Building a 30A extension cord

[user212_nr]

I've some need of an extension cord (temporary solution only). I've seen something about buying "rubberized stranded three wire cable" and then buying some plugs.

I'm looking at making 100ft 30A right now. That might be a little longer than needed, but is future proof.

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

I don't see any such "rubberized cable" at the Home Depot website, but there is 100ft of 10AWG wire available on a regular cord (Duromax XPC10100C 100 ft. 10/3 Gauge Triple Tap Extension Power Cord-XPC10100C - The Home Depot). Any reason not to cut that and install plugs?

 

[Puddles]

Do it! Be our probe unit!

 

[ZOMGVTEK]

Home Depot has the wire, it’s SJOOW or SOOW. It’s commonly used to make extension cords, no problem at all. You can chop the ends of that cord if you’d like too, that’s fine.

 

[JasJ]

Home Depot has the wire, it’s SJOOW or SOOW. It’s commonly used to make extension cords, no problem at all. You can chop the ends of that cord if you’d like too, that’s fine.

For a 100ft run you are way undersizing.

You need 8 guage wire for your use: http://www.cmewire.com/catalog/sec19-fcx/fcx-cu-01-amp.pdf

This is the stuff you need... plus the plug and receptacle parts...
8/3 SOOW Portable Cord 600V Non UL

or better buy a premade one, something like this: (less likely to set something on fire from undersizing the wire)
Heavy-duty NEMA 14-50 extension cord for EV, 100 ft. – EVSE Adapters

 

[woodguyatl]

I've some need of an extension cord (temporary solution only). I've seen something about buying "rubberized stranded three wire cable" and then buying some plugs.

I'm looking at making 100ft 30A right now. That might be a little longer than needed, but is future proof.

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

I don't see any such "rubberized cable" at the Home Depot website, but there is 100ft of 10AWG wire available on a regular cord (Duromax XPC10100C 100 ft. 10/3 Gauge Triple Tap Extension Power Cord-XPC10100C - The Home Depot). Any reason not to cut that and install plugs?

For flexible cord you will need 8 for 40 amps and 10 for 30 amps.

 

[kkillebrew]

I've some need of an extension cord (temporary solution only). I've seen something about buying "rubberized stranded three wire cable" and then buying some plugs.

I'm looking at making 100ft 30A right now. That might be a little longer than needed, but is future proof.

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

I've some need of an extension cord (temporary solution only). I've seen something about buying "rubberized stranded three wire cable" and then buying some plugs.

I'm looking at making 100ft 30A right now. That might be a little longer than needed, but is future proof.

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

I don't see any such "rubberized cable" at the Home Depot website, but there is 100ft of 10AWG wire available on a regular cord (Duromax XPC10100C 100 ft. 10/3 Gauge Triple Tap Extension Power Cord-XPC10100C - The Home Depot). Any reason not to cut that and install plugs?

The cord you speak of is not equivalent to 10 AWG, check out the Ampacity rating of solid vs stranded. I have, however, used it successfully for up to 25ft lengths, but I am not sure about 100ft. A three percent cable drop will manifest itself as heat so you need to consider duty cycles when sizing wire, connectors, breakers, etc. I've posted several times on how to build these with Home Depot components but never more than 25ft. I can tell you from hands on experience that you need to factor at least a 25% "headroom" for a stranded wire run (extension cord). The #10 rubberized works just fine at 25ft and 32 amps - less than .5% loss and zero heat after a full six to seven hour charge. You will get a lot of blowback from the FUDsters around here just for posting this, BTW, so I have quit posting how to make safe EV extension cords.

 

[ewoodrick]

I've some need of an extension cord (temporary solution only). I've seen something about buying "rubberized stranded three wire cable" and then buying some plugs.

I'm looking at making 100ft 30A right now. That might be a little longer than needed, but is future proof.

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

I don't see any such "rubberized cable" at the Home Depot website, but there is 100ft of 10AWG wire available on a regular cord (Duromax XPC10100C 100 ft. 10/3 Gauge Triple Tap Extension Power Cord-XPC10100C - The Home Depot). Any reason not to cut that and install plugs?

Read the print on the bottom. 15A.
You are going to need to look at camper stores for a 30A cord, but they are going to use the TT connector. They will have the NEMA 15-50, but 100 ft is EXPENSIVE.

 

[wws]

Read the print on the bottom. 15A.
You are going to need to look at camper stores for a 30A cord, but they are going to use the TT connector. They will have the NEMA 15-50, but 100 ft is EXPENSIVE.

That is what I use - in my case a 25' Camco TT-30 cable. I can connect it to the UMC via a evseadapters TT-30 adapter. I can also use some off-the-shelf RV adapters for 5-15 and 5-20 on either end. Even though TT-30 is intended for 120V, it all works fine at 240V. The cable itself is 600 volt rated STW. I have home made 14-[356]0P (neutral blade removed) -> TT-30R and 6-30P -> TT-30R adapters for use at 240V.

TT-30 is kind of fun because there are a lot of off the shelf RV parts, numerous vendors, and competitive pricing. Compared to 14-series cables, it only has three conductors instead of four - so is lighter, easier to handle, and less expensive.

 

[earthwormjim]

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

10 AWG solid strand will, 10 AWG stranded will not. You're looking at twisted strand wire, since this is a flexible extension cord. Go 1 standard size down, so 8AWG for 40 amps, giving you plenty of overhead for your 30 amps. Since these are low frequencies, the skin affect does not matter, thus what does matter is copper surface area, vs. the cross sectional surface area of the wire. Stranded wire has voids, solid wire does not, thus stranded wire has less usable surface area when looking at a cross section.

Resistance of stranded wire will be 3-5% higher depending on strand counts at 60Hz.

You need to make sure the ampacity tables you are using call out the same conductor type that you will be using.

10 AWG copper wire should handle 40 Amps, and it gets less that 3% voltage drop over 100ft.

3% Vdrop is a lot. The UMC itself could easily have another 3% on top, so you're wasting a lot of power in copper.

 

[Kirby64]

10 AWG solid strand will, 10 AWG stranded will not. You're looking at twisted strand wire, since this is a flexible extension cord. Go 1 standard size down, so 8AWG for 40 amps, giving you plenty of overhead for your 30 amps. Since these are low frequencies, the skin affect does not matter, thus what does matter is copper surface area, vs. the cross sectional surface area of the wire. Stranded wire has voids, solid wire does not, thus stranded wire has less usable surface area when looking at a cross section.

Resistance of stranded wire will be 3-5% higher depending on strand counts at 60Hz.

You need to make sure the ampacity tables you are using call out the same conductor type that you will be using.



3% Vdrop is a lot. The UMC itself could easily have another 3% on top, so you're wasting a lot of power in copper.

What does surface area matter when dealing with 60Hz? It doesn't. For 60Hz current carrying loads, 10AWG stranded wire should have identical current carry capability vs. 10AWG solid wire. The cross-sectional area is what matters, and those should be identical between 10AWG stranded vs. solid. You give up diameter for flexibility since the 10AWG stranded wire will have a larger outer diameter (due to the voids you mention).

Either way, 10AWG 240V should have ~2.5% Vdrop. That's totally fine from a NEC perspective. The only issue is if the feeder/branch circuits themselves have considerable voltage drop as well. NEC recommends max 5% for the full circuit... It really depends on how far OP's run is from whereever OP is plugging in. If it's already far from the actual mains, then uprating the wire would make sense.

All that said, it seems that buying a pre-built solution often is cheaper than trying to buy cabling from Home Depot etc. They seem to charge an arm and a leg for high gauge copper. Plus you don't have to deal with wiring it up yourself.

 

[earthwormjim]

What does surface area matter when dealing with 60Hz? It doesn't. For 60Hz current carrying loads, 10AWG stranded wire should have identical current carry capability vs. 10AWG solid wire. The cross-sectional area is what matters, and those should be identical between 10AWG stranded vs. solid. You give up diameter for flexibility since the 10AWG stranded wire will have a larger outer diameter (due to the voids you mention).

Either way, 10AWG 240V should have ~2.5% Vdrop. That's totally fine from a NEC perspective. The only issue is if the feeder/branch circuits themselves have considerable voltage drop as well. NEC recommends max 5% for the full circuit... It really depends on how far OP's run is from whereever OP is plugging in. If it's already far from the actual mains, then uprating the wire would make sense.

All that said, it seems that buying a pre-built solution often is cheaper than trying to buy cabling from Home Depot etc. They seem to charge an arm and a leg for high gauge copper. Plus you don't have to deal with wiring it up yourself.

Impedance of the wire increases with frequency as the skin depth becomes shallower than the cross section. At 60Hz, with these small conductors, it doesn't matter though.

When I said surface area, that is a typo, I meant cross-sectional surface area.

10AWG stranded does not have identical carrying capacity as 10AWG solid wire, there is less copper present in stranded wire, you have voids between strands.

3% drop from the extension cable alone is a concern, because the UMC has a 1-2% drop itself, and you have whatever the drop is feeding this 30A circuit's outlet, and drops from the extra outlet connections for the extension cord. It's better to oversize it, the cost difference between 8AWG and 10AWG isn't that significant if you're making your own cables.

 

[Kirby64]

Impedance of the wire increases with frequency as the skin depth becomes shallower than the cross section. At 60Hz, with these small conductors, it doesn't matter though.

When I said surface area, that is a typo, I meant cross-sectional surface area.

10AWG stranded does not have identical carrying capacity as 10AWG solid wire, there is less copper present in stranded wire, you have voids between strands.

3% drop from the extension cable alone is a concern, because the UMC has a 1-2% drop itself, and you have whatever the drop is feeding this 30A circuit's outlet, and drops from the extra outlet connections for the extension cord. It's better to oversize it, the cost difference between 8AWG and 10AWG isn't that significant if you're making your own cables.

I'm aware of skin depth. My point was it doesn't matter for power since 60Hz skin depth is 8.5mm in copper. That means you start to see effects if you have solid conductors that are larger than 8AWG each.

Cross-sectional surface area should be identical between 10AWG stranded and 10AWG solid wire. The original AWG is a measure of a single, solid, round conductor's diameter. Since that has shortcomings (e.g., non-round conductors, or stranded conductors), it's been translated to cross-sectional area. So by using identical cross-sectional area, you have identical current-carrying capability. Stranded wire gauges should always be measured in cross-sectional area, not diameter.

Regarding Vdrop, the UMC is going to drop however much it's going to drop no matter what. Since you can't change that, what does it matter? OP said this is a temporary solution, so there's no reason to spend extra money on upsized wire. The only reason to upsize wire is if the Vdrop is too much for the length (i.e., the UMC won't function), or if the wire literally cannot handle the current (i.e., non-code).

 

[user212_nr]

So after many hours on Amazon and Home Depot website, looks like the "L14-30 generator cord" is the one to get for 30A. The non-locking outlet isn't sold in the longer lengths and probably for good reason.

The 100 ft cables are also more expensive than joining two 50' cables, and even cheaper is two 40' cables. The 30A cables all use the same 10AWG so the price increase is just for the novelty.

Conntek 50 ft. 10/3 STW L5-30 Generator Power Extension Cord-20572 - The Home Depot
https://www.amazon.com/BougeRV-Generator-Electric-Extension-L14-30P/dp/B07FT4M77B

Comes out a little more than the DIY cable, but probably worth it.

Also, no discount on using a 6-30 3-wire cable. Just like the 100ft cable is a novelty.

For the 8AWG cable would need to get the 14-50 cable which is $450. I can just lower the current if voltage drop costs are an issue, don't really need 30A.

 

[Kirby64]

So after many hours on Amazon and Home Depot website, looks like the "L14-30 generator cord" is the one to get for 30A. The non-locking outlet isn't sold in the longer lengths and probably for good reason.

The 100 ft cables are also more expensive than joining two 50' cables, and even cheaper is two 40' cables. The 30A cables all use the same 10AWG so the price increase is just for the novelty.

Conntek 50 ft. 10/3 STW L5-30 Generator Power Extension Cord-20572 - The Home Depot
https://www.amazon.com/BougeRV-Generator-Electric-Extension-L14-30P/dp/B07FT4M77B

Comes out a little more than the DIY cable, but probably worth it.

Also, no discount on using a 6-30 3-wire cable. Just like the 100ft cable is a novelty.

For the 8AWG cable would need to get the 14-50 cable which is $450. I can just lower the current if voltage drop costs are an issue, don't really need 30A.

Functionally, there's no real difference between an L14-30 and an 14-30 outlet in terms of current carry ability or reliability. You're going to have to make a custom adapter to go L14-30 -> 14-30/14-50 anyways, so having the plugs on either side be regular 14-30 may be easier. Adapters are just more potential causes for failure. That being said, if you ever do need it for a generator... the L14-30 is the plug you'd need.

 

[wws]

I still think TT-30 parts are worth considering. Eliding the unneeded 4th wire makes the cable lighter, easier to handle, and hopefully less expensive. For example the Camco 55197 is 50' long and is currently selling at Amazon for $53 and change. I have the Camco 55191, which is 25' long, and about $30 at Amazon. It, with a bunch of adapters, easily fits in a duffel bag.

 

[user212_nr]

I still think TT-30 parts are worth considering. Eliding the unneeded 4th wire makes the cable lighter, easier to handle, and hopefully less expensive. For example the Camco 55197 is 50' long and is currently selling at Amazon for $53 and change. I have the Camco 55191, which is 25' long, and about $30 at Amazon. It, with a bunch of adapters, easily fits in a duffel bag.

Its a good deal definitely, didn't check the price before. Cheaper even than the "120v 15A" 10 gauge cord I had linked for $114.

Probably if I manage to get a L14-30 outlet I'll get the same cord just to get the satisfaction of "clicking it".

 

[n2mb_racing]

Check out 6-50 extension cords too. That might be exactly what you want, premade. There is a 6-50 plug for the UMC. So, you'd just need to adapt the plug of the extension cord to your outlet or install a 6-50 outlet...

 

[n2mb_racing]

Check out 6-50 extension cords too. That might be exactly what you want, premade. There is a 6-50 plug for the UMC. So, you'd just need to adapt the plug of the extension cord to your outlet or install a 6-50 outlet...

Also, if you can tolerate slightly slower charging, I'd recommend NEMA 6-20. There are also cheap pre-made extension cords. And you can easily install a 6-20 outlet, if you have 12 gauge wiring in the house.

You'll get 15 mph charging, which is enough to charge the car pretty quickly. I use that exclusively.

 

[mswlogo]

That Home Depot wire is NOT 10/3. 10/3 is 4 conductors, 2 Hots, 1 Neutral and Ground.

I agree, use one gauge up for 100 FT.

Also you only need 8/2 (you don't technically need a neutral) but some adapters don't exist without Neutral from Tesla.

As others pointed out. Notice that That Home Depot cable ONLY rates the 10/3 15 Amps, because they oversized it for the long run.

For the record a 30 or 40 100 Ft extension cord is a really bad idea.

 

[Kirby64]

That Home Depot wire is NOT 10/3. 10/3 is 4 conductors, 2 Hots, 1 Neutral and Ground.

I agree, use one gauge up for 100 FT.

Also you only need 8/2 (you don't technically need a neutral) but some adapters don't exist without Neutral from Tesla.

As others pointed out. Notice that That Home Depot cable ONLY rates the 10/3 15 Amps, because they oversized it for the long run.

For the record a 30 or 40 100 Ft extension cord is a really bad idea.

The reason why they use 1 size up (actually, 2 sizes up. 15A only requires 14ga) is because line loss on a 100ft cable at 120V is significant (and also because it's a NEMA 5-15 plug, so they legally can't say it can handle 20A). With 240V this isn't as big of an issue. Realistically, if line loss isn't a concern, there's really no reason why you can't use 14 gauge on a 100ft run. The wire itself will be totally fine. Problem is, for 120V, 14gauge would have huge voltage drop across that run.

Here's a link for recommendations based on length of a run, note that 100ft runs are totally cool with 10ga for 240V, 30A applications:
Voltage Drop Tables - Cerrowire

If you have a connected device that isn't sensitive to line load drops (which, Tesla UMCs aren't), thicker wire is just wasting money for temporary applications.