# Table saw started tripping gfci



## mercwear (Jan 19, 2015)

I ran some conduit in my garage shop a few weeks ago and all of my bigger tools (Table Saw, Jointer, Planer, Lathe etc..) from outlets that are run off of a 20amp gfci protected circuit.

Everything has been working fine up until today. I adjusted my table saw blade to 45 degrees (2 year old Rigid R4512), turned the saw on to begin my cut and the gfci tripped. The breaker did not blow, just the gfci. My first though was that my wiring job on the conduit may not be up to snuff so I checked everything and it's fine. I could not get the gfci to reset to I installed a new one (20amp) and the same thing happened. This time the switch reset so I tried the saw again and it stated up. I knew the problem was not fixed so I shut the saw down, waited for the break to stop the blade and turned it back on - gfci blew.

I can run ANY other tool off of that circuit but if I plug the table saw into any outlet on the line it will blow the gfci 95% of the time. Before I call an electrician to look at my conduit ($$$$) I want to rule out the table saw as my problem. From the research I have done it sounds like the table saw motor could be shorting out or the capacitor that gets the motor could be drawing too much power and tripping the gfci.

What really confused me is when I run an extension cord to another gfci outlet the saw will start up! but I run the same extension cord to the outlet that trips in my garage the saw wont start.

I really am at a loss here, any help is much appreciated. I know that one solution that has been given is to do away with the gfci all together, I want to avoid this.

Edit: I did look at the cord of the table saw and followed it to the switch and then the motor and there were no shorts that I could find. I have NOT opened up the motor yet.


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## agallant (Jul 1, 2010)

I would change the breaker/outlet (depending on which one it is) first. They can go bad and do strange things.


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## mercwear (Jan 19, 2015)

> I would change the breaker/outlet (depending on which one it is) first. They can go bad and do strange things.
> 
> - agallant


Thanks. I already swapped the gfci with a new one and the same thing happens.. The breaker has not flipped and I am not comfortable replacing it so that is something I would have to pay an expert to do =)


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## Burgels (Jun 10, 2013)

Is the breaker a 20amp as well? That's not common for a 110 line but not unheard of either. Why are you stuck to the idea of a GFCI? Unless you have the risk of water near your saw it isn't necessary. The breaker handles the job of not allowing too much current in the line. (I'm not an electrician but I've done some work in that area in my own shop)


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## mercwear (Jan 19, 2015)

> Is the breaker a 20amp as well? That s not common for a 110 line but not unheard of either. Why are you stuck to the idea of a GFCI? Unless you have the risk of water near your saw it isn t necessary. The breaker handles the job of not allowing too much current in the line. (I m not an electrician but I ve done some work in that area in my own shop)
> 
> - Shane


Breaker is 20amp yes. As for the gfci, I just want to keep my garage up to code if possible.


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## Burgels (Jun 10, 2013)

Ahh yeah that makes sense for a garage. My shop is a separate building so that isn't required. I guess the next thing would be to replace the breaker. I know you said you don't want to do it but it isn't hard at all. Scary, but not hard. Worst case have an electrician do that for you because you've pretty much ruled out everything else unless you got two bad GFCI's in a row


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## SignWave (Feb 2, 2010)

Since the problem doesn't happen every time, then look for something that is intermittent. A loose connection or a place where intermittent contact is being made, like a nick in the insulation of a wire.

A GFCI trips because the current in the neutral is not equal to the current in the hot, at the GFCI. That can either be because the neutral is making contact with ground, or hot is making contact with ground. (It doesn't have to be the same ground as the one in the circuit, any ground will cause a problem)

In your scenario, I'd look for a wire that got pinched or pulled when you adjusted the angle on the saw. If you have a multi-meter, test the resistance on the UNPLUGGED cord. Hot to ground should have infinite resistance, and so should neutral to ground. If you have working breakers and the problem is overcurrent, then the breaker should trip before the GFCI, almost every time.

I know a problem in the saw doesn't explain why it works on the other circuit. Maybe that other GFCI is bad and not tripping, or maybe it's just an intermittent problem.

The other thing I'd check is to make sure the neutral isn't nicked and making contact with the conduit or box (assuming metal, not plastic conduit and boxes).


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## TheFridge (May 1, 2014)

motor loads can kill gfcis. Some quick. Some not so.

That being said. Run the saw till it trips the gfci. Pull the plug. Turn the saws switch on. Check for continuity between either hot or neutral prong and the ground prong with a meter or something that tests for continuity.

If there is continuity between hot or neutral and the ground you have a short to ground in the motor

Or

The ground is touching the neutral somewhere.


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## clin (Sep 3, 2015)

I had something similar just today with a band saw. Yesterday it worked fine, today, it tripped the GFI as soon as it was plugged in.

Using an ohmmeter, I measured the resistance, at the saw plug, between ground and each of the plug conductors (hot and neutral). Darn if one of the legs measured something less than over-scale. It fluctuated but was below 100 K ohms. This means there was a path for current between that circuit leg and ground, Not a direct short, but enough to cause an imbalance that would trip a GFI.

I took a look inside the band saw electrical control box, nothing obvious there and a complex circuit board left me a bit lost. I decided to blow some compressed air in the electrical to make sure nothing was stuck in there. That made no difference.

Since I also had the saw open (as you would to change the blade) and had the compressed air at hand, I decided to blow all the dust out of the wheels and anything else in there.

While I wasn't expecting this to help my problem, it did. No more measurable resistance and it no longer tripped the GFI.

I really have no idea why. No electrical circuits or wires are exposed in the area where the blade moves. Perhaps there is already some failure of insulation on the motor and the dust provided an additional path for this to the ground body of the saw.

In any case, you might try giving the saw a good cleaning and see if the problem clears up. This also seems possible given the fact your saw didn't' act up until you tilted the blade to 45 degrees. Anyway, something to try.


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## ForestGrl (Jun 5, 2015)

> [Snip]
> What really confused me is when I run an extension cord to another gfci outlet the saw will start up! but I run the same extension cord to the outlet that trips in my garage the saw wont start.
> 
> - mercwear


I would think this is a major clue that the problem is in the specific circuit, and not in the saw, assuming the circuits have same amps. Have you tried hooking up another tool with similar power draw to the suspect circuit? I would first suspect the circuit breaker (really, you might be OK replacing that yourself. I did one years ago, and I hate electrical stuff!), especially since you already tried a new GFCI. (Hopefully you know you need only 1 GFCI for each circuit-it goes on the first outlet in the series of outlets IIRC). It seems odd that a 13 amp motor would pull more than 20 amps on start-up, unless the motor or capacitor is defective, but that's irrelevant if it works on a different circuit.

PS: Have you tried plugging in one of those tester-plugs that tells you whether or not the outlet is working properly?


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## ForestGrl (Jun 5, 2015)

OK, another question that seems insulting to ask, but I've made this mistake-is there anything else on that circuit that you might be overlooking?


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## mercwear (Jan 19, 2015)

> OK, another question that seems insulting to ask, but I ve made this mistake-is there anything else on that circuit that you might be overlooking?
> 
> - ForestGrl


Thanks for the reply. The saw is the only thing running on the circuit at the time.


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## mercwear (Jan 19, 2015)

> motor loads can kill gfcis. Some quick. Some not so.
> 
> That being said. Run the saw till it trips the gfci. Pull the plug. Turn the saws switch on. Check for continuity between either hot or neutral prong and the ground prong with a meter or something that tests for continuity.
> 
> ...


I tested the ground to hot and neutral on the ohm meter and never got a reading less than 1 (no change at all on the meter) so I don't thing the saw has a short.


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## TheFridge (May 1, 2014)

Well that's a good thing. Try blowing the motor out. Open the motor j box and clean it if it needs it. Could be the cord. Had to replace 50' of 8/3 SO cord on a job because one of the hots were messed up with no apparent damage to the cable.


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## jonah (May 15, 2009)

My first thought was that you pinched or pulled and damaged the cord when you tilted the blade. It's not the most likely scenario, but it popped into my head. A damaged cord could create a ground fault that would trip a GFCI outlet. However, you likely eliminated that as a possibility by trying the saw successfully on another outlet.

You could also have a damaged wire in the wall, in the conduit, or inside the receptacle box. You could have frayed insulation on a wire inside the breaker box. You could have a bad breaker (unlikely).


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## ForestGrl (Jun 5, 2015)

> OK, another question that seems insulting to ask, but I ve made this mistake-is there anything else on that circuit that you might be overlooking?
> 
> - ForestGrl
> 
> ...


Hopefully, you saw my first (more substantial, LOL) reply, which asked 2 questions about testing the outlet you're plugging the saw into.


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## LarryT (Sep 18, 2012)

I had a similar problem 2 or 3 years ago. I have an older Delta drill press with a motor 
that is probably 60 years old. These old electric motors are extremely durable but 
the insulation will not last forever. I had a GFCI trip and I tracked it down to the drill press as the cause. I had wired in an earth ground since the older motors had no such provision. When I disconnected my ground wire on the motor, the drill press would run. Testing with a voltmeter showed that there was about 30 to 40 volts on the frame of the motor and consequently on the press itself! Not a safe situation! I bit the bullet and installed a new motor. This eliminated the problem. The old motor had a high resistance leakage to the frame somewhere and it was enough to trip a GFCE. That's why code requires them in this environment. Motors are incredibly expensive today but it doesn't seem cost effective to try to have a fractional horsepower motor rebuild either.


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## mercwear (Jan 19, 2015)

> OK, another question that seems insulting to ask, but I ve made this mistake-is there anything else on that circuit that you might be overlooking?
> 
> - ForestGrl
> 
> ...


I did thanks! I am currently testing the circuit with one of those testers and going through my wiring again ;-/


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## mercwear (Jan 19, 2015)

I just spent all day trying to track down the problem. I finally ran the saw off of another gfci outlet and it started up like it did the first time I did this however I let it run and after about 3 minutes it tripped the outlet. So the saw does not play well with gfci for some reason or another. My solution at this point is to run a non gfci outlet for the saw, I don't like this solution but the saw has no ground faults so I think it's just the motor throwing off the current enough to drip the gfci.

Thanks for all the help!


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## PLK (Feb 11, 2014)

Maybe a real electrician can post some helpful info. I work construction and plug into gfci's on a daily basis, we normally last an hour max before running an extension cord into the house we are working on to not trip them. New electric codes require them, plug a 13amp hair drier into the new gfci's with the new panel codes and you will trip them.

The new gfci's and panels are a real pain in the ass.

paul


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## TopamaxSurvivor (May 2, 2008)

Sounds like your insulation is breaking down in your saw, probably the motor, but could be anywhere. The trip current for a GFCI is about 5 milliamps. That means you probably will not be able to accurately find the "short" with most meters. The resistance will be in the 25,000 ohms range. Seeing it will require a good meter such as a Fluke or maybe a high voltage mega ohm meter (megger). Since it is happening on 2 GFCIs at different timing cycles, my guess is insulation breaking down as the motor heats up. In that case, I doubt you can really test the motor without a megger unless you just get lucky.

The purpose of the GFCI is to trip well before the fault current is high enough to put the heart into ventricular fibrillation. Trust me, you do not want to got there! The first GFCI is probably tripping at a couple milliamps lower than the one that holds as is the new one.

FYI Forestgirl, All motors have infinite starting current for the first few cycles. Typically what can be seen on a good analog meter will be about 4x full load current. That has more to do with the limitations of the meter movement than the peak current of the first few cycles.


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## TheFridge (May 1, 2014)

Doin electrical for the last 15 years. Just sayin Paul. I hope that qualifies.

Sounds like the motors breaking down.


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## PLK (Feb 11, 2014)

> Doin electrical for the last 15 years. Just sayin Paul. I hope that qualifies.
> 
> Sounds like the motors breaking down.
> 
> - TheFridge


I wasn't calling you out, simply giving my own experiences with new gfci's and the new "safety" breakers being installed these days in new construction homes. I wasn't directing my comment to you at all.

Paul


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## CharleyL (Mar 10, 2009)

> motor loads can kill gfcis. Some quick. Some not so.
> 
> That being said. Run the saw till it trips the gfci. Pull the plug. Turn the saws switch on. Check for continuity between either hot or neutral prong and the ground prong with a meter or something that tests for continuity.
> 
> ...


Less than 1 on the meter is a dead short on the ohms scale. You should be reading infinity (opposite end of the scale) when touching one lead on the ground (green) wire connection and the other lead on either the black or white wire connection and the selector on R X 100 (and with the saw disconnected, of course). If the saw has a regular switch and not a contactor type start circuit, the power switch on the saw should be On when you do this. Any reading below infinity is resistance to ground and likely the reason why your GFCI is tripping. You have to know how to read your meter and basic electricity to understand this.

Charley


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## mrg (Mar 10, 2010)

What gauge wire did you run? How did you run the conduit if you are not comfortable to change the breaker, or did you run the line from another outlet/junction box. Check your connections, wire nuts etc. If you are running 14 gauge this may be your problem.


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## ForestGrl (Jun 5, 2015)

Well, here we go. Seems when the question involved electric problems, the room gets quite heated. So predictable, so unproductive. Just saying….....


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## ForestGrl (Jun 5, 2015)

I have a genuine and sincere question for those of you who think the saw motor is the culprit: Why is it, then, that he can plug the saw into a different outlet and everything is fine?


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## TopamaxSurvivor (May 2, 2008)

The problem with with using 99% of Volt Ohm Meters is they will read infinity with a 30,000 ohm short. None of them operate on more than 9 volts. That is not enough horsepower (pun intended) to break down the insulation and identify the short.


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## Burgels (Jun 10, 2013)

Yeah people were still arguing about my question a while back after I'd already finished it and moved on



> Well, here we go. Seems when the question involved electric problems, the room gets quite heated. So predictable, so unproductive. Just saying….....
> 
> - ForestGrl


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## mercwear (Jan 19, 2015)

> What gauge wire did you run? How did you run the conduit if you are not comfortable to change the breaker, or did you run the line from another outlet/junction box. Check your connections, wire nuts etc. If you are running 14 gauge this may be your problem.
> 
> - mrg


I ran 12/2. I am not comfortable with the breaker because I have never done that type of work before =)


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## mercwear (Jan 19, 2015)

> I have a genuine and sincere question for those of you who think the saw motor is the culprit: Why is it, then, that he can plug the saw into a different outlet and everything is fine?
> 
> - ForestGrl


In my last update I posted that the other Gfic did indeed trip after running the saw for a few minutes. So the saw seems to be the culprit =/


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## mercwear (Jan 19, 2015)

> The problem with with using 99% of Volt Ohm Meters is they will read infinity with a 30,000 ohm short. None of them operate on more than 9 volts. That is not enough horsepower (pun intended) to break down the insulation and identify the short.
> 
> - TopamaxSurvivor


My meter is reading 1 when I test the saw ground to hot / negative so it's probably not sensitive enough to detect the short.


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## mrg (Mar 10, 2010)

I understand not wanting to be in the panel. You said it started tripping on another gfi, maybe another brand gfi may do the trick. I had bought a couple and installed and one tripped for no reason a couple of times. Called my electrician and he told me to get a different brand from the supply house and haven't had a problem since.


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## mercwear (Jan 19, 2015)

> motor loads can kill gfcis. Some quick. Some not so.
> 
> That being said. Run the saw till it trips the gfci. Pull the plug. Turn the saws switch on. Check for continuity between either hot or neutral prong and the ground prong with a meter or something that tests for continuity.
> 
> ...


Saw is reading 1 when tested with ohm meter so either my meter is not good enough or the saw is not the problem.


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## TopamaxSurvivor (May 2, 2008)

> The problem with with using 99% of Volt Ohm Meters is they will read infinity with a 30,000 ohm short. None of them operate on more than 9 volts. That is not enough horsepower (pun intended) to break down the insulation and identify the short.
> 
> - TopamaxSurvivor
> 
> ...


I'm not sure what you are reading. The breaker should be tripping in that case, not the GFCI.


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## TopamaxSurvivor (May 2, 2008)

> I have a genuine and sincere question for those of you who think the saw motor is the culprit: Why is it, then, that he can plug the saw into a different outlet and everything is fine?
> 
> - ForestGrl


GFCIs trip at different levels of fault for various reasons, including not at all when improperly wired. Since it trips one immediately and the other after a few minutes, I suspect the motor insulation is beginning to break down and as it heats up it gets closer to failure. There is a small chance there is a problem elsewhere that vibration exposes, but not very likely. Nothing is ever 100% guessing at the symptoms over the WWW ;-)


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## TheFridge (May 1, 2014)

Topo, depends on the meter. I have a cheap meter that reads 1 or some other number instead of infinity.

Intermittent problem are the hardest to trouble shoot from afar. Maybe try getting it tested at a motor shop.

And Sorry to bomb your thread OP.

It wasn't heated. i was actually being nice.


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## TopamaxSurvivor (May 2, 2008)

> Topo, depends on the meter. I have a cheap meter that reads 1 or some other number instead of infinity.
> 
> Intermittent problem are the hardest to trouble shoot from afar. Maybe try getting it tested at a motor shop.
> 
> ...


That is interesting. How do you know what is going on with the circuit?

Sorry about it being too heated. I too should probably just ignore these electrical issues. Seems like a real electrician with nearly 50 years experience trying to educate the laymen just causes too much turmoil in the speculation.


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## ForestGrl (Jun 5, 2015)

> GFCIs trip at different levels of fault for various reasons, including not at all when improperly wired. Since it trips one immediately and the other after a few minutes, I suspect the motor insulation is beginning to break down and as it heats up it gets closer to failure. There is a small chance there is a problem elsewhere that vibration exposes, but not very likely. Nothing is ever 100% guessing at the symptoms over the WWW ;-)
> 
> - TopamaxSurvivor


I can't seem to find the post where he says it trips the other outlet after a few minutes (the outlet where it "starts fine").


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## TopamaxSurvivor (May 2, 2008)

> GFCIs trip at different levels of fault for various reasons, including not at all when improperly wired. Since it trips one immediately and the other after a few minutes, I suspect the motor insulation is beginning to break down and as it heats up it gets closer to failure. There is a small chance there is a problem elsewhere that vibration exposes, but not very likely. Nothing is ever 100% guessing at the symptoms over the WWW ;-)
> 
> - TopamaxSurvivor
> 
> ...


 Check post #s 18 & 30.


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## SignWave (Feb 2, 2010)

> I understand not wanting to be in the panel. You said it started tripping on another gfi, maybe another brand gfi may do the trick. I had bought a couple and installed and one tripped for no reason a couple of times. Called my electrician and he told me to get a different brand from the supply house and haven t had a problem since.
> 
> - mrg


I've had problems with cheap "contractor grade" GFCI's nuisance tripping under certain situations. Getting a higher quality GFCI did help. (in my case it was tripping from my TIG Welder's HF start, which was on a different circuit in the same panel.)


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## evilbadger (Sep 22, 2015)

It is the GFI. The motor draws a high current at start up and then settles in the extra current is returned through the neutral wire which trips the GFI. Most power tool and appliance manuals state do not use with GFI outlets. Don't drive yourself crazy. Do you have a 20 amp non GFI outlet you can run the saw on? Also GFI outlets are available in 15 and 20 amp you didn't buy a 15 amp did you?


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## mercwear (Jan 19, 2015)

> It is the GFI. The motor draws a high current at start up and then settles in the extra current is returned through the neutral wire which trips the GFI. Most power tool and appliance manuals state do not use with GFI outlets. Don t drive yourself crazy. Do you have a 20 amp non GFI outlet you can run the saw on? Also GFI outlets are available in 15 and 20 amp you didn t buy a 15 amp did you?
> 
> - evilbadger


I moved the pigtail for my conduit from coming off the protected gfic run to the hot and neutral that feeds the gfic outlet which bypasses the gfic for my conduit but leaves it in place for the gfic outlet (and 2 other outlet connected to the load on the gfic). Saw is running fine now so i'm happy =)


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## mercwear (Jan 19, 2015)

> Topo, depends on the meter. I have a cheap meter that reads 1 or some other number instead of infinity.
> 
> Intermittent problem are the hardest to trouble shoot from afar. Maybe try getting it tested at a motor shop.
> 
> ...


No need to apologize. At the end of the day, this forum lead me to a working solution so i'm a happy camper. I still plan to get the motor tested but the saw is under warranty so I will call Ridgid about that.


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## mercwear (Jan 19, 2015)

> I have a genuine and sincere question for those of you who think the saw motor is the culprit: Why is it, then, that he can plug the saw into a different outlet and everything is fine?
> 
> - ForestGrl
> 
> ...


Thanks for the help


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## ForestGrl (Jun 5, 2015)

> GFCIs trip at different levels of fault for various reasons, including not at all when improperly wired. Since it trips one immediately and the other after a few minutes, I suspect the motor insulation is beginning to break down and as it heats up it gets closer to failure. There is a small chance there is a problem elsewhere that vibration exposes, but not very likely. Nothing is ever 100% guessing at the symptoms over the WWW ;-)
> 
> - TopamaxSurvivor
> 
> ...


Got it, thanks. I'm bookmarking this thread. We had shop wired and added 220 not long ago, included GFCIs that weren't there before. So far, no problems. Unisaw is on 220, but all other tools on 110 circuits that have GFCIs.


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## MattB101 (Jun 18, 2015)

Unless you are within 6 feet of a sink you are "up to code" in most localities. You can always call your local building inspectors office with any questions. YMMV. 


> Is the breaker a 20amp as well? That s not common for a 110 line but not unheard of either. Why are you stuck to the idea of a GFCI? Unless you have the risk of water near your saw it isn t necessary. The breaker handles the job of not allowing too much current in the line. (I m not an electrician but I ve done some work in that area in my own shop)
> 
> - Shane
> 
> ...


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