Awaiting delivery of our new Model 3 over the next few days and had a question on home charging. Breaker panel is located on back wall of our garage exactly 20 feet from the garage door. The car won't be able to be parked in the garage regularly so need to charge in the driveway. Is a #4 or #6 "extension cord" about 5 feet long doable? Just looking to be able to have the plug next to the breaker box so we don't have a bunch of drywall work to be done.
NEMA 14-50 Question
- Thread starter billdougy
- Start date
From all the reading I have done on this type of topic here, the general advice is that its "best" not to use an extension cord, since it provides another place where a junction is made and can fail. The advice normally continues that, IF one is going to use an extension cord, you MUST ensure it is one suitable for carrying the load you plan to put on it.
In other words, if you are putting in a 14-50 outlet, you are not going to run down to lowes / home depot / your local big box center, and pick up a cheap extension cord that will be suitable for carrying that connection. You would also need to ensure that the cord is long enough to keep it out of the way, so that no one ever drives over it, trips on it, etc, especially when its under load charging your car.
Its not a great idea in general, to use an extension cord, but would work in a pinch. If you are already paying someone to put in a 14-50 it would not be a great idea to PLAN to have to use an extension cord to make it work. Just have them put the outlet where it needs to be so that you dont have to do the extension cord. If you are doing it yourself, still consider just putting it in the right place to begin with, and plan to hire someone to do the drywall work later. Drywall work isnt that expensive (relatively) here in california, and I am sure it cost less in texas than cali, so much better to do it "right" than PLAN to "jury rig it" right from the start.
In other words, if you are putting in a 14-50 outlet, you are not going to run down to lowes / home depot / your local big box center, and pick up a cheap extension cord that will be suitable for carrying that connection. You would also need to ensure that the cord is long enough to keep it out of the way, so that no one ever drives over it, trips on it, etc, especially when its under load charging your car.
Its not a great idea in general, to use an extension cord, but would work in a pinch. If you are already paying someone to put in a 14-50 it would not be a great idea to PLAN to have to use an extension cord to make it work. Just have them put the outlet where it needs to be so that you dont have to do the extension cord. If you are doing it yourself, still consider just putting it in the right place to begin with, and plan to hire someone to do the drywall work later. Drywall work isnt that expensive (relatively) here in california, and I am sure it cost less in texas than cali, so much better to do it "right" than PLAN to "jury rig it" right from the start.
An extension cord is an extra set of contacts to wear and overheat, and something to trip over and damage; I don’t think it’s a great choice for a long term solution.
Having said that, high amperage 14-50 extension cords are readily available because of the RV industry, and the car will charge on one just fine if all the connections are tight and the wires are big enough. A thirty foot version is a part of my road trip supplies for contingencies, though it very rarely gets used.
Having said that, high amperage 14-50 extension cords are readily available because of the RV industry, and the car will charge on one just fine if all the connections are tight and the wires are big enough. A thirty foot version is a part of my road trip supplies for contingencies, though it very rarely gets used.
You could also use EMT conduit (or possibly flex depending on local code) surface mounted instead of running the wires inside the wall. Better looking and safer than an extension cord.
I didn't think about this at all... that is a great idea... the biggest issue I was running in to was our walls are spray foamed interior and exterior in the garage and it was going to not be all that fun. I think the conduit idea is awesome.
Nobody seems to like extension cords and there are good reasons for that as listed above, this is especially true if it runs outside.
That not withstanding, a five foot rubberized piece of #10-3 will charge at 32amps without much or any loss, and little to no heat. I have a similar situation at a seasonal home and have encountered no problems with a six ft cord as described. BUT it does not run outside.
The NEC wire gauge ampacity ratings are based on 100ft runs and if you do the math, a five ft piece of #10 is not going to produce much if any resistance under a 240v 32 amp load, but there are other factors such as plug screw connections that can fail and get hot so I used a NEMA 50 amp plugs and outlets that can configure to a 30 amp form as well for flexibility in case they got too hot, but so far it has worked for when I am there.
It's a cheap solution to build one and try if you are so inclined but you need to monitor it for the first few times. As permanent solution probably not too good.
That not withstanding, a five foot rubberized piece of #10-3 will charge at 32amps without much or any loss, and little to no heat. I have a similar situation at a seasonal home and have encountered no problems with a six ft cord as described. BUT it does not run outside.
The NEC wire gauge ampacity ratings are based on 100ft runs and if you do the math, a five ft piece of #10 is not going to produce much if any resistance under a 240v 32 amp load, but there are other factors such as plug screw connections that can fail and get hot so I used a NEMA 50 amp plugs and outlets that can configure to a 30 amp form as well for flexibility in case they got too hot, but so far it has worked for when I am there.
It's a cheap solution to build one and try if you are so inclined but you need to monitor it for the first few times. As permanent solution probably not too good.
gavine
Petrol Head turned EV Enthusiast
If you use conduit, I believe you are not allowed (per code) to use romex/nm-b because of heat build-up. You need to run individual wires when in conduit. Maybe someone with more expertise can chime-in and clarify?
Correct, conduit (unless used in a small area for physical protection) requires THHN or such.
XLR82XS
D M C
I have run this extension cord long-term with ZERO issues:
https://www.amazon.com/gp/product/B0024ECIP0/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
No heat, no problems, charging everyday. Especially ia a hot south Florida garage.
The 14-50 extension cords are really heavy since they have four conductors. They could be lighter since you only need three.
There are some tesla specific 14-50 extensions that are lighter. I've also considered 6-50 extension cords because they are cheap, lighter and readily available. Tesla has a 6-50 plug for the UMC.
You can also consider 6-20. There are easy and lightweight extensions for 6-20, and a 6-20 plug for the UMC. I daily charge using a 6-20 outlet because my breaker panel could only support one 14-50 and one 6-20. 6-20 is fast enough to charge overnight. About 15 mph.
There are some tesla specific 14-50 extensions that are lighter. I've also considered 6-50 extension cords because they are cheap, lighter and readily available. Tesla has a 6-50 plug for the UMC.
You can also consider 6-20. There are easy and lightweight extensions for 6-20, and a 6-20 plug for the UMC. I daily charge using a 6-20 outlet because my breaker panel could only support one 14-50 and one 6-20. 6-20 is fast enough to charge overnight. About 15 mph.
Uh, no. 10AWG maxes out at a 30A circuit. Please don't use it for higher. You need 8AWG minimum for a 40A circuit.
This is a common misconception. The issue is that Romex is not allowed exposed in "wet" or "outdoor" locations, which garages are considered, even if it's in conduit. It's perfectly fine to put Romex in conduit in your basement or in a wall, for example, but anyone going to the trouble of putting in conduit will most likely pull wires through it, which happens to give a higher ampacity for the same wire gauge and lets you put more wires in the conduit. The conduit fill calculations for Romex in conduit mean that you really can't put much Romex in there compared to THHN/THWN.
In the real world, I doubt it would make a difference to have Romex in a properly sized conduit. The prohibition as I understand it isn't due to fire concerns but humidity/moisture fouling the paper liner inside the cable, and the fact that the outside insulation isn't waterproof, which could lead to mold growth inside the cable that causes the insulation on the individual wires to decay.
That depends if you are talking about NEC Electrical code or the OP's reality in this particular situation, as I explained. At five feet it works fine, at 100 feet as the NEC code and code calculations are based on, 10 is a definite no-no because the resistance of the wire is increased by a factor of 20 for a 5ft vs a 100ft. run. For shorter distances wire gauges can be decreased. It is simple science and ohms law, and it is not speculation, it is done safely in many applications. When we talk about electrical code it becomes very confusing for questions like this unless both NEC code, real science, and the individuals specific situation are put within proper context. He is talking about an extension cord after all...
I'm mostly a "hobbyist" level electrician but as I understand these things the "OP's reality in this situation" is subjective at best. It may work at 5 feet but I wouldn't bet my house on it. Similarly, I think the NEC has a lot of wiggle room built in to its ampacity ratings, but I'd spend the extra money to size up the cord and be safe. An EV charging circuit is one of the highest-power circuits in the house. But nowhere can I find evidence that 10AWG is suitable for a sustained draw of >30A.
Can you please walk me through your calculations demonstrating it is safe to draw 32A sustained on a 10AWG wire?
qingshan
18 lr rwd fsd
I bought a 50amp 10 footer for trips, so far I've only used it for 30 amps, very little heat build up.
At home I put the 14-50 next to the garage door - being in agreement that an extension at home is a bubblegum and clotheshanger kinda solution
At home I put the 14-50 next to the garage door - being in agreement that an extension at home is a bubblegum and clotheshanger kinda solution
I am not in total disagreement understand that. The info you seek is on the NEC spec pages in many places. You have to look at resistance per foot. And you won't find that #10 is good for a 50 amp run in most any literature because the standard is the assumption that the length is 100ft. But look in technical manuals and other electronics publications, or ask any first year EE student - 100 feet of copper is going to have 20 times more resistance that 5 feet and that is very significant. It makes no difference what someone reads or learns in electrician school, It will work and it will work with virtually zero heat at five feet. Have you considered the size of the wire in the Tesla mobile charger plugs or charging wand? It is not #10 it is likely #12 based on the rubberized size, and the wand cable was additional wires in it. They do this safely because of the short length.
Nothing wrong with your suggestion either, that he step down or use a fatter cable. I am a DIYer and I try to be clear about that.
Dangerous thinking by SilverString. Please do not use use extensions cords for charging, especially ones that are undersized and can burn your house down.
Ha ha I have always been a dangerous thinker, but at least I think. Extension cords are fine for occasional and/or emergency use, certainly not as a permanent solution. I do realize all electricians hate this talk about ohms law and wire length but no one ever refutes it in any way other than quoting back code. Code is meant to cover a broad range of circumstances, whereas this is a very specific conversation if you read the entire thread. If someone want to refute the math or Ohms Law or the electrical properties of copper #10 I would like to hear it.
Yeah, there are two factors at work. Voltage drop (dependent on length) and heat dissipation (not dependent on length for any nontrivial wire section). 10 Gauge copper has a resistance of 0.995 mOhm per foot. At 40 amps with round trip, that means 0.08V drop per foot of length, not a big deal for short runs. However, heat produced is 3.2W per foot of wire pair, 1.6W for each conductor per foot. Extension cords are able to be down sized due to being in free air which assists with keeping it cool (versus conduit or insulated wall). If the cord is constrained, covered, stacked in a coil, or run through walls, that margin is lost.
https://www.anixter.com/en_us/resources/literature/wire-wisdom/wire-and-cable-ampacity-ratings.html
FWIW, 10 gauge is rated for 55 Amps internal to an appliance: American Wire Gauge Chart and AWG Electrical Current Load Limits table with ampacities, wire sizes, skin depth frequencies and wire breaking strength
A big down side to using a UMC with an extension cord is that the thermal sensor in the UMC plug will not protect against overheating at the cord to outlet connection.
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