Power Supply Grounding

[Tim Ganz]

I have Rhino 120 to 24 dc power supply and it has 2 Positive and 2 negative terminals on the DC side but no ground terminal. Should I connect one of the negative connections on the power supply to a ground terminal block to be able to check the 24 volts to ground all along the machine? Power supply part # is PSL-24-030

 

[lfe]

The ideal is that you create your 0V line by connecting it to a single point to ground and that will be the common for the power source(s) and everything it supplies.

Even in your main cabinet, since it is grounded, you can use a distribution bare bar.

 

[OkiePC]

I generally don't ground the low side of my DC power supplies, but let them "float". Some power supplies include a ground for the AC input side, but that doesn't ground the output. I have worked in many panels where the designer does ground the low side of a DC supply and that can be convenient but also allow for ground currents or noise to affect sensitive analog signals supplied by that DC source.

 

[g.mccormick]

I "always" (or almost always) ground my DC-. I have seen this fix noise issues, and I have never seen it cause noise issues.

Not saying it is right/wrong/ whatever just what I have been doing since I ran into a bit noise issue with a panel and a bunch of analog IO. The low voltage (mv output) transducers were super noisy until I grounded the DC-.

 

[BobB]

Here is a link to an article at Control Automation about the pluses and minuses of earthing a DC supply. I never earth the output of a switchmode at all. I do earth batteries though and the negative of the charger but then go through a switchmode and do not eartj the secondary.

Negative Effects of Grounding (Earthing) a DC Power Supply - Technical Articles

DC voltage systems exist to provide controllers and field devices with stable power, but it is not always clear when these systems should be bonded with the earth ground of the AC line voltage supply.

control.com

 

[BryanG]

The biggest problem with not grounding is that you 'think' you have a floating system, but without some type of sensing system, you don't know. It might be floating when you install it, but you have no idea what happens after that. I read a similar article to the above written by a power supply manufacturer, he decided that the solution was to have two earths, one main one and one for the power supply, I nearly choked on my coffee.

 

[lfe]

I generally don't ground the low side of my DC power supplies, but let them "float". Some power supplies include a ground for the AC input side, but that doesn't ground the output. I have worked in many panels where the designer does ground the low side of a DC supply and that can be convenient but also allow for ground currents or noise to affect sensitive analog signals supplied by that DC source.

I used floating supplies too, until a compliance test exam on 90s said that "all supplies must have a ground reference"

Nor did it say that it had to be referenced to ground, it even seems that it could be connected to a phase of the power supply but in no case can it be left floating.

And it is logical since on something floating nothing can prevent it from reaching a very high voltage with respect to ground, even more so next to cables with high dv/dt such as the output of a VFD that can generate strong inductions.

From then I began to use a bare commons bar in the main electrical cabinet, isolated from the mounting plate but connected to a single point to ground, and you save many DIN guide terminals.

 

[Bit_Bucket_07]

I "always" (or almost always) ground my DC-. I have seen this fix noise issues, and I have never seen it cause noise issues.

Not saying it is right/wrong/ whatever just what I have been doing since I ran into a bit noise issue with a panel and a bunch of analog IO. The low voltage (mv output) transducers were super noisy until I grounded the DC-.

That's been my experience as well. Grounding the 0 VDC side of the power supply cleans up noise issues on analog IO far more often than it causes them. If you are using 24 VDC discrete IO, a floating system is difficult to troubleshoot in the field where you may not always have access to the 0 VDC common.

 

[robertmee]

If it's my design, ground the DC common always. I've commissioned many a system without grounded DC supplies also, but as noted, it's a pain to troubleshoot. I've never encountered noise issues on grounded supplies.

 

[lfe]

If it's my design, ground the DC common always. I've commissioned many a system without grounded DC supplies also, but as noted, it's a pain to troubleshoot. I've never encountered noise issues on grounded supplies.

DC supplies and AC supplies via transformer too, all can share the same common grounded at a low resistance central point.

You get a robust system against noise, much better than using the neutral of the electrical installation.
In new installations in Europe, the usual thing is that the three-phase power supply no longer has a neutral cable.