I think you need to polish up your definitions of neutral and bond.

I see now that my choice of words in my previous post was incorrect. I understand that the bond, under normal operation, should have no current flow and is solely for safety purposes - in theory, everything will work as designed without these connection points. Neutral, on the other hand, is ~24VDC or ~85VDC (in my application) less then the hot lines and is the return path for their respective currents.

Some questions:
1.) Do all DC sources and component bond connections need to be fed back to the incomming AC Earth Ground connection point on the metal plate or can I assume the conductivity of the metal plate is enough?
2.) Should I physically connected all instrumentation wire shielding to a common point on the metal plate? Furthermore, should I physically connect these shields to the common point as noted in question 1?
3.) The driver I am using (Oriental Motor part #RBD245A-V) has two power connections. They indicate one as '+' and the other as 'Ground' which is indicated to be connected directly to an Earth Ground Point. This setup does not seem logical as current flow is not directed back into the DC source.

Please correct me if I am wrong!

I do have a few more questions but I think that is enough for one night

Thanks for all the comments and suggestions!!! You Electrical guys ain't to bad after all!!

 

There are two schools of thought on keeping various supplies in a system galvanically separate, the other is to bond, where possible, all P.S. commons and bond these to a common earth ground star point in the enclosure.

DOH! Sorry but when you say Commons, you mean each component safety Ground or frame ground/bond, correct?

Thanks for the input Max! I had actually come across that reference a few months back, I will revisit it soon. For my particular application and component selection, bonding very well may be the best way to proceed until I can fully appreciate the concept of floating/ isolated system design.

Cheers!

 

I see now that my choice of words in my previous post was incorrect.

Sorry to act like a beach, but these are very important distinctions that make all the difference in the realm of safety. We really MUST be communicating on the same page.

Some questions:
1.) Do all DC sources and component bond connections need to be fed back to the incoming AC Earth Ground connection point on the metal plate or can I assume the conductivity of the metal plate is enough?

It depends. You can see from nsaspook (post #18) that the particulars of the situation can demand extraordinary measures. A lot of circuits just bolt to case (any sheet metal you can find) anywhere it's convenient, like the variable interval windshield wipers on my car. Some demand a private bonding wire from each sub-system to the one and only Bond point connector. If your brain systems get hinky, you're going to have to do that. Plan on it in the original design and you will have the problem solved before it happens.

2.) Should I physically connected all instrumentation wire shielding to a common point on the metal plate? Furthermore, should I physically connect these shields to the common point as noted in question 1?

NO! Instrument shields go to the "common" point of their subsection (a DC supply?). Then the subsection gets a single Bond wire to the one Bond point connection. The sheet metal pieces are a sort of armor against noise, but they are not the quench point, they are the antennas. All sorts of magnetic and electrostatic fields are intercepted by the sheet metal. They make their way to the one Bond point connection, but you don't want that traffic in your brain systems.

3.) The driver I am using (Oriental Motor part #RBD245A-V) has two power connections. They indicate one as '+' and the other as 'Ground' which is indicated to be connected directly to an Earth Ground Point. This setup does not seem logical as current flow is not directed back into the DC source.

Apparently you have a DC motor and the instructions ASSume that the negative voltage side of it is connected to this place called, "ground". Discard the word, "ground" as it has little use in this discussion. It only serves to obfuscate which ground we are talking about. We have Bond, Neutral, and the "common" point of each DC subsystem. All of them will get back to the planet eventually, but the motor winding is so far from the ultimate earth connection that to call it ground is like saying a leaf is connected to the roots. Well, it is, but it has only one path to get there. We're building the path right now.

Thanks for all the comments and suggestions!!! You Electrical guys ain't to bad after all!!

You're in a nest of nerds, but its OUR nest, so we don't feel threatened.

 

We need you to provide specific information about the DC supplies, sensors, motors, circuit boards, etc. and we'll figure out how to route things and when and where the rules can be "broken".

ps, when Max said, "common earth ground star point" he was describing what I am calling, "the one Bond point connection". Of course, that's based on me assuming you don't know exactly what, "star point" means. I might be wrong.

"Ground" and "common" are often used in a sloppy manner. I am trying to force rigid control of what we call, "ground", "common", "bond", "neutral" and, if you're not careful, a couple of other poorly defined words will sneak in.

 

I have to mention, the moment I think I've wrapped my mind around one concept, another seems to fade into obscurity!

 

I have to mention, the moment I think I've wrapped my mind around one concept, another seems to fade into obscurity!

That's OK. That's why time was invented. When time is filled, you will understand it all, or at least be able to follow instructions.

 

This is kind of what I have, so far:

 

I have attached the preliminary enclosure layout of the components. Some components have slightly different spec's than shown.. This was intended to organize my thoughts. I added some VERY rough wiring and a few notes. Obviously A wiring diagram would be much better but I do have access to the files at the moment. There are no fuses/breakers speced out yet as I am still trying to determine what requirements are needed on each branch circuit.. Most importantly I do indicate some of the bonds that are, after reading your comments, most likely wrong. Anyone feeling frisky enough to take a look and try to make sense of what I did?

 

3.) The driver I am using (Oriental Motor part #RBD245A-V) has two power connections. They indicate one as '+' and the other as 'Ground' which is indicated to be connected directly to an Earth Ground Point. This setup does not seem logical as current flow is not directed back into the DC source.

This is one reason I prefer not to use 'Ground' when just referring to a power source common terminal, as in N.A. it also means Earth.
The ground referred to with your motor, they most likely intended it to mean the common side of the power supply.
Just remember that any earth ground point or conductor referenced as such is never intentionally used as a circuit conductor.

You may also see a rule that the only place the AC neutral is connected to earth ground is at the service entry.
It can be re-referenced when using say a 240/120v control transformer where the secondary would be isolated, in this case it is permissible to connect one side of the secondary conductor to chassis immediately at the secondary point, the earth conductor and neutral then are both fed to their respective circuits.
This is termed a 'Local' neutral.
See transformer 1T in the PDF
Max.

 

You may also see a rule that the only place the AC neutral is connected to earth ground is at the service entry.
It can be re-referenced when using say a 240/120v control transformer where the secondary would be isolated,

Perfect example of when the rules can be, "broken".

 

This is kind of what I have, so far:

Thank you! Makes perfect sense. ayout I have in my head is much more complete. The loosely used nomenclature is throwing me off, I think.. Can I ask, if i have peripheral components running mains voltage outside of the box, does it matter if the wires are unshielded or shielded and if so, ground those shields strait back to AC earth star point.

Also, what is the best practice for the DC shielded power wires inside the box? I can connect both DC control and high voltage at both ends to a common point on the plate, But if I do that, the 24Vdc control shields are both at the same potential..Or am I thinking about this to much..

Thanks again! Sleepy time.

 

You generally don't shield power wires. They don't suffer from picking up noise because they are low impedance sources.

 

Perfect example of when the rules can be, "broken".

Necessary for Restoration.

Also, what is the best practice for the DC shielded power wires inside the box? I can connect both DC control and high voltage at both ends to a common point on the plate, But if I do that, the 24Vdc control shields are both at the same potential..Or am I thinking about this to much..
.

The Siemens PDF Chap 6 lays out the current practice of now earth grounding both ends of a shielded cable when equi-potential bonding is used in the system.
The older method recommended shielding one end only.

For power carrying conductors when a device is supplied with individual conductors it is important to make sure they are twisted together, this has the tendency to cancel out the radiated EMI.
Max.

 

This thread was supposed to be about grounding. It's not that hard after you learn the definitions. This guy carries current, that guy is just a safety ground, and the sensors get shielded. I wouldn't be surprised if the OP has this figured out and never comes back.

 

I wouldn't be surprised if the OP has this figured out and never comes back.

???
I assumed coming back with seven questioning posts he maybe needed a little clarification?
Max.

 

We'll find out. I just think maybe the light bulb is about to come on for him.

 

Hey guys and gals. I am still here #12!! Didn't have a change to check in last couple nights. After going through all the comments for the 25th time, It all makes perfect sense!!!!

The couple things that had me confused were cleared up with the help of #12's comments and simple diagram layout, and something Max posted -

This is one reason I prefer not to use 'Ground' when just referring to a power source common terminal, as in N.A. it also means Earth.
The ground referred to with your motor, they most likely intended it to mean the common side of the power supply.
Just remember that any earth ground point or conductor referenced as such is never intentionally used as a circuit conductor.

May sound silly but that Oriental Motor diagram was confusing the heck out of me. I was also unsure of the sensor shielding due to all the inconsistent schematics I have been reviewing. The schematic diagram that Max posted was a great help as well! I will be using that to expand on the one I have in process.

Again, thanks for all the help and pointers!!! I am working on the schematics and will post my finished design when it is complete.

 

The older method recommended shielding one end only.

Hey. I'm old. That's what I have to work with.

 

Looking at Max's drawing: That, "encased in conduit" marking, the conduit is supposed to be attached to the Bond point but it is not marked on the drawing.

You can see that each transformer secondary is attached to the Bond point.
That thing called "2LT" seems to be a light bulb (or some other kind of load). In my world, attaching it to Bond is not right. It should be attached to, "#16 AWG wht" (that vertical line on the right).

 

Looking at Max's drawing: That, "encased in conduit" marking, the conduit is supposed to be attached to the Bond point but it is not marked on the drawing.

You can see that each transformer secondary is attached to the Bond point.
That thing called "2LT" seems to be a light bulb (or some other kind of load). In my world, attaching it to Bond is not right. It should be attached to, "#16 AWG wht" (that vertical line on the right).

BTW, the drawing is picked out of the NFPA79!
I would assume that it would be an automatic assumption that the conduit would normally be grounded?
As to the light, I am not sure what they are trying to convey there, on the surface one would think that it would return to the #2 rail.
I see the neutral is also referenced to ground at that point for some reason I am not seeing?
Max.