Hello,
I was hoping that the people here, being close to the NEC-writing process, could address a topic that?s become something of a big controversy among some satellite systems installers, electricians, and engineers. It pertains to the installation standards for a new satellite broadband service from a company named WildBlue (www.wildblue.com).
The exterior components of the Wildblue system consist of a parabolic dish antenna mounted on a short mast, with some active transmit/receiver electronics in a small enclosure termed a Transmit/Receive Integrated Assembly, or TRIA. The TRIA is connected to the modem inside the house by a double run of coaxial cable, over which the TRIA also receives DC power.
Unlike other DBS and broadband satellite systems, the Installation Manual for the Wildblue system does not specify that the dish & mast be grounded with a separate grounding conductor. Instead, it specifies that the dish be explicitly bonded to the TRIA with a #10 Cu wire. It goes on to comment that the TRIA is grounded through the coax shields.
This lack of an explicit grounding conductor for the mast in accordance with 810-15 has caused some to maintain that the Wildblue installation manual is not in compliance with the NEC. Reading ?810 carefully, I don?t believe that is necessarily the case.
Article 810 covers antenna systems for radio, television, and amateur radio. While it doesn't explicitly mention dishes for broadband access, to the extent that any local enforcement entity cares about antenna compliance with the NEC, they would certainly look to this Article
One of the first paragraphs in the Article, 810.3, states: ?Coaxial cables that connect antennas to equipment shall comply with Article 820?. Since the Wildblue system uses coax, I read this to mean that the sections that cover antenna lead-in conductors in 810 do not apply, but instead 820 is used. For instance "antenna discharge units" are not required. Instead, per Article 820, the requirement is that the shield be grounded. The coax ground block grounding conductor must be insulated per Article 820, unlike Article 810 which allows it to be uninsulated (why are they different?). Also, per part Article 820, an additional ground rod must be installed if the grounding conductor would otherwise be longer than 20 ft., and this new rod must be bonded to existing GES by a #6 wire.
Also According to 810.3, 820.103 is applicable: ?Unpowered equipment and enclosures or equipment powered by the coaxial cable shall be considered grounded where connected to the metallic cable shield?. According to this, then, is not the TRIA grounded through the coax shield, and a separate grounding conductor is not required for it?
Also, there is 810-21(I), Common Ground, ?A single grounding conductor shall be permitted for both protective and operating purposes?. The coax shield serves as an operating (e.g., signal) ground. According to this paragraph, it may also serve as the protective ground required by this section. This clause just recognizes the physical reality that even if another grounding conductor is installed, much if not most of the surge or fault current would flow over the coax shield.
Now some have pointed to the conductor size requirements in 810.21 (H): ?The grounding conductor shall not be smaller than 10 AWG copper, 8 AWG aluminum, or 17 AWG copper-clad steel or bronze.? The shield of RG-6 coax has a resistance of about #12 to #14 copper, depending on vendor. Since this is greater resistance than #10, some installers are arguing that this in not sufficient, despite the language in 820.103. However, the coax shield has less resistance than #17 CCS, which is allowed under 810.21(H). I believe this is due to the fact that the size requirement in this paragraph is driven primarily by mechanical strength rather than electrical resistance. A piece of RG-6 should meet the mechanical strength requirement, and the electrical resistance requirement, of this paragraph.
Finally, there is the installation manual?s instructions to bond dish and TRIA together with a #10 Cu wire. I suppose that, to the extent that components of the antenna can be considered "Unpowered equipment and enclosures or equipment powered by the coaxial cable", they can, therefore be considered grounded. One should then be able to argue that a grounding conductor is not needed for equipment that is already considered grounded?. It?s not even clear to me that this bond wire is needed, as the TRIA, boom, dish and mast are all metal, and are effectively bonded together when assembled.
I was hoping that the people here, being close to the NEC-writing process, could address a topic that?s become something of a big controversy among some satellite systems installers, electricians, and engineers. It pertains to the installation standards for a new satellite broadband service from a company named WildBlue (www.wildblue.com).
The exterior components of the Wildblue system consist of a parabolic dish antenna mounted on a short mast, with some active transmit/receiver electronics in a small enclosure termed a Transmit/Receive Integrated Assembly, or TRIA. The TRIA is connected to the modem inside the house by a double run of coaxial cable, over which the TRIA also receives DC power.
Unlike other DBS and broadband satellite systems, the Installation Manual for the Wildblue system does not specify that the dish & mast be grounded with a separate grounding conductor. Instead, it specifies that the dish be explicitly bonded to the TRIA with a #10 Cu wire. It goes on to comment that the TRIA is grounded through the coax shields.
This lack of an explicit grounding conductor for the mast in accordance with 810-15 has caused some to maintain that the Wildblue installation manual is not in compliance with the NEC. Reading ?810 carefully, I don?t believe that is necessarily the case.
Article 810 covers antenna systems for radio, television, and amateur radio. While it doesn't explicitly mention dishes for broadband access, to the extent that any local enforcement entity cares about antenna compliance with the NEC, they would certainly look to this Article
One of the first paragraphs in the Article, 810.3, states: ?Coaxial cables that connect antennas to equipment shall comply with Article 820?. Since the Wildblue system uses coax, I read this to mean that the sections that cover antenna lead-in conductors in 810 do not apply, but instead 820 is used. For instance "antenna discharge units" are not required. Instead, per Article 820, the requirement is that the shield be grounded. The coax ground block grounding conductor must be insulated per Article 820, unlike Article 810 which allows it to be uninsulated (why are they different?). Also, per part Article 820, an additional ground rod must be installed if the grounding conductor would otherwise be longer than 20 ft., and this new rod must be bonded to existing GES by a #6 wire.
Also According to 810.3, 820.103 is applicable: ?Unpowered equipment and enclosures or equipment powered by the coaxial cable shall be considered grounded where connected to the metallic cable shield?. According to this, then, is not the TRIA grounded through the coax shield, and a separate grounding conductor is not required for it?
Also, there is 810-21(I), Common Ground, ?A single grounding conductor shall be permitted for both protective and operating purposes?. The coax shield serves as an operating (e.g., signal) ground. According to this paragraph, it may also serve as the protective ground required by this section. This clause just recognizes the physical reality that even if another grounding conductor is installed, much if not most of the surge or fault current would flow over the coax shield.
Now some have pointed to the conductor size requirements in 810.21 (H): ?The grounding conductor shall not be smaller than 10 AWG copper, 8 AWG aluminum, or 17 AWG copper-clad steel or bronze.? The shield of RG-6 coax has a resistance of about #12 to #14 copper, depending on vendor. Since this is greater resistance than #10, some installers are arguing that this in not sufficient, despite the language in 820.103. However, the coax shield has less resistance than #17 CCS, which is allowed under 810.21(H). I believe this is due to the fact that the size requirement in this paragraph is driven primarily by mechanical strength rather than electrical resistance. A piece of RG-6 should meet the mechanical strength requirement, and the electrical resistance requirement, of this paragraph.
Finally, there is the installation manual?s instructions to bond dish and TRIA together with a #10 Cu wire. I suppose that, to the extent that components of the antenna can be considered "Unpowered equipment and enclosures or equipment powered by the coaxial cable", they can, therefore be considered grounded. One should then be able to argue that a grounding conductor is not needed for equipment that is already considered grounded?. It?s not even clear to me that this bond wire is needed, as the TRIA, boom, dish and mast are all metal, and are effectively bonded together when assembled.