RS485 is bidirectional does it mean it is fullduplex?

This first one seems to be about Fibre Optic Cable. This is not the topic of discussion. The thread is about RS485 data links and whether or not to connect the shield at end of the cable run to frame earth connections, and the precautions that may be needed if both ends really had to be connected.

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This one seems to be about telephone system risers in buildings and the practices that apply to that. Why should that be relevent to discussion about RS485 networking?, especially in industrial settings.

I am not able to read that on this system (I'll have to wait until I am using a different one). I only have the segment you provided below for now.

Why should I be interested in that continuity tester?

[%X]

A lot of people attribute any number of things to odd causes

Except that I am fully aware of the leaps in the difference potential between pieces of equipment that are not attributable to ground loops but are a fact of their normal and expected operation.

Except that you keep going back to telephony/telegraph systems and straying away from this topic which is RS485 networks.

You still seem to be. Put your diagram up again and go through putting numbers up on that and show what happens to the energy in the system when the earth potentials differ. Until you do that I am leaving it lie there.

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Paul E. Bennett ....................
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Paul E. Bennett
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I don't plan to start posting either fiction or articles filled with gratuitous insults.

If posting *facts* insults him, that isn't *my* doing.

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You want me call it what it is? I was being *diplomatic*!

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

"get a better grip" and "many lines of imaginative fiction deleted" are not facts. They are mild insults.

All I can do is to express my considered opinion that using phrases such as "many lines of imaginative fiction deleted" is not an example of being diplomatic.

Reply to
Guy Macon

RUS Bulletin 1751F-815 concerns "aerial and buried cable." While I agree that this applies to outside plant telephone cable, I question whether it is appropriate for RS-485 digital cables, which have a 40 foot distance limit at 10Mbps and a 4,000 foot distance limit at 100Kbps. That's quite short for outside plant use.

RUS Bulletin 1751F-810 concerns "digital and lightwave telecommunications systems", which would seem to be more appropriate for RS-485 applications. It says (emphasis added):

1.3 The *Single Point Grounding System* described in this bulletin meets the protection requirements of most central office and other electro-optic equipment manufacturers. The described methods should be followed unless there are compelling reasons for change 2.13 Isolated Ground Zone (IGZ) A dedicated area within an office building where all equipment is *electrically insulated from all external grounds* except through *a single ground connection* between the GWB and the MGB. The isolated area should preferably extend a minimum of six feet (two meters) on all sides from the equipment frames and framework and where practical be separated from other equipment by permanent walls. The IGZ will normally house sensitive electronic components (Isolated Area). 7.2 Transmission Equipment Termination and Protection Digital carrier equipment and sensitive electronic pair gain systems should normally be located inside the IGZ. 7.2.1.1 Shields of intraoffice cable connecting the MDF to carrier equipment bays *should be open at the MDF end and grounded at one point* to the MGB or GWB. This grounding arrangement provides electrostatic shielding and maintains GWB integrity. 2.9 Ground Loop Ground loops exist when there is more than one electrical path to a ground connection. Such parallel paths to ground are normally not a problem if associated with nonsensitive circuitry located outside the Isolated Ground Zone (IGZ.) *Ground loops are undesirable for equipment located in the IGZ.* 2.21 Single Point Grounding A grounding system using a *single point*, usually the MGB, for a zero reference potential to ground for an entire system. While the voltage at this connection point may rise above zero volts-to-earth-ground under fault conditions, the entire system will also rise at the same rate to the same voltage. This helps minimize any circulating currents between components from lightning or power surges.
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Guy Macon
Reply to
Guy Macon

*READ IT!*

The primary topic might well be Fiber, but it is all compared to the copper cable they've had in place since the 1970's. It discusses a number of specifics, such as ground resistance, that have been mentioned in this thread, including the fact that NEC code *requires* the grounding you say shouldn't be done.

[drivel deleted]

It discusses cable entrance specifications, and specifically how the cable is ground at *each end* to the building ground. The grounding that you say doesn't need to be done, that they specify according the NEC requirements.

Go to the web page I gave you previously

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and download the pdf version then. Why do you need this much hand holding?

That is of course from an additional document, that you made no attempt to check at all. And we notice you aren't interested in discussing the quoted text either. Can't blame you for that head in the sand posture...

Because if those splice boxes weren't grounded just like I said they were, nobody would be interested in testing how well grounded they are. But, unlike yourself, others *are* interested in good engineering practice.

You probably should *very* carefully read some of the other RUS documents then.

I keep explaining comm cable engineering to you. Why not try to learn something that is useful instead of putting your head in the sand with trivial comments like "Oh, my it's about fiber." Or "Oh my, it's a continuity tester." etc. etc.

I've gone through everything necessary to understand the diagrams. Use Google and *read* it. If you won't actually read the material how do you expect to understand it?

Here's the water, whether you drink or not is up to you...

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

Guy, you've been on Usenet almost long enough to claim gray whisker, eh? Or, maybe not... you probably don't realize that before you were here, nobody cussed at each other on Usenet! That certainly hasn't been the case for a lot more than any 10 years now. Regardless, there is a *huge* difference between gratuitous insults, and saying something pertinent to the posted material that just also happens to be less than complimentary.

You initially admitted that abuse *is not* something I initiate. It is something I've tolerated.

If you actually do have a problem with the words exchanged, why weren't you chiming in with comments about 100 articles back?

[excess drivel deleted]

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

The point was, originally, that the flat statement that cables should have the shield ground *only* at one end, is not correct.

When that was challenged, I pointed out that comm cables are *all* grounded at 3000 or 6000 foot intervals. The response was that it is not true.

Obviously, it *is* true.

From that one can conclude that clearly the flat statement was in fact incorrect, just as I originally stated. The *reasons* that it is not correct *do* apply to RS-485, and certainly to anything that approaches 4000 feet (some claimed to be going far beyond that too). Specifically, it applies because in many of the applications being discussed the *very* *same* reasons to ground comm cables at multiple points exist for these short RS-485 loops.

It's good engineering.

I have discussed that in *detail*, in several articles.

And the specifics of that single ground connection, are what I discussed in detail.

I discussed *that* in detail. You do understand what "intraoffice cable" is, right? An how that fits what I said about the *single* ground connection to a building ground?

So just how many of these 4000 foot, or longer, RS-485 runs are totally contained within the IGZ? For that matter, how many of the runs that have been described in this thread have been in an IGZ, regardless of the length?

You can't cherry pick things that do not apply, without understanding the terms and the limitations being discussed.

As I've described... each building should have a single ground point, and each floor should also have a single ground point. Generally each *row of equipment* has a single ground, though sometimes individual racks are isolated.

Within a single row of equipment, or within a single rack, that has a single ground connection, you have an IGZ. There should not be two grounds on each end of a shielded cable.

I'll leave the rest as an exercise for the reader...

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

I can only assume from this that you agree that "get a better grip" and "many lines of imaginative fiction deleted" are not, despite your previous claim, facts.

Again I tell you that two wrongs don't make a right. Just because others behave poorly, that doesn't mean that it's OK for you to do so as well. Try to rise above those around you instead of engaging in a race for the bottom.

I agree that there is a huge difference between gratuitous insults and saying something pertinent to the posted material that just also happens to be less than complimentary. I do not agree that "many lines of imaginative fiction deleted" fits the latter description. It is clearly a gratuitous insult, and is clearly not pertinent to the posted material. It is, in fact, a generic insult that can be inserted into many different posts, and thus cannot be pertinent.

Wrong. I never expressed an opinion on that. What I said was that even if someone else initiates abuse, two wrongs don't make a right. Yet you continue to argue that they do.

I have no responsibility to express an opinion on every flame war that you get into, nor does my not expressing an opinion on previous flamewars mean that I am not allowed to express an opinion on future flamewars.

This one caught my eye simply because I use a Bayesian scoring system rather than a killfile system, and this thread has a high score. Looking at the inference file that contributed to that score, I see that by simply rating every post that I read I have instructed my scoring system to raise the score a lot if the thread contains the text string "Paul E. Bennett" and to lower it slightly if the thread contains the text string "Floyd L. Davidson." (Please note that this is not a reflection of merit, but rather of what happens to interest me.)

I am now in a position to express an opinion on whether you initiate abuse. You do. The above is an example. I have not written anything even slightly abusive or insulting in this thread, yet you chose to insert a gratuitous insult. I suggest a bit of introspection and owning up to your own behavior.

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Floyd L. Davids>The point was, originally, that the flat statement that cables

Perhaps you fail to see that "flat statements" need to be taken in the context of the discussion. The above is a fine example of this. Without referencing the previous discussion, I am left with you making a flat statement saying that comm cables are all grounded at 3000 or 6000 foot intervals. Obviously, that *isn't* true. Some are only 100 feet long. Some are (in the words of the spec) "shields of intraoffice cable connecting the MDF to carrier equipment bays" that "should be open at the MDF end and grounded at one point to the MGB or GWB." Just as any statement that all cables should have the shield ground only at one end is incorrect, so any statement that comm cables are all grounded at intervals is incorrect.

Please step back for a moment, drop out of "I am right and I need to convince these idiots of that fact" mode for a moment, and examine your own words. You just claimed that short RS-485 cables should be grounded at multiple points, calling that "good engineering." (No, I don't want to discuss everything that you have said in the previous dozens of posts. In the post that is on my screen right now you just claimed that short RS-485 cables should be grounded at multiple points, and in the post that is on my screen right now you called that "good engineering." Saying something that is true in a previous post does not justify saying something that is false in your current post.)

The result of you making such a claim in any group of electrical engineers is quite predictable, as is your usual response, which is best described with a quote from Calvin & Hobbes; "A little rudeness and disrespect can elevate a meaningless interaction into a battle of wills and add drama to an otherwise dull day."

Which is my point. The post I am replying to says "comm cables are

*all* grounded at 3000 or 6000 foot intervals." I understand you wanting to use a short phrase as a stand-in for previous discussions, but you have chosen a short phrase that is, quite simply, wrong. Combine this with a tendency to not give others the same consideration that you expect by looking at their statements in the context of previous posts, and you have a recipe for yet another technical flame war.

There's that argumentative tone again. You don't have a shred of evidence that I don't understand what "intraoffice cable" is.

It only takes one to falsify your claim that "comm cables are *all* grounded at 3000 or 6000 foot intervals." You (rightly) disagree with anyone who implies that that all cables should have the shield grounded only at one end, then you use language that strongly implies that no cables should have the shield grounded only at one end. Referring to previous discussions does nothing to decrease the inflammatory nature of making such statements.

There's that argumentative tone again. You don't have a shred of evidence that I don't understand the terms and the limitations being discussed.

You seem to be implying that an IGZ is limited to being a single row of equipment or a single rack. It has been my experience that IGZs are usually much larger than that; a large computer room or a small building is often set up as an IGZ.

Reply to
Guy Macon

All of your discussion above this point was complete drivel, and I've again deleted it. (Most of what was below it is too, but...)

But, since it *did* reference previous discussion (which we know you have read), and was *clearly* marked as a summary of that discussion, you would only be left as you say *if* you choose to be dishonest. You lack the integrity to interpret what people write in the way that it is intended. Shame on you.

All that meet NEC specs do.

Do those fit the obvious difference between "comm cable" and "intraoffice" cable that the context indicated, or are you just displaying your lack of integrity?

I've made it *very* plain as to when they should be grounded and when they shouldn't. If you want to purposely disregard the context, which we know that you *are* aware of, what choice is there but to point out your lack of integrity?

Your lack of integrity doesn't change what the facts are.

Your statements indicated that you do understand, and were purposely ignoring it. Obviously, given your further discussion, that was *precisely* true. A simple lack of integrity...

So in the end, the fact is that you know I've been correct right from the start. You want to play word games to have an argument. That is not appropriate. Shame on you.

Don't lie. I explained *precisely* the theory required to determine whether it should or should not be grounded.

Going around in circles playing word games is inflammatory.

You need to get a grip on it Guy. You don't understand what an IGZ is. Study the documentation again. If you come back with polite questions instead of trying to play word games, and I'll make an effort to explain it to you.

Keep playing word games suitable to a 10 year old, and I'll simply point out your lack of integrity again.

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

Thread PLONKED due to extremely poor signal to noise ratio.

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Reply to
CBFalconer

An excellent point, and one that worried me. An opto-isolated RS-485 transceiver would not cope without protection with the rapid risetimes associated with lightning strikes. Even ignoring opto flashover voltage, the capacitance between the two isolated circuits (and those rapid risetimes) would almost certainly ensure an equally rapid demise. [The usual "divert the excess energy to ground" philosophy might help (Tranzorbs et al). Not tried it in anger, but looks possible, in principle, at higher cost.]

RS-485 et al do have limitations. I've taken this one to mean "avoid using between areas where large/rapid ground potential differences are possible".

[Note: this post relates to opto-isolated RS-485 transceivers. It does not relate to common-mode or shield grounding issues discussed earlier elsewhere in this thread.]

Steve

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Reply to
Steve at fivetrees

Except that while you've avoided damage to the equipment, you've done nothing to protect persons working on the equipment. If there actually is that much of a potential difference (or even just so much as 60 or more volts) between grounds... then you

*MUST* ground both ends of the shield, otherwise you present a dangerous, and potentially fatal, hazard to personel working on the equipment who may come into contact with the shield and local ground at the end where the shield is not grounded.

That may or may not be covered by regulations in other countries, but the NEC requires it in the US.

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

Got a cite?

Reply to
GrumpyOldGeek

Yeah, probably not shielded properly....

Meindert

Reply to
Meindert Sprang

The RUS cite that I provided referenced the 1993 National Electrical Safety Code edition.

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

*plonk*

I deleted the rest of your post unread and set my filters so that I will no longer see anything you post. You are obviously unable to carry on a civil conversation on a technical subject without resorting to personal attacks. Responding to a technical discussion without being overcome with emotion and firing up the old flamethrower is a rudimentary skill that many of us "normal" people take for granted that everyone has an easy time of mastering, but we sometimes forget that there are "challenged" persons in this world who find these things to be difficult. I should have noticed that this is true in your case and never exposed myself to what you wrote. It just wouldn't have been "right." Sort of like parking in a handicap space. I wish you the best of luck in the technical, emotional, and social struggles that seem to be placing such a demand on you.

Don't bother replying. I won't see it.

"The most hostile group was the one with high but unstable self esteem. These people think well of themselves in general, but their self-esteem fluctuates. They are especially prone to react defensively to ego threats, and they are also more prone to hostility, anger and aggression than other people.

"These findings shed considerable light on the psychology of the bully. Hostile people do not have low self esteem; on the contrary, they think highly of themselves, But their favorable view of themselves is not held with total conviction, and it goes up and down in response to daily events. The bully has a chip on his shoulder because he thinks you might want to deflate his favorable self image."

-Roy F. Baumeister, _Evil: Inside Human Violence and Cruelty_ p 149

Reply to
Guy

You won't get one because none exists. The NEC has rules about what needs to be connected to what, but the absurd notion that the NEC requires the connection to be done through a shield exists only in the imagination of a person who is ineducable. You will, no doubt, get the usual handwaving, but no actual cite. An actual cite would make it obvious that the two grounds can be (and should be) connected with an ordinary building wire rather than through a cable shield.

In fact, if you tried to foolishly connect ground through a cable shield rather than with a seperate wire in a new installation, the electrical inspector would be asking some tough questions such as why the connection is being made with a wire that lacks NEC type markings (THW, TW, etc.), why it isn't marked with a voltage rating, why you have used a connector in a grounding wire, etc.

Reply to
Guy Macon
[more drivel deleted]

plonk

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Floyd L. Davidson           
Ukpeagvik (Barrow, Alaska)                         floyd@barrow.com
Reply to
Floyd L. Davidson

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