> On Jun 29, 2018, at 1:01 PM, Chuck Guzis via cctalk <cctalk@classiccmp.org>
> wrote:
>
> If anyone's wondering, here's a 1975 Bell System treatise on grounding
> and protection. Note that carbon-block protection was standard practice:
>
> http://bellsystempractices.org/500-/518-/518-010-105-i02_1975-09-01.pdf
>
> Note also, that the standard practice dictated that grounding at the
> dmarc should be tied to the power system ground, but that the grounding
> not use the power system ground (i.e. independent connection).
>
> Note also, if equipment frame/chassis grounds varied, bonding to a
> common ground e was recommended.
>
> This has loosened up quite a bit since the old days. On my home, built
> in 1980, the network interface box is tied to the old demarc box ground,
> which ran out to the pad-mounted transformer in the side yard. When the
> local utility moved the transformer pad to the front yard, they simply
> disconnected the telco ground and didn't tell anyone.
Yikes, that is a major error. As far as I remember the electric code clearly
requires all these things to be bonded to the building ground rod(s).
For one thing, if you don't tie things to a single ground you're likely to
suffer much greater damage if there is a nearby lightning strike. I found this
out the hard way because our house had cable TV coming in at the opposite side
from power and telephone, so it surge protector was tied to a ground rod 50
feet from that of the power. When we had a strike maybe 50 feet out from the
power entry, the currents due to mismatched ground levels were enough to fry
every single bit of electronics connected to the cable TV connection, even if 3
or 4 steps removed (like from cable TV to splitter to cable modem to router to
Ethernet switch to printer... all those were toasted).
I now have a single point ground, with commercial grade surge protectors all
bonded to a single sheet of copper directly connected to the power entry ground
system.
paul
