A tale of woe, including carelessness, stupidity and laziness....
paulkoning at comcast.net
Wed Aug 26 08:19:05 CDT 2015
> 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.)
More information about the cctech