VoIP Equipment Grounding [telecom]

Have a question or want to start a discussion? Post it! No Registration Necessary.  Now with pictures!

Thanks for reading this. I need information about grounding, and I'd
appreciate your help.

The IEEE 1100 standards have a lot of information on this topic, but
the printer versions cost hundreds of dollars, so I hope there's
someone in the TD world who can provide some less costly advice.

I was recently called to one of my customer locations, where the
Quintum AXM2400 VoIP endpoints had been damaged for the third of
fourth time by what the customer describes as "lightning".

As with previous visits, there was no sign of a lightning strike at
the site: no burned equipment, no reports of fire, no fire alarms, no
melter wire, no displaced cabling in the racks, no insulation burnt
off the wires. Most telling, to my mind, was the lack of damage to the
Mitek surge protectors that are used in place of bridging clips at the
"66" blocks where the dial tones from the Quintum VoIP adapters
appear. The UPS that powers the Quintum units has the usual surge
suppressors, and it's still putting out power and has no scorch,
smoke, flare, or other overvoltage marks.

I asked the site representative to show me the ground rod outside the
telecom room, hoping to find a broken connection or some other obvious
reason for the repeated callbacks. It turned out that there was no
ground rod: the telco room grounding leads, tied together in the usual way
at screw-down strips on the plywood backplane, eventually wound up in
a ground wire which went through the wall to the outside, up to the
eaves, around two corners, through another wall, around another couple
of corners, and into a three-phase electrical panel. The total length
of the ground is over fifty feet counting the interior legs, so I'm
wondering if a power surge or surges might have been prevented or at
least lessened by a shorter and/or more widely distributed ground.

So, the questions: what does the IEEE 1100 standard say about the
gauge and length of ground wires?

1. I've never seen a ground this long: is length unimportant if the
   ground admittance is within spec? If I take a "megger" to the site,
   what are the readings that are within the "good" range?

2. Are there limits on the number of devices placed on a single ground?

3. What's the "official" wire gauge requirement for grounds? The site
   has a mixture of #14, #12, #8, and #6 wires, with no obvious
   pattern: the main ground wire that exits through the wall appears
   to be #6, but I couldn't verify that.

Thank you in advance for your help.

Bill Horne
(Remove QRM from my email address to write to me directly)

Site Timeline