Thanks, I'm not concerned about the AC ground side of things. Internet searches on this subject generally seem to agree that DC ground doesn't and shouldn't be connected to the metal frame earth ground at any point. If it is either through a capacitor or a 100 ohm resistor.
I remember many years ago working on Trim & Form Equipment in The Netherlands we ran into problems with the PCs used for the User interface (Pentium 386) had the power supply internally connect the DC ground to the frame. Caused all sorts of havoc. I don't remember what the solution was. Jeff Birt also suggests not connecting DC ground to the frame on one group's posting. Obviously there may be Break Out Boards that break this rule but then they may also be made by hobbiests who have gone into the machine controls business and don't really know. John > -----Original Message----- > From: Gene Heskett [mailto:ghesk...@shentel.net] > Sent: July-12-18 1:16 PM > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] Grounding > > On Thursday 12 July 2018 15:12:40 John Dammeyer wrote: > > > Is it standard practice to connect the DC Servo and DC Instrumentation > > Bus to the machine frame ground which is connected to power line > > earth? Or is it more normal practice to keep the DC isolated from the > > 'earth' ground. > > > > John > > Generally speaking its a good idea to have then all come together at a > common bolt, also called a star ground. The bolt is the star center > point and all other ground circuits radiate from it.. The machines > frame ground should connect to this common point, and it should be > ohm-meter verified that there is not another connection between that > bolt and the machine frame if the frame grounding wire is disconnected. > > This means that its good practice to have shielded motor and sensor > cables, but the shield is cut short, not connected at the frame end of > the run. If there is another connection, then you have a ground loop > which can inject several tens of volts of noise back into the interface > card, potentially damaging it. Or worse, inject noise into a stepper > drive resulting in a gradual drift of the homed point which=wrecked, out > of spec parts. > > IOW, the motor power supplies should be the only circuit that connects to > the 3rd pin of the power cord, and that 3rd pin should be connected only > to that common bolt. Do not connect this 3rd wire to the supplies, but > to this bolt, and take a separate wire from the bolt back to the ground > symbol on the PSU's. And if that ground has continuity to the shell of > the PSU, mount it insulated to open that ground loop. A piece of pcb > material, glued to the chassis, and the PSU's glued to the pcb should do > it nicely. > > IHTH. > > -- > 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 ------------------------------------------------------------------------------ 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
