On Sunday 29 December 2019 13:32:09 John Dammeyer wrote: > I use > > The standard symbols on my drawings to represent what a ground is. > The nomenclature is so varied I believe the first decision should be > how to describe what is what. > > For me the EARTH symbol is the green (Green/Yellow) wire that goes > back to the circuit breaker panel and from there into a ground rod or > in my case a ground plate in the earth. > > At the machine, at only one point, this Earth is connected to the > frame of the machine. At that point the symbol in my drawings changes > to the GND symbol with the horizontal lines. Any AC powered drives, > motors etc. also connect their green (green/yellow) to this single > point. I believe the code here specifies that this mounting post must > either be double bolted or bonded (welded) in such a way that it > cannot vibrate loose. The green wires must use ring terminals, not > spade terminals so a loose nut doesn't allow the wire to vibrate off. > > If you have something that has AC (single or multiple phase) in it > that is metal and could have an AC line short to the metal box, it too > must have that green wire connect in a non-removable fashion to the > metal box, and return back to that single point earth point. Not to > some other metal part of the machine with hope that it will eventually > connect to the EARTH connection. Gene mentioned the ramifications > if it's not. > > If you have an isolation transformer from one of the 3 phase legs (or > two phase in North American 240VAC power) where 240VAC is changed to > 110VAC with the transformer, the output side of that transformer must > again be made into a proper neutral with a connection to EARTH to that > single point EARTH point. Simply because once it becomes > Black/White/Green headed out and wired to a standard AC outlet, that > Neutral has to behave in the same way it would as if it were embedded > in the wall. Just because it's isolated from the mains doesn't make > it any less lethal. > > And if the system has been taken apart, cleaned up, painted and > re-assembled, it's critical that DC continuity is checked between the > bolted together metal parts. I've seen systems that worked perfectly > and then were stripped down, painted, assembled and made ready for > shipping but developed the most interesting problem with electrical > noise. And the cause tracked down to what was a good electrical > connection now insulated with paint. > > IMHO. > > My bible for wiring these systems is this: Electromagnetic > Compatibility Engineering By Henry W. Ott published by Wiley. > > https://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry >-2009-08-24/dp/B01FIX96A8/ref=sr_1_2?keywords=Henry+W+Ott > <https://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henr >y-2009-08-24/dp/B01FIX96A8/ref=sr_1_2?keywords=Henry+W+Ott&qid=15776440 >03&sr=8-2> &qid=1577644003&sr=8-2 > > Page 119 of my copy, Section 3.1.7 is titled Grounding Myths is pretty > good. > > John Dammeyer
I don't have that particular tome John, but everthing you've added is valid stuff. I'll offer my recently purchased 6040 mill as prime evidence of paint pretty much destroying my ability to ground anything. And to complicate things even a Q&D TLO measure is prevented by ceramic bearings in the spindle which are an insulator. If I want to position a contact to measure TLO, I'll have to rig a contact that touches the nut, or the back flange of the collet, grounding it before the tool tip touches the contact. Or actually trip a switch with the tool. I'm leaning toward the latter but haven't cut anything yet. Need to heal first. My heart attack got in the way. But next year promises I'll feel much better than I have this past year. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
