26 Aug
2015
26 Aug
'15
6:19 a.m.
On Aug 26, 2015, at 2:20 AM, jwsmobile <jws at
jwsss.com> wrote:
..
Microdata card extractors were always engaged to a rail that was metal, and in one site I
was at, there was a CE sized hole in the wall behind a system when the engineer extracted
the printer card and the card extractors came free from the system. Turned out there was
a 120v potential between the "dedicated" power for the computer and the printer
which was plugged into the normal building power.
There was probably as much as an amp going thru the grounds from the terminals in the
building and the ground of the system. Miracle that he was not severely injured, and also
that the system was working at all.
Turned out that the entire building which had been expanded over a period of growth for
the business of about 40 years had had power panels installed with "outdoor"
grounds at the time to main panels in various places, and the grounds were all dropped to
local earth. 10 different grounds, with terminals connected and grounds coming back to the
main system.
I heard of this sort of thing happening to the DEC building at Marlboro. Supposedly it
had two mains entrances, served from different power lines (and different companies?
Seems odd). One of the machine rooms had feeds from both ends, and one particular system
was fed from both. What happened is that the "grounds" were offset enough, and
with enough of a current supply, that the ground strap that's supposed to connect the
row of RP06 drives melted.
This sort of thing is a major electric code violation: you can certainly have multiple
services, but all the grounds are required to be connected by substantial wire; you're
not allowed to stick ground rods in at multiple places and leave it at that. (The same
goes for lightning rods.)
paul