How to build a 30 Amp Extension Cord for 24 A, 240 V charging

[GSP]

I plan to make a 30A extension cord for temporary charging at vacation rentals. I most likely will go with 50 foot length, but I may need 75 or 100 feet. On one end I will use an L6-30P, and I will make adapters for the various 30 and 50 Amp outlets to an L6-30R. On the other end I will use a 14-30R. I am counting on getting a 14-30 UMC adapter from Tesla so that I can be assured that charging will always be limited to 24 Amps (Max for a 30 A circuit).

Reading an ampacity chart I found on the Internet, it looks like 10/3 SOOW cable is rated for 30 Amps for up to 50 foot lengths. I think this cable has three 10 gauge conductors, for the two hots and a ground.

I am looking for advice on the type of cable to buy, and the overall setup. Is the 30 A cable rating for the circuit breaker, and therefore this is the correct size for 24 A continuous loads? Is there a better/lighter/less expensive cable that I could use, perhaps with a smaller ground wire?

For people who have done this already, is 50' long enough for most places you have visited? If you need more that 50' is it necessary to step up to heavier, more expensive 8/3 cable?

Thanks,

GSP

 

[linkster]

I find myself rarely using my medium duty self-limiting charging kit #2 (L6-30 10ga) these days for two reasons, The first is, my QCP stretched 50' UMC usually reaches most friends/relatives dryer outlets and the second reason is that I like my lightweight kit #1 which uses a much lighter 12ga. extension cord that safely self-limits to 16A@240v. I purchase ready made L6-30 extension cords with machine crimped, molded ends on Amazon in various lengths. If i find that my car is upset with the voltage drop (due to many variables) I just reduce the amps a bit. I tend to plan a bit excessive, so I may carry a 100' extension on certain occasions.

It can be dangerous to use extension cords for charging which is why it is always best to follow Tesla's guidelines to never use them.

 

[GSP]

Linkster,

Thanks for the info. I like the idea of getting the UMC stretch better than using extension cords.

For occasions where the 50' UMC do you have more info on your lightweight kit #1 that you would share? Does it use L6-30 connectors with 12 gauge, or did you mean L6-20?

I already have a 12 gauge 100' extension cord that I have used with my Volt for 120 V charging. Could it be repurposed as a 240 V cord if the insulation rating is over 250 V?

Thanks again,

GSP

 

[linkster]

I purchased both EVSEadapters.com 10-30P->L6-30R and 14-XXP->L6-30R adapters. I cut off the L6-30R ends and re-wired both with 5-20Rs@240V by using L1, L2, + grnd. Both of these adapters are well labeled "WARNING 240V" and "TESLA CHARGING ONLY" with red electrical tape. Both QCP and EVSE will custom make these adapters for you including a 6-20P->5-20R@240V. I use an unmodified 5-20 terminated 12ga. 50' extension (Amazon) or an unmodified 5-20 terminated 10ga. 100' (Home Depot) with a Tesla UMC 5-20 adapter that self-limits to 16A@240 for 11-12 mph charge rate. I also use both of these off-the-self extension cords for charging on microwave and washing machine 20A 120V circuits for ~5mph charge rate if I have verified they are wired to properly carry a 20A load. I always check all connections at 15min, 30min, and 2hrs for excessive heat after charging starts to help insure a safe charging session and I learned (from @Cottonwood) to always spread out the extension cords and never leave them tightly coiled which can trap heat.

 

[GSP]

Thanks for the additional info. It is very helpful.

Based on your experience, I probably will not bother making a kit for 24 Amp charging, and go with a 16 Amp setup instead. Thanks for the details on your 16 Amp kit. I already have the 5-20 UMC adapter. I will get the newly re-released 14-30 UMC adapter anyway, even if I don't make an extension cord for it.

In case I do go ahead with a kit for 24 Amp charging, using L6-30 connectors and 10 gauge SOOW cable, is 50 feet the max length? What is the length of your "medium duty self-limiting charging kit #2?"

One final question. By "self-limiting" are you referring to the UMC pilot signal that is triggered by the 5-20 and 14-30 UMC adapters, or something else?

Thanks for your help,

GSP

 

[linkster]

Kit #2 consists of (2) 25' L6-30 unmodified extensions along with (1) 15' L6-30 extension with a 10-30R.

WRT to self-limiting, the car does not require the owner to manually reduce the amperage draw to a safe level.

 

[Rocky_H]

Reading an ampacity chart I found on the Internet, it looks like 10/3 SOOW cable is rated for 30 Amps for up to 50 foot lengths. I think this cable has three 10 gauge conductors, for the two hots and a ground.
GSP

By the way, here's a clarification on cable naming that I learned about from my electrician friend when I was getting my outlet installed. When they use that naming, like 10/3 or 6/3, that is telling how many of the thick wires are in it, but there is also an extra bare thin ground wire in the cable as well. So for a real 14-50 or 14-30 install, it needs Hot1, Hot2, Neutral, and Ground. That's three conductors plus ground, so you would use 10/3 or 6/3 or whatever.

Sorry it seems like a long setup, but here's the point. If you are making an extension cable that just needs to carry 240V for Tesla charging, you only need 2 conductors plus ground, so you can use 10/2 cable for that. You just don't connect the Neutral. That saves weight and makes it more flexible. Obviously this is not "correct" for actual things that are supposed to have a neutral, like a real 14-30 outlet, but for Tesla charging, it works fine. Just label the cord that it's for Tesla charging only.

 

[jbwinton]

By the way, here's a clarification on cable naming that I learned about from my electrician friend when I was getting my outlet installed. When they use that naming, like 10/3 or 6/3, that is telling how many of the thick wires are in it, but there is also an extra bare thin ground wire in the cable as well. So for a real 14-50 or 14-30 install, it needs Hot1, Hot2, Neutral, and Ground. That's three conductors plus ground, so you would use 10/3 or 6/3 or whatever.

Sorry it seems like a long setup, but here's the point. If you are making an extension cable that just needs to carry 240V for Tesla charging, you only need 2 conductors plus ground, so you can use 10/2 cable for that. You just don't connect the Neutral. That saves weight and makes it more flexible. Obviously this is not "correct" for actual things that are supposed to have a neutral, like a real 14-30 outlet, but for Tesla charging, it works fine. Just label the cord that it's for Tesla charging only.

very helpful info BUT I'M GETTING CONFLICTING answers:
1. tesla says the car will adjust to amperage/voltage supplied . some owners have said "be sure to dial down the setting on the car" if using 30amp extension cord

2. i'm rigging a 100' cord for EMERGENCY use. the 240v tesla male plug is 4 pins. you say "don't need neutral" just use 3 wires. are you sure? so 2 wires + ground is enough? i have a 3 wire outlet available and would rather run 8/3 for the 100' than 8/4 . actaully 10/3 would be even better (lighter) and if the car charged slower that would be fine. DOES THE TESLA AUTO ADJ. to what the cord and power supplied can handle???

 

[TexasEV]

How many threads are you going to ask some version of this question in? Tesla sets the amps based on which UMC adapter is being used. If you use extension cords with homemade adapters it does NOT adjust for the supply and will be dangerous. Especially when you don’t understand what you’re doing, as seems to be the case here.

 

[Rocky_H]

very helpful info BUT I'M GETTING CONFLICTING answers:
1. tesla says the car will adjust to amperage/voltage supplied . some owners have said "be sure to dial down the setting on the car" if using 30amp extension cord

No, you're not getting conflicting answers. Perhaps they just need a little more explaining. A piece of charging supply equipment will send an official informational signal telling the car how many amps are available. So when you go to a public charging station, and put the handle into your car, the station is sending a signal to negotiate with the car to say, "I have 60A available". And the car says, "OK, I can only use 40A, so send me 40A." Or the station says, "I have 20A available.", and the car says, "Yes, I can take all of that; send 20A."

That is the auto adjusting Tesla is talking about. You don't need to mess with anything IF AND ONLY IF you're letting it all work officially. A wall outlet, though, doesn't have that signal, so the Tesla mobile charging cable (UMC) creates that signal. It does that by using the different adapters that snap onto the end. So if you snap the 5-15 adapter onto it, the UMC will create the signal to say, "I have 12A available." Or if you snap the 14-50 adapter on there, it will say, "I have 40A available."

The thing that makes you manually need to adjust something is that by using another third party pigtail adapter, you're basically giving wrong information to the UMC about what it is plugged into. The 14-50 Tesla piece is attached, so it's going to signal for a 50A outlet type, but you're using an unofficial thing to make it fit into a 30A outlet type. You need to correct for the mismatched information.

2. i'm rigging a 100' cord for EMERGENCY use. the 240v tesla male plug is 4 pins. you say "don't need neutral" just use 3 wires. are you sure? so 2 wires + ground is enough?

Yes, I am absolutely sure. You just need the Hot1, Hot2, and ground. The neutral isn't used and is actually just a dummy pin that's not connected in the Tesla adapters. The car will detect and figure out on its own whether there is 120V or 240V on those two hot lines.

i have a 3 wire outlet available and would rather run 8/3 for the 100' than 8/4

Those would be called 8/2 and 8/3, by the way, since they don't count the thin ground wire in the naming.

actaully 10/3 would be even better (lighter) and if the car charged slower that would be fine. DOES THE TESLA AUTO ADJ. to what the cord and power supplied can handle???

The car does not officially auto adjust based on wire size. It can't specifically detect that, unless it's really wrong and too thin and causes bad voltage drop. That is a safety feature it has. I looked it up, and 10 gauge is OK for up to the 30A level, so that would be OK for 30A circuits, like this L6-30 or dryer outlets like 10-30 or 14-30. But don't use it for anything more than 30. That's why people sometimes go for the thicker ones like at EVSEAdapters, because they can handle for 50A or lower circuits, so there's more flexibility of use cases. Please do check a little on ampacity charts for wire gauge.

 

[brkaus]

@jbwinton If you want it to auto-adjust, be sure to use a 30a outlet on the Tesla side of your extension and the matching 30a plug from the tesla.com store. Then it will "auto-adjust" (limit to 24a)

Voltage drop over 100ft of single 10ga at 240v/24a is

Voltage drop: 4.79
Voltage drop percentage: 2.00%
Voltage at the end: 235.21

And yes, why so may postings? It's a bit annoying.

 

[jbwinton]

@jbwinton If you want it to auto-adjust, be sure to use a 30a outlet on the Tesla side of your extension and the matching 30a plug from the tesla.com store. Then it will "auto-adjust" (limit to 24a)

Voltage drop over 100ft of single 10ga at 240v/24a is

Voltage drop: 4.79
Voltage drop percentage: 2.00%
Voltage at the end: 235.21

And yes, why so may postings? It's a bit annoying.

thanks for your help on this. sorry if too many postings. i'm new at this and didn't know the heck i was doing!

 

[jbwinton]

No, you're not getting conflicting answers. Perhaps they just need a little more explaining. A piece of charging supply equipment will send an official informational signal telling the car how many amps are available. So when you go to a public charging station, and put the handle into your car, the station is sending a signal to negotiate with the car to say, "I have 60A available". And the car says, "OK, I can only use 40A, so send me 40A." Or the station says, "I have 20A available.", and the car says, "Yes, I can take all of that; send 20A."

That is the auto adjusting Tesla is talking about. You don't need to mess with anything IF AND ONLY IF you're letting it all work officially. A wall outlet, though, doesn't have that signal, so the Tesla mobile charging cable (UMC) creates that signal. It does that by using the different adapters that snap onto the end. So if you snap the 5-15 adapter onto it, the UMC will create the signal to say, "I have 12A available." Or if you snap the 14-50 adapter on there, it will say, "I have 40A available."

The thing that makes you manually need to adjust something is that by using another third party pigtail adapter, you're basically giving wrong information to the UMC about what it is plugged into. The 14-50 Tesla piece is attached, so it's going to signal for a 50A outlet type, but you're using an unofficial thing to make it fit into a 30A outlet type. You need to correct for the mismatched information.


Yes, I am absolutely sure. You just need the Hot1, Hot2, and ground. The neutral isn't used and is actually just a dummy pin that's not connected in the Tesla adapters. The car will detect and figure out on its own whether there is 120V or 240V on those two hot lines.


Those would be called 8/2 and 8/3, by the way, since they don't count the thin ground wire in the naming.


The car does not officially auto adjust based on wire size. It can't specifically detect that, unless it's really wrong and too thin and causes bad voltage drop. That is a safety feature it has. I looked it up, and 10 gauge is OK for up to the 30A level, so that would be OK for 30A circuits, like this L6-30 or dryer outlets like 10-30 or 14-30. But don't use it for anything more than 30. That's why people sometimes go for the thicker ones like at EVSEAdapters, because they can handle for 50A or lower circuits, so there's more flexibility of use cases. Please do check a little on ampacity charts for wire gauge.[


great answer. thanx. makes sense now . i just need to buy the "magic" adapter from tesla to rig a 50' or 100' x 30amp cord