6.5 - Grounding & Lightning Protection
Grounding & Lightning Protection
(Section 6.5 in ODN Field Services Manual)
The antenna mount should be grounded, as well as the shields of the RF cables at the antenna. Also, in the interior of the equipment shelter or building, lightning surge protectors should be installed in the path of both the receive and transmit RF cables. The modem itself should also be grounded in the equipment rack. Grounding hardware that would carry current, including wire, terminals and clamps should be made of copper, tin-plated copper or galvanized steel. Grounding hardware made of aluminum should NOT be used in the ground circuit path.
Exterior grounding:
At tower sites, a non-penetrating frame of a satellite antenna must be grounded. The frame-to-ground connection should employ a 2-AWG sized copper wire. The main 2-AWG wire should be connected via a crimped 2-bolt flat lug terminal bolted to a ground bus. [Figure 6.5.1] A ground bus can usually be found near the RF cable ingress normally provided on the equipment shelter, or a ground bus provided on another nearby structure such as at the tower base or an ice bridge. The copper 2-AWG path should take the shortest practical path to the nearest ground bus. Clean the connection surface of ground bus before attaching the terminal.
Exceptions:
•If the antenna frame is directly mounted to the radio tower, ice bridge, or other grounded metal structure via a tower leg bracket, then the addition of a copper 2-AWG wire is not necessary.
•In a situation where there is no ground bus provided, such as the roof of an office building, a 2-AWG ground cable can instead be connected to the nearest building structure that is a confirmed electrical ground, such as an exposed beam on an HVAC platform. Other variables may come into play in an office building situation that are outside the scope of this publication.
[Figure 6.5.1]
[Figure 6.5.2] The copper 2-AWG wire to the antenna frame should be connected via a crimped 2-bolt flat lug terminal. 3/8" holes will need to be drilled in the frame to accomplish this. [Figure 6.5.2] Also, the connection to the frame can be made via exothermal welding if the technician is so qualified and equipped.
[Figure 6.5.2]
The dual RF cable destinations can be grounded with 3/8” loop terminals at the BUC & LNB RF connections. The ground wire can be constructed in such a way that the LNB ground wire is crimped into the loop terminal on the BUC connector. [Figure 6.5.3]
A 6-AWG ground wire then travels down the antenna feed arm to connect to the main frame ground point. [Figure 6.5.2 & Figure 6.5.4 ]
[Figure 6.5.3] [Figure 6.5.4 ]
Interior Grounding
The modem should also be grounded to the ground bus on the equipment rack. This can be accomplished with a pair of ground wires attached with ring terminals and 3/8” nuts to the RX and TX connections on the rear of the modem. [Figure 6.5.5]
“Polyphaser” in-line lightning surge protectors should be installed on the interior of the equipment shelter near the RF cable egress. There is commonly a ground bus provided at that point. [Figure 6.5.6] The connection from the polyphasers to the ground can be made with a short span of 6-AWG stranded copper wire terminated with a crimped lug terminal and bolted to the interior ground bus.
[Figure 6.5.5] [Figure 6.5.6]
Grounding Supplies:
In the grounding scenario detailed above (for a typical tower site), the supplies used would be as follows:
•(approx. 20 feet) 2-AWG stranded copper wire. (for antenna frame to exterior ground bus)
•(3) 2-bolt flat lug terminal for 2-AWG crimp. (for exterior ground bus connections)
•(approx. 8 feet) 6-AWG stranded copper wire. (for grounding of exterior RG6 cable and interior Lightening surge suppressors)
•(4) Ring terminals with 3/8” hole for 6-AWG crimp. (for connections to BUC, antenna frame & interior ground bus)
•(approx. 3 feet) 10-AWG stranded copper wire with green insulation. (for grounding modem and merging ground between BUC and LNB)
•(2) Ring terminals with 3/8” hole for 10-AWG crimp. (for modem RF & LNB ground connections)
•(2) Ring terminals with ¼” hole for 10-AWG crimp. (for equipment rack ground bus connections)
•(2) Lightening Surge Suppressors, such as Polyphaser model GT75-FFF
•(2) Ring terminals with 5/8” hole for a 6-AWG crimp. (barrel-style Surge Suppressor connections)
•(8) Bolts, 3/8” OD X 1” long + Nut & Lock Washer (connections of lugs to ground busses)
Aside from the usual hand tools such as a socket set and wire cutters, a hydraulic crimping tool capable of properly crimping the above-listed terminals is recommended
Above: Photo of connectors per average site for reference.
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Grounding & Lightening Protection.pdf
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