I have some new corded equipment coming in, and until I know where its permanent placement will be in my workshop, it will be connected via an extension cord. But, there’s a problem – what size extension cord will I need?
Short Answer: consult with your user manual.
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Medium Answer:
For an extension cord that will be used with a 110V power tool or high-powered device, I prefer full 15A-rated extension cords of the following sizes:
25-foot extension cord: 14 AWG (or 12 AWG)
50-foot extension cord: 12 AWG (or 10 AWG)
For up to 12A, I could go with 14 AWG or 12 AWG for a 100′ extension cord. For 220V 20A tool use I’m going with 10 AWG.
The lower the AWG value, the thicker the cable and wire conductor diameters.
Longer Answer
Selecting an extension cord shouldn’t rely on any guesswork.
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Which extension cord you could and should use depends on 2 things:
- Current draw of the tool or device
- Desired cord length
The voltage and plug styles are also important, but that’s independent of the cord size.
Let’s say you have two sizes of water pipes – one has a 1/2″ inner diameter, and the other a 3/4″ diameter. Which pipe is more restrictive? Electrical cords are similar in concept.
When you have higher electrical current moving through a narrower cord, you get voltage drop and heat.
How do you know how much current a tool draws from an electrical outlet? This information will usually be listed on the tool itself and in the product manual.
Motor and power tools can be tricky since the current draw and electrical load can sometimes spike. Generally, equipment makers will offer recommendations as to their tools’ different power needs. Refer to their guidelines, and if in doubt consult with an electrician or other authority.
Extension Code Size Charts
What brought all this up is that I have a machine coming in that requires a 220V outlet with 20A circuit protection. I have one 220V outlet in the corner of the workshop, with in-wall wiring rated for 20A and a 20A circuit breaker.
The tool itself is rated at 9A per motor specs. Since the equipment is 220V and doesn’t come with a plug built-in, I could potentially use 15A or 20A plugs with it. My wall outlet can work with 15A or 20A plugs.
I could dig up calculation charts and best-practice guidelines, but that might still involve some guesswork and judgement calls. It’s easier to refer to manufacturer’s extension cord size charts, especially since their experts (and legal teams) have triple-checked the accuracy of their recommendations.
The equipment manufacturer recommends a 20A circuit, and so I’m going by that, rather than motor specs. Extra overhead is a good thing, although the downside is that the higher gauge cords are thicker and heavier.
This is the chart Powermatic provides in their user manual for extension cord guidance.
The tool still hasn’t shipped yet, and so I could wait until it’s here to see what the motor plate says, but I’d rather have as much as possible prepared before that.
I have read a few examples of cord bottlenecks where motor start-up can be affected. I assume that if start-up (inrush) current is higher than the typical operating current, you’re going to get a higher voltage drop, and this could affect start-up operation.
When in doubt, it’s usually better to size-up to a thicker gauge wire. With wiring, the lower the gauge number, the thicker the conductor size. Meaning, a 10 gauge wire has thicker conductors than 12 gauge wire and can handle higher current.
Going with a cord and plugs that are rated for 20A removes any doubt here.
Even it were suitable to go with 15A plugs, something that’s not clear until I see the motor plate of the new equipment, that’s still on the border of 10 and 12 AWG recommendations.
Additionally, I have just one piece of 220V equipment coming in right now. But what if I buy a table saw next? Or a stationary air compressor?
I’m going with 20A plugs to be future-proof, and so the cord needs to be able to handle 20A of current.
Plus, I’m making the assumption that the 20A of circuit protection extends to the minimum recommendation between wall outlet and device wiring.
So, this means 10 AWG. This way, I don’t have to make assumptions about whether a cord rated to 15A is sufficient or not. If myself or anyone else ever sees the cord with 20A cord ends, they don’t have to question whether it can be used with 20A devices.
I could probably get away with using 12 AWG cable and 15A cord ends, but setting it up for 20A means I don’t need to build a separate 20A-rated extension cord later on. Making sure the extension cord is rated for 20A ensures there’s no guesswork here.
As for the 220V vs 110V, there’s not much of a difference since the cord is rated to 600V. Even if I went with lighter duty cord, the voltage rating would be 300V. I went with the standard 600V rating for greater durability. The 300V-rated cord is very slightly less expensive (~5%), but has a ~13.8% smaller diameter and is ~16.7% lighter.
If going by the cord ratings, brand I’m looking at rates their 10 AWG to 30A, and their 12 AWG to 25A based on manufacturer specs. They’re simply quoting NFPA 70 NEC Table 400.5 (A)(1) specs for these ratings. Their 14 AWG cord is rated to 18A.
I’ve seen some online sources recommend that you can use 14 AWG for loads up to 20A, but that’s simply incorrect, as the maximum NEC rating is 18A.
You can’t go by cable rating alone, because length matters, and you can’t go by self-calculations such as voltage drop because there are other factors such as NEC guidelines.
I’m going by the manufacturer’s guidelines, which is usually a safe default. 10 AWG can be more difficult to work with, but I also ensured I went with plugs that are rated for it.
Let’s say I wanted to buy an off-the-shelf extension cord for general workshop use. Going by the Powermatic chart above, any cord carrying 15A current would call for a 12 gauge cord (at least).
Different equipment makers have different requirements when it comes to extension cord use.
Flexzilla – the brand of extension cord shown above – says their 14-gauge 25′ extension cord has a 15A load rating. They also have a 14-gauge 50′ extension cord rated at 15A and a 100′ cord rated at 13A.
There’s a disagreement here. According to Powermatic’s recommendations, 14 gauge would be insufficient to carry a 15A load. The cord is UL-approved and presumably safe to use as rated.
So what do you do? Generally, I follow the tool-maker’s recommendations and step up to a higher wire gauge if in doubt.
Some brands base their recommendations on different things. When in doubt, I go with the higher-gauge recommendation.
Here is the extension cord chart Dewalt gives for one of their corded table saws.
This particular Dewalt 120V table saw is rated at 15A. So, according to their chart, can you use a 14-gauge 25′ extension cord? Yes. Can you use a 14-gauge cord that’s 50′ long? No, or at least they don’t recommend it, they recommend a 12-gauge cord.
Bosch’s recommendations for their corded miter saw are similar to Dewalt’s.
I follow a similar rule of thumb for myself and bought a 14-gauge 25′ extension cord and a 12-gauge 50-foot cord. Since I bought them for general purpose tasks, rather than specific tools, I know that I can safely use them between any 15A tool or device and any 15A-rated wall outlet.
Some tools aren’t recommended for use with 100′ extension cords, presumably because the voltage drop would be too low. Keep in mind that there is also wiring between the outlet and the circuit breaker, and that contributes to a voltage drop as well.
There might be the option to step up to 10 AWG cables for longer 15A extension cords.
I also made sure the extension cords I purchased were UL-listed, which I take to mean they went through 3rd party safety testing.
You can buy extension cords of different sizes. There’s a UL-listed 100-foot cord with 16-gauge cable, and it’s rated at 10A. For specific uses, that’s okay. But if you go by any of the above charts, all of the brands above would recommend higher-gauge cables to be used with the specified equipment.
If you have an extension cord that physically fits between a heavy duty power tool plug and your wall outlet, are you going to remember whether the cord is under-rated or not?
Speaking personally, I don’t know what I might want to use any particular extension cord for, as usage needs can change under different circumstances, and so I try to ensure any of my cords can handle any of the loads that might be plugged into them.
If I’m not home, and my wife needs to plug in a wet/dry shop vacuum, I don’t want there to be a situation where the wrong extension cord could potentially create a fire hazard.
So, I size my extension cords to match the device form factor or circuit protection.
Basically, for 110V 15A cords I go with 14 AWG for 25′ length and 12 AWG for 50′ lengths. For my new 220V 20A cord, I’m going with 10 AWG for a 35′ run. This is all based on 3-conductor cables.
When in doubt, consult your device user manuals. If still in doubt, consult with an electrician or other electrical safety authority.
Charts like those above remove the need for guesswork.
I’ve have seen color-coded charts where they make “light duty,” “heavy duty,” and “extra heavy duty” recommendations, but you don’t need much more than a current vs. cord length chart.
Is it safe to go with a lower-rated cable? Possibly, but why take any risks? Improper extension cord sizing could at the least affect tool performance, and at worst start a fire.
One thing to keep in mind is that it’s not always clear what brands are basing their recommendations on. Powermatic’s chart, for instance, does mention that their recommendations are based on 5V max voltage drop at 150% of the rated current, I assume because their tools can have high inrush voltage spikes.
Since Dewalt’s chart has different values for 120V and 240V, they’re likely looking at a maximum voltage drop percentage. Since 240V is 2X 120V, a fixed-value voltage drop is 1/2 the percentage at 240V than at 120V.
You could also make your own Ohm’s Law calculations based on conductor size and voltage drop limits, but that’s not always the best approach as discussed above. Are you sure you have the correct wire gauge and resistance value table? Are there any other considerations involved such as NEC guidelines?
It’s usually good advice to use the shortest extension cords possible, and to uncoil them for use to help with heat dissipation.
There are a lot of good brands out there, but here is what I use for my 110V 15A-rated extension cords:
Buy Now: Flexzilla 14AWG 25′ via Amazon
Buy Now: Flexzilla 12AWG 50′ via Amazon
More FlexZzlla Options via Amazon
I have used Yellow Jacket-branded extension cords and power blocks with great experiences.
Buy Now: Yellow Jacket Cords via Amazon
Reader Recommendations?
Do you guys have any recommendations regarding extension cord brand or size selection?
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Bill Bahmuller
Can’t go wrong with Yellow Jacket. Always a good product in my experience. Just never use a cord while it is still coiled up unless you want to create a molten plastic and copper donut. Even a properly rated cord will overheat if it is bundled up to tight.
Dan Watson
Any announcement forthcoming on the Milwaukee packout 3 drawer toolbox giveaway?
John
Be mindful of choosing the right cords for products that have dual functions. My Toro leaf blower and vacuum worked just fine with a 100′ 16AWG cord when using the blower. That same cord overheated and started to smoke when I vacuumed leaves for a couple hours. The cord had seen it’s fair share of abuse and had a couple nicks in it, but the extra current draw when vacuuming up leaves was enough to roast the cord and make it smoke. I replaced it with a proper14 AWG cord and it works much better.
Stuart
Exactly. For my 110V cords, I assume that they will inevitably be used for 15A loads, and size them accordingly.
I’m doing the same now with my 220V extension.
Kunkel
I’ve done the same. I can save a couple bucks today because i only need to run 12A on this… but then 3 months later I have to run 15A on it. Buy once, cry once,
Bert
I know this is a several year old post, but this is especially true with vacuum or pump type functions and doubly so when the device is first starting. A device that is rated 10A may pull a lot more than that while the motor is locked in place trying to overcome the initial static pressure of whatever it is pushing or pulling.
JoeM
Interesting side topic on this one: Power Strips/Bars for chargers. The specs in the manuals for cordless tools have similar charts for a single (included) charger for the tool… What kind of math do we need to do when setting up, say, a wall, shelf, inner toolbox lid, whatever else, with a Power Strip for all your chargers?
Do we Add up the Amps drawn per charger, then average them for all that would be plugged into the same Power Strip? Or do we just add them up per strip?
When shopping for a new strip to use, for example, do we take all our chargers and add up their requirements, then use that number to decide how many strips we need?
Now That would be one awesome read for me. I have a handful of corded tools, but I use Power Bars of all sorts for all my tech. I’m in the habit of using Power Bars for my chargers, with free sockets for the handful of nearby corded tools as well.
I have several “In Your Pocket” type reference books, but none of them cover Power Strips and Tool Battery Chargers. I have Pocket Ref 3rd and 4th editions, the Handyman in Your Pocket sibling, plus an Electronics Pocket Reference 3rd Edition I got in College with one of my text books. (The text book was for the Electricity class, go figure. That year they packaged the book with the pocket reference book, so bonus. It also contains the Phonetic Alphabet, Semaphore, and Morse Code, so it’s a very extensive pocket reference, for its size. Yet still doesn’t cover Power Bars and Tool Battery Chargers.)
It would be an interesting thing to read, wouldn’t it? An actual guide to the use of power bars and chargers for the tool industry?
Stuart
Current draw is cumulative.
If you have two chargers, one with a 1.5A input rating and another with a 2.5A input rating, you should assume that using them at the same time will draw up to 4.0A of current.
Tom D
In theory you add up the ratings of each charger and size for larger than the sum.
In practicality just get a power strip with a circuit breaker built in and you’ll probably never flip it no matter how many chargers you chain (as most chargers sit there not charging most of the time).
JoeM
So you guys are saying “Sum the requirements of all your chargers, then find a power strip that can handle that total draw. If it can’t but, comes close, get more than one, and just divide up the chargers among the total draw of the power strip/bar” then?
Is it really that simple? I thought there would be some more to it, somehow. Just Add and Divvy Up among power strips? Alrighty… Sorry that went nowhere… I thought it would be way more exciting than that… Cool though! Thanks both of you!
Stuart
Also keep in mind safety recommendations. I don’t remember what they are, but I believe it’s maybe 80%. If that’s the case, try to keep your load below 12A on a 15A circuit, and that’s for a dedicated circuit with nothing else running.
Corey Moore
Minimum safety factor I’ll put on a spec or new circuit for customers is 125% of expected load. So if you’re planning on a circuit that’ll see 15 amps (corded saw+dust collection, or whatever) rating on circuit hardware and protections needs to be at least 18.75 amps.
Stuart
Thanks!
I know one company recommended 20A protection for a 16A-rated load. This might help me remember it for good.
16A is 80% of 20A, and 20A is 125% of 16A.
Bert
125% of 80 is 100. conversely, 80% of 125 is 100.
Same principle, however you remember it.
Vards Uzvards
80% it is. *Sustained* draw on an AC circuit shouldn’t be more than 80% of nominal value. I.e. 12 Amps on a 15 Amps circuit, or 16 Amps on a 20 Amps one.
Nathan
I’m glad you brought up voltage drop % – that’s one issue that creeps up fast when you either have higher voltages or you have a very long run.
I see my neighbor running his leaf blower device on 4 connected extension cords and it gives me concern every time. I got him to at least put the thick ones right by the outlets and use the thin one on the last link but still .
As the volts drop the amps can go up – which makes the cable fire issues increase.
If you can gage up a size – do so but it’s not always necessary.
notinuse
“I got him to at least put the thick ones right by the outlets and use the thin one on the last link but still .”
The order of the cords does not affect the voltage at the tool.
blocky
but the one that’s most likely to start smoking is outside next to you and not back in the house.
notinuse
If that’s the problem, probably shouldn’t own a house. 🙂
Nathan
actually not quite. the thicker cables have more capacity so they drop less and have more feed then if you were to put the smaller cable first which might restrict current flow and drop power.
Thinner wires carry less current so if you are at capacity or near it you’re better off with the bigger wires that aren’t at capacity getting more power further down the line.
Next time you look at ac ductwork where it necks down as you get further from the blower. This is a similar idea.
notinuse
No, that is not how electricity works.
Nate B
That’s definitely not how electricity works. All the resistances in a series circuit sum together, period. The order of resistors (cord segments) in a series circuit (which is how the cords act when feeding a tool at the end) does not matter.
If you had a branch in the middle with another tool hanging off there, yes it would matter and putting the thicker cords upstream of that would be the right idea. But if it’s just a single tool, it does not matter at all. Draw it out, look up Kirchoff’s Current Law, and sit down with Ohm’s Law until you understand it.
Norse
I have come to prefer the US wire extreme cords. As a building contractor, the cold weather flexibility is very good with these. I refuse to buy anything smaller than 12 gauge because most of my bigger saws are 15 amp. I use a 100 foot 10 gauge for a leader when I need to go that far from an outlet. My 10 gauge cord is a Ridgid brand. It is very heavy and tiresome to roll out or roll up, but my tool’s longevity and my sanity from not popping circuit breakers constantly make it worth it to me. The flexibility and durability of the jacket on the cord are just as important to me as the wire gauge. Nobody likes to deal with a slinky to roll up or trip over on a busy site. I try not to let my cords get driven over, but they get stepped on and dragged over some pretty rough objects regularly.
John Cashman
Keep in mind that it’s not just the wire size that’s important, but the quality of the connectors. I’ve seen cheap extension cords that use 12 gauge wire, but ends that were only listed for 15 amps. Some might think a 25 foot, 12 gauge cord is fine for 20 amps, but not with an undersized plug and socket.
Peter Fox
I gave up on pre-made extension cords 10 years ago.
The cheap ones suck and the expensive ones are not much better.
My main issue lies with the fact that molded receptacles are all junk. The contacts are thin brass and rely on the molded plastic to provide the necessary compression (spring force?) to make good contact with the mating plugs blades. I have never seen one that did not wear out quickly and fail to solidly hold the mating plug. Voltage drop across a poor cord plug can be as bad or worse than the actual cord it self and in my opinion is more likely to get hot and melt or possibly worse under heavy loads.
All of my extension cords are made with good quality type SJOOW cord (14 or 12 AWG ) and basic black Leviton field install-able plugs and cord receptacles (part numbers 515PR and 515CR). The contacts inside the any decent field install-able cord receptacles are much thicker brass and retain their spring force much better. If I ever damage a cord near the end all I need is a screwdriver, wire stripper and a knife (or just a multi-tool) and I can cut it a bit shorter and re-attach the end.
There is also a big difference in the quality of the actual cord used. The cheap orange ones are type SJTW which is PVC insulation and jacketing. Stiff when cold and not as flexible at room temp, and generally not as durable. The better more flexible ones are type SJEW or SJEOOW which is synthetic rubber jacketing (thermoplastic elastomer) however these tend to be somewhat softer tend to cet cut easily. The really good ones are made with SJOOW which is real rubber insulation and jacketing. Flexible even in cold and very durable. Even with SJOOW there are big differences in manufacture and product lines. The pre-cut lengths from the local hardware store are much softer and more squishable than the Southwire ROYAL series industrial grade cord even though both are type SJOOW
I have around 600 feet of cords made up ranging from 10 ft to 100 feet all are better quality than anything I have ever seen pre-made and my cost was about the same as buying any of the “better” grade extension cords.
My vote build rather than buy, better quality for the same or less.
BF
This guy extension cords.
JoeM
Honestly, if I was allowed to just build whatever I wanted to, I would probably do the same. I haven’t needed an actual extension cord in decades. But if I was to need one? I think I would share a wish to custom make one.
I kinda lament this “throw away society” we live in. I get more pleasure out of life when I do things myself. I don’t like having to call in others to do things I know how to do, I just lack a license for.
Paul
You missed a couple. The “S” means flexible cord. “J” means junior grade. Extra tough cords delete the “J”. For instance in movie and television production basically the whole “set” is all temporary wiring. Code mandates extra heavy (SO) style cords. It is also used extensively in industrial plants wherever a flexible cord is needed such as the final connection to a motor that moves or vibrates. The difference in cost between junior and non-junior cords is peanuts if you are really serious about making your own.
Two “O’s” (OO) means oil and water resistant, and “W” means weather (sunlight, UV) resistant. “E” means elastomer (more flexibility). So SEOOW is kind of the “ultimate” rating as far as NEC goes. However many different kinds of thermoset and thermoplastics can qualify for these ratings so this is really just the tip of the iceberg.
One “mistake” many people make is that at least according to UL, you can’t just whack off the end of the extension cord and replace it with one of the plugs you mentioned. A molded cord is UL Listed as the assembly. and cutting the end off is a modification. You can only use “DIY” ends (according to UL) if you buy cord and make your own. However federal inspectors will nick you on this minor technicality in many areas, which just proves that they are not interested in safety so much as making money for their department. As a service technician damaged cords get turned into “cheater cords” (test tools).
Peter Fox
Thanks I was thinking of explaining the cable type nomenclature further but I already had a wall of text.
Good point to the type “S” (hard service or 600V rated) versus type “SJ” (junior hard service or 300V rated). You will find that it is quite hard to get 12 or 10 AWG SOOW into a 15 amp 120 volt plug. But if you want a super durable cord it is an option.
Beyond traditional flexible cord I have seen plenty of industrial high flex type cables that would make excellent extension cords maybe not usable in a commercial setting due to UL rating but way tougher than normal PVC and rubber jacket cable. Some of those cable jackets are really tough to strip.
Jorn
I like these HDX cord/reel combos for around the shop:
20 ft. 16/3 Retractable Extension Cord Reel with 4-Outlets
https://www.homedepot.com/p/203287419
Addison
I use cordless tools, when I need corded the tool is usually high amperage. I use 3 kinds of cords, 12 gauge (mostly 25 feet), light weight crappy extension cords for outdoor seasonal lights, and a 25 foot 10 gauge 10 outlet “gang box”. If I am sanding a floor or jack-hammering concrete, I usually try to plug into kitchen outlets, and use other circuits for other tools.
Joe H
I plan to get a 100 ft length of 10/3 cord but would it really be an issue connecting two 50 ft 10/3 cords together? What kind of voltage drop would we be talking about or would it be negligible?
Stuart
In theory, 2x 50′ 10/3 cords should have the same functional resistance as 1x 100′ 10/3 cord, assuming the cable and conductors are identical for both.
To calculate voltage drop you need to know the current.
V = I x R, with I being the current and R being the resistance.
Ignoring the cord ends, the total length of wire would be the same for 1×100′ or 2×50′, and so the resistance would be the same. For the same current and same resistance, you’ll have the same voltage drop.
RKA
Depends on the tool connected to them. If you’re pushing the limits of the cord, the extra set of connectors do add a bit of resistance, so you’ll be better off with a single 100ft run.
JoeM
Have you noticed there’s a lot of “Joes” here? And also “mikes” as well. That would be an interesting little chart… how many fellow-named users do we have, and what ones are the most common?
We all know there’s only one fred. The rest are just pale reflections of him.
James Moore
I like the Flexzilla cords quite a bit. I have had one problem with them. I have a 50′ 12/3 and the cord casing pulls from the female end. Have had it happen on 3, I just keep exchanging them at Menards. I have a bunch of 25′ that I use all the time. I don’t use the 50′ enough for it to fail in such a short time.
Dave Schwartz
I refuse to buy anything small than 12AWG for use with tools. 25 or 50 feet doesn’t matter to me because some idiot (maybe me) will eventually plug two of them together.
But, I do have lots of lighter-weight cords for seasonal lights. (Amp load isn’t an issue for tiny LED lights and flexibility may really matter.)
One suggestion: Color code your cords. For example:
All my “seasonal” cords (16AWG) are dark green.
All “tools” cords (12AWG) are yellow.
This reduces confusion for “helpers” and allows me to spot problems instantly.
fred
You can go to a lower gauge than 10 if you look around – but many #8, #6 and #4 may have terminal ends for receptacles other than standard household fare.
We sometimes rolled our 3-phase stick welder around in the shop and had 4 and 5 wire extension cords with #4 wire. But we also had outlets in the shop with Russell Stoll 4-pole receptacles to match.
JoeM
You say that, and all I think is “We can always cut off the end, strip some wires, and wire it up to the receptacle format of our choice, as long as we know what we’re doing.”
I could see “Recovering” the cable from a dead Welder, in order to create a short extension cord out of its internal wires with the lower numbered gauges of wire in it. Would you ever see a problem with that, fred? I mean, even the outer insulation, one could effectively strip off, revealing only the low-gauge-number wire inside. Then just use them in the combo you need, in a new cable, with new plug and socket… Overkill? Perhaps… But maybe it might also enable someone to reroute a large amount of current, safely and efficiently, through a conduit, to a circuit breaker or breaker box?
I’m not an electrician, obviously. I just look at what you’re saying here, and ideas pop into my head. If the cables can handle more power, without overheating, wouldn’t these short, recovered cables be helpful in running high-draw circuits into freshly renovated workspaces?
fred
I’m more a plumber than an electrician. But the lugs or screw-tightened terminals that I’ve seen on 110/220V class wiring were probably designed for 12 gauge and smaller. The older Russel Stoll connectors we had used soldered-in wiring. I think that the newer ones used some sort of screw tightened connection.
https://images.tradeservice.com/9ETBOIYK8205G6UU/ATTACHMENTS/DIR100233/THOBETE76656_10-13_26_28_34_37_40_45.pdf
In our other businesses we used more conventional ready-made extension cords that would mate with typically found 110V and 220V residential and commercial services. Sometimes on big new construction sites – the electricians would run temporary cabling to outlet-stations – in order to avoid having extension cords snaked all over the place.
JoeM
Ah… This is what I get for getting a degree in Computer Science instead of going into the Trades… I was already looked down on for going for a “Blue Collar” style career in my family… Had anyone from either side said “Did you know there’s these things called ‘Trades’ Where you get to build things all day, every day, and get paid a genuine wage?” then I would sound far less like an idiot on these topics.
I just read that you had tools with much higher current wire in them all the time, and overthought the applications of such a thing, instead of just shutting up. Sorry fred.
fred
I kind of backed into the trades – buying a small family business after earning degrees in engineering and business. I don’t regret having obtained the disciplines that came with the education – nor the good fortune of being able to grow and expand a small business into something larger – with the help of partners and lots of great employees.
Dave P
Best short answer: don’t own anything smaller than a 14 and just grab whatever cord is the closest.
As far as a 12 or a 10: I’d bet the wiring in your wall is 14…..
Personally, my shop is wired with 12 on 110v circuits but I doubt you urbanite’s homes are.
Just don’t buy cheap junk. Follow that rule and don’t give it another thought.
Mac
Garage, kitchen, and outdoor circuits should be 12awg minimum. Living spaces and lighting circuits can be 14awg.
A 10awg cord plugged into a 12awg circuit will have less resistance than a 12awg cord at the same distance. Really only matters for tools pushing the limits of a 20a circuit. Most 15a max tools would be fine on 100ft of 14awg. Extended use could create heat (fire in extreme cases). Voltage drop on 120v is minor on any ‘normal use’ lengths
I agree that cords shouldn’t be smaller than 14awg.
Paul
Stuart you missed a couple important issues. The first and most critical is that you produced a lot of different charts from people selling extension cords. They make a lot of money upselling them, so it’s no wonder that they are grossly overstating things.
Second, this whole thing has NOTHING to do with current carrying capacity. Look at the following link with a chart from the 2011 NEC. It’s an older link but this chart hasn’t changed in almost 50 years.
https://barr-thorp.com/wp-content/uploads/2011/04/Digest-176-NEC-Tables.pdf
The chart includes a maximum temperature based on heating up the wiring. There are 3 columns: 60, 75, and 90 C. 75 C is the column we normally use for building wiring because most terminals are only rated to 75 C, unless we have multiple runs in the same conduit in which case we use the 90 C column, derated for multiple cables in the same conduit. But I’m just trying to illustrate a point here. Notice that at 90 C, everything up to #16 is easily able to carry up to 18 A of load. At 75 C (so we don’t melt down the receptacle) we have to go up to #14 but now the limit is 20 A! And since in receptacles typically we have 15 or 20 A breakers, clearly current handling is more than adequate for almost any extension cord on the market except the really cheap small ones for holiday lighting that probably shouldn’t be used to run a table saw.
Also please take note of NEC’s length limits….that’s another chart that you won’t find. Let me repeat that…there is NO length limit under NEC. Want to run 1000 feet of #16 to power your table saw? No problem. NEC protects the insurance companies from someone burning down their house. They could care less if you burn up your table saw motor though.
Your water analogy is a good one. Let’s say I go to the gas station to fill up the service van. While I’m there I stop and get the super mega 64 ounce cup and fill it full of my favorite beverage. But there’s a problem…no large drinking straws. All they have is those teeny coffee straws. And the 64 ounce cup is very deep. So I just force one straw into another one and stack 3 together. One thing is for sure with this setup, I won’t be gulping anything down too fast because the pressure drop through the straw is just too high.
Same thing with running too small of an extension cord. The cord itself is in NO DANGER of being damaged at all except if the plugs don’t get a good connection. The circuit breaker will shut things down just before the wiring gets hot enough to be damaged. But the voltage drop causes excessive voltage drop at the power tool. Performance is weak at best and after cycling it several times trying to get the job done, there is a pretty good chance of burning up the motor or at least shortening its life a lot. Voltage drop is the whole point of those cord charts.
Second issue is that all the charts you showed were produced by people selling cords. Needless to say, they tend to grossly overstate things in order to upsell you on the biggest, most expensive cord they can. I would try to either do the calculation yourself (looking for no more than 3% voltage drop) using one of many online calculators or use someone more independent such as ESFI. This explains why your ratings are all over the place. NEMA and ANSI standards generally allow up to a 5% voltage drop to the tool and generally recommend no more than 2-3% through the facility wiring and this allows 2-3% through the cords out of the remaining 5%…hence the length limit.
Third what you didn’t mention is that there are two different kinds of “power strips”. On job sites there are much more extensive power centers or power distribution centers which include among other things, circuit breakers and generally GFCI’s. These tend to cost hundreds of dollars and are great to set down in an area as a sort of “temporary power panel” and run cords from it. Generally you can do anything you want with one. The other type are the ones you can find almost anywhere that cost usually under $50. No matter whether or not they are painted yellow or orange they are all the same. Their purpose is simply to multiply the number of receptacles. According to their UL Listing, you can have one extension cord and one “power strip”, PERIOD. No daisy chaining power strips or cords.
Another issue with extension cords is that it is not a substitute for permanent wiring. If you have to use one permanently in your shop/garage, have another receptacle run to where you need it at.
Mac
NEC sets maximums and then defers to product ul listing/manufacturer specs. Romex (building wire) is rated to 75° because of its protective jacket, multiple wire bundling, and likelihood of being buried in building insulation. Receptacles are rated to handle a little over 20a. 90° (there are also 105°) rated wires are encased in different insulation, stranded, and single conductor. They then need to be derated (oversized) depending on how many are grouped near one another. If the ambient temperature is higher than this rating, they also need to be derated. These higher heat wires are capable of safely carrying larger currents. Deferring to cord manufacturer makes sense, as long as cord is listed (important)
While a maximum length is not set by NEC, obscene lengths of small wire would cause more voltage drop than NEC calls a safe electrical system. This would also lead to fire, which the NEC specifically dislikes. There are short length exceptions, but no maximum lengths because the voltage drop can be overcome with proper sized wire (huge for 1000ft) or transformers. OSHA thinks more than 100ft is too long.
The circuit breaker will not necessarily trip before an undersized cord catches fire or burns up. With enough resistance built up the wire can overheat while still under the overcurrent protection limiting.
OSHA again is the codes for job sites, and prohibits daisy chaining, splicing, damaged or repaired or self made cords. This is where the permanent wiring comes into play also. OSHA has decided any cord over 90 days old is trash. OSHA hates extension cords, ladders, and roofers. Also trenches. NEC merely specifies that extension cords are not to replace permanent wiring by being ‘run through walls’. At no point should an extension cord be behind the face of a wall, or penetrate through. They would also really prefer cords are not run through doors or windows. Newer buildings are required to have outdoor receptacles by doors for this reason.
Tool Junkie
Paul, thanks for this info, it was great!
Stuart, I bought a couple of corded reels for my shop and then ceiling mounted them. It keeps the shop tidy.
I never buy less than a 12AW cord. I did pop my breaker a few times when running my Bosch table saw, but I had a sub-panel run and put a couple of 20 amp outlets out in the ceiling.
I have a couple of these n which are nice when I need power out in the driveway: https://www.amazon.com/dp/B07PM96JQ7/
Stuart
Thanks! I do intend to buy one or two cord reels as well.
Right now I need a 220V extension, hence the research, and I’ve read you won’t find many suitable reels due to heat concerns. Made sense.
Stuart
None of these companies sell cords.
These charts are all “get something on your own that fits these recommendations” types of numbers.
Brands’ goals are likely to 1) ensure proper specs, and 2) ensure proper designed-for use and performance. Powermatic, Dewalt, and Bosch don’t sell any extension cords that I know of.
The NEC chart I posted above is for flexible portable cord, such as SJEOOW, SJT, SOOW, and so forth.
The chart you provided applies to building wire. You can’t apply THHN wire standards to portable power cords. THHN in say conduit, where maximum, fill volume considerations come into play, will heat up differently than portable cord which is wrapped up into a tight bundle under the jacketing.
For my use, I’m stepping up to a 20A cord over 15A because of what I read about certain tools misbehaving a little if the voltage drop is too high during start-up due to inrush current. Stepping down to 14 AWG for a 20A load would be a fire hazard.
Maybe tool manufacturers follow an abundance of caution, but an abundance of caution is always a good thing when it comes to fire hazards.
When looking for a sizing chart for 220V and 20A loads, I came across a huge amount of shockingly bad advice.
“Oh, looking at power tools, use a heavy duty cord.” Well what’s a heavy duty cord??
What you also have to keep in mind is that I’m not giving safety advice here, I’m describing what I do, and also relaying brands’ extension cord sizing recommendations.
NEC says that 12 AWG flexible cord can handle up to 25A of current. Powermatic’s recommendations seem to require a 50% safety factor and they discuss a 5V max voltage drop.
I sized-up to avoid any “is this the right size cord??” questions. It will *definitely* handle my current and future needs. That’s how I select extension cords.
Even though your chart shows that 16 AWG building wire is rated up to 18A, NEC code says that 16 AWG portable cord is rated up to 13A. Too makers’ guidelines mean you don’t have to guess whether a cord is suited for the task.
And, voltage drop does come into play as you mentioned, presumably because some tools can be more sensitive to it than others.
As mentioned, I don’t intend to use my extension cord as permanent wiring. I don’t know where my machinery will go. So, I’ll try different things, plugging the cord in for use, and then have additional outlets where I need them. I could also add a longer cord to the machinery, but I’d rather use an extension cord short-term and add better placed outlets long-term.
fred
The 220V AC induction motor circuit in the Powermatic tool that you allude to has both real and reactive power components. I’m sure that Powermatic has added a capacitor to the circuit to improve the startup power factor (induction motor no-load power factor can be as low as 0.2) – but as you say inrush current (to provide the needed magnetic field and get the motor rotating) can be much higher than normal current draw. On old fuse-protected circuits this could be an issue so a slow-blow fuse might be specified. Normal (rather than AFCI and GFCI) home circuit breakers seem to be more forgiving in dealing with short spikes.
Corey Moore
Modern breakers have that forgiveness by design, and the trip is temperature related. So you wind up with a window in which the circuit will briefly surpass it’s rating, and allow for the load to normalize without tripping. Same reason you hear about folks complaining that their breaker tripped, they unplugged stuff and they tried resetting it immediately only to have it trip again and again. Still hot, still trips.
John
So for a 50’ retractable in my garage/workshop I probably need a 12g?
Stuart
Depends on what you’ll use it for, but probably. For my own use, I wouldn’t use a 14 gauge reel for something like that unless it was dedicated to light duty tools. I’d get one with a built-in breaker to ensure it’s not accidentally over-taxed.
Tool Junkie
Yes, it would be a better idea. I have two of them. If you are running a light load over the wire like a corded drill, then you could just have a 16AWG. But remember that a 50′ cord still has the current run 50′ whether it’s coiled or extended. If you have a heavy current draw motor, i.e. a 15amp table saw or compresser running, it won’t be able to pull the power as well; especially, if you have more than one tool going on the same cord. When I had my table saw going and my buddy was using my ROS on the same cord, it upped the load over 15amps. On a 16AWG, you run the risk of overheating the wire or tool.
frampton
This is an important subject. I cringe when I see someone with an undersized cord – even pros.
Koko The Talking Ape
In my experience (which is limited), the parts that heat up are not the conductors themselves as much as the plugs and sockets. If they are loose or corroded, there’s lots of resistance, and they get hot. Twice I’ve had outlets smoke from heat.
I wish we used a better connector that created more positive contact and wasn’t so sensitive to wear or corrosion. Also, they pull out too easily, as we have all seen. I don’t know what a better connector would look like, but those connectors for electric cars chargers can handle hundreds of volts and dozens of amps. Why can’t our household outlets be more like that?
I know changing the standard would cost bejillions and take decades. But still.
OldDominionDIYer
I’m a fan of overkill. I buy the largest gage available and usually only buy 50 or 100 foot extension cords. I assume at some point I will fully load it and don’t want any issues. Nothing is less than 12 ga, some are 10 ga. More exspensive sure, but more piece of mind too. I don’t have time to sort through my extension cords and try to match them to the load. With some many cordless tools I find myself more and more not reaching for an extension cord though.
Jim Nichols
Wire codes
http://www.chem.cmu.edu/groups/bier/procedure_files/general/powercords.pdf
Robert Adkins
I fully understand gage requirements, but I just don’t like bulky cords. If they’re heavy, bulky, or stiff, I avoid them and they gather dust. I use the slimmest, shortest cord that will reach my work, so why buy the bulky ones? The good cords with thin, supple silastic insulation and supple wire are hard to find and comically expensive. I also dislike gimmicks, like huge bulky plugs, extra-wide prongs, USB, lights, breakers, etc. They always end up giving me grief.
Al
I’ll just run through my code calcs excel file
Phase Single
V 120 Volts
K Copper
I 15 amps (say a worm drive)
D 100 feet
VD 3% (NEC requirement)
Load Noncontinuous
If I had to size my wire: 10AWG considering a 3% VD. Any more, and the motor won’t see the required voltage, and it’d have to draw more current (more current, more heat).
I think 10AWG or 12 AWG should be a minimum for 100 ft extension cords. We see those long cords on construction sites. I wouldn’t even purchase 14AWG or unless those were 50 ft long. I mean those are fine at home.
The only other major factor is if they light up when powered. That’s mandatory in my book.
I’m trying to think of what uses 15 amps on the construction site beside a worm drive. A 1 inch rotary hammer corded uses 8.5amps, which is a lot less than anticipated. A shop vac uses 12 amps (which seems standard for vacuums). A cement mixer uses 11-12 amps. I think a coring system (which cores holes in masonry/cement) uses 15 amps. Ah yes, the pipe threader, which is 15 amps for 115/120V, and 8 amps for 230/240V. Air compressors tend to draw a good share of amps.
Welders often ask us to run their own dedicated circuit with a 50amp rated cord.
So if you’re not running that sort of equipment, you can get by without a heavy duty 10 gauge extension cord.
Blaine
I nearly went postal a couple of months ago trying to find a black, 12 gauge, 10-15 extension cord.
I knew exactly what I wanted and why (a heater for my wife, and an inconspicuous color for inside the house). But every site I tried refused to heed my search terms and kept offering me “heavy duty” 18 & 16 gauge cords.
Overkill for the length? Maybe. Sometimes overkill is the right answer. I like big margins.
Stuart
Were you able to find what you needed? Or did you build your own cords?