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Old 04-08-2010, 08:36 PM   #1
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Delta table saw trips GFCI


I have a 15 year old Delta contractor's table saw with a 1 1/2 HP motor. It has started tripping the GFCI in the garage as soon as I turn it on.

I've checked the wiring all the way down to the motor, and found no problems. The frame of the saw is grounded according to my ohmmeter. The saw has had very little use, and is in pristine condition.

I plugged it into an unprotected outlet, and (carefully) turned it on. It runs fine, and there is no voltage present on the frame of the saw.

I'm obviously worried about using it. The news story about the angry wife who rewired her husbands table saw to energize the frame and collect insurance is still fresh in my mind . My wife promised me that she didn't touch it. Rewiring a saw is probably above her skill level, anyway.

Any thoughts on what to check next?

Rick


Last edited by houseinthewoods; 04-08-2010 at 08:40 PM.
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Old 04-08-2010, 09:02 PM   #2
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Delta table saw trips GFCI


You might find it better to ask that question on the electrical thread of this site. The electricians deal with these sort of questions all the time.

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Old 04-08-2010, 10:18 PM   #3
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Delta table saw trips GFCI


Try the saw on another gfci.
Gfci's do go bad from time to time.
If it trips on another gfci, the motor may be going bad, and an ohm meter will not detect it.
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Old 04-08-2010, 10:22 PM   #4
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Delta table saw trips GFCI


Welcome to the wonderful world of the incompatibility of capacitor start motors and GFCI.

If you want the technical reason, a capacitor causes a phase shift between input and output which means that the current flow on the one side of a GFCI is different than the current flow on the other side of the GFCI and it trips. Use a none GFCI protected circuit.
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Old 04-09-2010, 01:24 AM   #5
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Delta table saw trips GFCI


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Originally Posted by hayewe farm View Post
Welcome to the wonderful world of the incompatibility of capacitor start motors and GFCI.

If you want the technical reason, a capacitor causes a phase shift between input and output which means that the current flow on the one side of a GFCI is different than the current flow on the other side of the GFCI and it trips. Use a none GFCI protected circuit.
If that is what is happening, wouldn't the saw always tripped the GFCI. I believe the OP said the saw is 15 years old and this just began which implies to me that he has had the saw on the same outlet for some time without any problems. Also, I have a 1-1/2HP table saw in my garage on a GFCI protected 15 Amp outlet and it doesn't trip the GFCI Mine is new and the GFCI is working. (A hairdryer frequently trips it.)
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Old 04-09-2010, 08:27 AM   #6
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Delta table saw trips GFCI


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Originally Posted by Klawman View Post
If that is what is happening, wouldn't the saw always tripped the GFCI. I believe the OP said the saw is 15 years old and this just began which implies to me that he has had the saw on the same outlet for some time without any problems. Also, I have a 1-1/2HP table saw in my garage on a GFCI protected 15 Amp outlet and it doesn't trip the GFCI Mine is new and the GFCI is working. (A hairdryer frequently trips it.)
Wether he's just started to use it or it just started to trip the breaker you have to remember on a motor there's a whole lot of places where you can lose a little current....and a little is all it takes to start to start tripping a gfci. Could be something as simple as the motor windings starting to break down a little. Most cases a motor will start to leak a little current to the armature when they age.
Best advice i can come up with is to try it on another gfci to make sure it's not just a worn out plug. Most likely it's just a case of a motor getting old.
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Old 04-09-2010, 08:49 AM   #7
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Delta table saw trips GFCI


Actually, there is another fact I omitted from the OP. The garage originally had a single 15 amp GFCI outlet. The saw did not trip this outlet. I had an electrician pull a new 20 amp circuit from my panel, and install 3 new plugs along the wall of the garage protected by a new 20 amp GFCI. I've started using these plugs for the saw, and it's the NEW plugs that are tripping.

I suspect that the newer GFCI is more sensitive than the 15 year old one. I guess I'll just use the old socket for the saw.

Thanks!

Last edited by houseinthewoods; 04-09-2010 at 08:57 AM.
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Old 04-09-2010, 08:58 AM   #8
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Delta table saw trips GFCI


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Originally Posted by houseinthewoods View Post
Actually, there is another fact I omitted. The garage originally had a single 15 amp GFCI outlet. The saw did not trip this outlet. I had an electrician pull a new 20 amp circuit from my panel, and install 3 new plugs along the wall of the garage protected by a new 20 amp GFCI. I've started using these plugs for the saw, and it's the NEW plugs that are tripping.

I suspect that the newer GFCI is more sensitive than the 15 year old one. I guess I'll just use the old socket for the saw.

Thanks!
do yourself a huge favour and go spend 10 bucks on a plug tester at home depot that has a gfci tester on it just to make sure. You can never be too carefull.
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Old 04-09-2010, 02:03 PM   #9
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Delta table saw trips GFCI


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Originally Posted by houseinthewoods View Post
Actually, there is another fact I omitted from the OP. The garage originally had a single 15 amp GFCI outlet. The saw did not trip this outlet. I had an electrician pull a new 20 amp circuit from my panel, and install 3 new plugs along the wall of the garage protected by a new 20 amp GFCI. I've started using these plugs for the saw, and it's the NEW plugs that are tripping.

I suspect that the newer GFCI is more sensitive than the 15 year old one. I guess I'll just use the old socket for the saw.

Thanks!

Listen to Andrew and get the tester. The problem may be that there has been a ground fault in your saw for some time, but it wasn't detected by a bad GFCI on the old 15 A line. Then, again, you paid for a new line and it is possible that the new GFCI is the culprit. If it tests bad and the 15 tests good, I would call the electrician who installed the new line.
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Old 04-09-2010, 02:36 PM   #10
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Delta table saw trips GFCI


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Originally Posted by Klawman View Post
If that is what is happening, wouldn't the saw always tripped the GFCI. I believe the OP said the saw is 15 years old and this just began which implies to me that he has had the saw on the same outlet for some time without any problems. Also, I have a 1-1/2HP table saw in my garage on a GFCI protected 15 Amp outlet and it doesn't trip the GFCI Mine is new and the GFCI is working. (A hairdryer frequently trips it.)
It will depend on the value of the capacitor and the charge state of the capacitor when the motor is started.
Jack
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Old 04-09-2010, 02:41 PM   #11
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Delta table saw trips GFCI


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It will depend on the value of the capacitor and the charge state of the capacitor when the motor is started.
Jack
We just learned that the saw is no longer on the same line but a new 20 A circuit.
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Old 04-09-2010, 02:53 PM   #12
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Delta table saw trips GFCI


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Originally Posted by hayewe farm View Post
It will depend on the value of the capacitor and the charge state of the capacitor when the motor is started.
Jack
A few points that should be cleared up. Certain conditions have to be met before a capacitive start motor throws out a gfci. Being as the saw worked fine for many years on a gfci I'm lead to believe these conditions weren't met.
The gfci doesn't really care what the line to ground current is....it's measuring to see wether or not the same amount of amps is going out on the line as is comming back on the neutral. Hence the current loss in the armature could be triggering it.
I'm wondering if the old circuit was a gfci plug and the new circuit is on a breaker? The extra wire from the point where the GFCI is and where the saw is could have a big impact on this and could very well be the problem. With motors of any type it's best to keep the gfci as close as possible to the actual point of attachment of the motor.
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Old 04-09-2010, 03:57 PM   #13
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Delta table saw trips GFCI


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I'm wondering if the old circuit was a gfci plug and the new circuit is on a breaker?
The original plug was a GFCI plug, and that was the only thing on the circuit (as far as I know).

The new circuit has two regular plugs downstream of a GFCI plug. I was plugging the saw into the farthest downstream plug, but it's only about 10 feet between this plug and the GFCI. Not sure why he put in a plug instead of a breaker.

I tried plugging the saw into the old plug, and it runs OK. I will pick up a tester the next time I'm at the toy store.

Here's the news story about the angry wife:
http://apnews.excite.com/article/201...D9D5U2FO0.html
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Old 04-09-2010, 05:34 PM   #14
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Delta table saw trips GFCI


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Originally Posted by andrew79 View Post
do yourself a huge favour and go spend 10 bucks on a plug tester at home depot that has a gfci tester on it just to make sure. You can never be too carefull.
For what it's worth, GFCI manufacturers NEVER recommend using a GFCI tester to test GFCI's. Always test using the test and reset buttons!
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Old 04-09-2010, 05:42 PM   #15
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Delta table saw trips GFCI


Quote:
Originally Posted by hayewe farm View Post
Welcome to the wonderful world of the incompatibility of capacitor start motors and GFCI.

If you want the technical reason, a capacitor causes a phase shift between input and output which means that the current flow on the one side of a GFCI is different than the current flow on the other side of the GFCI and it trips. Use a none GFCI protected circuit.
IMHO a Starting Capacitor Motor by itself will not trip a GFCI device. Because the GFI device does not respond to a difference between Line and Load. It is designed to sense the difference between Hot and Neutral, thus preventing the effects of leakage current. !

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