Jointer trips gfci when turned off?

[Bruce Wrenn]

With jointer running, simply pull the plug. This will tell you if switch is the problem

[Paul Kusnierz]

I appreciate all the responses.

Bruce, I tried that and nothing happened. It just turned the maching off, but I don't see how that would prove it was the switch causing the problem. Seeing it only happens when the motor is winding down, pulling the plug would not eliminate the motor causing the GFCI to trip when it is winding down.

I have also plugged the macine into other GFCI outlets on seperate lines through out the house and had the same result. Trips every time the motor is winding down. This tells me the problem is not a sensitive GFCI. It's something happening when the motor is winding down.

Is it a problem where I need to send the motor out to be serviced or would I be fine plugging the machine into a non GFCI protected outlet like I have been doing for the past several years? This problem only came up when I wired in GFCI protected outlets in my shop. Prior to that non of my machines were on protected outlets.

Also is it possible something happened to the wiring over years to cause it to deteriorate to this condition or is this particular machine just fickle with GFCI protection?

[Mike Henderson]

A GFCI trips when there's an imbalance in the currents in the two wires supplying the load. If you're breaking the hot wire on a 120V system, and your GFCI trips, your motor has to be conducting current between the white wire and ground (which it shouldn't do). Ideally, you'd find out why this is happening but a bypass that should work is to put a double pole switch on the tool and break both supply wires when you turn it off.

I think this is what Bruce was suggesting when he said to pull the plug - it would simulate a double pole switch for the tool.

I tried to think of other situations, such as a capacitor discharging, but I can't imagine how a capacitor could be connected to the white wire on one side and ground on the other, and still get charged. Someone had suggested that the motor might act like a generator when it's spinning down, or that the collapsing magnetic field in the field windings might supply some current, but the problem is how the circuit would be completed. And if the black (hot) wire in a 120V system is opened, the only way the circuit could be completed is through ground. And in a properly wired motor, that simply shouldn't happen.

Mike

[Paul Kusnierz]

Thanks for the response. It makes more sense now about the reason for changing the switch. Is it possible something happened over time to cause this condition or this motor was just never intended to work with a GFCI?

[Mike Henderson]

Thanks for the response. It makes more sense now about the reason for changing the switch. Is it possible something happened over time to cause this condition or this motor was just never intended to work with a GFCI?

You got me. This is the first time I've heard of such a situation. But I spent my career in communications, not power. I have a reasonable understanding of motors and how electricity works but I'm sure there are people reading this that have a lot more knowledge and experience with motors than I have. Hopefully, one of them will chime in.

Mike

[Rod Sheridan]

Thanks for the response. It makes more sense now about the reason for changing the switch. Is it possible something happened over time to cause this condition or this motor was just never intended to work with a GFCI?

GFCI receptacles are really designed for use with hand held power tools.

On a stationary machine the frame is grounded, so unless there is a grounding failure, ground fault sensing isn't required.

It's not uncommon to find the a GFCI receptacle will trip when shutting down an induction motor, or de-energising a transformer.

We have a drill press at work that does it 1 in 4 times, so we added a non GFCI receptacle for the drill press...........Regards, Rod.

[Paul Kusnierz]

Thanks Rod. Seems like a similar issue to the drill press. In about a dozen times shutting the jointer down, I have had one time where it does not trip the GFCI.

[Jim Neeley]

Rod,

I agree that GFCI's were originially intended to go with hand power tools. The kink is that as of at least the 2008 NEC it states that "all 125V single-phase, 15- and 20-ampere receptacles installed in locations (1) through (8) [(2) is garages] shall have ground-fault circuit-interrupter protection for personnel."

Exhibit 210.10 in the NEC handbook goes on to show a sketch where a freezer (plugged into a wall mounted receptacle) and garage door opener (plugged into a ceiling-mounted receptacle) are required to have GFCI.

[Jim Neeley]

Paul,

Have you tried the obvious and replaced the GFCI? It contains electronics and can go bad. The new "spec" grade (industrial) GFCIs I have been buying are supposed to disable the receptacle when the GFCI fails and contains circuitry to light a failure-indicating LED.

You've probably already done this but I'd hate to see you chasing the jointer if it was the GFCI failing.

Jim

[Paul Kusnierz]

Jim,

I did not try replacing the GFCI yet. The reason was I had tried running it from other GFCI protected lines and had the same result, so I assumed it wasn't the GFCI. It is also a newly purchased GFCI. I guess I should give that a try because it's worthing spending the twenty bucks to see what happens.

[Don Jarvie]

Why are you running the jointer on a line with a GCFI? You may want to use a regular plug and see if that solves the problem.

[Jim Neeley]

Jim,

I did not try replacing the GFCI yet. The reason was I had tried running it from other GFCI protected lines and had the same result, so I assumed it wasn't the GFCI. It is also a newly purchased GFCI. I guess I should give that a try because it's worthing spending the twenty bucks to see what happens.

Paul,

If the other lines are protected by a different GFCI unit then it's probably not a problem. On the other hand if the other receptacles were daisy-chained from the first GFCI.. maybe so.