110v extension cord sizing

[Mark Wells]

So I know I'm over-thinking, but this will give a chance for some of the folks with electrical religion to let off some steam.

I have 3 machines that all need short (

[Greg O]

My thoughts are to remove the factory cords and add a 10-15 foot power cord. A little more work, but no fussing with extension cords either. Buy 12 guage extension cords, cut off the female plug and rewire to your machine.

12 guage cords are fine as long as the run is relatively short. 10 guage is overkill for 10-15 feet. Greg

[Donald Guzzetta]

10 gauge is good to about 25 amps sometimes 30 depending on the wire insulation, the 12 gauge will be good to about 20 amps. you never want to push 14 gauge over maybe 12 amps. try to keep the wire at least 20 percent heavier than you need if possible. Extension cords use strand wire because it is more flexible. but it does not carry current as heavy as solid wire in romex.

[Jody]

10 is overkill for that short of run. Get some 12g so or soj and some woodhead plugs and make your own. If you don't move your tools or put them in the same general spot then wire right to the motor. You would only need one plug per cord.

[Matthew]

Anyone advising against extension cords must live REALLY close to a power plant, cause all wiring is essentially an extension cord :)

The short answer: You can add 10 feet of 12 gauge on all three machines, no problem, but I agree with Greg that it is cleaner just to put longer cords directly to the electrical connections in the machine. No extra plugs to get dirty, trip over, and pay for.

The longer answer: If you really are curious, what you care about is a) voltage drop, and b) internal heating.

Internal heating is usually not an issue unless the cable is wound into a tight bundle or run in an enclosed space (like conduit). For stretched out cords, the heat generation is distributed over the length of the cord. You could (in theory, at least) run 15A of current thru miles of 14ga wire, and it would never overheat -- but the voltage drop would limit you way before that.

Voltage drop: this is where length is important. Lower gauges are bigger wires, so their resistance is lower; for the same current, they have less voltage drop per length. 12 is about 1.7 ohms per 1000' (suprisingly little) while 14 is 2.6 ohms per 1000'. So a run of 14 will drop 50% more voltage than a run of 12. Ratings are pretty conservative: 100' of 14gauge at 15A will drop a reasonable 8V (4 on the hot, 4 on the neutral). 1000' would lose 80V -- which clearly would not work in a 110V system.

This is why power transmission lines are high voltage (lowering the current for the same power), At low voltage, the losses would be way to large to tolerate.

As far as prepackaged extension cords: One reason the cords may be rated is

15A is not the cable but the connectors (the plug itself). Connectors carry a rating, just like cable does, or outlets, etc. Usually, the rating has to do with the internal construction and regulatory testing. Often an plug carrying too much current will heat up long before the cord it is attached to. You will notice it when you grab the plug to unplug it -- it is warmer than expected. Vacuum cleaners are notorious for this, as the plugs have a tendancy to get uplugged with a quick yank on the cord (tsk, tsk). Time to fix the plug or get a new one.

FWIW,

Matthew

[Bob]

12 gauge all the way. I agree with Greg - replace the stock cord with a longer one. Either way, I think you will be happier making your own cords, instead of buying what's available in the hardware stores. You can buy heavy duty rubber covered SO cord at Lowe's or Home Depot and buy the connectors to fit also. SO cord is rugged and much more flexible than the things you get in the store.

Bob

[toller]

Unless your DC is pretty close to the circuit box, you are already seeing some voltage drop on 18a. Adding another 10' is not a great idea. I would recommend using a 10 gauge extension cord, or (even better) wiring the DC for 240v.

A voltage drop calculator is at:

don't want to go over 3%. Length is house wiring, extension cord, and DC cord.

And finally, I sure hope you are not using more than one tool on a 20a circuit, and that there is nothing else on the DC circuit, like lights.

[Richard Cline]

I prefer around a one foot power cord and a ten foot extension. When I go to move the machine it is easy to disconnect and not have to trip over the trailing cord. I use the heavy rubber cord protectors on the floor where I walk over the extension cord.

Dick

[Charlie Self]

Mark Wells asks:

I really, really love the "don't use extension cords" types. The other choices are direct wiring, or replacing machine cords with longer ones.

You're sizes are fine. AFAIK, ampacity of 12 gauge wire is sufficient for 20 amps, no matter which kind of cord you use, up to about 50'. It's in longer lengths that voltage drops become a problem. Going with the #10 for the dust collector is wise, because it allows for start-up surge.

Charlie Self "Absolute faith corrupts as absolutely as absolute power." Eric Hoffer

[Charlie Self]

Novel approach. About like what's been done to small kitchen appliances. But I use the cord as an indication of the machine's being unplugged when I'm changing blades, cutters, belts, etc. I drape the cord over the table so the plug is visible. If I can't see the plug, I won't work on the machine until I can see it.

Charlie Self "Absolute faith corrupts as absolutely as absolute power." Eric Hoffer

[Clint]

The nice thing about having the short cord on the tool then is you don't end up walking back and forth to the wall plug all the time. Make it just long enough to loop it somewhere you can see it, and away you go!

Cl>

[Larry Jaques]

On Sat, 18 Dec 2004 02:38:21 GMT, "Mark Wells" calmly ranted:

Amen, Brother!

I'd run more wire, like 20', for each tool in case you want to swap them around at a later date. You could easily run 12ga for your short runs but if they'll get run over at all, 10ga would be the call I'd make. I have all 5' rubber-wheeled casters in the shop, so they're easy on cords when that happens. the cast iron wheeled tablesaur is the exception, but it has the armored, 3/4" thick 10ga cabling on it.

Here is the cable rating for extension cords. ------------------------------------ | AMP RATING | LENGTH 25' 50' 100' | |------------------------------------| | 0-6 amps | gauge 16 16 16 | | 7-10 | 18 16 14 | | 11-12 | 16 16 14 | | 13-16 | 14 14 12 | | 17-20 | 12 12 10 | | 21-30 | 10 10 NO | ------------------------------------ (if you're not running a fixed width font, you'll get dizzy on that) Figures courtesy of the Grizzly G1012 instruction manual.

It's stranded-wire vs. the solid-wired Romex, and it has an entirely different jacket. Other than being -totally- different animals, they're quite alike, just as you say. ;)

When in doubt, go heavy. What's an extra 30 cents a foot, anyway? I bought 50' of 12ga for my 220v bandsaw and dust collector, 25' apiece. The 30' cable on the table saw is 10ga and is nearly double the thickness of the new stuff. That cable is thick and protects the wiring inside better, so it's worth the few extra bucks. I think it was 25 or 30 cents a foot more, but if I needed a 100' extension cord for a power tool, I'd go with the thicker stuff despite its cost and weight. It could mean the difference between smoking the tool or running it nicely. The difference in price there would be more than enough to warrant the heavier gauge.

-- Sex is Evil, Evil is Sin, Sin is Forgiven. Gee, ain't religion GREAT?

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[Larry Jaques]

On Sat, 18 Dec 2004 02:38:21 GMT, "Mark Wells" calmly ranted:

Let me restate that: Don't put -extension- cords on those machines, RECABLE them, wiring from the switch to the wall with new, high-quality cable and a grounded male plug on the end.

-- Sex is Evil, Evil is Sin, Sin is Forgiven. Gee, ain't religion GREAT?

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Sin-free Website Design

[Mike Marlow]

I have to disagree Larry. For a lot of us, our tools have to move around, in and out of parking places. Extension cords are much more versatile for that than hardwired cords. Properly made extension cords are every bit as good as a hardwired configuration and for us that have to deal with moving and storing, they're better.

[Mike Marlow]

I have to disagree Larry. For a lot of us, our tools have to move around, in and out of parking places. Extension cords are much more versatile for that than hardwired cords. Properly made extension cords are every bit as good as a hardwired configuration and for us that have to deal with moving and storing, they're better.

[Larry Jaques]

On Sun, 19 Dec 2004 18:55:49 GMT, "Mike Marlow" calmly ranted:

Because about 90% of extension cords out there are insufficient for use with a major power tool, you're asking for trouble telling people to use them. People tend to save money and an extension cord is the WRONG place to save it. Most are 18ga, some as heavy as 16, but VERY few are heavy guage wire. Those that do use it are usually found only in contractor sales areas or high-end shops and at 5 times the price of a homeowner cord. Most folks won't buy them.

But that's your call, Mike. My general advice is "DON'T USE ONE!" unless I'm talking to someone who knows what voltage drops can mean and they have a contractor-grade cord. Fried motors are no fun and I won't be a party to someone frying theirs, thanks.

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[Charlie Self]

Larry Jaques responds:

If you read the early answers here, I think you'll find that the emphasis was on proper sizing for the tool. No one that I saw recommended the kind of light duty lamp cord extensions you seem to be afraid of.

Top quality extension cords are available in HD and Lowe's and in most hardware stores, not just contractors' stores. The prices are about five times what a lamp extension costs, but so what? We're not writing of lamps here, nor do I feel someone who knows a tool is going to be stupid enough to add an 18 gauge extension to a 120 volt 18 ampere table or other saw.

Give most woodworkers a bit of credit for a gram or two of common sense when it comes to electrical cords. Sure, there are idiots out there, in plenty, but you can't limit everyone to the slowest person in the overall category. We're no longer in school.

Charlie Self "It is when power is wedded to chronic fear that it becomes formidable." Eric Hoffer

[Mark Wells]

Thanks for everybody's feedback. I went to the BORG and checked out the electrical supplies. Comparing apples-to-apples the best I could, making my own 12 gauge extension cords from supplies at the BORG ($0.89/ft + $4/end) versus buying pre-made from McMaster-Carr ($15 for thermopastic case with lighted end) is roughly the same, so I'm just going to order pre-made ones. The BORG does sell 25 foot, 12 gauge extension cords, but I want to stick with 10 footers.

I also checked the machines themselves. The power cord to the two 1 HP machines (Jet) is only 16 gauge wire, so I can definitely see the reasoning behind replacing the entire cord. I'm still trying to figure out the best way to get my shop arranged, so I think extension cords are a better option at this point. However, I may do the pig tails. One reason I like that idea is that it keeps the male plug off the ground where it can get stepped on.

On the dust collector, I don't think it actually draws 18 amps. The Penn State site says "Reflects capacity of motor - running amperage will be significantly less." A friend of mine started a company that, among other things, makes an inline tool to monitor volts, amps, power quality, etc.

I keep meaning to get him to come over and actually see what each tool draws. If I ever get around to that, I'll post the results.

Mark

[Mike Marlow]

5 years ago I would have come close to agreeing with you Larry - except that I'd have said "don't buy one, build one" in order to get a good heavy cord. But today, that's completely different. 10 and 12 gauge cords are commonly available from Wal Mart, Home Depot and every place that sells cords, and they're priced right down with what people always paid for junk 18 gauge cords. Check out the prices of 10 and 12 gauge cords next time you're out and about. They aren't even double the cheap things, let alone 5 times. Voltage drop across a 10 or 20 foot cord is something you'd have to look at as well. I don't know off the top of my head what it is, but that's a very short distance and I'm not so sure there's such a big issue at hand. On that point, I could be wrong, but it just does not seem there should be.

I prefer to give advice that is appropriate. I'd suggest a fellow use a 10 or a 12 gauge cord. That, IMHO is a lot better advice than "don't do it". It can be better advice than to hardwire, especially in situations like I suggested in my reply. Which - by the way, you didn't address.

[Mike Marlow]

Don't be in a rush to replace the machine wiring if that's what you're saying here. The machine wire is not a feeder line.