grounding a network distribution panel
Hi,
I installed one of those Leviton home networking panels which distributes phone and broadband (cable in my case) throughout the home using CAT5E cable. The instructions recommend grounding the metal frame of the panel.
Is it safe and code-compliant to run a solid bare copper wire directly from the panel to the grounding wire exiting my electric breaker panel box (which runs directly to a steel rod driven into the earth)? I was thinking I could clamp the copper wire from the dist. panel onto the electric grounding wire, which would save me drilling a new hole in the side of the house–something I prefer to avoid when possible!
And by the way, is the idea here to prevent the possiblity of injury (or damaged computers, etc.) from an unexpected surge through the phone line or broadband cable?
Thanks.
Replies
I drive a dedicated ground rod. Lightning is unpredictable. The phone company has their own rod, the power service has its own, lightening rods (if any) have their own. Make sure you have a whole-house surge suppressor on the main panel. Also get a whole-house telephone line suppressor. Much harder to get, but worth it. If you get hit by lightning and don't have the phone line suppressor, it will do more damage. Just fixed a Leviton system. House had a full lightening rod system, whole-house suppressor and phone suppressor. Strike was to the wellhead 100 feet away. Several ceiling fans fried plus one satellite box. Much harder to find were the half dozen RJ-11 connectors plugged into the Leviton panel where the ends got melted. They got off easy. If the surge suppressors were not there, who knows. Maybe nothing, but maybe a lot of fried stuff. With probably $20K to 50K worth of electronics in that house, a couple hundred for suppressors is cheap insurance.
Most every utility has some sort of lightning protection. Its designed to protect their equipment, not yours. Run the heaviest copper you can to the ground rod. I use #6 bare copper. Stranded is better if you can get it.
Since Ground is not always Ground it is best not to install a new ground rod, but rather to tie this back to the ECG.
All of the stuff in this network box (either internal LAN or TV Cable), etc connect to equipment that is grounded by the ECG.
When you get a lighting strike you want all of that to float to the same level.
I don't actually agree with that approach. You never know how good the grounds are that are already driven, or how good the connection between that ground and the main panel. This is a protective ground, rather than signal ground. I like it to be as close to true earth ground as I can get. If you do get hit by lightning, all bets are off. It goes wherever it wants. Maybe you can get a hair more protection by having the best possible ground, maybe not. The idea is more to encourage the strike to go somewhere else by having a good ground. I never had a major strike on the systems I installed. Somewhere over a hundred at this point. Can't say whether that's luck or because I do a separate ground rod. I've fixed systems where almost every piece of electrical gear was fried (not ones I installed). Also fixed ones where damage was minor. Some of those were mine. Wherever it is possible, I do a dedicated ground. Not practical in a high rise or some situations, but I'll keep doing it so long as it seems to work.
Bob,
I hear exactly what you're saying about not knowing how good the house ground is (i.e., grounding electrode system, grounding electrode conductor). A clamp-on ground resistance tester would be just the ticket, really nice, but not at $1200!
For the reason you mentioned, I drive two new rods for any service upgrade that I do. An outfit in Montana makes a ground rod driver called the "ground hawg" that uses a hole hawg drill motor to screw the rod in (you put an auger tip on the rod). Then you fill the annular space with a conductivity-enhancing slurry. It's a slick system, better even than a roto-hammer; you can back the rod out if you hit a rock!
Anyway, since you're referring to what you install as a "dedicated" ground, I have a question: do you bond this dedicated ground rod to the electrical system of the building, using wire at least the size of the grounding electrode conductor?
Cliff
Do you pull it out and re-use the auger tip, or does it get abandoned in place?
A friend of mine used to do grounds for TV transmitters and recording studios. His method was to solder together 60 ft of 3/4" type K water pipe, put a 3/4 NPT fitting on the top end, hammer the bottom end flat, and poke a few holes in it. With a long hose and running water, this thing would drill its way down into the ground. It would even erode around rocks in the way and shove them aside.
-- J.S.
Water can be pretty effective in creating holes in the earth, as most kids have found out. The problem is that you want the ground rod to be in maximum contact with the earth to give as low a resistance between the ground rod and the earth as possible. The water created hole is generally too large and too irregular to allow maximum contact and thus minimum electrical resistance to the earth. Perhaps if you backfilled around the ground rod with some type of conducting material and tamped it down securely...
John,
The auger tip is a little die-cast zinc jobby. They cost about $2/per, and each one comes with a bag of the conductivity enhancer. You leave the auger tip at the bottom of the hole.
Unless you want to back the rod out--like when you're pulling a temp power pole setup (i.e., construction power). I used to dig down a foot and cut the rod off. Now I reverse the ground hawg and back the rod out, and can re-use both the rod and the auger tip. Pretty slick.
Cliff
Hey Cliff,
Isn't that required? Bonding all of the grounding electrodes?I don't do very much VDV work but when he was describing having multiple idependent grounding electrodes it didn't sound right.
Barry
Barry,
You're absolutely right--all grounding electrodes for the same building have to be bonded.
I also got the impression that he wasn't bonding the additional rod. I just didn't want to assume so, before I flamed him! Setting up an "dedicated ground rod"--if it's not bonded to the grounding electrode system--shows a lack of understanding of what the grounding system is intended to do.
Not that it's a unique misconception. I've heard several case studies (from Mike Holt and others) where an otherwise quailified individual is misinformed on the issue, and figures that an independent ground rod will solve problems. Instead it makes things worse, either immediately, or later when a fault condition develops.
Work safe--
Cliff
Edited 11/4/2003 11:27:05 PM ET by CAP
Yes, I bond the extra rod and still feel this gives gives better protection. I see many systems where the rods are not bonded. Lightning rods, for example. The telephone company around here does not bond their rods to the building ground. Bonding the rods possibly gives some extra safety if you manage to short the AC line to the telephone system or network. I think it does nothing so far as lightning or surge protection.
Bob,
Good show. Hey, the more earthing, the better for lightning protection.
Work safe,
Cliff
By that reasoning, every large piece of accessible metal should be bonded to the electrical system ground. I'm going to bond my copper roof to ground, just in case some future owner accidentally nicks a wire on Christmas lights or some such thing. At least that way the downspouts won't go hot. ;-)
-- J.S.
Would you mind explaining a bit further the concept of bonding all grounding electrodes ?
We own a 2-meter house next door.
The main floor service was upgraded to 200-amps and I buried three grounding rods. (Inspector liked that.)
I am in the middle of upgrading the second service to 200-amps and will be burying another three rods.
Or can I run #4 bare copper to the existing three rods ?
If I bury the three additional rods, how I am not clear on how the 'bonding' would be accomplished.
Run a #4 between the first of the two sets of ground rods ?
Thanks for your help.
Good advice to ground everything, within reason, that you can. You never know when something will go wrong and something that should be as dead as the dodo will reach out and grab you. ie:
While troubleshooting a circuit that was partially dead we decided to check to see if the cable want out onto the roof of a single story house. We had tracked it to an inaccessible portion of the attic where it disappeared. We had walked around and concluded the roof was the only spot we hadn't checked.
We walk round back and see a fairly tall, about 50', steel TV tower next to the house. Being game and no wanting to go round to the truck to get a ladder we start up the tower. Half way up to the roof a wet branch contacts the roof and is close to the tower. When my partner contacts the branch he gets a shock and jumps down.
We figure that somehow the tower had become live. Problem is that we can't figure out how. Didn't seem possible as the tower was not in use and the cables were all disconnected. Trying to make everything simple we rigged a long lead, a 500' roll of #12 THHN, back to the panel as a ground reference. We check the tower - nothing. I climb the tower and as a joke I check the tree branch. 116v!
Nothing made sense. No voltage at the tree base but voltage at the top. Branches rested on the roof but the roof was three tab shingles. We check anyway. Nothing. No joy until we check the galvanized drip edge. The drip edge has a full 120v. The current was traveling from the drip edge to the wet branches and shocking the guys climbing the well grounded, base set in reinforced concrete in wet earth, tower. The drip edge around the whole house was live.
Story made sense only when the HO came home and mentioned that she had roofed over the attached carport on the other side of their house herself and bragged about doing an extra good job using screws instead of nail and extra long screws at that. The entire metal roof section above the carport was live.
We never found the offending screw and made do by abandoning the damaged section of cable and fishing in a new cables to feed the the other end. Some days are just too strange.
Hi. If all grounding systems are to be bonded together I assume my steel TV tower( which has its own groundrod) is to be bonded back to the service panel? Would putting a ground clamp on one of the bottom tower straps and running #4 or #6 back to the panel be advisable? The electrical inspector (15 years ago) never mentioned that. Thank you.
The NEC does not allow separate, unbonded, ground rods, period. If more than one is installed, they must be bonded together with at least a #6 copper wire.
Besides the breaker trip issue mentioned earlier, the occurance of a ground current surge due to a local lightning strike, or power line short to ground, is far more likely than a direct strike. This may result in two separate, unbonded ground rods being at different voltage potentials, if only briefly, by hundreds and maybe thousands of volts. Not good for equipment where part of the system is hooked to one ground, and part to the other.
Getting back to the orignal question, I put one in my place recently; I grounded it by tying the grounding wire to the Grounding Electrode Conductor with a split bolt, as was suggested earlier.
"Besides the breaker trip issue mentioned earlier, the occurance of a ground current surge due to a local lightning strike, or power line short to ground, is far more likely than a direct strike. This may result in two separate, unbonded ground rods being at different voltage potentials, if only briefly, by hundreds and maybe thousands of volts. Not good for equipment where part of the system is hooked to one ground, and part to the other."
That is my though exactly. That is way I brought it up.
But I see that he does bond them all together. I did not get that impression from the orginal.
Ed,
In similar network panels I've installed, I've installed a receptacle outlet for things like a power amp for CATV. The equipment grounding conductor of the branch circuit is bonded to the network panel. As you mentioned, the purpose is to keep the metal of the panel at ground (zero)voltage, so that does it.
If you're not installing a receptacle in the network panel, you could run a wire to the grounding electrode conductor, sure. No Code issue. Use a split bolt to make the connection. A C-tap crimp-on connector is another way, and is excellent--if you can get the use of the corresponding crimper.
Other ways to bond the network panel to ground are to either run the grounding wire back to the breaker panel, or grab a ground from a nearby receptacle outlet. A #14or #12 wire green insulated copper wire will do the trick, depending on the gage of the branch circuit wire.
If you install a telephone line surge arrestor or CATV grounding block in the distribution panel, and you're not installing a receptacle outlet in the panel, you ought to run a #10 copper grounding wire to the ground bar of the electrical panel. The telco practice here is to run a #10 from their protector to the electrical panel ground (called the house ground). If the run is long more than 20 feet), use #8 to keep the impedance low.
One very important point on grounding is to make sure that all parts of the grounding system for the same building are bonded (electrically connected) together. That's especially important with supplementary grounding electrodes (additional ground bars) serving the same building. All such grounding electrodes MUST be wired together and connected to the grounding bar at the main panel or service disconnect. If you don't, you're creating a dangerous situation; a fault to whatever is hooked up to the independent ground bar likely will not trip the breaker for the circuit that's the source of the fault. A real safety hazard. Even a small voltage diference will set up circulating currents, wreaking havoc on electronic equipment.
As far as a whole house telephone line surge protector, they are available. The kind I've used fit onto a 66 type connecting block used for telephone wiring. You punch down each wire into a V-shaped clip that makes a moisture- and gas-tight connection. The protectors fit onto the clips of a 66 M-block, and protect both sides of the line. You run a grounding wire back to the house ground.
Most network panels are set up for 110 style insulation displacement blocks, used more for data than vioce (though they can be used for both). You can make space in the network panel for a short (6-pair) 66 block.
If you want a source for the 66 blocks and surge protectors, e-mail me.
Have fun with the project!
Cliff
Edited 11/4/2003 12:23:59 AM ET by CAP