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#447073 09/25/07 10:06 PM
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94astro Offline OP
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We cable high-rise suites often, sometimes the contractors give us a ground terminal sometimes not. Today they did not.

My question is, is it OK to run a ground wire in the same conduit as the tie cable, so we can ground directly to a ground strip in the tel closet on the floor? Or is it better to have a seperate conduit for the ground?

My second question is what gauge ground wire should I use?


Aaron
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#447074 09/25/07 11:12 PM
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It would be nice to have more information. What is the ground for? What's the cable installation for?

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#447075 09/27/07 07:21 PM
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94astro Offline OP
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The ground would be strictly for the telephone system.

We're cabling voice and data.


Aaron
#447076 09/27/07 09:12 PM
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Yes, you may run the equipment grounding conductor within the same conduit. You may also save yourself some time and trouble by bonding your system's equipment grounding terminal to the nearest piece of building structural steel, a metallic cold water pipe or the building's electrical grounding conductor.

You don't necessarily have to follow the same path that your tie cable pairs follow. You also don't have to run the "ground" wire that far. Look for any copper cold water pipe or iron framing member (not steel studs) and you will be fine for a grounding point.


Ed Vaughn, MBSWWYPBX
#447077 10/02/07 02:13 PM
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Ed's correct about not grounding to the building's frame. That's just not good practice. As far as gauge goes, you are looking for >1/4 ohm from end to end of your ground cable, which simply means the longer the run the larger the gauge. 4 gauge copper has a resistance of .2533 ohms per 1000 feet but 6 gauge is .4023 ohms per 1000, so you could only go about 625 feet before you exceeded your 1/4 ohm limit.

#447078 10/02/07 02:54 PM
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Ed, I thought a cold water pipe was a no-no for grounding these days?


Jeff Moss

Moss Communications
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#447079 10/02/07 04:44 PM
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I thought a cold water pipe was a no-no for grounding these days?

Only because plastic (PEX) is being used a lot these days and rarely a section of copper will be replaced with it. If you are sure that the pipe gets back to ground it's probably better than building steel. First check for any AC voltage between the pipe and the electrical receptacle ground, if it's more than a couple of volts you don't want to use it. If none then check with the ohm meter. An analog meter like the "kick meter" is best for this. Nearly all digital meters have a high input impedance and will give a false voltage reading on open circuits when it's actually zero.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#447080 10/02/07 04:48 PM
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Unless the cold water pipe switches to PVC at some point before entering the earth, it is an excellent ground.

#447081 10/02/07 04:54 PM
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Remember that it's the electrician's job to ensure that all metallic piping is bonded to the electrical service and to the building's steel structural members. This does NOT mean steel studs. Regardless, the electrician may do a perfectly fine job during the building's construction, but over time, plumbers come in and replace parts of the metallic piping systems with plastic. They don't have a clue as to the risk they are causing in doing this. They also aren't going to place a bonding jumper around the replaced piping; they just walk away with a check in hand once the water is running.

This is why you really can't trust any grounding point except the one that's used for the building's electrical service. Even that can be compromised due to hack repairs, but at least there's a good chance that the power company's ground at the pole or transformer will be good enough.

Perhaps the most popular misconception that can be made is that if you provide your own ground rod for the phone system, you'll have a good ground. Nothing could be farther from the truth. Doing so will actually invite problems AND is illegal under the NEC.


Ed Vaughn, MBSWWYPBX
#447082 10/02/07 07:48 PM
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Since the phone system is usually plugged into a wall outlet by a 3-prong plug, I don't see how running a separate cable to the building's electrical grounding conductor would give a better ground. That third prong on the plug is supposed to go to the building's electrical grounding conductor. Can you explain this? Is it just for redundancy?

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