I'm curious how a satellite dish is grounded on top of a building, whether it's walmart or a skyscraper. Can anyone clue me in? thanks.
How do you ground on top of a building?
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water pipe?
chip out some concrete and ground to a rebar system?
I suppose if the building frame is steel construction that would work too.
Ya alot of old installs used to be grounded to "cold water' to the the copper pipes.. Now a days alot of new homes are plumed using PVC type pipeing and the NEC also says its not proper anymore to ground to cold water.. But I think in a large building if thats the only option its what you need to do.. Also most large sky scrpers have a ground rod/lightning rod on top of it i assume you could ground to that as well.
For gods sake do not ground to a water pipe. All you need is a lighting strike moving through the water system looking for some poor sap just trying to wash his hands. Water pipes can only be grounded too within in 5 feet of the pipes entrance INTO the building. EXPECTION: If the water main is unaccessible within 5 feet due to sprinkler control valves. Those rooms are usually off-limits.
Many commercial buildings have a ground bus bar made of copper. Other than a bus bar, there is usually no way to ground in a commercial building following the NEC. Then again the NEC "as is" is usually not followed by local code enforcement. The best alternative is to ground to a large metal electrical conduit (1.5" or larger) that is housing main feeder lines between panels. Even that is not to the NEC, but usually is accepted.
Do not ground to a EMT feeding a HVAC unit or other roof top appliance. You should also not ground to a sub-panel that is serving as a disconnect to a HVAC unit.
If the building has a metal structure, and it is grounded (do a continuity test across the building and power ground) you can ground to that.
In some cases, you cannot obtain a valid ground and in those cases, I do not ground. It is safer to NOT ground than to ground to a water pipe on a roof top. You should never ground to another electrical device (HVAC, FAN, light ect..) or the conduit housing the power to power those devices.
All that said. If your local electrical inspector says you can ground to a HVAC unit, then do it. It is their call to allow that, not yours.
You best move is to contact your local electrical inspector and ask them. After all, if you get sued someday because you killed someone with an improper ground, it is the inspector you will see testifing either for you or against you, not me or anyone else in any forum.
Regardless of what the NEC says, I say or what you think, it is ONLY the inspectors opinion that matters.
http://www.dbsinstall.com/whatis/Whatisgood-5.asp
Many commercial buildings have a ground bus bar made of copper. Other than a bus bar, there is usually no way to ground in a commercial building following the NEC. Then again the NEC "as is" is usually not followed by local code enforcement. The best alternative is to ground to a large metal electrical conduit (1.5" or larger) that is housing main feeder lines between panels. Even that is not to the NEC, but usually is accepted.
Do not ground to a EMT feeding a HVAC unit or other roof top appliance. You should also not ground to a sub-panel that is serving as a disconnect to a HVAC unit.
If the building has a metal structure, and it is grounded (do a continuity test across the building and power ground) you can ground to that.
In some cases, you cannot obtain a valid ground and in those cases, I do not ground. It is safer to NOT ground than to ground to a water pipe on a roof top. You should never ground to another electrical device (HVAC, FAN, light ect..) or the conduit housing the power to power those devices.
All that said. If your local electrical inspector says you can ground to a HVAC unit, then do it. It is their call to allow that, not yours.
You best move is to contact your local electrical inspector and ask them. After all, if you get sued someday because you killed someone with an improper ground, it is the inspector you will see testifing either for you or against you, not me or anyone else in any forum.
Regardless of what the NEC says, I say or what you think, it is ONLY the inspectors opinion that matters.
http://www.dbsinstall.com/whatis/Whatisgood-5.asp
I love it, more grounding questions! RONTGLMAO!
All you have to do, is either call the City/County NEC Inspector, or find a qualified Electician, and they can solve the problem of your question... Don't try grounding something yourself, unless you are qualified, and by your question, you are not!
All you have to do, is either call the City/County NEC Inspector, or find a qualified Electician, and they can solve the problem of your question... Don't try grounding something yourself, unless you are qualified, and by your question, you are not!
Oh, you're profiling now? Maybe I'm a DISH installer that thought one day while grounding a DISH network system, "gee I wonder how they ground big satellite systems on downtown buildings, if and how they are grounded etc... just for the knowledge of it. Doesn't mean I'm going to do it. Sorry I asked.
What a dick!
I have wondered this too. Especially very tall buildings. There are always tons of antennas on top of them (dish, 2way, tv, etc).
Just for sake of discussion, I am not up on this sort of thing, but what is the maxium distance you can ground? 3 stories, 10 stories? That is if you did not have something to ground to, and had to run a ground wire to the "ground". Just curious.
There is no maximum distance for the mast ground. The maximum coax ground length using a 10 awg copper wire is 20 feet. If you use a larger gauge wire, you should be able to go longer. The NEC does not address a larger ground conductor, but 20 feet of #10 = 1 Ohm DC resistance. It is my conclusion that a ground conductor with no more than 1 ohm of DC resistance, at normal temps, should be accepted. It really depends on your local inspector. The reality is, your local inspector probably has no clue.
If you have a tall commercial or MDU building that you are concerned about, contact your local electrical inspector and ask them. I have found them to be VERY understanding when you have a building that has no practical ground available. As long the inspector signs off, then you have no worries.
If you have a tall commercial or MDU building that you are concerned about, contact your local electrical inspector and ask them. I have found them to be VERY understanding when you have a building that has no practical ground available. As long the inspector signs off, then you have no worries.
I've said it before, and I'll repeat it here. You have done a wonderful job with that site Todd.
Thanks
You can ground to the metal structures of commercial / industrial a/c units or to an electrical conduit inside the structure wich is what most installers do. There is nothing wrong with grounding to a cold water pipe so long as it is grounded, but also make sure that its not pvc. If you can find the water meter make sure that there is a groundwire jumping from one side to the other, most of the water meters that are being put in either new or as upgrades have pvc in them.
No you can not if you are required to meet NEC. The locations of where you can bond are CLEARLY defined in the NEC. A chassis of a AC unit is NOT anywhere close to any of the defined grounding locations. What if the AC unit is removed? Are the installers who remove the AC unit required to provide your system with a new ground?
You cannot ground to any OTHER system, which may be removed. It is completly resonable to expect an HVAC unit to be removed. What if someone installed a small tower for a 2M radio, and ran a guy wire to your non-pen mount? Every system must be isolated from each other. The emt conduit feeding power to HVAC units is part of the HVAC system.
If the conduit is providing power between panels within the primary power distribution system, then that is usually accepted. The conduit cannot be a EMT that is feeding power to a branch circuit, which MAY be removed. This is not stated in the NEC, but the inspectors I have talked too consider any part of the electrical system that may be removed cannot serve as a ground point. If during a building remodel, an EMT is removed, your ground is gone. The rigid conduit between sub-panels is considered, sometimes, to be an integral part of the power system. However, they all said, they would prefer a ground to the building framing, or grounding components.
That is so wrong in so many ways. Remember, this discusion is about grounding on a roof. I have never seen a water pipe on a roof that meet the required conditions to serve as a proper ground.
250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe.
A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing effectively bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.
Exception: In industrial and commercial buildings or structures where conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system, provided that the entire length, other than short sections passing perpendicular through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.(2) Metal Frame of the Building or Structure.
The metal frame of the building or structure, where effectively grounded.
(3) Concrete-Encased Electrode.
An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than I 3 mm (½ in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.
(4) Ground Ring.
A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG.
(5) Rod and Pipe Electrodes.
Rod and pipe electrodes shall not be less than 2.5 m (8 ft) in length and shall consist of the following materials.
(a) Electrodes of pipe or conduit shall not be smaller than metric designator 2 1 (trade size ¾) and, where of iron or steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.
(b)Electrodes of rods of iron or steel shall be at least 15.87 mm (~/8 in.) in diameter. Stainless steel rods less than
16 mm (~/8 in.) in diameter, nonferrous rods, or their equivalent shall be listed and shall not be less than 1 3 mm (½ in.) in diameter.
(6) Plate Electrodes.
Each plate electrode shall expose not less than 0. 1 86 m2 (2 ft2) of surface to exterior soil. Electrodes of iron or steel plates shall be at least 6.4 mm (¼ in.) in thickness. Electrodes of nonferrous metal shall be at least 1 .5 mm (0.06 in.) in thickness.
(7) Other Local Metal Underground Systems or Structures.
Other local metal underground systems or structures such as piping systems and underground tanks.
(B) Electrodes Not Permitted for Grounding.
The following shall not be used as grounding electrodes:
(1) Metal underground gas piping system
(2) Aluminum electrodes
250.53 Grounding Electrode System Installation.
FPN: See 547.9 and 547.10 for special grounding and bonding requirements for agricultural buildings.
(A) Rod, Pipe, and Plate Electrodes.
Where practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.
(B) Electrode Spacing.
Where more than one of the electrodes of the type specified in 250.52(A)(5) or (A)(6) are used, each electrode of one grounding system (including that used for air terminals) shall not be less than 1 .83 m (6 ft) from any other electrode of another grounding system. Two or more grounding electrodes that are effectively bonded together shall be considered a single grounding electrode system.
(C) Bonding Jumper.
The bonding jumper(s) used to connect the grounding electrodes together to form the grounding electrode system shall be installed in accordance with 250.64(A), (B), and (E), shall be sized in accordance with 250.66, and shall be connected in the manner specified in 250.70.
(D) Metal Underground Water Pipe.
Where used as a grounding electrode, metal underground water pipe shall meet the requirements of 250.53(D)(l) and (D)(2).
(1) Continuity. Continuity of the grounding path or the bonding connection to interior piping shall not rely on water meters or filtering devices and similar equipment.
(2) Supplemental Electrode Required. A metal under-ground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(7). Where the supplemental electrode is a rod, pipe, or plate type, it shall comply with 250.56. The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the nonflexible grounded service raceway, or any grounded service enclosure.
Exception: The supplemental electrode shall be permitted to be bonded to the interior metal water piping at any convenient point as covered in 250.52(A)(1), Exception.
(E) Supplemental Electrode Bonding Connection Size.
Where the supplemental electrode is a rod, pipe, or plate electrode, that portion of the bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
(F) Ground Ring.
The ground ring shall be buried at a depth below the earth’s surface of not less than 750 mm (30 in.).
(G) Rod and Pipe Electrodes.
The electrode shall be installed such that at least 2.44 m (8 ft) of length is in contact with the soil. It shall be driven to a depth of not less than m (8 ft) except that, where rock bottom is encountered, the electrode shall he driven at an oblique angle not to exceed 45 degrees from the vertical or, where rock bottom is encountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in a trench that is at least 750 mm (30 in.) deep. The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10
(H) Plate Electrode.
Plate electrodes shall be installed not less than 750 mm (30 in.) below the surface of the earth.
250.54 Supplementary Grounding Electrodes.
Supplementary grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.11 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.56, but the earth shall not be used as the sole equipment grounding conductor.
250.56 Resistance of Rod, Pipe, and Plate Electrodes.
A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(2) through (A)(7). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1 .8 m (6 ft) apart.
FPN: The paralleling efficiency of rods longer than 2.5 m (8 ft) is improved by spacing greater than I .8 m (6 ft).
250.58 Common Grounding Electrode.
Where an ac system is connected to a grounding electrode in or at a building as specified in 250.24 and 250.32, the same electrode shall be used to ground conductor enclosures and equipment in or on that building. Where separate services supply a building and are required to be connected to a grounding electrode, the same grounding electrode shall be used.
Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense.
250.60 Use of Air Terminals.
Air terminal conductors and driven pipes, rods, or plate electrodes used for grounding air terminals shall not he used in lieu of the grounding electrodes required by 250.50 for grounding wiring systems and equipment. This provision shall not prohibit the required bonding together of grounding electrodes of different systems.
FPN No. 1: See 250.106 for spacing from air terminals. See 800.40(D), 810.21(J), and 820.40(D) for bonding of electrodes.
FPN No. 2: Bonding together of all separate grounding electrodes will limit potential differences between them and between their associated wiring systems.
250.62 Grounding Electrode Conductor Material.
The grounding electrode conductor shall be of copper, aluminum, or copper-clad aluminum. The material
Sorry Fantasy, I wasn't trying to be hard on you, just giving you advice... LOL BTW, my name is Bob, or Doc, and not dick... RONTGLMAO... Of course, if you really were an installer, you might have let us know that, and perhaps someone could have more guidance. Todd does a great job of putting down all of the NEC rules and Regs, but even then, the local inspector has the last word, not matter what the NEC says, Soooooooooooo, If you are truly looking for answers, my advice is still to contact your City or County Inspector, for the answers you are looking for...
Your gonna love this one. I contacted the electrical inspector at the City's codes compliance dept, I know him personally since I am an Engineer working at the City. He stated that the dishes do not have to be grounded as they are low voltage. But he also said that that requirement changes per locality. I grounded my mast anyway
Unless you can get it in writing, or if the inspector can provide the local code that OVERRIDES the NEC (assuming they adopt the NEC to begin with) I would be careful of that advice. I had one inspector give me information when I went into their office, but when the site was inspected, it failed. Another inspector had other interpretations of the code. Pissed me off, but the problem was simple to correct.
On a side note to all installers. Even if the local code does dismiss grounding, you may be subject to the grounding requirements of the system provider.
On a side note to all installers. Even if the local code does dismiss grounding, you may be subject to the grounding requirements of the system provider.
