where a GFCI outlet was installed down-stream of another GFCI outlet which was protecting the circuit. This was in a kitchen setting where there were several outlets installed above a kitchen counter. The first outlet was providing protection but someone had removed the little stickers that are supposed to be adhered to the other outlets and -- probably out of prudence and in good conscience -- one of the ordinary outlets that was already protected was replaced with a GFCI outlet. When loaded with a high-current appliance like a toaster oven, the upstream outlet would trip. Replacing the downstream outlet with an ordinary outlet resolved this problem.

I can think of several reasons why this may have occurred -- including a defective GFCI or other problem not related directly to the circuit. But I mentioned this to a friend who said she saw the same behavior in a bathroom situation which was corrected with the same remedy.

Again, this may all be random and I don't want to turn an "old wives tale" into an "old bear's tale."

 

You'll find plenty of references to that precaution on various electrical web pages. What can happen is that if you test the downstream GFCI or if it trips, the upstream one will interpret that as a ground fault. (Which it actually is.) Then you have to go find the other GFCI. So, besides besides wasting money, you've also made your life a little bit harder. But it is safe and the circuit protection will do its job.

As for plugging in a device like an EVSE into a GFCI outlet, it can be hit or miss but it should work. I have one GFCI outlet that will trip every time I try to use my OEM EVSE in it. But no problems using it on other GFCI circuits.

 

why not get the heavy duty version of it? it's the same price.
https://www.lowes.com/pd/Utilitech-Pro-15-Ft-12-3-SJTW-Yellow-Extension-Cord-w-Indicator/1003051800

 

Same response as the other thread:


The heavy duty and medium duty both have the same item number, same price, and same quantity in stock. So one of them is obsolete and the other is the replacement.

 

I walked by these in the store today, but they didn't specify an amount of duty (or not that I noticed).

 

I've been looking around and it seems US Wire and Cable makes some good quality options. Opinions?
Example:
U.S. WIRE 10 GAUGE EXTENSION CORDS – NIS Tools

 

Rob:
I just got a 2022 Prius Prime LE. I'm using the cord that came with the car and plugging into a 115v GFI outlet. 5 hrs. for a full charge.
I bought this house 3 years ago, and the previous owner had a 2-car lift in one of the bays of the garage. I sold the lift
to a friend of mine, and there is a 220/240V? plug hanging from the ceiling. Since I wasn't using it, I just shut off the 2 breakers at the box that supplied power to it. A few months ago, I bought a 220v Jet table saw which I have yet to set up. I don't think it has a power cord. My question: I want to draw power from the ceiling plug for the table saw AND to charge the Prius at 220v. And I'm gonna need a 50 ft. cord to get to the Prius charge port. I know I'm never gonna use the table saw and charge the car at the same time, but I need to know what to look out for with this potential setup.

 

Rob hasn't visited here in almost two years, so don't expect any answer from him. Though others may chime in.

 

the only concern is the quality and gauge of the cord. you can find the spec online for 50 at the primes charging amperage, buy a quality cord, and check both ends where it's plugged in for heat while charging.

B08RBV5GKW

 

Every foot of the cord is dropping the power available at the end of it. There are plenty of online, reliable and knowledgeable, sources for you to learn everything you need to for this project and what to look out for. Take the time to search them out and you will be better equipped to tackle it safely and be able to recognize when someone actually knows what they are talking about.

 

If you want to do that, the key word is "voltage drop".

 

And a little thing that accompanies that voltage drop, which is where a really significant problem occurs, an increase in amps. Wrong breaker, BIG PROBLEM. That is the reason to learn all you can on this type of project, and this really isn’t the place for that information.

 

Lousy cord = high resistance (either contact resistance or long, small wires) and high resistance always results in lower amp.

That is, unless you have a short, which is generally going to lead to a huge increase in current for a very short time (fraction of a second).