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I don't understand how it can be the supply line when its the MOTOR breaker that is popping and not the panel circuit breaker. These motors may draw a high amperage on starting, but I doubt even under load they are drawing full rated current.

I think we're assuming it's the supply breaker, not the motor overloads?? He did say"It's breaker" in OP. Now you've got me wondering. Is it the breaker to the machine or the overloads on the motor????

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Rob

The voltage drop across a long cord if it is undersized for the amperage it is carrying will cause the motor to labor and draw even current, so yes a cord can cause these kinds of problems. I also read the 1st post wrong and assumed the breaker in the panel was opening the circuit.

Fred

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Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

Fred, you used to be an electrician or electical engineer, right? How does an undersized cable cause an induction motor to draw more current? I'm a mechanical engineer, so I'm a bit lost here.

Mike, I'm not a motor guy but I am a EE and at work, we test our machines, which have motors in them, for current draw at all rated voltages. As the voltage goes down the current draw always increases.

The power needed for the motor to do the job comes from the voltage and current (recall Power = volts x amps). If you try to get a motor to do the same job with less voltage then the current is going to increase. Load it down enough and it'll pop the breaker on the machine or even the breaker in the panel depending on how it is sized. There's more to it, of course, but this is close enough. Maybe Fred will add something.

Most of us are familiar with motors in our large tools that can run on 120 or 240 volts. If you look at the rating plate you'll see that the motor will draw about 1/2 the current at 240V as it does at 120V. Same idea. There are other inefficiencies that crop up at lower voltages such that your motor running on 240V will also provide a bit more power then it will at 120V.

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Steve Smith
"Music is what feelings sound like"

Ok, so if the extension cord is undersized ( higher resistance) them that could cause a voltage drop that would cause the motor to draw more current?

One more thing. I have a table saw that can run 120 or 240. I heard there was little advantage to rewire for 240, but u seem to indicate better efficiency (less heat) and a bit of power increase. True?

If I only needed a ten foot cord I would either get a 25' #12 cord, cut it down to 10' and add a new end to it (heavy duty of course) or start from scratch and buy 10' of 12 gauge 3wire cable and add a plug and recepticle to it.

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Joe Beaver
Maker of Sawdust

I did what Joe suggested in my shop, made my own extension cord out of 10g wire

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Formerly known as Adaboy.......

We seem to have lost the OP in this thread to find out which breaker is popping, whether the wall circuit is 15 or 20 amps, and the length and gauge of the extension cord he's using, among which are most likely the clues to his problem. In general though, I just always wire outlet circuits for 20 amps with 12 gauge wire. There is no special reason an extension cord is bad or shouldn't be used, it just needs to be sized properly. There are charts for amps versus gauge versus length. To keep it simple and be safe, continuing a 12G/20A outlet with a 12G cord ought to be fine almost always, unless your run is getting really long. Voltage drop due to over long runs is weird. I don't think it's a linear Ohm's law thing where voltage drops so current (amps) increases. Even if it is, this won't pop a breaker if you're still below it's amp rating, so you can run a motor at too low a voltage and burn it right up, as has been mentioned. It's funny I never see voltage drop mentioned in regards to in-the-wall wiring (it's probably there if the code book were dug into deep enough). I guess it's assumed that no wire run in a building (well, residence anyway) is going to get long enough to be a voltage drop problem. But sometimes they can be pretty long, and a long extension cord in the outlet at the end of it could be more of a problem than some other outlets. All this is also why using 220 volts is cool. Only half the amps are needed to deliver the same power (watts) versus 110V, so you can go longer distances over smaller wire. I've had several machines that can run on 110 or 220, and I've always converted them to 220, and always felt they ran better on 220. So I thnk it is good even when voltage drop is not at issue.

Not sure the above is relevant to the thread, but there you go nonetheless...

Peace,
Sanaka

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...imagine there were no hypothetical situations...

True.

When you run a motor on 120V you still have the lower voltage/ higher current thing going on. The higher current means there will be more voltage drop in all of the wiring from the breaker panel all the way into and icluding the motor windings. This means less voltage is available to the motor for work. The situation just gets worse when you load the motor down.

During 240V operation the higher voltage means current is essentially cut in half. Less voltage drop, more available to the motor. Motor starts faster and everything runs cooler. Also more available when you start to load the motor down. Essentially the motor just runs more efficiently.

So 240V wiring makes sense for motors that are operating with a load such as stationary tools, dust collectors, and compressors. Helps you to get a little more out of them.

If we have any real motor folks out there feel free to jump in here. I just use em, I don't design them.

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Steve Smith
"Music is what feelings sound like"

The reason we lost him is because he has been getting ready to leave for vacation, and since runs a one man business that means he works all hours of the day. He will be gone till next Saturday or Sunday I believe.

I will try to answer some of these questions and maybe even go over to his house and run some experiments to get more info so we can try to figure this out. It is the breaker on the motor that is popping. I don't know what the wall circuit is I will have to find that out. and depending on the organization of our shop/garage this week the extension chord could very well be the problem I know we have some newer larger gauge chords, but also some old not so good ones mixed in. I will try to get more information for you guys.

Thanks for the help so far.

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--Kyle Burner--

The thing that's definitely true is that at 240v, it will draw half the current it does at 120v. If your wiring is marginal, it can make a difference.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

My wiring is not marginal! It is exceptional!

After talking to the people at Jet - they thought it sounded like a faulty motor reset switch.

A little over $20 and about 2 minutes of install and my drum sander is running as good as new.

No more shutdowns at all.

Whey - glad that was an easy one.

I AM running to a direct outlet now just to be on the safe side. (I eliminated my extension cord)

Thanks to all who replied!

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P A U L B U R N E R
Burner Guitars

Man! Not a single one of us got it right. We suck!

Mike

Onr thing to consider when requiring a motor from 120 to 240 .. they dont really run any cooler - here is why. Eng school was a while back but here goes ...

Power = volts x amps = amps ^2 x resistance (this formula shows where the heat factor can vary the R value)

So ...the amps do get cut in half .. sort of - at least in the wall wiring. What you are doing when converting the motor is taking two sets of coils in the motor, that were running in parallel at 120, each coil seeing half the amps, say 9 of 18 ( I had a 1.5 hp that had that rating way back as an example )and converting them to series. Now the two coils are in series, and they have 240 across them, with 9 amps still running thru both coils, just not in parallel. heat is the same as the current is the same in each coil. The voltage drop thru the line is better though (less loss to heat - , volts =IxR, watts = I^2 R calculations, R goes up as the heat increases for pretty much any metal), as is the heat loss in the line. Power at the motor is marginally better as the voltage should be higher, but even then, that could be rectified in the 120 V scenario by using larger cable. There is also less loss in solid vs stranded cable - wall vs ext cord.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Glen,
I have the 16-32 also. When I first started using it, I would blow the breaker on the machine a lot. I was taking to much off in one pass. Or, the paper would get clogged and overwork itself. Go to Home Depot and buy 10' of 12 gauge wire and a male and female end and make your own cord. It will be cheaper than buying a long cord. An undersize cord will definitely cause a motor to overheat. And eventually ruin the motor. I have 20 amp breakers on my 110 outlets also. 15 isn't enough in a shop. The breaker on the 16-32 is set to go when the motor reach's a certain temperature. Check your manual.

Sorry Glen, I didn't see you found the problem. That is good to know in case it ever happens to me.

Glad you got it working okay.

FWIW, with my 16-32 I only take off 1/16th of a turn at a time, max. I read somewhere that for good results, the max you should take off is the thickness of the grit on the sandpaper you are using....

Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"