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Code Q&A

Jun 23, 2004 1:48 PM, By Mike Holt

Q. A large number of satellite professionals ground the satellite system to the nearest available water hose bib. Does the NEC permit this installation practice?

A. No. The satellite mast (810.15) and discharge unit (ground block) [810.20(C)] must be grounded (actually bonded) in accordance with 810.20. The electrode that’s suitable for this purpose includes the nearest accessible [810.40(F)(1)]:

a. Building or structure grounding electrode system (250.50).
b. Interior metal water-piping system, within 5 feet from its point of entrance [250.52(A)(1)]. (see the Figure)
c. Accessible bonding means [250.94].
d. Metallic service raceway.
e. Service equipment enclosure.
f. Grounding electrode conductor or the grounding electrode conductor metal enclosure.

Grounding the lead-in antenna cables and the mast helps in preventing voltage surges from static discharge from reaching the inner conductor of the lead-in cable. Because the satellite sits outdoors, wind creates a static charge on the dish as well as the wire attached to it. This charge can build up on the dish and cable until it jumps across an air space, often through the electronics inside the LNBF or receiver. Grounding the coaxial cable and dish to the building grounding electrode system helps in dissipating this static charge.

Nothing can prevent damage from a direct lightning strike, but grounding these systems in accordance with the NEC with proper surge protection (not NEC required) can help reduce damage to satellite equipment as well as protect other related equipment from nearby lightning strikes.

Got a Code question for Mike? Send it to him at mike@mikeholt.com.

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