240 volt extension cord.

[Richard Wolf]

Will this work? I have a barn 80' from my laundry room dryer outlet. I would like to use my Sawstop in the barn but I don't have 240 available. Doing it the right way with a sub box and buried cable is not an option at this time. Can I make an extension cord to plug into my 3 prong dryer outlet when I want to use the saw? What size wire? Help.

[Jim Becker]

Richard, for that kind of distance, you'll want to seriously upsize any "extension cord" you use and it's not going to be pretty cost-wise. If the saw runs on a 20 amp circuit normally, upsizing to 10 gage probably will work, but hopefully the "sparky folks" here can confirm or deny that. HD carries heavy rubber coated 10 gage cord-stock (I use it for machine specific cords/extensions in my shop). I don't know if they have heavier.

[Richard Wolf]

Thanks Jim, I was hoping to use 10 gage or maybe even 8 if necessary. Just hoping for some insight about about doing it. The dryer plug is only a 3 prong, I assume 2 hot and a neutral/ground, do I need 10/2 or 10/3 wire?

[John K Jordan]

Thanks Jim, I was hoping to use 10 gage or maybe even 8 if necessary. Just hoping for some insight about about doing it. The dryer plug is only a 3 prong, I assume 2 hot and a neutral/ground, do I need 10/2 or 10/3 wire?

You should look at the current requirements of the saw under load and base the wire size on the maximum voltage drop you want to tolerate for that distance. There are online calculators. I don't like dropping the voltage much (which causes even more current draw in motors) so I tend to oversize the wire. The last 220v extension cord I made was 20' long for a welder on a 50amp circuit to weld outdoors. Probably 8/2 with ground - can't remember. Stranded wire, bought from an electrical supply house.

JKJ

[Art Mann]

Here is a little arithmetic you may find useful. A 10 gauge wire has a resistance of about 1 ohm per thousand feet. You are talking about a wire that is 160 feet (80 feet there and back). Therefore, the resistance in the wire will be about 160/1000 or 0.16 ohms. If your saw draws 20A, which I suspect is a significant overestimate, then you will lose 20 X 0.16 or 3.2 volts under full load. That isn't enough to make any difference unless your house voltage is already critically low or has an unusually high inherent resistance for some reason.

There is one other thing I want to mention. "Ground" and "neutral" are absolutely not the same thing and it is vital that you know the difference. Ground is a safety connection and is never intended to carry any current unless you have a fault condition. The neutral wire carries the return current from a 120VAC load and carries the imbalance current in a complex 120/240VAC circuit. Your load is one simple 240VAC element so you only need a safety ground and not a neutral.

[Tom M King]

By the time you buy type no. 8 SO wire, and Hubbell plugs for the ends, you're into the buried wire, and subpanel cost fairly substantially.

[Robert Hayward]

My opinion is 10 gauge is probably okay for your distance if you are just doing hobby work. If you are going to run production then you should go 8 gauge. You can get 10/3 100' extension cords at Home Depot.
https://www.homedepot.com/p/American-Contractor-100-ft-10-3-SJEO-Outdoor-Heavy-Duty-T-Prene-Extension-Cord-with-Power-Light-Plug-017990002/204667740
Cut the ends off and put on whatever 220 plugs you need.
If you want to do it by the book follow John and Jim's advice. My opinion is based on what has worked for me over the years.

[Brian Holcombe]

The wire in the wall may not be heavy enough.

[Tom M King]

Good point, and also the length of the no. 10 wire from the breaker to the dryer outlet.

[Art Mann]

Dryer outlets are typically wired for 30A so there is no problem with the wire size in the wall unless the house was wired wrong. If that is true then all bets are off. That does bring up a good point though. The extension cord needs to be sized at 10AWG or larger if the original poster expects the dryer breaker to protect it.

I don't see why being a hobbyist or professional has anything to do with wire size. Either the wire is large enough for the saw or it isn't, regardless of how much it is used.

[Wade Lippman]

IIRC a 3hp SS is 13a.
If the current wiring is for an electric dryer, it will be heavy enough that it can be ignored for this purpose, though it is prudent to confirm what it is.
A voltage drop calculator is found at https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=13.17&voltage=240&phase=ac&noofconductor=1&distance=100&distanceunit=feet&amperes=13&x=56&y=17
It is considered proper to have 3% voltage drop to your tool.
As you will find, you don't need that much of a cord.

Over the July 4th our neighborhood was getting 102v. I shut everything off, but I didn't hear of anyone else suffering any damage.

[Darcy Warner]

I don't really worry about voltage drop until I am pushing 200 feet from my panel.

[Richard Wolf]

Thanks every one for your help. The dryer is about 10' from the breaker box. My saw is 5hp and draws about 20 amps. Maybe I'll see if I have enough room in the box to wire a dedicated outlet.

[Jeff Duncan]

Hmmm, if your going to go through the trouble to wire in an additional outlet, (which is probably a good idea BTW), maybe think about slapping an exterior receptacle box on the side of your house so your not constantly going in an out to plug your extension cord in? Not much more work or expense and very likely well worth once you start using it;)

Oh and if you don't currently have room in your panel, you can get double single pole breakers to open up some space. They're basically two breakers that take up the space of one. A couple of those will open up space for your new outlet.

For what its worth I use a 60' - 10 gauge extension cord to run 3 phase machines I haven't gotten around to wiring up yet. Been doing it for years on motors up to 7-1/2 hp and it gets the job done.

good luck,
JeffD

[William Hodge]

It's worth getting an electrician in to set you up right. Once that's done, adding on is easy. Wires will also be grounded as they enter the buildings. I have had lightning problems.

You could run the saw on a portable generator for a while, until you are wired up. It never hurts to have a portable generator, or two, around. I ran my shop on a portable generator for two weeks when we had a bad storm take the wires down a few years ago.

[Tim M Tuttle]

Which SS motor? According to the manual on my contractor saw, the 1.75 at 220v requires a 14 ga cord (not extension cord) for 50-100 feet. That seems pretty slight though.

[Bill Dufour]

You can use NM cable and after you get tired of rolling and unrolling it all the time you can put it in some conduit.
Bill D.

[Tom Bender]

If you run a 12 ga cord you will have very little voltage drop until you load up the motor. Your usage may be different than mine but I rarely load up my 1.5 hp motor. If you are working a 7.5 hp motor hard you are cutting some big stuff pretty fast.

[Richard Wolf]

Thanks for all the responses.

[marlin adams]

https://www.southwire.com/support/voltage-drop-calculator.htm

1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 2.10% or less when supplying 30.0 amps for 80 feet on a 240 volt system.

[Bill Dufour]

https://www.southwire.com/support/voltage-drop-calculator.htm

1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 2.10% or less when supplying 30.0 amps for 80 feet on a 240 volt system.

60 feet so 24.1

120 feet, not 60, so 4.2% voltage drop. 10% drop is about where it becomes an issue.
Bill D

[Matt Mattingley]

You’re coming off a dryer plug which is 30 A? Just build yourself a 30 amp extension cord (SJOOW) which would be 10 gauge. Put a 30 amp plug on the end of the cord and your tablesaw. Under the NEC I believe this will be Acceptable plug-in,if the tablesaw has an FLA of 20 A.

Why worry about voltage drop if you use a adequate sized extension cord? Circuit that is there is 30 A. If you’re going to the trouble just make a 30 amp cord with 30 amp plugs on either end.

[John K Jordan]

Why worry about voltage drop if you use a adequate sized extension cord? Circuit that is there is 30 A. If you’re going to the trouble just make a 30 amp cord with 30 amp plugs on either end.

The question to answer is what size of extension cord is adequate. Regardless of the amperage rating at the receptacle, the voltage at the end of a cable depends on the wire size, the length of the wires, and the current draw of what is plugged in. The 10 gauge may be perfect but for me knowing is preferred to assuming.

Here's a simple on-line calculator: https://www.southwire.com/support/voltage-drop-calculator.htm

For the receptacle on the end of the cord, it might be most useful to have one that matches what is on the equipment.