How do you ground on top of a building?

[Doctor Bob]

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

See, they can override the NEC... LOL However, as Todd stated, if the provider of the Equipment requires specific grounding applications, then you might be held to their standards... RONTGLMAO....

There are time, in which you cannot win, no matter what you do!!! LOL But because you are are an Engineer, working for your City, you understand better than anybody, the hoops that you have to jump through!!!

That is why, when someone brings up a grounding question, I "ALWAYS" refer them to their local inspector!!! It is so funny!!! RONTGLMAO....

Great Post Vurbano!!! Keep on Laughing!!!

 

[FantasyChannel]

All this makes me wonder also if every dish you see at a tv station, cable headend or teleport has a ground wire attached to every damn one of em'. ESPN has 27 dishes at it's Bristol headquarters and the ariel photos show them spread all over, ...on the ground, on top of the building, in the middle of the parking lot! I think i will die if someone tells me there's a grounding system under the asphalt. This is all very interesting.

 

[AntAltMike]

Virtually every highrise has HVAC units on top of them that are supported by structural steel, meaning "I" beams. I sometimes ground to them. But technically, they would have to be "bonded" to the building's ground system, which can be done either by welding them together or by using conforming, "bonding jumper" hardware, so if they were attached to the ceiling steel using only big bolts that I can't see, the resistance would measure as though I had a valid ground path but, technically, that steel would not qualify as a code conforming ground point.

Nearly all highrise buildings in my market have some kind of lightning rod system on them. Sometimes I attach to that.

I'll still attach to a cold water pipe in a large building. The reason for the change banning that practice is that so many repairs are now done with plastic pipe that the future integrity of a cold water ground cannot be assumed, but in my highrise buildings, I know I can rely on common cold water pipes to always be repaired with copper if the ever have to be repaired at all.

Fortunately for me, I'm not a fulfillment installer, so I don't fear having my installation commission deducted from my account if some nit picker believes a ground I have connected is non-conformant.

 

[AntAltMike]

All this makes me wonder also if every dish you see at a tv station, cable headend or teleport has a ground wire attached to every damn one of em'. ESPN has 27 dishes at it's Bristol headquarters and the ariel photos show them spread all over, ...on the ground, on top of the building, in the middle of the parking lot! I think i will die if someone tells me there's a grounding system under the asphalt. This is all very interesting.

I don't think that dishes in a parking lot have to be grounded. In fact, technically, no dishes or antennas have to be grounded. The NEC required that the MASTS of antennas that are attached to buildings be grounded, not the antennas themselves.

 

[Todd Humphrey]

I don't think that dishes in a parking lot have to be grounded. In fact, technically, no dishes or antennas have to be grounded. The NEC required that the MASTS of antennas that are attached to buildings be grounded, not the antennas themselves.

Even when I post the NEC for all to read, someone still fails to read it.

The NEC states that a mast must be grounded. NOWHERE does it say a single thing about where the mast is located.

The NEC mast grounding requirement comes from the fact that in arid / dusty communities, or those that experience heavy lightning, a TV antenna mast can collect a static charge. This charge can discharge to the electronics. A mast ground drains that charge to ground.
This code goes back decades. The reason the code does not say the antenna has to be grounded is because the antenna actually collects the RF energy. If you ground the antenna the signal would go to ground. A satellite dish is not an antenna, it is a reflector. The LNB houses the antenna. That is VERY important thing to understand.
It makes no difference whether or not an antenna mast is on your roof or on the ground. The ability for a mast to collect static is the same.

When satellite came around, the NEC simply rolled us into the existing antenna rules. If your area is not arid, or has any significant lightning to speak of, you can try to get your local codes changed. The NEC is the NATIONAL Electric Code. it must assume the worst case scenarios for the entire country. It is up to your local authorities to amend the NEC for local issues, if they even choose to require the NEC at all.

The national fire protection agency (NFPA), who writes the NEC, has a VERY tough process to get the NEC changed. I have filed two petitions to have the NEC modified, but the bottom line is, any local authority can choose to not require mast grounding. The NFPA is not about to change the NEC, if it means the reduction of safety. It cost very little to ground the mast, there has not been single case where a mast ground caused problems, so there is no reason to change the NEC.

The next version of the NEC is due out in 2008. The cut-off date to file a request to change the NEC was last year at this time. The final draft of the 08 NEC is being written at this time. The next version is due in 2011. If you want file a request for a change, you must have it submitted by early 09 (I think that date range is correct)

The NEC is VERY simple to understand if you just read it, and not try to interject your opinion into it.

 

[Todd Humphrey]

All this makes me wonder also if every dish you see at a tv station, cable headend or teleport has a ground wire attached to every damn one of em'. ESPN has 27 dishes at it's Bristol headquarters and the ariel photos show them spread all over, ...on the ground, on top of the building, in the middle of the parking lot! I think i will die if someone tells me there's a grounding system under the asphalt. This is all very interesting.

Yes they are heavly grounded.

 

[Todd Humphrey]

Virtually every highrise has HVAC units on top of them that are supported by structural steel, meaning "I" beams. I sometimes ground to them. But technically, they would have to be "bonded" to the building's ground system, which can be done either by welding them together or by using conforming, "bonding jumper" hardware, so if they were attached to the ceiling steel using only big bolts that I can't see, the resistance would measure as though I had a valid ground path but, technically, that steel would not qualify as a code conforming ground point.

Nearly all highrise buildings in my market have some kind of lightning rod system on them. Sometimes I attach to that.

I'll still attach to a cold water pipe in a large building. The reason for the change banning that practice is that so many repairs are now done with plastic pipe that the future integrity of a cold water ground cannot be assumed, but in my highrise buildings, I know I can rely on common cold water pipes to always be repaired with copper if the ever have to be repaired at all.

Fortunately for me, I'm not a fulfillment installer, so I don't fear having my installation commission deducted from my account if some nit picker believes a ground I have connected is non-conformant.

I have been told that it was NEVER allowed in the NEC to ground to a water pipe beyond five feet from POE. It was a common practice, and maybe allowed under local codes, but not under the NEC. But then again, 5 foot ground rods are NOT allowed under the NEC and yet almost every major satellite distributor sells them. And HUGHESNET Corporate installers use them. (Shame on you HughesNet)

Just because something is done, and not enforced by local inspectors does not mean it is allowed under the NEC.

The reason you do not want to ground to a water pipe beyond the feet mark is simple. If you have a ground wire grounded to a water pipe on the OPPOSITE end of the house from the water lines POE, and a lightning bolt strikes, do you want to be taking a bath, with the water flowing, and the drain in your home is cast iron? There is nothing to prevent some currant from flowing through the water, into the tub to reach the grounded cast iron drain. This is not an impossible scenario, even if extremely unlikely.
The NEC is all about addressing the unlikely.

The NEC is very specific about where you can ground. A HVAC unit is NOT one of those points. I do not care where any installer grounds, all I want is for those installers that actually want to follow the rules to understand that an HVAC unit is NOT allowed under the NEC. If you can get permission from your local inspector, then fine, but I have NEVER had such luck.

Sometimes the labor and materials to provide a proper ground can exceed what some installers are paid for a job. At that point, most installers start to justify breaking the codes because they cannot afford to follow the codes. After a while they start believing they are doing the job correctly. They show other installers what they do, they come to these forums and pass on what they do as OK, when it may not be allowed.

It is up to every installer to know the codes applicable in their area. Do not trust me, or anyone on these forums to tell you what is right or wrong. When you take the time to talk to local inspectors and actually BUY a copy of the NEC, you become a better installer. I can tell you what the NEC says and does not say. I can tell you generally accepted interpretations of the NEC by inspectors and those that wrote it. I can even tell you WHY some codes are written, the way they are written, but NO ONE can tell you what your local inspector is going to say when you ask them, "How do you ground at the top of building?"

 

[AntAltMike]

I have been told that it was NEVER allowed in the NEC to ground to a water pipe beyond five feet from POE. It was a common practice, and maybe allowed under local codes, but not under the NEC. But then again, 5 foot ground rods are NOT allowed under the NEC and yet almost every major satellite distributor sells them. And HUGHESNET Corporate installers use them. (Shame on you HughesNet)

Just because something is done, and not enforced by local inspectors does not mean it is allowed under the NEC.

The reason you do not want to ground to a water pipe beyond the feet mark is simple. If you have a ground wire grounded to a water pipe on the OPPOSITE end of the house from the water lines POE, and a lightning bolt strikes, do you want to be taking a bath, with the water flowing, and the drain in your home is cast iron? There is nothing to prevent some currant from flowing through the water, into the tub to reach the grounded cast iron drain. This is not an impossible scenario, even if extremely unlikely. The NEC is all about addressing the unlikely.

The NEC is very specific about where you can ground. A HVAC unit is NOT one of those points. I do not care where any installer grounds, all I want is for those installers that actually want to follow the rules to understand that an HVAC unit is NOT allowed under the NEC. If you can get permission from your local inspector, then fine, but I have NEVER had such luck.

It is up to every installer to know the codes applicable in their area. Do not trust me, or anyone on these forums to tell you what is right or wrong. When you take the time to talk to local inspectors and actually BUY a copy of the NEC, you become a better installer. I can tell you what the NEC says and does not say.

The last time I actually had my own reference copy of the NEC, it was in its 1999 version. I think it gets amended every three years. Back in 1999, the mast and and coax ground wires were to be connected to the ground electrode system. Elsewhere in the code, the ground electrode system was defined to include the cold water pipes. I believe it was the 2002 revision that specifically limited using the cold water pipe connection to within five feet of its point of entry.

The minimum length of the mast ground rod was shortened from eight feet to five feet in the 2002 revision for at least one of its applications. I think that at the same time, they specified that the maximum length of the ground conductor to the ground rod was 20 feet, which is sometimes physically impossible, like if the coax penetrates the building on the third floor. It was excerpted at AVSForums, but I am on a low speed internet connection and it would take me all night to find it in their archives. They also began allowing a 12" by 12" plate instead of a ground rod in certain applications.

I think that the requirement that the ground conductor of the outer coax be solid and insulated was relaxed in the 2002 revision as well.

I did not recommend grounding to what is being loosely being called here an HVAC unit, but the structural steel it is mounted on MAY technically be part of the ground electrode system if it is bonded, through welding, to the rest of the structural steel.

I've read the state statutes in a few states purporting to "adopt" the NEC. The general framework of those statutes is that they say that the XXXX edition of the NEC is adppted with the following exceptions: and then, they specifically exclude certain chapters or subchapters or modify others. State with sandy soil have more demanding ground electrode standards. Some states "bend" on what is allowed for temporary electrical facilities while a building is being constructed, and I have been told that some western states have actualy excluded the mast grounding reqirement, but I have not actually seen that particular exclusion.

 

[rglore]

The worst thing you can do is to drive a ground rod at the dish location for a ground. In electrical storms, there will be a huge voltage difference between the dish location and the building ground that your receiver is plugged into. Large currents will flow in the coax trying to equalize this difference and may damage the LNB, receiver or switches and could start a fire.

The dish mast should always be bonded only to the building ground. No ground would be better than a seperate ground as the coax shield would be able to drain off normal charge buildups but a ground rod is capable of putting large currents on the coax.

 

[Todd Humphrey]

The minimum length of the mast ground rod was shortened from eight feet to five feet in the 2002 revision for at least one of its applications.

No it was not!!! Below is the code from the 2005 NEC, which is word for word the same as the 2002 NEC. NO WHERE does it say 5 foot ground rods are allowed, and the fact that you said they are allowed is what I am talking about, when mis-information is passed from installer to installer.

I know you mean well, but you used "I think" ALOT. Like I said before, everyone should own a copy of the NEC that applies to thier area. By now almost everyone should have to meet the 2002 code. My local county only adopted the 2005 code this year.

The NEC, both 2002 and 2005, state that the cable can be solid or stranded.
The cable must insulated. 820.40 (A)(1)(2)




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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 ft) 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 selected shall be resistant to any corrosive condition existing at the installation or shall be suitably protected against corrosion. The conductor shall be solid or stranded, insulated, covered, or bare.
250.64 Grounding Electrode Conductor Installation.
Grounding electrode conductors shall be installed as specified in 250.64(A) through (F).
(A) Aluminum or Copper-Clad Aluminum Conductors.
Bare aluminum or copper-clad aluminum grounding conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum grounding conductors shall not be terminated within 450 mm (18 in.) of the earth.
(B) Securing and Protection from Physical Damage.
A grounding electrode conductor or its enclosure shall he securely fastened to the surface on which it is carried. A 4 AWG copper or aluminum or larger conductor shall be protected if exposed to severe physical damage. A 6 AWG grounding conductor that is free from exposure to physical damage shall he permitted to be run along the surface of the building construction without metal covering or protection where it is securely fastened to the construction; otherwise, it shall be in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, or cable armor. Grounding conductors smaller than 6 AWG shall be in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, or cable armor.
(C) Continuous.
The grounding electrode conductor shall be installed in one continuous length without a splice or joint, unless spliced only by irreversible compression-type connectors listed for the purpose or by the exothermic welding process.
Exception: Sections of busbars shall he permitted to be connected together to form a grounding electrode conductor
(D) Grounding Electrode Conductor Taps.
Where a service consists of more than a single enclosure as permitted in 230.40. Exception No. 2, it shall be permitted to connect taps to the grounding electrode conductor. Each such tap conductor shall extend to the inside of each such enclosure. The grounding electrode conductor shall be sized in accordance with 250.66, but the tap conductors shall be permitted to be sized in accordance with the grounding electrode conductors specified in 250.66 for the largest conductor serving the respective enclosures. The tap conductors shall be connected to the grounding electrode conductor in such a manner that the grounding electrode conductor remains without a splice.
(E) Enclosures for Grounding Electrode Conductors.
Metal enclosures for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Metal enclosures that are not physically continuous from cabinet or equipment to the grounding electrode shall be made electrically continuous by bonding each end to the grounding electrode conductor. Where a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the appropriate raceway article.
(F) To Electrode(s).
A grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available in the grounding electrode system or to one or more grounding electrode(s) individually. The grounding electrode conductor shall be sized for the largest grounding electrode conductor required among all the electrodes connected to it.

 

[AntAltMike]

The minimum length of the mast ground rod was shortened from eight feet to five feet in the 2002 revision for at least one of its applications. I think that at the same time, they specified that the maximum length of the ground conductor to the ground rod was 20 feet, which is sometimes physically impossible... It was excerpted at AVSForums, but I am on a low speed internet connection and it would take me all night to find it in their archives. .

No it was not!!! Below is the code from the 2005 NEC, which is word for word the same as the 2002 NEC. NO WHERE does it say 5 foot ground rods are allowed, and the fact that you said they are allowed is what I am talking about, when mis-information is passed from installer to installer.

...5 foot ground rods are NOT allowed under the NEC and yet almost every major satellite distributor sells them. And HUGHESNET Corporate installers use them. (Shame on you HughesNet)

Apparently, beginning in 2002, the NEC authorizes the use of five foot ground rods in certain circumstances in section 800, as is elaborated upon below.I just visited the AVSForums archives and found an archived thread in which grounding was discussed, and have copied relevant posts from that discussion

*********************************************************************

Opening post: by Greywolf AVSForums, 04-25-04
http://www.avsforum.com/avs-vb/show...908#post3714908 has a discussion on antenna and dish grounding. It's been reported that the latest NEC codes have some changes. If anyone here has access to the latest codes, any additions to the thread would be appreciated.



Larry Fine (Richmond, VA Electrical contractor) 04-25-04

I have both the '99 and '02 NEC's on my computer, so I can quote anything you need. Ask a specific question, or tell me what you want to know. I can insert or link to any text you need. www.fineelectricco.com



Jim Parker (Posts from DBSTALK, excerpted into AVSForums thread by AntAltMike)

10-24-03
I'm an electrical engineer with 30 years in the construction field, so I have some expertise with this

(10-27-03)
There is a revision to the 2002 NEC, 800.40A4 (communication cable) and 820.40A4 (Community Antenna TV), that states that the ground wire for communication circuits entering 1 and 2 family dwellings be less than 20 feet. If the building grounding system is more than 20' away, a ground rod shall be driven, and that rod shall also be bonded to the building ground with a #6 wire. The rod must be at least 5'x1/2".

Some of the above is paraphrased, but that is the gist of it.


Larry Fine 05-11-04 AVSForums Archive

Art. 800 refers to communications, and Art. 820 refers to CATV (& cable-radio), while Art. 810 refers to satellite TV, which was the topic of the original post.

The 5ft. rod is mentioned in Art. 800, where "no other grounding means" are present, but not in Art. 810 or 820.

*******************************************************************

Now, I do not have the 2002 or 2005 NEC in front of me, so I cannot see whether either 810, 820 or both have explicit requirements for an 8 foot ground rod that override the section 800 specification. I also cannot definitively determine whether the grounding of a satellite or off-air antenna downlead can definitively be said to be governed by section 800 or 820. Apparently, HUGHESNET, which has a much bigger stake in this than do you or I, believes that the five foot rod now satisfies their system's grounding requirement for whatever application they say it does. Do they say in their published installation instructions whether they intend for the five foot rod to be used for mast grounding, outer conductor grounding, or both?.

...I'll still attach to a cold water pipe in a large building. The reason for the change banning that practice is that so many repairs are now done with plastic pipe that the future integrity of a cold water ground cannot be assumed, but in my highrise buildings, I know I can rely on common cold water pipes to always be repaired with copper if the ever have to be repaired at all....

I have been told that it was NEVER allowed in the NEC to ground to a water pipe beyond five feet from POE. It was a common practice, and maybe allowed under local codes, but not under the NEC."

Posted by:
BarryO (Communications Engineer, 1,300+ AVSForums posts) 05-11-04 (AVSForums)
quote:
--------------------------------------------------------------------------------
Originally posted by Larry Fine
b. The grounded interior metal water piping systems, within 1.52 m (5 ft) from its point of entrance to the building (boldface added)...
--------------------------------------------------------------------------------

The part in (boldface) is new in the 2002 code; it isn't in the 1999. Pre-2002, you could connect the grounding electrode for the mast & grounding block anywhere to the metallic water piping.

*************************************************************

The eternal restriction that the service ground connection to a cold water pipe be confined to the first five feet from its point of entry into building, which you site from section 250, appears to govern the formation of the building's ground electrode system to which the power service is connected and adequately grounded. Section 800, 810 and 820, governing the grounding of communications electronics, have not always been so demanding and, prior to 2002, the communications grounds could be attached to a cold water pipe anywhere.

I think that the requirement that the ground conductor of the outer coax be solid and insulated was relaxed in the 2002 revision as well....

The NEC, both 2002 and 2005, state that the cable can be solid or stranded. The cable must insulated. 820.40 (A)(1)(2)

You are apparently now using the term "cable" to describe the grounding conductor. I do not believe the NEC uses that term to describe it in these sections, and doing so tends to confuse matters since 820 governs cable TV installations and specifically, the grounding of the outer conductor of the coax cable.

Grounding requirements germane to grounding satellite and television reception devices are found in at least four places in the NEC: the 250s, 800, 810 and 820. Finding something said in one of those four sections does not mean that inconsistent language is not still found in another one of them. Your reading of, "The NEC", such that, "the cable can be solid or stranded", is ambiguous in that I can't tell whether you are reading that from a mast grounding requirement or from an outer conductor groundling requirement, but if it does pertain to the outer conductor ground, then it tends to support my belief that the requirement was relaxed starting in 2002.

Even when I post the NEC for all to read, someone still fails to read it.
The NEC is VERY simple to understand if you just read it, and not try to interject your opinion into it.

A lot of people disagree. Unfortunately, those forum members most knowledgeable on the subject, like Larry Fine and BarryO, both cited above, no longer bother to post in threads on the subject of grounding, surely because the subject matter became repetitive.

It is regrettable that this law is owned by a private party and we are not allowed to substantially reproduce it, even though we are obliged to conform to it. The last time I checked at a local electrical supply house, a copy of the NEC sold for $60. I didn't want it that bad. I have to visit the University of Maryland library to research an unrelated matter this week and will try to make time to also go to their engineering library and copy whatever version of the code they have.

 

[AntAltMike]

The section 250 code passages, excerpted and furnished by Todd Humphrey, become easier to read and interpret if one inserts spaces between subsections, and adds interlinear analysis:

250.53 Grounding Electrode System Installation...
(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)...
.
(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.

(Note: the exception alluded to here is that a Supplemental Electrode can be connected to the water pipe further than five feet from where it enters the building, provided the building is commercial, is professionally maintained, most of the water pipe is exposed, etc., etc.)

Continuing...

250.53 Grounding Electrode System Installation...(contination)...

(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....

So section 250.53 appears, to me, to govern the installation of something called the Grounding Electrode System, which I believe to be the safety ground responsible for the bonding of the entire Class A electrical system to earth, and satisfying the conductivity resistance and reliability requirements of that section can involve using Supplemental Grounding Electrodes, such as a rod that is at least eight feet long. But the grounding requirements for "equipment", surely including low voltage communications electronics devices, begins here:

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....

Notice, first, that 250.54 is defining Supplementary Grounding Electrodes, whereas 250.53 defines Supplemental Electrodes. Supplemental Ground Electrodes complete the development of the Ground Electrode System, whereas Supplementary Ground electrodes facilitate the grounding of attached equipment.

Supplementary Grounding Electrodes do not have to meet the more robust current capacity sufficiency standards of Sections 250.50 and 250.53(C) that Supplemental Grounding Electrodes must meet, and, in the Communications electronics sections, it specifies that their bonding requirement can be met by #6 copper wire. They also do not have to meet the resistance requirement of Section 256. There is no minimum rod length given for such Supplementary Grounding Electrodes mandated in 254.54, and so the five foot rod that has been referenced in cited posts by electricians Jim Parker and Larry Fine is not inconsistent with anything I read in the limited excerpts of NEC 250 that have been posted in this thread. Now, whether this five-foot rod length referenced in Section 800 is applicable to satellite or terrestrial antenna mast grounding, antenna downlead grounding, or cable TV entrance wiring would depend on the actual wording of and interpretation of the current language of sections 810 and 820.

 

[Todd Humphrey]

You make a couple critical errors.

Section 800 does not apply to TV antennas or satellite dishes as you state. It does not apply to any form of antenna distribution system. Any part of 800 cannot be used to argue that 5 foot ground rods are allowed for satellite, cable, or MATV.

Article 800 applies to Telephone, telegraph (except radio), outside wiring for Fire Alarm and burglar alarm, and similar central station systems: telephone systems not connected to central station systems but using similar types of equipment. methods of installation and maintenance.

Like I said before NO ONE should trust what is said in these forums. You have fallen victim to that very thing.

There is a revision to the 2002 NEC, 800.40A4 (communication cable) and 820.40A4 (Community Antenna TV), that states that the ground wire for communication circuits entering 1 and 2 family dwellings be less than 20 feet. If the building grounding system is more than 20' away, a ground rod shall be driven, and that rod shall also be bonded to the building ground with a #6 wire. The rod must be at least 5'x1/2".

That text in red does NOT appear in the 2002 NEC. As stated Article 800 does not apply to satellite or cable TV, so any part of that is meaningless. Article 820.40(A)(4) says this.

(4) Length.
The grounding conductor shall be as short as practicable. In one- and two-family dwellings, the grounding conductor shall be as short as practicable, not to exceed 6.0 in (20 ft) in length.

Exception: In one- and two-family dwellings where it is not practicable to achieve an overall maximum grounding conductor length of 6.0 m (20 ft), a separate ground as specified in 250.52(A)(5), (6), or (7) shall be used, the grounding conductor shall be grounded to the separate ground in accordance with 250. 70, and the separate ground bonded to the power grounding electrode system in accordance with 820.40(D).

(D) Bonding of Electrodes. A bonding jumper not smaller than 6 AWG copper or equivalent shall be connected between the community antenna television system’ s grounding electrode and the power grounding electrode system at the building or structure served where separate electrodes are used.

Added to the 2005 code
FPN: Similar grounding conductor length limitations applied at apartment buildings and commercial buildings will help to reduce voltages that may be developed between the building’s power and communications systems during lightning events.


Your whole part on supplemental grounding does not apply to satellite, cable or MATV. The NEC says when a metal water pipe is used as a grounding electrode it shall be supplemented with ground rod. NEC 2002 Article 250.53(D)
This article has no bearing on satellite.

The NEC is very simple to understand. The problem starts when people do not actually READ the NEC and trust what others say. Another problem is the attempt to apply parts of the NEC that do not apply.

If you read nothing else please read the next section. It will make you think, I promise.

Here are the basic truths about satellite and antenna grounding.
To meet the NEC requirements, you must ground your mast and coax in accordance to 810. The coax must also comply with 820 (810.3), but that does not remove the requirements to meet 810, it only adds additional codes, not provide in 810.

This is were most people miss the boat. 820 is used for the installation methods and types of coax cable ie.. fire rating. The grounding section of 820 (820 section 3) is almost word for word the same as 810. The only major difference is the size of the grounding conductor. 820 says 14 awg, whereas 810 says 10 awg copper, 8 awg aluminum or 17 awg CCS. This is were things get a little interesting.
If you ground the mast using 17 awg CCS, you can ground the coax using 14 awg copper. Or can you? As long as you can argue that 14 awg copper has lower resistance than 17 awg CCS, you should have no problem. Remember, you must meet both 810 and 820. 810 does not mentioned the use 14 awg. It only mentions 10 awg copper, 8 awg aluminum, and 17 awg CCS. Since 17 awg CSS has more resistance than 14 awg, you cannot use that for the coax since it fails to meet the 820 requriement of 14 awg. Since 810 does not say you can use 14 awg, that only leaves 10 awg. However, if your local authoriteis agree that 14 awg copper exceeds the properties of 17 awg CCS (who would not agree) , you can use 14 awg copper, and meet NEC. You may not meet other requirements, but you will meet NEC

So why then do we use 10 awg???

Because every installer has been trained to connect the mast ground to the ground block and then use 10 awg to ground the ground block. This practice is not technically allowed under the NEC. The mast ground and the coax ground are required to be grounded to the same proper grounding points. When you ground the mast to the ground block, you are not grounding to an ground point allowed for under the NEC. You are in effet piggy-backing two grounding wires to one

I have no idea who first started grounding the mast to the ground block, but it has caught on. The concept is simple. A 10 awg copper can handle the grounding requirements of both the 17 awg CCS and the 14 awg coax ground. The ground block combines the two grounds into one. This is a logical adaption of the NEC. While not to the letter of the code, it does meet the spirit of the code. This is why I so strongly believe that installers MUST understand the code. When they are faced with a situation where you cannot meet the codes requirements, only with an understanding of the code can you hope to find an alternative means, that still provides a safe installation.

I would like to thank AntAltMike for a pleasant conversation. To me this is what forums do best. Provide a means for professionals to discuss issues.

 

[Todd Humphrey]

One thing I left out. I stated that you could use 14 awg to ground the coax, so long as you grounded the mast separately using 17 awg CCS. That is ONLY true if your local authorities agree. Please check.

There is another problem. It is very hard to get 17 awg wire to bond to a 6 awg or larger ground conductor. You should also use separate split bolts (or whatever you use) to bond the mast and coax ground. Those damn things are not cheap. It actually becomes cheaper in most cases to ground the mast to the ground block and use 10 awg.

To really mess you all up, I will leave you with this thought. How many coax cables can be grounded with a single ground wire? The code does not address issue. I have been told that EVERY coax providing service TO a building must be grounded. Not every coax entering a building, just those providing service to the building. CATV only has one coax servicing the building, but satellite can have four or more coax cables providing service to the building. I am not suggesting that you must install a 10 awg for each coax from the dish.

But ask yourself this. Why do four coax cable ground blocks have four lugs to install a ground wire? Why do three coax cable ground blocks have three lugs. You only need one lug for the mast ground and one for the ground wire.

Could it be that to be UL approved, the manufacture must provide one ground wire attachment point for every coax providing service, because according to UL you really need to separately ground EVERY coax from a dish? That would be the most strict interpretation of the NEC.

Think about it. Logic dictates that at some point as you increase the number of cables servicing a structure, a single 14 awg ground wire would fail to provide aduquent protection. At some point you need to provide separate grounding means. Could it be that it has already been determined to be ONE servicing coax per ground conductor? How else can you explain that for every coax grounded via a ground block, there is a separate ground lug on that block?

 

[AntAltMike]

One thing I left out. I stated that you could use 14 awg to ground the coax, so long as you grounded the mast separately using 17 awg CCS. That is ONLY true if your local authorities agree. Please check.

More precisely, we were never explicitly prohibited from using 14 gauge wire, but the 1999 revision said that whatever was used also had to be approximately equal in current carrying capacity to the outer conductor of the coax, and all electrical inspectors I have talked to are of the opinion that at the high frequencies of a lightning strike, where the electrons travel on the outside of the conductor, that its current carrying capacity is determined almost entirely by its outer diameter, and they would not allow 14 gauge to be used in that application. The cable companies in New Hampshire and Massachusetts used 12 gauge solid insulated to ground the coax outer conductors, but one inspector required me to use 6 gauge. He said that even though 6 gauge was probably not equal in current carrying capability, he could not justify requiring anything larger because the code allowed the ground rod bonding jumper to be 6 gauge, so no purpose would be served by using something larger when the 6 gauge bonding jumper would still be the weakest link in the ground path.

There is another problem. It is very hard to get 17 awg wire to bond to a 6 awg or larger ground conductor.

I take small, strong needle-nose pliers and bend tiny zig-zags into the 17 gauge wire before I even attempt to join it to a larger wire in a clamp.

You should also use separate split bolts (or whatever you use) to bond the mast and coax ground. Those damn things are not cheap. It actually becomes cheaper in most cases to ground the mast to the ground block and use 10 awg.

Two installations parts whose prices defy reason: One is split bolts. The other is the 1/8" and 3/16" guy wire clamp U-bolts. If you go into the wrong hardware store, the tiny U-bolt clamps cost over $3 each, but I can buy them in bulk for $.22 each.

If they now allow stranded ground wire for the outer coax conductor, which your 2002 and 2005 section 820 abstraction suggests, then at least it is now possible to buy conforming ground wire in a home supply/hardware store. They always stock 10 gauge stranded insulated, both green and black, but they never stock 10 gauge solid insulated. I always have to buy that from an electrical wholesaler, at a price that is anything but wholesale.

To really mess you all up, I will leave you with this thought. How many coax cables can be grounded with a single ground wire? The code does not address issue. I have been told that EVERY coax providing service TO a building must be grounded. Not every coax entering a building, just providing service to the building. CATV only has one coax servicing the building, but satellite can have four or more coax cables providing service to the building. I am not suggesting that you must install a 10 awg for each coax from the dish.

But ask yourself this. Why do four coax cable ground blocks have four lugs to install a ground wire? Why do three coax cable ground blocks have three lugs. You only need one lug for the mast ground and one for the ground wire.

Could it be that to be UL approved, the manufacture must provide one ground wire attachment point for every coax providing service, because according to UL you really need to ground EVERY coax from a dish? That would be the most strict interpretation of the NEC.

I've never seen a three or four coax ground block. Do we even call them Siamese blocks, or has perhaps some contemporary science fiction character been honored?

Until DBS came along, the hole in most single coax ground blocks wasn't even big enough to accommodate 6 gauge wire. They had to be reamed out, which meant that we were voiding the UL listing by making them more suitable.

One electrician claimed that if RG-6 coaxes have the approximate current carrying capacity of 6 gauge solid copper, then four of them in parallel have the current carrying capacity of 2 gauge copper.

I think that the four lugs are provided, not for a one-coax/one ground wire relationship, but because, realistically, no installer is going to carry any ground wire larger than he thinks is adequate for the grounding of a single coax. It is plausible that the UL will only approve a ground block that has the capacity to reliably connect enough ground wire cross-section as the likely coax outer conductors will need to be grounded in conformity with NEC 820. But even then, if you used RG-11 quad...

 

[Todd Humphrey]

I think that the four lugs are provided, not for a one-coax/one ground wire relationship, but because, realistically, no installer is going to carry any ground wire larger than he thinks is adequate for the grounding of a single coax.

The key part to your comment is ".....carry any ground wire larger than he thinks is adequate... "

The installer should not have to think, just follow the code. Nice thought in an ideal world. However, if the NEC requires one 10 awg ground wire per coax, they do not come out and say it, but then you have that whole equal in currant carrying capacity comment. But since COAX is not rated on its currant carrying ability, there is no cut and dry decision that anyone can make. I will admit that this part of the NEC is not clear. Or maybe it is, and coax cable manufacturers are not doing their job by providing the specs we need?