Is a 30' 14-50 extension cord really long enough?

NM-B cable (Romex) is *very* stiff at AWG 6... I wouldn't use it for an extension, mainly because of the stiffness of the cable and because over time, bending it back and forth can weaken the thicker strands.

My preference is that 6/4 is used and that neutrals are properly wired, or you use 6/3 and make a 14-50P to 6-50R extension, and use the 6-50 adapter with the UMC. This is because of the danger of using that cord with an RV if someone else grabs it. If you insist, use 6/3 cable with 14-50 to 14-50, but label the cable well with "Tesla charging ONLY! Do not use on RV!".

Here is a length of 30' 6/4 SOOW, to make a proper 14-50 extension cord, $99
30 SOOW 6 4 Cable Portable Indoor Outdoor Wire USA | eBay

here is a general search, there is also 6-3 as well, just change the search...
6-4 SOOW | eBay

Might you consider a Hobart p/n 77064 14-50P to 6-50R adapter along with either a Coleman p/n 1917 8/3 6-50 STW or a CyberWeld 25 or 50' 8/3? This combo has all factory machine assembled molded ends with a nice durable STW jacket and is smaller than the bulky 6/3 or 6/4 at the small expense of pulling a few less amps.

linkster said:

Might you consider a Hobart p/n 77064 14-50P to 6-50R adapter along with either a Coleman p/n 1917 8/3 6-50 STW or a CyberWeld 25 or 50' 8/3? This combo has all factory machine assembled molded ends with a nice durable STW jacket and is smaller than the bulky 6/3 or 6/4 at the small expense of pulling a few less amps.

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At 0-50 feet, 8 AWG is only rated for 40A (UL standards for STO, STOW, and SOOW cable). Not a good idea to put 50A plugs and receptacles on it without some type of over-current protection built in. There's a big difference between a welder, typically operating at less than 10% duty cycle, and a continuous load that will be offered by the Tesla. (There is an exception, where a welder is used to power a Xenon lamphouse for a film projector, but that's one of my frankenstein projects. )

Keep in mind that while the Tesla will memorize your charging current at a given location, it isn't fool-proof. Over the past 16 months, my garage has been detected as 3 different GPS addresses, and each time it detected a new one, Model S defaulted to the maximum current supplied from the pilot current. Also, during one of the v4.x updates, the charging current reset to the maximum as well.

As a result, you're better off carrying the AWG 6 cord, IMO.

If you can find it, you'd be better off with SEOOW cable (note the 'E'). It's rated for more amps and has the same temperature rating as EVE cable which is made specifically for EV charging applications (105C).

mitch672 said:

Here is a length of 30' 6/4 SOOW, to make a proper 14-50 extension cord, $99
30 SOOW 6 4 Cable Portable Indoor Outdoor Wire USA | eBay

here is a general search, there is also 6-3 as well, just change the search...
6-4 SOOW | eBay

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hcsharp said:

If you can find it, you'd be better off with SEOOW cable (note the 'E'). It's rated for more amps and has the same temperature rating as EVE cable which is made specifically for EV charging applications (105C).

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it's on eBay, it's very expensive, here is a 100 foot length of 6/4 SEOOW cable, $355
I don't think it's worth the additional money, but that's each persons decision

100 Seoow 6 4 600V Indoor Outdoor Portable Power Cable | eBay

Here is 100 feet of 6/3 SEOOW for $315
100 Seoow 6 3 600V Indoor Outdoor Portable Power Cable | eBay

landover said:

I did get ahold of my friend that works at the wire company. She can sell the 6/3 to me for 3.01 per foot. A little less then ebay. If anyone needs any of this let me know and I will see what shipping would be.

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You can buy 6/3 SEOOW for $2.65/ft here.
And 6/4 (better so you can safely use it for other 14-50 applications) is only 3.25/ft.

Here's another option for 40 amp charging. This cable is the same stuff used in the UMC, however it has more control wires.

If you're making a "dumb" extension cord, you don't care about the control wires.

This does not meet any codes, just like the Tesla UMC (you have to double up parallel conductors):

Quick Charge Power

You know, it depends on whether this is a temporary travel solution or an in-place extension cord for your usual overnight charging. If the latter, go for the suggested thick-wire solutions.

But if it is for visiting relatives occasionally and tapping into their laundry room, consider the following. The general considerations concerning extension cords are heat loss and safety, if we ignore the absolutism of Tesla's lawyers. The hazard is from a junction that overheats, not from long wire overheating. You can get by on thinner wire if the series voltage drop (=IR) does not take you below the cutoff (don't know the 220 specs but for ordinary outlets 105 volts is the bottom, below which the charger may disconnect during the night).

Yes, you charge a little slower and you do waste some energy via heat loss. If this is a temporary situation, you may be able to rationalize this.

But the strong cautions about using extension cords are mostly misplaced for temporary situations. The heat hazard is from junctions, not length, and is mostly from overused outlets with insecure connections that spark and scar. For dryer outlets, that problem is unlikely; for RV parks, beware.

wcalvin said:

But the strong cautions about using extension cords are mostly misplaced for temporary situations. The heat hazard is from junctions, not length, and is mostly from overused outlets with insecure connections that spark and scar. For dryer outlets, that problem is unlikely; for RV parks, beware.

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You wouldn't normally need an extension cord at an RV park because the oulets are right by your parking space--at least they have been in all the RV parks I've been to. RV parks sometimes have poor power but typically the UMC will turn red in a very short time (15 minutes or less). You then move to another space.

wcalvin said:

But the strong cautions about using extension cords are mostly misplaced for temporary situations. The heat hazard is from junctions, not length, and is mostly from overused outlets with insecure connections that spark and scar. For dryer outlets, that problem is unlikely; for RV parks, beware.

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I disagree, and your host's homeowners' insurance is likely to disagree as well. While you are right in that more problems come from junctions, heat is a big concern when you're talking about hours of continuous load charging. Just because it works, doesn't mean it's safe.

FYI, found that Amazon Prime has 6-3 SEOOW, which is the 105 degree C insulation (better for EV charging), they have 25' lengths in stock for $80 (free 2 day shipping)
Amazon.com: Coleman Cable 096030008 SEOOW SEOPRENE, 6/3, 25-Foot: Home Improvement

FlasherZ said:

My preference is that 6/4 is used and that neutrals are properly wired, or you use 6/3 and make a 14-50P to 6-50R extension, and use the 6-50 adapter with the UMC. This is because of the danger of using that cord with an RV if someone else grabs it. If you insist, use 6/3 cable with 14-50 to 14-50, but label the cable well with "Tesla charging ONLY! Do not use on RV!".

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I want to bring this up again. I would buy a 3 prong connector (6-50, or 10-30) to use with 3 connector cable. It makes it much safer, and harder to misuse.

I have a female NEMA 10-30 on my 6/3 SOOW cable. and a male 30A twist lock (I forget the number designation) on the other end. I then have two 'adapter' pig tails with large labels on them. One that goes to 14-50, and one that goes to 10-30.

Having a straight extension cord with the 'same' style pug on both ends is a lot easier to use improperly than obvious pig tail adapters. But making sure people can't plug into your cord with both neutral and ground is a very good idea, that is worth more than the $45 6-50 adapter you would need.