GFI outlet issues

KevinM said:
Me and some others were having random non-GFI breakers trip instantly on startup on a variable speed lathe before the motor would actually be turned on. The only thing that stopped it for me was a 30A breaker.
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If by variable speed lathe, you mean one powered by a DC motor, there is a possible cause. DC motor require rectification of of the ac supply followed by a filter capacitor. On initial energization, the circuit is subject to a large inrush current due to charging the capacitor.

This can be dealt with in a number of ways. The simplest is to add a small resistance to the input to limit the surge current. This however reduces the efficiency of the supply which can be objectionable for high current devices like a lathe motor.

Another way is to use a negative resistance device, aka varistor or inrush current limiter. It has a fairly high resistance when cold, limiting the inrush current but as it heats up, the resistance drops significantly. This method is often used for switching power supplies. One that I used was this: https://www.digikey.com/en/products/detail/ametherm/AS32-10015/2614390
 
In defense of GFIs: I have them in my kitchen, but not in the garage. The ones in my kitchen proved their value once when I plugged in a coffee machine with a shorted heating element; it shut off the power immediately. In cases like that, they are nice to have.
For the garage, I never had any GFIs, just standard outlets. I don't think GFIs in the garage are required in my area, if they are original
I'm not sure what the code says about hard-wired machinery in residential garage settings. I wonder if hard-wired stuff is given a pass on the GFI requirement? Sure, you'd have to cut the plug off, but it's a small price to pay
-Mark
 
RJSakowski said:
If by variable speed lathe, you mean one powered by a DC motor, there is a possible cause. DC motor require rectification of of the ac supply followed by a filter capacitor. On initial energization, the circuit is subject to a large inrush current due to charging the capacitor.

This can be dealt with in a number of ways. The simplest is to add a small resistance to the input to limit the surge current. This however reduces the efficiency of the supply which can be objectionable for high current devices like a lathe motor.

Another way is to use a negative resistance device, aka varistor or inrush current limiter. It has a fairly high resistance when cold, limiting the inrush current but as it heats up, the resistance drops significantly. This method is often used for switching power supplies. One that I used was this: https://www.digikey.com/en/products/detail/ametherm/AS32-10015/2614390
Click to expand...
$5 30A breaker and 5 minutes was pretty simple for me. :) My state only requires GFI in kitchens and bathrooms, washing machines and water heaters get a pass.
 
I am thinking of a new product here. It is a GFI breaker that has been internally re-wired to be a regular breaker. You could only sell it on the dark web with bitcoin payment. Or maybe in the HM sales section!
Robert
 
MikeWi said:
@RJSakowski How is this used? Is it placed in series with one leg?
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Yes, in series with one current carrying leg.

For the one that I chose, the initial room temperature current was around 10 ohms, limiting the peak current to 15 amps. As it heats up, the resistance drops to a small fraction, the final value depending on current draw. When the power is cut, the varistor cools down again. In a circuit like a switching power supply, this isn't a problem since the supply draws what is needed to provide the proper output voltage and current. If you are switching a lathe or mill motor off and on, the varistor needs a cool down period to cool. If you are powering a lathe through a VFD, the main power would remain on continuously with control being performed downstream so it behaves much like a switching power supply.
 
I've had this issue a couple of times. Most recently was with a Jet Wood Lathe my wife picked up with a variable speed drive. The solution for me has always been put a robust power strip in-between the device and the GFI protected circuit. Simple fix.
 
RJSakowski said:
The annoying one though is the one in our half bath.The room has no windows so you are totally dependent on the lights which are pulled off the GFIC outlet. You sitting on the toilet and decide you really have to switch on the exhaust fan and you trip the GFIC. Now the GFIC is across the room from where you're sitting so there you are, in the dark, wondering how to solve your dilemma. Fortunately, there is a nearby door so you can crack the door to let in some light so you can finish what you were about. The fan motor is a simple synchronous motor with a piddling little current draw. Yes, I know that I can rewire the outlet so the light circuit is on the line side rather than the load side. The problem is that I only think about it when the GFIC acts up.
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As stated, that circuit was wired incorrectly. Use this thread to remind yourself to get off your butt (when it isn't an issue) and fix that now. :D
 
Also, different localities use different editions of the NEC Code Book and the locality can not adopt everything in the code or conversely, as in my case, be more restrictive. We can't use 14 gauge wire on 15 amp circuits, everything is minimum of 12 gauge. You also can make the argument that the circuit you are using is for an "industrial" type setting, which allows you to not have a GFCI on your machine circuits.
 
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