I see that, my question was more in using the NEMA 14-50 in a NEMA 14-30 outlet which also has a neutral wire, but a different shaped prong so they don't mate properly, but would if the neutral prong is removed.
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How to build a lightweight 50A extension cord
- Thread starter mitch672
- Start date
I see that, my question was more in using the NEMA 14-50 in a NEMA 14-30 outlet which also has a neutral wire, but a different shaped prong so they don't mate properly, but would if the neutral prong is removed.
TonyWilliams
Active Member
The downside to having a NEMA 14-50 with the neutral removed is that you CAN plug it into a 30 amp home dryer outlet (NEMA 14-30) and pull 40 amps with the UMC.
It will pop the dryer's circuit breaker, or worse, if the breaker doesn't pop, it will possibly damage the home wiring. So, you need to know that and keep the UMC at 24 amps for home dryer plugs.
bollar
Disgruntled Member
The risk is in forgetting to set the car's charging to 24 Amps. If you allow the car to charge at 40 Amps, at best, the circuit breaker will blow, at worst, the receptical or wiring could overheat and start a fire.
Is that what you were asking?
Yep, as FlasherZ would state "worst case is you could burn down the house, if the breaker fails to trip and the wiring overheats"
You need to be aware of what you are plugging into, and you should probably check the amperage of the circuit breaker feeding the outlet so you do remember to lower the amperage to 24A. As an alternative, you can buy a 14-30 or 10-30 adapter for the UMC and build the adapters needed for the cord you built... This is always the safest method, as the proper adapter on the UMC will limit current to 24A without any user intervention.
I have the adapter for the UMC. The problem is that the outlet I wanted to use last weekend was more than 18' from the car. I had a 30' NEMA14-50 extension cord but no adapter for it. So the only risk is if I don't remember to turn down the amp draw...good to know.
You can build adapters for your 14-50 cord (one for each end), you can always run 30A through a 50A rated cable.. Just buy the male and female CAMCO 14-50 connectors on Amazon, then whatever end you need to match your 30A outlet/UMC adapter.
That's the safest method.. You could just remove the neutral on your extension cord (in a pinch) and turn down the amperage. I would tend to build the adapters, if this is something you'll be doing on a semi regular basis.
Thanks, I ordered an adapter that very weekend I ran into the issue, but I wish I'd known about cutting off the neutral prong...that would've helped and saved me $60
Evan, Via Tapatalk
Cutting off the neutral prong on an adapter cord so that it fits a 50A and 30A receptacle will technically work for the Tesla, but makes it a dangerous adapter. Try to use it on an RV and you'll blow up half (or more) of the appliances and bulbs in it, because RV's do require the neutral pin. Label it well, throw it away when you're not using the car, dial down the amps, and remember the risk you're taking. Buying the adapter from Tesla is a much better and less dangerous solution. 
Cutting off the neutral prong on an adapter cord so that it fits a 50A and 30A receptacle will technically work for the Tesla, but makes it a dangerous adapter. Try to use it on an RV and you'll blow up half (or more) of the appliances and bulbs in it, because RV's do require the neutral pin. Label it well, throw it away when you're not using the car, dial down the amps, and remember the risk you're taking. Buying the adapter from Tesla is a much better and less dangerous solution.
Thanks Flasher, I have the Tesla adapter, but am limited by the 18' UMC. My weekend in Little Rock I was within about 23' of a NEMA 14-30, so needed the extension cord.
Evan, Via Tapatalk
SCW-Greg
Active Member
Okay, correct me if I'm wrong...
I think more than a few of us might like to have the ultimate MacGyver extension cord on hand. This would be say a 20' cord, that would allow you to plug into (smartly, no amperage guessing) a 14-30, 10-30, 14-50, or maybe 6-50 outlets in the wild.
To do that (perhaps not cheap when all said and done), you'll build on the 4 wire cable (3 #6, and one #8 wire), using 14-50 female connectors on either end, then you make one set of adapters for the wall side accordingly....
1) 14-50 male to 14-50 male
2) 14-50 male to 14-30 male
3) 14-50 male to 10-30 male
4) 14-50 male to 6-50 male
And you use the 14-50 connector with UMC Tesla provides to mate on the other 14-50 female end of the extension cord.
In this way, the final wall-side connector determines the pilot signal (through only the wires in use) to the UMC, what the load can be... is this feasible/correct?
I think more than a few of us might like to have the ultimate MacGyver extension cord on hand. This would be say a 20' cord, that would allow you to plug into (smartly, no amperage guessing) a 14-30, 10-30, 14-50, or maybe 6-50 outlets in the wild.
To do that (perhaps not cheap when all said and done), you'll build on the 4 wire cable (3 #6, and one #8 wire), using 14-50 female connectors on either end, then you make one set of adapters for the wall side accordingly....
1) 14-50 male to 14-50 male
2) 14-50 male to 14-30 male
3) 14-50 male to 10-30 male
4) 14-50 male to 6-50 male
And you use the 14-50 connector with UMC Tesla provides to mate on the other 14-50 female end of the extension cord.
In this way, the final wall-side connector determines the pilot signal (through only the wires in use) to the UMC, what the load can be... is this feasible/correct?
As far as the Tesla picking out the correct amperage to draw, that is determined by the adapter you plug into the UMC. So if you always use the 14-50 adapter, then the car will think it can draw 40 amps. So if you want to use your own adapters plugged into the UMC 14-50 adapter, then you have to manually dial down the amperage. Here is a how-to document that explains all this: http://cosmacelf.net/Home%20Made%20Adapters.pdf
Bringing this back from the dead, there is 6/3 SOOW "non-UL" cable available that 80% of the weight the one OP got. As far as I can tell the UL listing is just for physical abuse and flame resistance? Should I be worried about something else? Given it's for emergency use, I think it should be fine. Although buying it from ebay, it's probably not really UL listed anyway.
If it's SOOW cable, it's properly typed from an NEC perspective. If it's truly SOOW, then you shouldn't have any issue.
I've built this "lightweight" cable, and although I have no doubt it is lighter than the camco cable, I think it's quite obvious that it is serious overkill. 8/3 SOOW would have probably done just fine, especially for an emergency cable for travel. I didn't cut the UMC cable open, but I'm guesstimating that's what is in there. See how much hotter the UMC cable runs after 30 minutes of charging.
2x14AWG for each conductor, so 4x14AWG total for power carrying conductors.
NEC ampacity tables don't apply to appliances, so the parallel conductor rule doesn't apply and neither does the ampacity table.
#14 conductor has a cross-section of 2.08 mm^2. 2 of them would create cross-sectional area of 4.16 mm^2. My IEE book, table 4E4A, says that a 4 mm^2 conductor in a 2-core single-phase cable is rated at 52A in free air conditions.
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Actually, it seems we're both wrong. And my bad recollection comes from further up in that thread, where I guessed at 2x #14.
Tesla Model S UMC cut open and modified to J1772 - Page 2
Ingineer says they're 2.5 mm^2, which is roughly #13.
So, back to my trusty IEE table 4E4A, a thermoset cord utilizing a 5.0 mm^2 conductor for each leg would be rated at roughly 59A or so in free air.
Each leg uses 2 power conductors, ground uses 1 power conductor, and the 2 18ga are used for the signaling (proximity / pilot).
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We only count half since it's the same circuit... and #8 has 8.34mm cross section. Wish I did this before I bought the cable.. Could have saved another 4-5lbs probably.
