I wonder what kind of motor I actually have on my HF 2hp dust collector???

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kooshball

David
Corporate Member
Ok, so the internet and the manual for the 2HP HF dust collector say that my motor is 20a but the machine label says that it is 14a, then I look at the cord and see that it is 16AWG which according to this link is good only for 10a:
http://www.epanorama.net/documents/wiring/wire_resistance.html

I have been running this machine on a 15a circuit along with a 3.5 amp fan and some light without and fuse issues or overheating; I am guessing that the motor is really only pulling 10a at startup.

Sooo, what kind / size motor is actually attached to the "2hp" dust collector??
 

ehpoole

Administrator
Ethan
It isn't uncommon for power tool cords to use undersize power cords. There are two determining factors when choosing a wire gauge for a cord: 1) voltage drop over a given length and 2) heat generated by that voltage drop, which must never exceed the insulation temperature rating (even on the hottest of days -- and given that most cords are rated at 60C (140F) to 105C (221F), that usually isn't the primary limiter).

Because tool cords tend to be short in length, the voltage drop over that limited length is generally within accepted limits for the tool (by which we usually mean the 'motor').

Now, if you were going to extend that power cord -- or plug it into an extension cord -- you would obviously want to use a larger 14ga or 12ga cord to ensure that the maximum voltage drop remains within accepted limits.

That all said, if you are running this 2HP motor on 120V AC (which I am assuming by the 15A to 20A quoted), then you clearly cannot be drawing 20A! If you were drawing 20A then you would most likely be tripping your breaker/fuse quite regularly -- even without the extra loads you quote. Generally, on a 120V circuit, the maximum that any single device should draw is 16A, and if you are using the more common 15A plug/receptacle, then that maximum is 15A. From this, you can likely infer that your motor is drawing no more than 15A.

To really find out how much your motor is drawing, however, you will need to use an ammeter (clip on, or with a plugin induction coil) to measure the actual power draw -- or for the average user a Kill-a-Watt plugin meter will provide all the info you wish for 120VAC circuits of 15A or less (note that volt-amps (120V --or actual measured voltagte-- multiplied by Amps) will give a truer estimate of peak load than amperage, which will represent the average load over the course of the AC waveform for any device with a less than 100% power factor).
 

eyekode

New User
Salem
Nice summary. Also note that startup current can be > than the current listed on the motor. For example if your motor is rated at 15A and your circuit is 15A it is quite possible that for an instant the startup current is > 20A and it will not trip your circuit breaker.

Also note that running a motor without load will have a much lower current then when under load. The HP rating is for maximum HP and does not imply a constant HP. For example a 5HP motor will not draw significantly more current than a 3HP motor if the load is < 3HP.

Salem
 

Ray Martin

New User
Ray
Some anecdotal 'evidence' to add to Ethan's comments...

When I was a field engineer, I was once called out to service a drive unit that was supposed to be tripping a breaker. The drive's motor was supposed to pull 7 amps running. Using a clip-on ammeter, I found the motor drawing just under 7... as the label advertised. However, when I powered the unit up (from off to on), there was a draw of about 22 amps for 1 to 2 seconds.

Manufacturers often take a bit of creative license with tool specs. A 20 amp tool sounds so much more powerful than a 10 amp tool.

How was the amperage measured? Start-up versus steady run? With versus without load on the tool? All too often, you will not see anything in the fine print about how the measurement was taken.

By-the-by... same kinds of questions apply to advertised horsepower ratings... particularly when you see ratings of 3 or more horsepower on a 110V line.
 
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