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Old 07-23-2010, 09:14 AM   #1
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woodworking machine is tripping GFI


my jointer had been working perfectly for a few months of light use.
lately it's been snapping the GFI the second i turn it on.

opened up the switch and took the electrical plate off the motor.
when i first opened it up it looked like the black leading to the switch had broken off one of the terminals, but i wasn't sure which.

there were some frayed wires coming out of the motor, so i taped everything up.

i've been playing around with all the possible combinations of re-wiring this thing. i either get:

1) motor spinning backwards but doesn't trip the GFI
2) a quiet hum but no movement
3) motor spinning correctly but instantly trips the GFI as soon as i turn the switch on.

the switch is a standard single pole light switch.

the jointer is from the 40s and the motor is an old craftsman - age unknown but probably almost as old.

throughout the past few weeks it's been on and off, like every once in awhile i'd get lucky and be able to use the jointer for 20 minutes. come back a week later and the GFIs trip.

by the way, i've got 50 amps of service to my garage, and three different 20 amp outlet circuits. there is a GFI at the beginning of each circuit with a regular breaker in the panel.
i regularly use a table saw and miter saw in there as well and have never once had a problem with either, nor any other tool in the shop.

any ideas what is happening here? do i need a new motor?
thanks.

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Old 07-23-2010, 09:29 AM   #2
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woodworking machine is tripping GFI


GFCIs trip because the current flowing in the neutral leg doesn't match the current flowing in the hot leg. It is interesting that the motor will run one direction without tripping. What else can you say about the motor. Can you tell if it is capacitor start or split phase? Is the motor case grounded?

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Old 07-23-2010, 09:42 AM   #3
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woodworking machine is tripping GFI


thanks for the reply, a7.
just snapped a few pics.
the motor is capacitor. not sure how to tell if it's grounded.

can't even tell which wires are coming from the motor as they are so faded.

it looks like 2 whites, a black and a red, with a black and white up top, white and red on bottom, with black to switch.

i would think the empty terminal was for the black, but the motor does nothing if i put it there.

thanks.



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Old 07-23-2010, 11:39 AM   #4
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woodworking machine is tripping GFI


The default fix is to replace the GFCI, but with a DVM and a 100 mA fuse you can actually check the current in the machine's ground lead, assuming it has a ground lead.

For test purposes you could also try putting it on an extension cord to slightly reduce the inrush current on startup.

Last edited by Yoyizit; 07-23-2010 at 11:55 AM.
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Old 07-23-2010, 11:45 AM   #5
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woodworking machine is tripping GFI


Have you looked closely at the motor tag to see if there is a connection diagram? I don't see the start capacitor so does it say it is capacitive start? I have a 3/4 HP Craftsman Repulsion Induction motor on a table saw and the plate has a diagram. Don't forget to check the back side of the cover plate.
Is this a 120/240 volt motor?
One other thing, I'd pull the connection wires out of the romex box connector and check for any insulation breakdown. Check the entire cord for any problems.

Last edited by a7ecorsair; 07-23-2010 at 01:23 PM.
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Old 07-23-2010, 01:59 PM   #6
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woodworking machine is tripping GFI


hey guys, and thanks.

a7 - the tag on the motor says "capicitor..."

get this: i just tried running a long extension cord from inside a regular 15 amp house outlet.

WOW. completely different experience. most notably, the jointer is super quiet and soft upon startup. it always used to "snap" on.
it sounded like a metallic snap, i assumed it was either the blade guard being bumped against the fence, or the belt housing vibrating against itself.
but wow, what a difference. super quiet, almost like a "soft start," and the motor is quieter and smoother during operation, too.

i'm pretty sure it's wired right. i've been out there for 30 minutes jointing boards.
only thing that could be messing with the GFI i guess is frayed wires and current "leaking" out?

thanks guys.
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Old 07-23-2010, 02:57 PM   #7
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woodworking machine is tripping GFI


Large motors trip GFCI very easily, to the point that garbage disposals are exept from the GFCI requirements.

its the nature of the beast.
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Old 07-23-2010, 05:20 PM   #8
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woodworking machine is tripping GFI


Quote:
Originally Posted by schmolze View Post
hey guys, and thanks.

a7 - the tag on the motor says "capicitor..."

get this: i just tried running a long extension cord from inside a regular 15 amp house outlet.

WOW. completely different experience.
Now just for fun, plug that extension cord into your shop GFCI and see what happens. Is the house outlet GFCI?
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Old 07-24-2010, 07:49 PM   #9
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woodworking machine is tripping GFI


What gauge cord, what length?

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