Ground

It is better to run a separate 0V conductor and ground/earth the 12VDC supply at its source only. That way, a simultaneous overcurrent in both the 12VDC system and in the mains system will not overload the ground/earth conductor at any place. Reference British Standard 7671.

Yes, excellent point. I am not sure where the op was going with this, but standards are definitely in place for a reason. Since there is a published reference for this situation, I would go with that.

Have you ever noticed 24VDC battery bank of generator with a negative end connected to generator case?

Where does the case, in its turn, connect to? The common grounding bar.

So if I leave the mains ground alone and use the common grounding bar it would be fine right, would the positive D/C need to be as a 12 gauge or 14 gauge wire then?

Well, that depends upon the current the system is expected to supply, the permissible voltage drop and the electrical code applicable at the location of the installation.

This is the first time I have heard of anyone grounding a 12V system through the earth. Is this normal?

I thought that DC was not normally grounded because of the potential for corrosion of the electrode.

That is why US telephone systems, which run on a 48V battery supply, use a positive ground.

Why are you are hellbent on inviting trouble? That is my only question.

You must adhere to code. However, the answer provided by "Beenaround" is the most logical approach. He provided an excellent engineering answer. The safer thing to do is to not use a common ground.

There will be always risk. Better have separate earth or draw separate wire wire from earth source.

Got it and great answer.

I agree with leveles. Others have pointed out if you have a problem on the 'high' voltage side it could get complicated even lethal. Keep the two separated. Some transformers have an earthing connect point but it has nothing to do with low voltage side, its there to ground the system if something goes wrong 'high' voltage side.

Everyone here had pretty good answers, but for me I would not want the 12 volt hum in my 110 appliances. Also, like one gentlemen said, if house current wants a new path to ground, there goes your DC stuff. Could end up being very costly, especially if you are renting.Always keep DC ground seperate from AC grounds. In my ham shack, I never mix the two. ALL my stuff is costly, and some irreplaceable. Have a good day guys.

Common Ground Systems are used all the time, just take a look at switch-mode power supplies the usal case is that netural is connected to ground, the only time that this is not the case is with sensitive systems that cannot afford voltage or current fluctions.

Cheers Joe

And common ground system here is the main grounding system of the house not the 12VDC equipments.

Opp's i said that the netural was connected to the ground, which it is but I meant to say that the negative is connected to the ground

Cheers

Joe

Hi Hein

As long as the Ground is only used as a Ground system, I don't have a problem with that. If the Ground is used as the main return path, I would have some problems.

Cheers

Joe

Holy crapadocius! I am not sure where this thread went overnight...If you look at a standard DC power supply in just about every computer in the world (for example), the case of the power supply is connected to the case of the computer. Both are effectively grounded to the ground terminal of the power cord.

They share ground...period!

The very basics of power supply construction shows a clear connection in the rectifier circuit to what? Ground! Where is that ground from? The case! Where is the case connected to?

Do I need to keep on?

Hey Cuba Pete,

Does your computer case/frame carry current? No,it is really a safety ground...not a DC current carrying "ground". DC ground is closer to but still very different to AC neutral.

No, not normally...I don't suspect anybody's does (!). The OP and, I believe, intent of this thread was to ground a DC power supply, not use the frame as a current carrying device for negative DC power. Those are very different things.

I have attached, as a matter of course for all interested, a schematic of a simple AT switching power supply. Please note the connections to frame ground, which references the ground supplied by a standard three prong plug. All effectively the same...continuous...bonded...ground.

If the image is too small, it may be found here: http://www.cmheong.com/work/schematics/at_psu_3.gif

Nevermind...I read back through the OP and subsequent responses and I don't think I really understood what the original intent was.

I think I must recuse myself from this discussion.

My question was. I want to use the commons ground of the mains for the common ground of my D/C system, will there be any problems with doing this or do I need to run a complete seperate D/C wiring system?

That was the start of this discussion.

The answer is.

It could work - but don't do it, unless you want to risk killing someone!

OK! SO I now have in scenario A< mains wiring and D/C wiring, Seperate systems and now how far aprt should they be in the travel from light source to some given distance from the light source. Can there be interference between the fields of each power supply. In other words, could their be a potentilial probblem with them in close proximity or overlapping in conduit or should that be seperate?

Hi again,

You are certainly asking some interesting questions here. I want to respond from my experiences of 46 years with everything from shipboard radio, radar, sonar; with house wiring, computer room wiring ( 1968 to present) where the computers were large enough to walk inside and the whole system could fill rooms 40' x50' for one system. We had motor alternators to buffer surges from the power company (pre- outlet strip protection) I am familiar with transient spike coming across or through a grounding system, radiated from electrostatic air cleaner, electronic ignition for factory overhead furnaces.Static electricity from moving belts or material. I am familiar with radio and radar using waveguides and antenna theory. Enough of the bragging.

Please provide some very specific information of what devices you will be powering with the 12VDC. What type of signal you are concerned may be interrupted. You mention distance from "light source", what is this light source? Fluorescent, led, incandescent? Are you using the 12VDC as a control signal, to carry data or information, or radio signals? There are ways of shielding for radiated electrical interference even to the extent that the military used in the 70's to prevent spying during the cold war. Also provide and unique 120 VAC devices connected.

Well with out mixing things up I need to tell you that I have another submission called LPCS here on the discussion board. With that be said then i wanted to know about cost saving by utilizing wiring already in place and only adding one more for the positive wire and utilizing ground as is in the mains and have D/C to go to some location, component or storage system somewhere with in the environment producing the light in the first place. The LPCS will move the D/C, and I do say I have my own opinions on the amount of voltages but for now that is what my task is. To get D/C power from point a to point b and do it as cheaply as possible. I was concerned that if the total combined D/C voltages around 14.4 volts and over 200 amps collectively of course, would that be a concern when in the close proximity of the 120 v A/C mains supplying power to the lights. I know it seems complicated but it turns out rather simple. The part about electomagnetic interference and the such is my concern, or for that matter any type of interference. I know their is an answer just not sure i am askng it correctly.

Thanks for your help.

LPCS /Gary

200 Amps!? 12 gauge will simply melt.

You are going to need something like 3/0 copper or better depending on the length and allowable voltage drop.

I was pondering this too. A car battery is rated between 500-700 cold cranking amps, so what are "cold cranking amps" verses normal amps. Yes, 4 or larger and the distance/lenght can play in so it should be the fine strands or face the drop. Now the OP does say "cummalative" . Is that code for "many circuits"?

Cold cranking amps is the rating of the battery. That is a capability of the battery, not what it is actually delivering.

The current draw is determined by the load, not by the capability of the source.

I have a lighting panel in my facility. The panel is rated at 125A. The lights only actually pull around 30A total, all circuits.

Starting my car on Christmas morning in Bismarck, ND would require much more current than starting it in Honolulu, HI (on just about any day!), rhetorically speaking.

In this case it means number of individual LPCS in series to produce the current to the system. For instance store a has 4000 of these overhead artificial lights and they basically are on 24hrs day. If done correctly at any given time the result will be well over 200 amps but I am sure we could work out the logistics of the system and make it very efficient with some inverting along the way to mains or basically wherever it would be needed.

Are you trying to run a single wire for the DC + side and use the AC ground for the DC - side?

100% yes!

exactly !

Then the answer is NO.

The ground conductor is there for a specific reason, to provide a safe path for ground fault currents.

LPCS:

Why you want to do that? For safety or operation ground?

For safety, having half a loaf is better than no bread.

For operation, apple is apple. Banana is banana.

Hope that helps.

You could use the ground for both if the house was connected to a TT systems which it probably is not. The factory I work in is TT and all neutrals and earths of AC & DC are connected to the same earth. Some motors are on a IT system whis different again.

Sorry for being late to the party but there needs to be a distinction made between common and ground. They are NOT the same thing. For instance, a DC electrical system may have a common negative (not ground) or a common positive (again, not ground). Normally you do not want to directly tie your DC common to ground (take a look at a Siemens DC power supply for 24VDC out and 110VAC input - it has 5 terminals, 3 on the AC side (L1, N, PE) and two on the DC side (+, -). THAT PE on the AC side absolutely must be tied to ground for safety. Connecting the + or - on the DC side to ground is asking for trouble. So the upshot is NO, don't connect your DC common to ground, but do connect your metal chassis to ground.

You nailed an important point there. You raise the reference. GA.