I have a workshop, that is detached from the main house, with electrical service off the main box. In that workshop, I have installed 14 ga. retractable extension cords. My question is how can I make sure the power being supplied at those outlets is enough to power my tools? I’m guessing some type of meter, but I’m not sure what to be checking for. I would assume amps, since most of the tools have an amp rating on them. Help.
14 ga. in house wiring is rated at 15 amps. My 7" circular saw at 1-1/3 HP takes 9 amps. I wouldn’t be making 50’ runs of extension cord but #14 sounds adequate to me.
What kind of tools? Power drills or big honking tablesaws?
Big tablesaws or other power hungry equipment would be better off driven directly from a 20A source rigged with 12 gauge wire. Or use a heavy duty extension cord, as short as possible. (You lose a bit of voltage over long runs of extension cord due to the inherent resistance in the wire, and according to at least some owner’s manuals, that can shorten the motor life on some tools.)
I don’t think you’d ever actually measure the output of your power outlets (it would be hard to get useful results), mostly you’d just run the aforementioned 20Amp circuit(s) to the workshop. Realistically for most tools, you can get away with a 15 Amp circuit.
Here is how the New Yankee Workshop is set up:
We have 200 amps available in our shop. Table saw and surface planer operate on 220v as does the large sander. Everything else is 110v. We have outlets in floor for the table saw. Others along the walls and also in the ceiling. Each wall has its own dedicated 20A circuit. Our experience is that rarely do we have more than one tool at a time running thus no need for super power **but many outlets close to the tools without the need for extensions is the objective. **
Lighting is by skylights on the north facing roof augmented by two long strips of fluorescents.
Service is run back to the main panel to avoid power hits in the other buildings on the property.
Hope this helps.
**
Emphasis mine.**
Okay, some more background. I have the workshop wired with 20A outlets every 8 feet. So, all the big tools, table saw, jointer, drill press, etc., get plugged into them. As extra coverage, mostly for hand tools, I installed two 30 ft. 14 ga. retractable extention cords. If I want to power the 12" miter saw, for example, with one of these, would I be getting enough power? We ran, I believe, a 60A capable line from the main breaker box out to the building, then 20A circuits from there. I just don’t want to have the level of power degrading too much to run some of my bigger hand tools.
Thanks for your thoughts, so far.
To answer the original question, yes it’s the amps (or “load”) you need to look at on the data plates when evaluating the wire size, breaker size, etc.
You don’t say whether your outlets are ganged onto one breaker or if they are fed separately. This is important in case you are ever running more than one tool at a time. If a friend is running your miter saw and you start using a large grinder, you could trip the breaker.
Also, I hope you wired with GFCI protection.
Each half of the workshop is on it’s own breaker. The lights are on their own, and the wall unit a/c is on it’s own. Usually, I’m only operating one big tool at a time. So far, I’ve never tripped a breaker.
As for the GFCI question, I did not allow for that. Isn’t that something that is usually done in bathroom, to safeguard against water shorting the circuit? Tell me more about why I should have done this, and if I should go back and rectify now.
Nah, I would keep using AC if I were you.
Look on the nameplate of the miter saw. A 12" saw sounds like it might be close to the 15 Amp. limit for your extension cords. Although with an operator right there the chance of anything bad happening is minimum you will have combustibles in the form of sawdust around and if you run the saw for a long time the cord could get a little hot. Since you say the extensions are 30’ long
Since you say the circuits are protected to 20 Amp. you might put in a few heavy duty #12 extensions for the bigger hand tools.
With #14 wire drawing 15 Amp. the line loss will be about 2-1/4 V. at room temperature. With that current in an extension cord it will heat up resulting in more resistance and a higher loss. Added to that is the voltage drop at the plugs which is not insignificant and the plugs will also get hot.
In fact, after you check the current on the miter saw nameplate why don’t you take one of your extension cords, plug the miter saw in and check its perfirmance. Run it long enough to give a good test and saw some scrap to increase the motor load. After the test feel the extension and the plugs to see how hot they are. If you can grip them firmly and hold on they aren’t over about 135-40[sup]o[/sup] F which is hot but should be OK.
Generally, GFCIs are required in kitchens, bathrooms, garages and outdoors, as well as on jobsites (there are some other requirements, but it’s irrelevant to this discussion). Water is not required to be present for a fault to occur. Here is a discussion on the requirement for GFCIs in a workshop.
They’re inexpensive and can save your life.
I checked miter saws and found a Porter-Cable 12" that uses a 15 amp. motor so you probably should get a #12 extension cord for that. Also make sure your outlet is a 20 amp. outlet. The run-of-mill is 15 amp. As I recall the 20 amp. outlets these days have one prong with a horizontal bar or tab on it in order to identify it as 20 amp. capacity.
Only thing missing in the commenary so far is that there is nothing that you can easily measure do determine if your cords are suitable. It’s all either calculations or observations.
There are 2 factors to extension cord wiring - Voltage drop and amp heating.
Amp heating is the wiring getting hot from the current flowing in the wire. This is what the code bases wire sizes on. Go per code and you should be OK for this.
Voltage drop is how much the voltage on your line drops when the tool is operating. A long cord sized adequately for code could still have excessive voltage drop to degrade tool performance. If you do not have a tool plugged in, you can measure the voltage at the end of your extension cord. But if you do not have a tool plugged in, there will be no current draw, and so no voltage drop, and you will measure whatever the power company is sending into your house. OK, I suppose that you could plug a power strip into the end of your extension cord, run your tool of choice from one plug on the power strip, and check the voltage on any of the other plugs off the power strip. That would tell you the voltage drop. If your voltage drops below 100 V you are likely to see performance drop on tools.
Nameplate Amp data is often pumped up as a marketting tool (oooh, this one has 15 amps! That’s better than 12A!) but usually has little bearing on tool amp draw in actual use. If you can plug it in to an outlet, you are safe to use it on that outlet (Assuming that your house is to code). Worse thing that will happen is you will blow the breaker.
After all that, I’d say just plug your tools in and see if they work to your satisfaction.
You could make an easy conversion to GFCI if you know how the outlets are run. You can put one GFCI at the beginning of the circuit to make all outlets GFCI protected.
Absolutely correct and also code-compliant.
I was in a similar situation, trying to decide how to install AC outlets. I kept flip-flopping.
Hahaaa - electrician joke! 
(I’m not an electrician - I didn’t get it until I looked up “rectify”: “to make an alternating current unidirectional”)