On Saturday 14 July 2018 01:22:12 Chris Albertson wrote: > On Fri, Jul 13, 2018 at 9:25 AM Roland Jollivet > <roland.jolli...@gmail.com> > > wrote: > > > That's pretty much standard these days. > > > > I don't understand the desire to connect two lines together because > > they 'seem' to be of the same magnitude. 0VDC is Not equal to Gnd > > Many systems will have multiple 5V power lines, heavy, light, > > designated. Do you want to link all those up too? > > Generally you want you power supply and logic nd safety grounds to be > separate. But at ONE and one one point would you connect them. > > What's happening here is that some "grounds" are carrying current > exactly equal to the power supply current and unless yu are using > "super conductor" cable cool with liqi=ud helium there *will* be a > non-zero voltage on the "ground" cable. That is the problem with > interconnected grounds, all those return currents and by Ohm's law > "return voltages". But if yu do connect safety and return grounds at > ONE point current can't flow. But this is hard to do. Really hard > if there are multiple 3-prong power plugs. > Just one of the reasons I've incorporated a power strip in the AC wiring of one of my later builds. That way I have both a common power switch, and just one 3rd pin connecting back to the common-ized point in the the electrical service via the 4 plex on the wall
With care, and cheap two wire extension cords cut up for power wiring, I can stop 99% of the ground loops. I've taken a somewhat different tack with power switching on the Sheldon, which has a separate 250 volt single phase service cable, possible since I have a surplus of gpio's in the 7i90, I've used 2 gpio's to switch a couple 40 amp SSR's controlled by the F2 button, so if F2 is not enabled, only the pi and the interfaces and a 4000 lumen led lamp above the lathe bed are left on. All motor power including the spindle vfd are shut down. The lamp draws maybe 18 watts, so it and the pi is on unless I kill that 125 volt leg with a toggle switch in a 4 plex mounted on the stick that used to hold the drum switch. Makes a good night light. :-) > > On 13 July 2018 at 18:05, andy pugh <bodge...@gmail.com> wrote: > > > On 13 July 2018 at 16:52, Dave Cole <linuxcncro...@gmail.com> wrote: > > > > That's pretty much standard these days. > > > > > > > > I'm not making this stuff up. That's how its done. > > > > > > I think that there is still some confusion out there. I used to > > > work for a company making specialist test equipment (brake dynos, > > > motor / pump testers, that sort of thing). > > > Our electricians were convinced that everything needed an > > > yellow/green earth connection. Every panel for the control > > > cabinet, the doors, the individual devices bolted to the machine > > > bed. We would spend ages making things look nice and painting > > > them, and then they would come back festooned with stripy wires > > > and with a hole drilled in every separate metal part for the earth > > > stud. > > > > > > -- > > > atp > > > "A motorcycle is a bicycle with a pandemonium attachment and is > > > designed for the especial use of mechanical geniuses, daredevils > > > and lunatics." > > > — George Fitch, Atlanta Constitution Newspaper, 1916 > > > > > > ------------------------------------------------------------ > > > ------------------ > > > Check out the vibrant tech community on one of the world's most > > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > -------------------------------------------------------------------- > >---------- Check out the vibrant tech community on one of the world's > > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users -- 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
