Common, -VDC, Chassis Ground?

[garybergin288]

Have my control box all layed out and getting ready to wire everything. My confusion is with the common circuit to my understanding the "common" is the same thing as DC negative, and on a video for wiring the acorn someone said to tie the psu DC neg output to chassis ground bus. So is the Common wire aka DC Negative supposed to all be tied into the ground bar of the panel? And does this all tie into my "star point ground"

[lavrgs]

I just went through connecting COM to GND and it solved my noise issues. I was told to be careful of is if there is a voltage differential. In my case there wasn't

[centroid467]

Hello Gary,

Are you following any specific Centroid or other schematics? If so, please post the number or file.

We have been shipping Acorns with pre-wired power supplies with the DC negative tied to earth ground for a while now. You shouldn't need to make that connection again. DC negative and earth ground should only be connected at a single point.
All of the DC negative lines should be tied together at a common point as well. The main exception to that is if something truly needs to be isolated from the rest of the power network. They can branch off but you should avoid loops.

[garybergin288]

Hello Gary,

Are you following any specific Centroid or other schematics? If so, please post the number or file.

We have been shipping Acorns with pre-wired power supplies with the DC negative tied to earth ground for a while now. You shouldn't need to make that connection again. DC negative and earth ground should only be connected at a single point.
All of the DC negative lines should be tied together at a common point as well. The main exception to that is if something truly needs to be isolated from the rest of the power network. They can branch off but you should avoid loops.

i am following the acorn schematics for wiring leadshine dm stepper driver s14976, i have a total of 5 psu one for each axis at 60vdc one 24vdc for my inputs and contactor and the acorn 24/5vdc so should i just connect the earth ground to my vdc- the way the acorn power supply is to all my other power supplys?

[centroid467]

No, you don't need to connect the other power supply negatives to earth ground. Only the Acorn supply should have its negative tied to earth ground.

[Richards]

Ground is a common connection. Earth ground, chassis ground, and power supply ground should all be on a common bus (tied together) inside a electronics cabinet. If you have more than one cabinet and if those cabinets are supplied with AC power from different sub-panels, then you DO NOT connect the grounds from one cabinet to the grounds on the other cabinet; otherwise you may have a ground loop which is caused by the resistance between the two sub-panels.

If you think of ground as the number zero in math, then it becomes obvious. You can't have zeros with different values. Zero is zero. Ground is ground. The concept is the same.

.

[garybergin288]

Ground is a common connection. Earth ground, chassis ground, and power supply ground should all be on a common bus (tied together) inside a electronics cabinet. If you have more than one cabinet and if those cabinets are supplied with AC power from different sub-panels, then you DO NOT connect the grounds from one cabinet to the grounds on the other cabinet; otherwise you may have a ground loop which is caused by the resistance between the two sub-panels.

If you think of ground as the number zero in math, then it becomes obvious. You can't have zeros with different values. Zero is zero. Ground is ground. The concept is the same.

.

this is where it gets confusing the post above yours says i should not tie the negative from the psu to earth ground im getting conflicting answers lol i dont know now?

[Richards]

Welcome to the joys of electrical engineering. Ground is ground. AC ground is zero volts. DC ground is zero volts. There is no difference in the voltage potential. All grounds whose source voltage(s) come from the same panel or sub-panel MUST be zero volts or they are not ground. Different sub-panels may have their earth grounding rods located at the panel. The resistance in the earth (dirt) may cause their electrical potential to slightly differ. That's why only one panel (sub-panel) is bonded to earth (dirt) ground. The other panels are bonded to the originating panel.

Some designers have been told that AC ground and DC ground are different. They are not. DC power originates from AC power. It is simply rectified AC that generally has filtering capacitors.

If there is a difference in ground potential, i.e., a measurable voltage between grounds, then something is wrong and the voltage potential can damage electronics or cause physical harm.

It took me awhile to be convinced that all grounds should be connected until George Baulding, chief electrical engineer at Kaiser (yes, that Kaiser, the company that makes top-secret electronics for the military) sat me down and explained what grounding is and how to connect things properly.

[garybergin288]

Welcome to the joys of electrical engineering. Ground is ground. AC ground is zero volts. DC ground is zero volts. There is no difference in the voltage potential. All grounds whose source voltage(s) come from the same panel or sub-panel MUST be zero volts or they are not ground. Different sub-panels may have their earth grounding rods located at the panel. The resistance in the earth (dirt) may cause their electrical potential to slightly differ. That's why only one panel (sub-panel) is bonded to earth (dirt) ground. The other panels are bonded to the originating panel.

Some designers have been told that AC ground and DC ground are different. They are not. DC power originates from AC power. It is simply rectified AC that generally has filtering capacitors.

If there is a difference in ground potential, i.e., a measurable voltage between grounds, then something is wrong and the voltage potential can damage electronics or cause physical harm.

It took me awhile to be convinced that all grounds should be connected until George Baulding, chief electrical engineer at Kaiser (yes, that Kaiser, the company that makes top-secret electronics for the military) sat me down and explained what grounding is and how to connect things properly.

so it would seem to me that the most direct route for my power supplys would be to wire them the same way the acorn psu comes with the ground and vdc neg connected correct?

[Richards]

Usually that will work; however, there is one problem. DC supplies are usually mislabeled. A 24VDC supply is usually labeled +V and -V where +V = +24VDC and -V = 0VDC. If you buy a power supply that has a negative DC voltage, be sure that you know which terminal is 0V. That terminal should be connected to the ground bus. (When I first started building process computers, we used RS232 communications. The power supply was usually +5VDC, +12VDC, Common, and -12VDC.)

The reason that we tie Grounds together and we tie AC neutral to DC common (Ground) and we tie Earth Ground to AC neutral to DC common is to reduce electrical noise. An NPN transistor turns on when its base voltage is as low as 0.2VDC (germanium) or 0.6VDC (silicon). If grounds are allowed to float (unconnected), a transistor can be triggered unintentionally simply because of electrical noise. Proper grounding reduces that problem. Although we think of electricity running through wires, what is really going on is that when electricity is flowing, it creates an electrical mechanical field. That field extends beyond the wires. Anything we can do to reduce the effects of that electrical mechanical field improves the stability of our controller.