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Tablesaw tripped breaker

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Forum topic by RobHannon posted 08-17-2019 04:01 PM 507 views 0 times favorited 26 replies Add to Favorites Watch
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RobHannon

304 posts in 1010 days


08-17-2019 04:01 PM

Topic tags/keywords: tablesaw breaker trip dado

So I want to chalk this up to it just being too hot outside but it has me paranoid enough that I want some lumberjock second opinions.

Was using a dado stack on my tablesaw cutting about 3/4” wide by 1/4” deep rabbet on the end of a piece of oak. Width of the oak was about 2” and I had just finished ripping a small pile of the same oak. Breaker tripped at the end of the cut.

Few details. Brand new 8” dado stack that I was getting used to. Table saw is a 3hp PM2000 on a dedicated 30amp circuit. Circuit run is under 12’ from the panel. 10g THHN wire in EMT. I am 99% sure everything electric wise is more than sufficient for the saw and it has never tripped a breaker in the past. My shop does not have AC and it is probably about 100deg inside right now. I am hoping that is all it is. The thermal reset in the saw took about 3 min to reset. No idea if that is normal or not since I have never had it trip.

After it reset I completed the other 9 of the same cuts and 5 9” long dadoes of the same dimensions. Everything seems perfectly normal now.

I have a cabinet project coming up that will require about 80’ of a similar size dado in soft maple for shelf edging. Bit of a time constraint on this project and that is why I am worrying more than I typically would.


26 replies so far

View ibewjon's profile

ibewjon

905 posts in 3273 days


#1 posted 08-17-2019 07:01 PM

I would try it on a cooler day before you get too worried about it. If it does it again, then you could have a problem. Was it the breaker, thermal in the motor, or both? Are you running 120v or 240v?

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Sark

174 posts in 840 days


#2 posted 08-17-2019 07:52 PM

My experience is that the same motor on 240 v runs cooler than on a 120 v, and produces more noticeable power. If your motor can be run at 240 v, by all means switch it over. Hopefully that will solve the problem. One of the aggravations with my expensive European slider saw with its 9 HP motor, is that the thermal protection would kick in on production runs when the temperature got hot. You would think that such a very powerful tool/motor with sophisticated controls would do better.

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Kazooman

1346 posts in 2432 days


#3 posted 08-17-2019 08:43 PM

Check to be certain the bell housing on the fan of the TEFC motor hasn’t gotten clogged up with sawdust.

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RobHannon

304 posts in 1010 days


#4 posted 08-17-2019 09:31 PM



I would try it on a cooler day before you get too worried about it. If it does it again, then you could have a problem. Was it the breaker, thermal in the motor, or both? Are you running 120v or 240v?

- ibewjon

Tripped both. Saw is 240v. Plate says 13amp, but I know inrush would be higher. Circuit is oversized because there was a 5hp saw there previously.


Check to be certain the bell housing on the fan of the TEFC motor hasn t gotten clogged up with sawdust.

- Kazooman

Good idea. I checked in the cabinet to make sure nothing got in there that would be rubbing on the blade, but didn’t pay much attention to the other side of the motor.

Ripped and dadoed about 3/4 of the maple for the project after I had lunch and reset my brain. No issues, but I have noticed that there is a squeak when I start it up with the dado stack installed. Gonna order replacement belts for piece of mind.

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ibewjon

905 posts in 3273 days


#5 posted 08-17-2019 09:54 PM

Start up current is about 3x no load running current.

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CaptainKlutz

1757 posts in 1974 days


#6 posted 08-17-2019 10:48 PM

Hmm, Let me think about this:
if you motor thermal breaker tripped, then either the motor was drawing too much current, of the thermal overload is failing.
A proper 30A circuit with wimpy 3HP motor needs a pretty major failure to trip main breaker; either had a temporary short, or 2X 3HP FLA for many seconds? :-(

I wager a small bet that you have a capacitor failing in your 3HP motor, or maybe a lose wire.
But then again, #IAMAKLUTZ not an expert?

FWIW – As capacitors age, the foil plates move closer together and they lose capacitance. Heat shortens a capacitors life, so they often act weird when hot. If capacitor develops a small enough internal short, it will sometimes melt the internal foils and open/remove the short. This might or might not trip breaker. Many times the motor and capacitor will continue to work almost like normal for weeks, until one day the continued degradation results in a bigger short that can not heal. Sometimes a failing capacitor will warn you it’s failing, without tripping a breaker. Motor spin up begins to take longer, and/or might not have as much power when cutting. Another clue is when capacitors are failing, they generate a lot of extra heat due the higher current density in smaller plate area. Check start and run capacitors for unusual surface temperatures, or look for bulging case.
IME – Best way to check them is with a capacitance meter, but only us engineering geeks own those toys.

So I would open up the wiring, look for shorts, and disconnect the caps and check them.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View Fresch's profile

Fresch

450 posts in 2400 days


#7 posted 08-18-2019 11:35 AM



My experience is that the same motor on 240 v runs cooler than on a 120 v, and produces more noticeable power. If your motor can be run at 240 v, by all means switch it over. Hopefully that will solve the problem. One of the aggravations with my expensive European slider saw with its 9 HP motor, is that the thermal protection would kick in on production runs when the temperature got hot. You would think that such a very powerful tool/motor with sophisticated controls would do better.

- Sark

Watts are watts 120v or 240v same.

View Fresch's profile

Fresch

450 posts in 2400 days


#8 posted 08-18-2019 11:39 AM



So I want to chalk this up to it just being too hot outside but it has me paranoid enough that I want some lumberjock second opinions.

Was using a dado stack on my tablesaw cutting about 3/4” wide by 1/4” deep rabbet on the end of a piece of oak. Width of the oak was about 2” and I had just finished ripping a small pile of the same oak. Breaker tripped at the end of the cut.

Few details. Brand new 8” dado stack that I was getting used to. Table saw is a 3hp PM2000 on a dedicated 30amp circuit. Circuit run is under 12 from the panel. 10g THHN wire in EMT. I am 99% sure everything electric wise is more than sufficient for the saw and it has never tripped a breaker in the past. My shop does not have AC and it is probably about 100deg inside right now. I am hoping that is all it is. The thermal reset in the saw took about 3 min to reset. No idea if that is normal or not since I have never had it trip.

After it reset I completed the other 9 of the same cuts and 5 9” long dadoes of the same dimensions. Everything seems perfectly normal now.

I have a cabinet project coming up that will require about 80 of a similar size dado in soft maple for shelf edging. Bit of a time constraint on this project and that is why I am worrying more than I typically would.

- RobHannon

Did you start/stop a lot?

View ToughCut's profile

ToughCut

71 posts in 2086 days


#9 posted 08-18-2019 12:10 PM

OK, It sounds like you simply over worked the motor and the internal overload did its job. You say it is 100 degrees in your shop but inside your saws cabinet it would be a lot hotter as this is were the motor dumps it heat. If you were feeding the wood to fast this would contribute to the problem. Also check the fan end of your motor. Bottom line is the thermal overload in the motor sensed to much heat in the motor. It is possible the thermal overload in the motor is defective but unlikely. PS I am an electrician.

-- If you are not willing to learn, No one can help you. If you are determined to learn, No one can stop you.

View ArtMann's profile

ArtMann

1425 posts in 1296 days


#10 posted 08-18-2019 01:45 PM

In the original post, the person stated that the motor was 3 horsepower. If that is true, then you can stop all speculation about whether the motor was running on 120VAC. Ain’t gonna happen.

View ibewjon's profile

ibewjon

905 posts in 3273 days


#11 posted 08-18-2019 03:14 PM

And why not?

View Sark's profile

Sark

174 posts in 840 days


#12 posted 08-19-2019 02:47 PM

“Watts are watts” and therefore the voltage doesn’t matter… true on the face of it, but my experience is that the same motor clearly has more torque when run at the higher voltage. The motor in question was a 2 hp Taiwan tablesaw motor. When I switched it to 240 v it started quicker and ran stronger.

Why is this? There are fewer watts lost to resistive loading at a higher voltage. One formula for calculating wattage is to square the current and multiply by the resistance. (I-squared r). The current (amperage) of a 2hp motor running at 240 volts is exactly 1/2 the current of the same motor run at 120 volts. Which means that the resistive load (or heat losses) generated by the 240 volt motor is 1/4 the amount of the motor run at 120 volts. Which means that the 240 motor will run cooler and have more power.

Assuming that it’s possible, the OP’s motor could very well perform better if converted to the higher voltage for reasons just stated.

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ibewjon

905 posts in 3273 days


#13 posted 08-19-2019 02:55 PM

Artmann:. There are plenty of 3hp motors running on 120v. It just takes a larger circut.

View ToughCut's profile

ToughCut

71 posts in 2086 days


#14 posted 08-19-2019 04:45 PM

Sark, your math is wrong P=IV therefore Watts is exactly the same regardless of the voltage. IE 1500 watts = 120 X 12.5 or 1500 watts = 240 X 6.25. If your wiring is long or undersized yes you will notice a difference.

-- If you are not willing to learn, No one can help you. If you are determined to learn, No one can stop you.

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Sark

174 posts in 840 days


#15 posted 08-19-2019 05:33 PM

ToughCut, your statement P=IV is one of way of stating OHM’s law. But another way of stating the same law is to consider power as it relates to resistance and current. I refer you to Jules Law, which can be stated as follows:

“A quantitative form of Joule’s law is that the heat evolved per second, or the electric power loss, P, equals the current I squared times the resistance R, or P = I2R. The power P has units of watts, or joules per second, when the current is expressed in amperes and the resistance in ohms.” Reference here

I was talking about electrical power loss, which relates to resistance in the system, and so the formula I proposed is a more useful tool to understand what happens when voltages are changed. Power losses (caused by resistance) are directly rated to the square of the current flowing though it. So if your halve the current flowing through it, the power loss will be cut by 75%. Therefore, when I have a choice of running a tool at 120 or 240 v, I will always go for the higher voltage.

But will it make a noticeable difference in every case? Did with my old table saw motor. When tools are run close to their maximum operating temperatures/capacities, a higher operating voltage could make an important difference. Less power-loss = more power provided = cooler running. Cooler running might solve the OP’s problem.

Resistance comes in many forms, as you suggest, size of wire, length of wiring, quality of the plugs/connections and switches, and the internal resistance of the motor itself. All of these resistance sources consume power by the square of the current flowing through them.

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