LumberJocks

Table saw started tripping gfci

  • Advertise with us

« back to Power Tools, Hardware and Accessories forum

Forum topic by mercwear posted 10-01-2015 12:19 AM 5778 views 0 times favorited 46 replies Add to Favorites Watch
View mercwear's profile

mercwear

30 posts in 691 days


10-01-2015 12:19 AM

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.


46 replies so far

View agallant's profile

agallant

530 posts in 2354 days


#1 posted 10-01-2015 12:33 AM

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

View mercwear's profile

mercwear

30 posts in 691 days


#2 posted 10-01-2015 12:47 AM



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 =)

View Shane's profile

Shane

294 posts in 1278 days


#3 posted 10-01-2015 12:53 AM

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)

View mercwear's profile

mercwear

30 posts in 691 days


#4 posted 10-01-2015 01:11 AM



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.

View Shane's profile

Shane

294 posts in 1278 days


#5 posted 10-01-2015 01:29 AM

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

View SignWave's profile

SignWave

324 posts in 2503 days


#6 posted 10-01-2015 02:01 AM

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).

-- Barry, http://BarrysWorkshop.com/

View TheFridge's profile

TheFridge

5765 posts in 953 days


#7 posted 10-01-2015 02:04 AM

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.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View clin's profile

clin

514 posts in 463 days


#8 posted 10-01-2015 02:05 AM

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.

-- Clin

View ForestGrl's profile

ForestGrl

445 posts in 553 days


#9 posted 10-01-2015 02:12 AM


[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?

-- My mother said that anyone learning to cook needed a large dog to eat the mistakes. As a sculptor of wood I have always tried to keep a fireplace. (Norman Ridenour)

View ForestGrl's profile

ForestGrl

445 posts in 553 days


#10 posted 10-01-2015 02:19 AM

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?

-- My mother said that anyone learning to cook needed a large dog to eat the mistakes. As a sculptor of wood I have always tried to keep a fireplace. (Norman Ridenour)

View mercwear's profile

mercwear

30 posts in 691 days


#11 posted 10-01-2015 02:52 AM



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.

View mercwear's profile

mercwear

30 posts in 691 days


#12 posted 10-01-2015 02:53 AM



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.

- TheFridge

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.

View TheFridge's profile

TheFridge

5765 posts in 953 days


#13 posted 10-01-2015 03:03 AM

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.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View jonah's profile

jonah

687 posts in 2766 days


#14 posted 10-01-2015 03:10 AM

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).

View ForestGrl's profile

ForestGrl

445 posts in 553 days


#15 posted 10-01-2015 03:26 AM


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.

- mercwear

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

-- My mother said that anyone learning to cook needed a large dog to eat the mistakes. As a sculptor of wood I have always tried to keep a fireplace. (Norman Ridenour)

showing 1 through 15 of 46 replies

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com