Can this happen

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  #1  
Old 03-19-05, 07:15 AM
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Can this happen

Not sure whether to post in tools or here but thought I would get a more precise answer here.

Harbor Freight is advertising a table saw that supposedly has a 3 hp motor that draws 14 amps at 110 volts.

Someone said it's either magic, a misprint or a lie.

Any electrician help me out on this. I would be hooking it up to a 15 amp circuit. And it and a small shop vac would be the only items running (besides lights). But I am more interested in finding out can a motor be 3hp, draw 14amps at 110volts?

Thanks,

Pete
 
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  #2  
Old 03-19-05, 08:11 AM
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Pete,

You are right to question their numbers.

The hp rating that tool manufacturers use is maximum developed hp.
This is the maximum hp developed before stalling and only reflects a motor's power when starting against a dead load.
The proper way to measure hp and one that makers of industrial motors use is continuous hp. HP that can continuously be maintained.

Another deceiving thing about the numbers on these tools is that although they brag about the maximum developed hp, the amperage shown, which will be correct btw, is the amperage when running under maximum continuous load.
A 110 volt motor that draws 14 amps will be about 1 1/2 continuous hp.

I have two air compressors that are spec'd as follows.
One uses an industrial 3 hp compressor motor that draws 14 [email protected] volts.
The other is a Speedaire that has a 5 hp motor that draws 15 amps @220 volts.
One amp for the extra 2 hp looks pretty efficient wouldn't you say!!!

Although not entirely accurate I would look at the amperage as a sign of power.
If looking at air compressors, cfm at 90 psi would tell you the capacity of these.

Also, keep in mind that if you purchase this saw, it will require a dedicated 20 amp circuit so as not to be constantly tripping the breaker.
 
  #3  
Old 03-19-05, 08:35 AM
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You need more circuits. You can't run a table and a shop vac onthe same circuit at the same time.
 
  #4  
Old 03-19-05, 09:50 AM
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Thanks Greg and Joe. Both answers are what I suspected. Could I run this saw without the shop-vac?
 
  #5  
Old 03-19-05, 12:53 PM
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Greg or Joe or anyone,

The HF saw specifically says 110v, 60Hz, 2300 watts, 22.2 amps, 3 HP, 3,400 RPM for its electrical requirements.

If I only have the overhead light on and not the shop vac, you sure this can't be run on a 15 amp circuit.

What is the easiest way to test the amp? We just purchased this house and not all the circuit breakers are labeled? Our laundry is in the back of the garage and the washing machine is on a 15 amp, dryer on heavy duty line.

One out and garage door opener/outlet left. I am not sure a new separate line can be run (easily). I would imaging it can be done but I know I can't, maybe an electrician who is good at fishing could pull the wires...

Pete
 
  #6  
Old 03-19-05, 01:15 PM
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You might be mixing things up. The numbers don't make sense.
Provide a link to the exact saw you are looking at.

The maximum load you can draw continuously on a 15 amp circuit is 12 amps.
 
  #7  
Old 03-19-05, 02:51 PM
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Different types of motors have different ratings
Below is the most common average ratings.

Full-load amps for universal motors.
This will be for motors that have brushes. most (not all) Hand power tools like your drills, saws, shop Vac...

At 120 volts

1 HP @ 9.5 amps
1-1/2 @ 13.2 amps
2 HP @ 17 amps
3 HP @ 25 amps
-----------------------------------
-----------------------------------
Single-phase AC induction motors.
Most (not all), washing machines, dryers, fans, air compressors, table saws...
Most induction motors need to pull over 3 times the amps for starting. Maybe less then 3 seconds.

Full load Running current at 115 volts.

1/2 Hp @ 9.8 amps
3/4 HP @ 13.8 amps
1 HP @ 16 amps
1-1/2 HP @ 20 amps
2 HP @ 24 amps
3 HP @ 34 amps
 
  #8  
Old 03-19-05, 06:52 PM
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Here is the link to the manual. Information I gave is on page 2.

http://www.harborfreight.com/manuals...6999/46813.pdf
 
  #9  
Old 03-20-05, 02:01 AM
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I would guess it has a 3/4hp or 1hp induction motor.
It may or may not start on a 15 amp circuit.
The required starting current can be over 3 times higher then the running current of 14 amps.
somewhere in that hi starting current is that 3 hp calculation only at start up.
3 hp starting torque.

Most circuit breakers have some delay that may let you get the motor started.
If your plug it more then 40 feet from your main panel that can add to starting problems.
If your blade gets dull more then likely your going to trip the breaker.

If an induction motor does not start up within about 5 seconds that hi start-current can burn up the motor or shorten its life.
 
  #10  
Old 03-20-05, 04:50 AM
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psal2,

The 22.2 amps referred to in the manual is the recommended circuit amperage.
The product information says this saw will draw 14 amps.

A 20 amp breaker may not hold the load and you would likely need to supply a 30 amp 120 volt circuit to this saw.
Many saws like this are capable of being rewired to 220 volts which would reduce the wire size considerably. It doesn't say you can do that to this one.
 
  #11  
Old 03-20-05, 05:09 AM
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GregH,

Thanks for the information. I will get a local electrician to visit to discuss this with him. I am not sure about rewiring it to 220 either. If I could, then I could maybe run it off the dryer outlet. Do they make 220 extensions...LOL...because it would be about 30 feet away from where I would need to set up the saw?

This is good advice and I do appreciate it.

Pete
 
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