Definitely do not tie 0VDC to ground. It will often cause problems with the switching power supply.
On 13 July 2018 at 04:55, Dave Cole <linuxcncro...@gmail.com> wrote: > Typically in a multi-panel control system setup there is a ground bar in > each panel. The incoming AC power ground is tied to this and the 24 volt > power supply negative is tied to the local ground bar just as I described > before. If all of these panels are on a common machine frame, the ground > bars are oftentimes linked together with a heavy bonding copper cable (like > a 4 gauge or heavier bare cable). > > You don't want to rely on the machine frame to be the ground conductor. > The systems I used to work on way back when were all AC, 120 volts for the > controls and you could run control wire circuits for 1000 ft with only > occasional problems. Way back when, a controls electrician typically > didn't carry a voltmeter with him. He used a wiggy. > https://en.wikipedia.org/wiki/Solenoid_voltmeter > > Now you just pull Ethernet cables between control panels. > Not much 120 VAC control wiring is being installed any longer. > > Dave > > > > > On 7/12/2018 6:33 PM, John Dammeyer wrote: > >> So what happens when the equipment with the 24V supply is 30m long in >> multiple steel frames? There would be a bonding wire from frame to frame >> since you wouldn't want to bond one end to one AC ground outlet and the >> other end to a different AC ground outlet. >> >> What if you have 30A, 24V supplies at each end of the machine or in each >> module. If each 24V supply minus terminal is grounded to the frame and >> you run a common ground bus through the machine you now have the frame and >> the ground bus serving as the DC ground path. You wouldn't want to run DC >> ground on the frame. >> >> I worked on a machine once that had I think 42 modules. Each one was >> independent and inserted two advertisement flyers into newspapers. A >> client would buy the number of modules they thought they would need for the >> number of insertions. I don't think they ran 24V from the front end all >> the way through so probably AC to each module and a 24V supply for the >> motors and relays (and air valves). The entire set of modules was also >> connected via CAN bus so we have the CAN signal ground in that match too. >> It was a long time ago and I was brought in to solve CAN bus problems so I >> never really looked closely at the power. >> >> What about if you have a vehicle instead. Might have equipment mounted >> on frames that need to be bonded together. If they run an independent >> battery pack and/or genset then the DC ground doesn't need to touch the >> frame. But what if the vehicle 12V battery which does have negative >> connected to the frame also provides some sort of vehicle connection. Say >> a radio that has a modem that connects to a PC. >> >> Logic would dictate you want the DC ground of everything connected to the >> frame with some bond wires even if just for lightning protection. But now >> you run risk of ground loops on the 12V circuits interfering with the >> system battery pack. >> >> Do the hybrid electric cars connect the negative DC of the high voltage >> battery pack to the frame? >> >> I'm amazed at the can of worms this question raises. We haven't even >> discussed the electrical noise issues coupled through the lowest impedance >> path. >> >> John >> >> >> -----Original Message----- >>> From: Dave Cole [mailto:linuxcncro...@gmail.com] >>> Sent: July-12-18 2:57 PM >>> To: emc-users@lists.sourceforge.net >>> Subject: Re: [Emc-users] Grounding >>> >>> I think you need to define what you mean by "grounding". >>> >>> If you have a 24 volt DC powered control system, like an industrial >>> control panel, typically the 24 volt DC power supply/s will tie the 0V >>> terminal on the power supply to frame/panel ground.�� These are the big >>> 10, 20, 40 amp 24 volt DC power supplies that power the control panel >>> components. >>> >>> There are some good reasons to do this. >>> Many industrial control components have loose ties frame ground >>> internally and if you don't tie 0V to frame ground they malfunction! >>> Many of these components have specifications for the number of volts >>> that the M, 0V terminal can be away from chassis ground. >>> >>> The grounding is normally done by a single green wire from the power >>> supply 0V terminal to the ground bus bar.�� That way if there are >>> grounding/common issues you can lift that wire to aid in debugging the >>> system. >>> >>> When you get into 5V systems, breakout boards, etc, I tend to keep those >>> isolated from frame/panel ground.��� I think there are only downsides to >>> connecting the 0V terminal of a 5 volt power supply to frame ground. >>> >>> If you look at industrial drives, they always separate the frame/safety >>> ground from the signal "ground" or "reference" terminal.�� They are >>> usually two different terminals.� One is oftentimes a cable lug or >>> bolt-cable lug connection, and the other a small screw terminal. >>> >>> FWIW, I am in the machine controls business.� PCs are common >>> components >>> in machine controls. >>> >>> Dave >>> >>> >>> On 7/12/2018 4:31 PM, John Dammeyer wrote: >>> >>>> 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 >>>> >>> ------------------------------------------------------------ >>> ------------------ >>> 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 >> > > ------------------------------------------------------------ > ------------------ > 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
