grounding DC

Hello
Should I ground the negative from my DC power suppy to the control cabinet like I ground the ground wire for the AC?

It's usually smart to fuse one side of your control circuit, and ground the other side. If one of your signal wires becomes grounded, this should cause a short circuit, and blow a fuse causing your machine to shut down rather than continue to run erratically.

In any case you must evaulate your application and provide the final analisys. Check the codes that cover your machine also.

Mike.

It doesn't cause any problems having the AC and DC grounded together?

No.

Are you desinging a control panel?

elevmike said:

No.

Are you desinging a control panel?

Click to expand...

Yes

What is the primary power supply?

What control voltages do you need? does it include a PLC?

Are you using sink or source I/O?

Are you controlling motors or servos?

What is the application?

OK, I have 120ac powering my power supply, plc, and a few outputs. The power supply is 12amp 24dc. DC is for my touch screen, both sink and source inputs and a few outputs. Yes I will be controling a few motor boards for motors but no servos. This is for a bottle fill line.

The reason I brought up the question was it would make sense like you said to ground the neg so if I had a short in the pos I would blow a fuse. But I worked with other machinery at work built buy pros and they did not ground the dc.

Thanks for the help so far.

There is a line of thought (I don't know how valid it is) that by NOT grounding the common you give yourself a little better noise rejection. Assume you come off of your power supply with leads going to several different locations and you cannot (for some unspoken logistical reason) run the positive and common as a twisted pair. One wire could see a noise pulse and the other might not. This gives you a voltage difference between the two. If nothing os grounded the whole circuit can float with the noise and you won't see a potential difference anywhere in the circuit.
Like I said, I don't know how valid this is but I have heard this somewhere along the line.

Keith

Ready, and Keith,

There are a lot of theroys on noise and grounding, none are correct, and none are incorrect. It all depends on the application and the enviroment. Keiths theroy may hold some water in some apps.

However:

Depending on your enviromnet, and if your application is only using 24vdc signals that go from high to low and not somewhere inbetween, I would definately ground all commons. Addtiionally I would make sure every box, panel, and all metal equipment on or around the machine is grounded via a ground wire (dont rely on bonding through conduit). You want to design your circut so that if any feed or signal wire becomes grounded, it will cause a short and blow a fuse or breaker on your powersupply output and thus cause an immideate shutdown. Pick the fuse or breaker carefully and test it when your panel is complete. (read up on fusing, a big subject).

When designing your control circuit, ALL loads, (coils, lights, etc) will be grounded on the common side. On your drawing, everything to the right of the load will be your signal/control circuit, and nothing but common/ground on left side of load. By LOAD im refering to relays, starters, indicators, etc.

The idea here is geneeral safety and protection. It's just good practice.

Mike,

You have to be careful when saying everything. Traditional wiring ladder diagrams have the control (120VAC, 24VDC) coming in from the left of the load and Neutral/0VDC going out on the right.

Bob

Bob,

What a DUMMY am I!! Thanks for the correction. So does that mean the North Pole is'nt in Antartica? And I'm not left handed?

I hope Ready picks up on your post! I cant belive I said that.....

BTW Your an old Navy man so you may know the answer here:
There was a standard for controlers and ladder drawings that was developed in WWII for all goverment contractors, and the Armed services. What was the name of the standard?

Do you mean P&ID's?

elevmike said:

So does that mean the North Pole is'nt in Antartica? And I'm not left handed?

Click to expand...

Question: How can you tell if you're in an elevator that Mike programmed?...

Answer: You select "Lobby", and the elevator starts going UP!...

beerchug

-Eric

I guess I deserve that.....

Eric,

OUCH!!

lol

Mike,

It has been 16 years since I was in. The only standards that I remember are MILSPEC (MILitary SPECifications) Standards but I do not remember what the spec numbers are.

The jist of it was that all electrical controls documents had to have Basic Block Diagrams (showed system interconnects), detailed Block Diagrams (showed how the individual cards where connected), wiring schematics (for us they were horizontal ladder diagrams down to the component level of each board), and connector pinouts. There may have been more but that is all that I remember right now.

/e dusting cobwebs off of brain...

Bob