On Wednesday, November 25, 2015 at 10:14:12 PM UTC-6, wrote:
On Wed, 25 Nov 2015 19:18:07 -0800 (PST), Uncle Monster
wrote:

On Wednesday, November 25, 2015 at 8:50:55 PM UTC-6, wrote:
On Wed, 25 Nov 2015 18:21:11 -0800 (PST), Uncle Monster
wrote:

On Wednesday, November 25, 2015 at 7:09:04 PM UTC-6, wrote:
On Wed, 25 Nov 2015 12:15:14 -0800 (PST), bob_villain
wrote:

As you say, with your experience you may have used specs for isolated-ground applications. Then, the mounting tabs are insulated and there's only a dedicated ground on the receptacle.

IG is mostly snake oil. IBM dropped the requirement in the Carter
administration.

The electrical inspection department around here still requires it for data processing equipment or any computer, medical or electronic gear. ^_^


You can't be talking about the code inspector so I am guessing someone
in your IT department still has a leisure suit in the closet.
It was determined decades ago that IG did nothing to make computers
work better and compromised surge protection.
You want as much bonded together as you can get with as short a path
as you can get. The IG made the ground too far away to do much in a
serious transient event like a nearby lightning strike.

It may have changed in the last few years but the inspection department here didn't necessarily follow the NEC word for word. They had things that they required that weren't required by the NEC. It was my understanding that the isolated grounds were to help cut down on electrical noise getting into electronic equipment. Back in the 1980's when I did electrical wiring for a mission control center that contained a super computer, atomic clock and all sorts of other electronics, the crew installed ground rods all over the damn place. I even drilled through the concrete slab under the raised flooring in at least a dozen places, installed ground rods then bonded the rods to the system ground and raised flooring. The crew installed ground rods every 10 feet around the outside walls and all the grounds were bonded. I always did what the electrical inspectors or The Core Of Engineers demanded.. O_o


I was around for that, we were using braided ground straps on every
floor post and ferrites on anything that wasn't grounded. The thought
was very short ground paths and ferrites to slow down the signal long
enough to slow down the transient in the signal lines until it was
shunted out ... or some such thing. Whatever it did work for esd and
common mode transients.
When we finally analysed the "noise" we identified the enemy and it
was us!
The noise was not external at all, it was coming from 100-200a switch
mode power supplies in the mainframes.
The next generation of machines (30xx and 43xx) had quieter power
supplies and all of that stuff went away (circa 1980 or so).

A few years later we took that "short ground path" stuff out of the
glass house and into the hinterlands to protect all of those little
machines you see in "retail" from lightning (banks, hotels,
restaurants and stores)

We had people plugging their terminals in regular outlets and using
the IG for the operator's space heater.
We were telling people

I repaired or replaced a lot of small UPS units that secretaries plugged in one of those small electric heaters they brought from home. ^_^

As I recall, weren't the building transformers derated due to the prevalence of switching power supplies in computer and office equipment which were putting (I can't remember the term,"asymmetrical?") loads on the transformers? I seem to remember that switching power supplies have a lot of filtering on the incoming power, not necessarily to keep electrical noise from getting in but to keep it from getting out. o_O

[8~{} Uncle Switching Monster