Shopsmith Forums

AEA wrote: ↑Thu Apr 01, 2021 5:32 pm By the way paulrussell has the best icon, avatar, symbol, or what ever. (except now I can't get the tune out of my head)

My 500 w/ 1 1/8 hp motor has tripped the GFCI twice in as many years - never while using it - so if there's a problem, it's a subtle one.

My Garage/Shop has GFCI 20 A protected circuits. I have not had any problems tripping the Ground Fault with any of my Tools. When using the Dust Collection and any of my Shopsmiths they are plugged into separate circuits. That includes the Mark 7, Mark V 520, Model 10's, etc. I do not plug the Mark 7 directly into a GFCI outlet but into one downstream on the circuit.

OK, you guys convinced me. I added a GFI outlet to my dust collector. The book for it suggested it might be a good idea. My woodworking shop is in my house so very few circuits are on GFCI. Until now, only the kitchen, bathrooms, and the laundry had them. I now have one in my shop. I probably won't add one for the Shopsmith as it probably isn't needed.
My garage outside has at least a dozen GFCI receptacles and they don't give me any problems out there. But, out there, they are required by code. I don't do any woodworking out there.

What is there about a DC that makes a GFCI 'a good idea' ?

JPG wrote: ↑Sat Apr 03, 2021 2:56 pm What is there about a DC that makes a GFCI 'a good idea' ?

I didn't write the book. I only read it. There was a "suggestion" that since dust collectors can create static electricity and dust can explode, a GFCI would be a good idea. I never thought GFCI's were there to help that, but what do I know? My Shopvacs have always created static electricity, but I use them either with or without GFCI receptacles.

For a better explanation, you need to ask the people who write this stuff.

I asked because I think who ever 'wrote' that is full of beans.

I was also suspicious that that static was the cause for that misinformation.

You are likely correct. Every time I do research on a subject, I find conflicting information from so-called experts. My theory on all this is read a lot of opinions, but use your best judgement on what you think is true. The internet is a great source of misinformation.

On this subject, I figured that I would use a GFCI if enough other people are using them without false tripping problems. It appears that is happening so I figured I would try it too. I don't see that it would do any harm, but maybe it is a "good idea".

Okay, I do have some experience in this area (having designed ESD/EOS protecting circuits) so let me to try to give a bit more context to help in understanding this. First it is helpful to understand what a GFCI does so I have copied an explanation from the internet below that matches my own understanding. Key points to understand here is that all a GFCI does is sense a difference in current flow between the hot and neutral wires. That current has to flow somewhere so the presumption is it is flowing through the operator (human) and into Earth ground. This is why the majority of applications that a GFCI hopes to protect against involves water where a leakage path may be created, e.g. using a corded electric weed eater/lawnmower while standing in wet grass or a puddle, hair dryer falling in bath tub or sink, etc., etc. The other key point is about the timing, i.e. a GFCI must respond no slower than 1/30 of a second so it has to react faster than 33ms or 0.033s. This is to avoid latching in electrocution where you are being shocked and can't put the tool down.

Static electricity, e.g. in/around a dust collector creates the potential for an ESD event. Electro-Static Discharge (ESD) can be unpredictable in ways but also very predictable in others. It is always seeking the lowest resistance path to Earth ground. ALL ESD protective circuits function to give that accumulated static charge an easier (lower resistance) path to ground, hopefully protecting equipment/people in the process. One simple ESD circuit (DC - direct current applications) are back-to-back diodes. A better method is an ESD clamp created using Zener diodes or SCR's. For AC applications often an MOV (metal oxide varistor) is used. These circuits all provide shunt paths for very high voltage discharges to get to ground. Why am I pointing all of this out? Okay, an ESD event is typically on the order of 10ns for its pulse or 1E-8s which is 0.00000001s. This means that an ESD event will be long over before the GFCI circuit even has time to see it, i.e. it can't respond fast enough (and likely never knows it was there). This is a good thing because you don't want what the GFCI intends to do when a static event happens. Remember the GFCI interrupts current flow to the tool. IF this happened then that static charge is contained in the tool but now with the power disconnected it has to find the next lowest resistance path to Earth ground which may be you!!

I am not going to go against the NEC, whatever that is for a shop situation, but I do discourage the use of GFCI's except where they are required (and hopefully make sense). IF some technical writer (or engineer) wrote an owner's manual for a dust collector and encouraged the use of a GFCI circuit for it I would be highly skeptical reading it. In reality it is likely some part-time do-gooder that thinks they are helping when in reality they are not. Could also be a lawyer just trying to protect the company from liability litigation. Of course if you operate your dust collector standing in a puddle of water with shoes off then please install a GFCI to protect against electrocution and don't worry about static electricity.

Bottomline is that a GFCI doesn't (and can't) protect against static electricity (ESD) events.

GFCI Operation Explained:
"If an appliance is working properly, all electricity that the appliance uses will flow from hot to neutral. A GFCI monitors the amount of current flowing from hot to neutral. If there is any imbalance, it trips the circuit. The GFCI senses a mismatch as small as 4 or 5 milliamps, and it can react as quickly as one-thirtieth of a second. That's a key specification, because at around 10 milliamps, human muscles "freeze" from electrical overload, meaning that you're unable to let go of an object that's causing a shock; just two seconds at that level of current can cause death"
https://home.howstuffworks.com/question ... 20circuit.

Thank You! The GFCI I understood. Thanks for the new knowledge re ESD.