atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Outside Plant OSP Construction grounding between buildings

I have done sound jobs that required multi buildings to tie together for public address. I had 3 hangers (about 1500' apart) at an airbase that I measured 70 volts between grounds. Fried several amps on that one. I have also seen times where the ground difference melted the shield of cheap balanced line cables run between systems.

metelcom's comment is the SCARIEST.

Thinking: Air Force Base (and I suppose commercial) runway, taxiway, hanger foundations, are at least 18 inches thick, in my limited experience. I know that buildings bolted to concrete slabs are assumed to be grounded, but I don't buy it! I know of no concrete, or rock for that matter, that conducts anywhere near as well as iron, never mind copper! The only reason it's gotten away with is the HUGE effective 'conductor'

But, try to get permission to drill through the slab to dirt. Good Luck! Never mind the relatively poor ground under the slab, especially in low rainfall areas.
John C. (Not Garand)

Gentlemen,
I'm a newbie to the forum but a long time browser. I've got a question, and Im sure its been answered somewhere in this thread, but I didnt see it exactly.Guy called me last week to splice some cable at peds for townhomes, 25pr in and 4- 6pr out. I bonded all 5 sheaths together in ped but didnt tie to ground rod. Then terminated 6 prs at nids, grounded sheath, and tied to ground at nid.Assuming 25 pr is sheath is grounded at mdf, is the the right way? Not sure if the ground feeds at ped and nid are origionating from same ground rod, theyre only 50-75' apart.

Thanks,
Gene Hudson
ACT,Inc

Gene:

That sounds like the right way to go, but you really should have a ground rod at the pedestal.

Also, the pairs shouldn't be hard-spliced together; the 25 pair should terminate on a block designed for mounting within the pedestal. The 6-pair drops should only connect to the necessary number of binding posts on a per-address basis.

How come you are doing this work? Shouldn't this be the LEC's responsibility or is this on private property?

Ed,
Im sure this is private deal, townhomes and such,theres a headend bldg. somewhere on site where CATV and phone come in and the guy that hired me(underground utility contractor) seem to be responsible for cable placement and connectivity past that.I agree, the pairs shouldnt be dedicated in the ped, but thats the way they want it, and they are only having me splice 2 pr on each 6 pr thru.There is a bare copper #6 ground coming up in ped, I just didnt tie to it.Thanks for the reply. Gene

There is a bare copper #6 ground coming up in ped, I just didnt tie to it.

What do you think it was there for? Was the ped located together with a CATV ped and an electrical transformer? We always make sure all three are bonded together to the utility provided ground rods at the transformer.

I wouldn't have bonded the 6 pair sheath at the NID. NID ground should go to the electrical ground, not a separate ground rod if anybody is thinking of that.

I had 3 hangers (about 1500' apart) at an airbase that I measured 70 volts between grounds... I have also seen times where the ground difference melted the shield of cheap balanced line cables run between systems.

Yup, that's what I'm talking about.

I know that buildings bolted to concrete slabs are assumed to be grounded, but I don't buy it! I know of no concrete, or rock for that matter, that conducts anywhere near as well as iron, never mind copper!

Believe it. It's called a ufer ground after George Ufer who invented it many years ago. Connecting a ground wire to the rebar that is inbedded in damp buried concrete such as the footing around a building provides a much better ground than any ground rod, even several tied together. Matter of fact it's so good that the latest NEC now requires in all new building construction that a piece of the footing rebar be left stubbed out and exposed so it can be bonded to in lieu of ground rods for the electrical, telco and CATV services.

-Hal

Gene:

I agree that you sometimes have to do what you are told since there's really no enforcement body in place to dictate otherwise with outside plant. I'd still go ahead and tie into the #6 that's there to the pedestal's bonding bracket.

Hey, look at it this way: At least you made the effort to get a second opinion.

Thanks Guys. I guess my point was( athought I didnt express it) is that Ive always heard that grounding cable on each end to seperate grounds made an antenna. I did a college in Pa. and the elec. engineer would only let me ground the MDF end.

gelehu....therein lies your problem.....

MGN ground is there for a reason. What if you lose the grounded sheath between the end of the run and the MDF? Buried plant inducts little voltage, multiple grounds drain it over short distances. Why not ground? :shrug:

Why then doesn't aerial cable running for miles below high voltage lines not cause problems? Because it is grounded and bonded at intervals or every power pole that has a ground on it.

What does an electrical engineer know of OSP? Let him go hang a transformer! :p :bang: :toothy:

Oops, forgot to click 'add reply', duh-uh!

Hal, the info about the rebar stubout being required is 'file-away' stuff. Now if the contractors will really do it!

Ken, did you really mean "hang FROM the transformer TERMINALS"? John C. (Not Garand)