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Posted by Dioclese on June 4, 2008, 1:13 am
>
>>
>>> Back when I used to install PBX's, the manufacturer REQUIRED a
>>> #6 (min.) ground wire be run from the PBX service panel in the
>>> PBX room to, with no taps, the xformer that provided the power.
>>> If we simply wired the ground to the panel that provided power
>>> to the PBX room or building ground then we would void the
>>> warranty. Also, nothing that was fed from the PBX panel could
>>> be in contact with building ground. With some of the installs
>>> being in the range of millions of dollars, we were told that we
>>> could loose our job if we didn't get the electrician to wire the
>>> ground "correctly." There were many times that this would lead
>>> to a heated argument between us and the contracted electrician.
>>> We did mostly new construction. To put things into perspective,
>>> some of the larger installs would require as much as up to 6-30
>>> amp 220 volt feeds (if I remember correctly) and would power,
>>> truck sized banks of batteries and refrigerator sized inverters
>>> and rectifier units. The PBX's ran on 48 to 54 volts DC and each
>>> of the up to 6 rectifier units could pump out up to 50 amps DC.
>>> Was it simply a matter of the manufacturer not wanting to put
>>> trust in the local wiring?
>>> Was it a matter of trying to eliminate any chances of ground
>>> loops? Was it a matter of the manufacturer trying to get the
>>> cleanest power available?
>>> Was it just a Nortel nuance?
>>> ???
>>>
>>> Just wondering.
>>>
>>> Chris
>>>
>>>
>> For a while back in the 70s, the state of the art in electronics
>> was very susceptible to noise, especially ground mode noise. I can
>> remember having an electrician completely rewire half a panel's
>> worth of circuits because he tied the isolated ground recepticles
>> to the flex-duct, even though that totally destroyed the concept of
>> the isolated ground. Even today, one is more likely to find
>> 'mission-critical' equipment being feed with isolated ground
>> circuits, especially in things like medical equipment were they are
>> dealing with extremely lov voltage inputs.
>>
>> An example: In my younger days I used to be part of the IT staff
>> at a major automotive engine plant. We had a T1 rack in the
>> computer room feed off of the dedicated service panel for the room.
>> (This was in the days before T1 = SDSL) We had been having problems
>> for about six months with one or more of the cards locking up
>> and/or apparently failing in the rack. I was in the process of
>> pulling together the documentation to demand that the phone company
>> replace the whole rack when one of my associates found an old Sola
>> Power Conditioner in a corner of an old store room. For lack of
>> anything better to try, we plugged it in and used it to feed the T1
>> rack. Lo and Behold, not another problem.
>>
>> Question - Did you really have to run that line all the way back to
>> the transformer itself, or were you allowed to tie to the neutral
>> at the main service entrance/disconnect?
>> ** Posted from http://www.teranews.com **
>
>
> I called one of my old co-workers to ask him about this today and he
> pointed me to a URL that provided some of this information.
>
> www142.nortelnetworks.com/bvdoc/meridian1/m1254x/P0943943.pdf
>
> It looks as though I got part of it wrong, the voltages are 208 or 240 not
> 220.
> The grounding section starts on page 16 and indicates that the green #6
> ground can be connected to a dedicated service panel
>
> In part it says (from page 23) . . .
>
> "The isolated ground bus within the dedicated AC service panel serves as
> the "system" SPG [single point ground]. The dedicated AC service panel
> should be supplied from the buildings principle ground source, usually the
> transformer which is located within the building."
>
>
> So it looks like the ground didn't have to be run all the way to the
> transformer if the panel was a dedicated panel and the ground for the
> panel is a dedicated run to the transformer.
>
> I now wonder if the senior install technicians didn't make the
> electricians do this simply to make sure that the ground was actually a
> dedicated one and not simply tied to the building frame once the wires
> disappeared behind the wall.
>
> Sorry for the confusion.
>
> Chris
>
>
Just an observation based on my own experiences and electronics education.
Sensitive electronic equipment and its power supply should not use the same
grounding line, if feasible, as basic electrical equiipment. But, you
probably know that and why...
--
Dave
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