I’ve had an electrician add a couple of dedicated circuits for shop machinery to the garage in our new house, but on testing my Powermatic 64a contractors’ saw, it pops the GFCI button, even before I get the chance to turn it on.
I thought the outlet must not be powerful enough, but the electrician tells me that the saw must not be grounded properly. The outlets work fine with other tools, like drills, my bandsaw, and circular saw. I’m worried that if it’s a power issue, my dust collector won’t work with other machines simultaneously. I haven’t set everything up yet, so I don’t know by testing.
Is this just a matter of proper grounding like the electrician says, and how does one ground a Powermatic 64a to work in a GFCI outlet? Or will replacing the GFCI outlet with a regular one solve the problem (albeit a little less safely)?
Thanks for any ideas…
Rob
Replies
You can get around the gfci requirement buy making the outlet your plugging in your saw into ,what's called a single device outlet. What that means is you can only plug in one device into that outlet verses two on a typical duplex receptacle. Is the outlet protected buy a gfci outlet or gfci breaker? If it's an gfci outlet change it out to a single device receptacle. If it protected by an gfci breaker change the breaker to a regular breaker and change the receptacle to a single device receptacle as well. Also check to make sure that the breaker is the proper size to handle the load and is the right voltage (I've or 220v),the tag on the motor should tell you how many amps it draws and at what voltage. One more thing you might want to check,is whether the motor is wired for 120V or 220v some motors can be wired for either. Your owners manual should have a wiring diagram for both. You can do this yourself ,the terminals inside the motor are numbered all you need to do is match the numbers in the manual to the numbers on the terminals inside the motor. Hope this helps!
Bill Bleiler
Edited 12/30/2002 6:52:02 PM ET by BBLEILER
Thanks Bill. It's a GFCI outlet, so I'll switch for a non GFCI one. The circuit itself is 20A, which I believe should be compatible with the 15A, 120V saw motor.
We'll see if that works!
Rob
"The circuit itself is 20A, which I believe should be compatible with the 15A, 120V saw motor."
Rob, yes it should, but also check the start up amp rating. A lot of the machinery requires a few extra amps to get them started and then they drop to their normal amp rating. If you had something else running on the same circuit when the powermatic was turned on it would trip the breaker even though the sum of both amps is 19. I have my dust collector hooked up to a dedicated circuit.
Marcello
Rob, I'm not an electrician but having just built my own shop ans several others in the neighborhood, I do understand the concepts here.
Your electrician is right. If the gcfi pops before you turn on the saw you have a ground problem. Address this problem before you start changing receptacles. If its more than you can do ask the electrician to track down the problem. You will be wasting your time & money switching out these receptacles if you don't get the saw fixed.
Also, the 20 amp breaker is more than enough for that saw, even at startup.
good luck, Hugh
Hmm. Maybe at this point, I'll just have the electrician over, assemble my dust collector and table saw, and say "I need these to work together, safely. How do we do it?"
The grounding issue may have something to do with the new plug I put on the table saw cord. It's a three prong grounded one, but I'll check to make sure it's rated for at least 20A and 115V.
Thanks for all the advice,
Rob
GFCI = Ground Fault Circuit Interrupter and it does exactly what it says. Inrush current has no effect on a GFCI. A GFCI senses any imbalance in the phase and/or neutral conductors. These are very sensistive, high-speed devices and operate at 5 mA (thousandths of an amp). 4 to 6 mA is the acceptable operating range. Have the electrician test the GFCI and if it trips below 4 mA it should be replaced. Besides being expensive they can also be a pain in a s s as you now know. The code allows 2 exceptions for GFCI based on accessibility and dedication. Dedicated receptacles for stationary machines can use regular grounded plugs. Single for 1 machine and duplex for 2 machines on the same outlet.
Assuming the GFCI is operating properly, the fact that yours trips by just plugging in the saw indicates the trouble is probably a short in the cord or switch or a wiring error in the switch if it's magnetic. UNPLUG THE CORD. Both prongs on the cord with the switch off should test over 24,000 ohms to the ground prong (tested separately). If not, there may be a short in the cord or the switch. Disconnect the UNPLUGGED cord from the switch and test again. Replace the cord or the switch. This assumes the saw has a simple toggle-type swtich, not a magnetic starter. In that case the problem may be a short or leakage in the starter coil or a wiring error in the starter. UNPLUG THE CORD. Check that there are no white wires connected to green wires or the metal case. This would cause an imbalance that would trip the GFI. The only place a white (neutral wire) should be grounded is in your meter/panel board. John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
Well, I'm pretty sure the GFCI is working properly as the outlets and circuits are brand new, part of a basement overhaul.
If the saw worked fine on a non GFCI outlet in my previous apartment, would that eliminate the switch (which is a 'stop' and 'start' button switch, which I assume is functionally the same as a toggle) as a source for suspicion? If so, I could just install a new GFCI 20A plug on the cord; when I replaced the original, I just picked the first one that looked right.
Considering my 12" Jet bandsaw works fine on these outlets with its factory plug, I'm becoming more and more suspicious of my choice of replacement plug for the tablesaw...
Rob
I wouldn't assume the outlet is OK. It could be bad right out of the box. It happens all the time. These things are really sensitive. The non-GFI performance at the old place isn't relevent. 0.005 A of imbalance current flowing thru the ground is all it takes to trip the GFI. A 20A breaker protecting a standard outlet would never trip even if the saw was pulling close to 20A. Thats 4000 times the current. About the plug, I'm not familar with a GFI plug except the ones on hair dryers, just the receptacles that mate up with standard plugs. Unless you wired the plug with a short to ground I can't see how that would cause the problem your having. If you plugged a shorted plug into a regular outlet it would trip the breaker in a heartbeat (not recommended). Have you tried the saw in a another GFI outlet? If so what happened?John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
It trips regardless of which GFCI outlet I plug it into, but the bandsaw doesn't. Weird...
Rob
Rob,
If you can disconnect the motor end of the power cord - at least the black (hot) and the white (neutral) at the motor terminal strip, you can then plug in the cord/plug combination into the GFCI. If it trips, the plug is the culprit, or the cord is damaged. Be sure to tape up the loose leads so they don't contact anything while doing this test.
Possibly you wrapped a tiny filament of wire from the white or the black across the ground (green) terminal. It happens all the time.
If you plug the saw into a non GFCI outlet it will either trip the breaker in the panel or possibly just burn away the tiny filament. But that's not recommended.
The least likely possibility is that you have an insulation breakdown in the saw that somehow resulted from moving the unit. However I'd bet 99% it's the new plug.
Good luck!
Thanks to all for contributing to fixing my saw/GFCI prob. It turned out the culprit was the new plug I had installed a while back; I had a few stray filaments from the + touching the ground. I put in a bigger plug and kept the filaments separate, and lo and behold, the saw fired up like a dream. Not only that, but my dust collector works on a different circuit without dimming the lights, so I'm good to go!
All I gotta do now is buy hoses, Y's, and blast gates for the dust collection system.
Thanks again, all!
Rob
How many time does it turn out that (i) you have a problem, (ii) you think about all of the complicated possibilities that would explain the problem, (iii) you eliminate all of those possibilities one by one, and (iii) the problem turns out to be caused by the simplest possible thing? It happens to me all the time.
Yeah, the problem is always nerve racking, but finding the solution and implementing it just rocks. There's nothing like fixing something on your own that looked insurmountable. Woohoo!
I've been doing electrical design and engineering up through 115 kV substations since '75 and I still manage to be humbled on occasion. I had a similar experience with an intermittant failure of my daughter's car stereo shortly after I put in some nice Boston front speakers for her birthday. Every once in a while the speakers just quit working. The stereo itself was powered up but no output, even from the headphone jack. I jumped to the conclusion that there was a short (correct) in the unit (incorrect). She bought a new stereo which I installed and the same thing happened. As I went through all the proper trouble shooting (isolating each speaker and wiring of all four channels) which I should have done in the first place, I narrowed it down to the new left front speaker. The speaker mounts in a plastic box with a metal frame and brace which in turn mounts into the dash. The speaker worked in it's box until I put it in the dash and tightened the screws. When I soldered the + lead to the speaker terminal it was long and very close to the speaker frame. When the box was screwed down tight in the dash the lead shorted to the speaker frame and to ground through the box frame/brace. To make matters worse I had chucked the old stereo 'cause it was bad. I paid for the new one. Doh!John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
The easy job here would be to check out the cord plug set. You might have a white & black reversed if it is 120 volt. (Silver is more common than Gold...) Or the green wire could be unconnected and not doing its job.
A cord is cheap as is a plug. Argubly the stop start switch could have worn contacts, but that is pretty far out there.
As for GFCI's New rules just came down. Left the sheet at work but there will be some changes in the testing and performance of the GFCI in 2003. Oh yes the inventory on everyone's shelves is ok to install. Manufactured goods as of Jan 1 need to meet the new specs. Theoretically it will thin out the off shore 7 dollar GFCI manufacturers. There are many disfunctional GFCI's installed in the market. Theoretically this is to make the performance more reliable.
Yours could be bad but it is unlikely. More likely is a miswired motor.
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