Reply by Floyd L. Davidson●June 20, 20052005-06-20
Guy Macon <_see.web.page_@_www.guymacon.com_> wrote:
[more drivel deleted]
plonk
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Reply by Guy Macon●June 20, 20052005-06-20
GrumpyOldGeek wrote:
>[deleted] wrote:
>
>> 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.
>
>Got a cite?
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 by Guy●June 20, 20052005-06-20
Floyd L. Davidson wrote:
>All of your discussion above this point was complete drivel
*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 by Floyd L. Davidson●June 20, 20052005-06-20
GrumpyOldGeek <grumpyoldgeek@gmail.com> wrote:
>> but the NEC requires it in the US.
>
>Got a cite?
The RUS cite that I provided referenced the 1993 National
Electrical Safety Code edition.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Reply by Meindert Sprang●June 20, 20052005-06-20
"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:42B5E1B6.CC84447E@yahoo.com...
> "Floyd L. Davidson" wrote:
> > Guy Macon <_see.web.page_@_www.guymacon.com_> wrote:
> >
> > >> [excess drivel deleted]
> >
> > 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...)
>
> Thread PLONKED due to extremely poor signal to noise ratio.
Yeah, probably not shielded properly....
Meindert
Reply by GrumpyOldGeek●June 20, 20052005-06-20
Floyd L. Davidson wrote:
> "Steve at fivetrees" <steve@NOSPAMTAfivetrees.com> wrote:
>
>>"Paul Keinanen" <keinanen@sci.fi> wrote:
>>
>>>On Wed, 15 Jun 2005 15:40:22 -0800, floyd@barrow.com (Floyd L.
>>>Davidson) wrote:
>>>
>>>
>>>>The specification includes the maximum ground offset voltage
>>>>permissable. (I don't recall what it is, or how realistic it is
>>>>for common 4000 foot runs of twisted pair cable.)
>>>
>>>It would be unrealistic to assume that the grounding electrodes of two
>>>separate buildings would stay within the -7.. +12 V common mode range
>>>at all times (especially during thunderstorms), so optoisolation
>>>should be used to keep the grounds separate. The real question is, is
>>>the 0.5 - 2.5 kV isolation found on many RS-485 cards enough or should
>>>a fiber optic cable be used instead.
>>
>>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.]
>
>
> 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.
Got a cite?
Reply by Floyd L. Davidson●June 20, 20052005-06-20
"Steve at fivetrees" <steve@NOSPAMTAfivetrees.com> wrote:
>"Paul Keinanen" <keinanen@sci.fi> wrote:
>> On Wed, 15 Jun 2005 15:40:22 -0800, floyd@barrow.com (Floyd L.
>> Davidson) wrote:
>>
>>>The specification includes the maximum ground offset voltage
>>>permissable. (I don't recall what it is, or how realistic it is
>>>for common 4000 foot runs of twisted pair cable.)
>>
>> It would be unrealistic to assume that the grounding electrodes of two
>> separate buildings would stay within the -7.. +12 V common mode range
>> at all times (especially during thunderstorms), so optoisolation
>> should be used to keep the grounds separate. The real question is, is
>> the 0.5 - 2.5 kV isolation found on many RS-485 cards enough or should
>> a fiber optic cable be used instead.
>
>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.]
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.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Reply by Steve at fivetrees●June 20, 20052005-06-20
"Paul Keinanen" <keinanen@sci.fi> wrote in message
news:hs42b11ldt006jlv9pkcu2u0dbu33egb1a@4ax.com...
> On Wed, 15 Jun 2005 15:40:22 -0800, floyd@barrow.com (Floyd L.
> Davidson) wrote:
>
>>The specification includes the maximum ground offset voltage
>>permissable. (I don't recall what it is, or how realistic it is
>>for common 4000 foot runs of twisted pair cable.)
>
> It would be unrealistic to assume that the grounding electrodes of two
> separate buildings would stay within the -7.. +12 V common mode range
> at all times (especially during thunderstorms), so optoisolation
> should be used to keep the grounds separate. The real question is, is
> the 0.5 - 2.5 kV isolation found on many RS-485 cards enough or should
> a fiber optic cable be used instead.
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
http://www.fivetrees.com
Reply by CBFalconer●June 19, 20052005-06-19
"Floyd L. Davidson" wrote:
> Guy Macon <_see.web.page_@_www.guymacon.com_> wrote:
>
> >> [excess drivel deleted]
>
> 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...)
Reply by Floyd L. Davidson●June 19, 20052005-06-19
Guy Macon <_see.web.page_@_www.guymacon.com_> wrote:
>> [excess drivel deleted]
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...)
>>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.
>
>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
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.
>making a flat statement saying that comm cables are all grounded
>at 3000 or 6000 foot intervals. Obviously, that *isn't* true.
All that meet NEC specs do.
>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."
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?
>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.
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?
>engineering." (No, I don't want to discuss everything that you
>have said in the previous dozens of posts. In the post that is
Your lack of integrity doesn't change what the facts are.
>>You do understand what "intraoffice cable" is, right?
>
>There's that argumentative tone again. You don't have a shred of
>evidence that I don't understand what "intraoffice cable" is.
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...
> You (rightly) disagree
>with anyone who implies that that all cables should have the shield
>grounded only at one end,
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.
>then you use language that strongly implies
>that no cables should have the shield grounded only at one end.
Don't lie. I explained *precisely* the theory required to
determine whether it should or should not be grounded.
>Referring to previous discussions does nothing to decrease the
>inflammatory nature of making such statements.
Going around in circles playing word games is inflammatory.
>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.
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.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com