User guide

Canopy System User Guide Grounding the Equipment
pmp-0229 (Mar 2013)
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Grounding Scheme
The proper overall antenna grounding scheme per the NEC is illustrated in Figure 136 on Page
399. In most television antenna or dish installations, a coaxial cable connects the outdoor
electronics with the indoor electronics. To meet NEC 810-20, one typically uses a coaxial cable
feed-through block that connects the outdoor coax to the indoor coax and also has a screw for
attaching a ground wire. This effectively grounds the outer shield of the coax. The block should be
mounted on the outside of the building near the AC main panel such that the ground wire of the
block can be bonded to the primary grounding electrode system of the structure.
For residential installs, in most cases an outdoor rated unshielded twisted pair (UTP) cable is
sufficient. To comply with the NEC, Cambium provides the antenna discharge unit, 600SS,
for each conductor of the cable. The surge suppressor must be
• positioned
o outside the building.
o as near as practicable to the power service entry panel of the building and attached to the
AC main power ground electrode, or attached to a grounded water pipe.
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o far from combustible material.
• grounded in accordance with NEC 810-21, with the grounding wire attached to the screw
terminal.
The metal structural elements of the antenna mast also require a separate grounding conductor.
Section 810-15 of the NEC states:
Masts and metal structures supporting antennas shall be grounded in accordance with
Section 810-21.
As shown in Figure 136 on Page 399, the Cambium recommendation for grounding the metal
structural element of the mounting bracket (SMMB1) is to route the grounding wire from the
SMMB1 down to the same ground attachment point as is used for the 600SS discharge unit.
Use 10-AWG (6 mm
2
) Copper Grounding Wire
According to NEC 810-21 3(h), either a 16-AWG copper clad steel wire or a 10-AWG copper
wire may be used. This specification appears to be based on mechanical strength considerations
and not on lightning current handling capabilities.
For example, analysis shows that the two wire types are not equivalent when carrying a lightning
surge that has a 1-microsecond rise by 65-microsecond fall:
• The 16-AWG copper clad steel wire has a peak fusing current of 35,000 amps and can carry
21,000 amps peak, at a temperature just below the ignition point for paper (454° F or 234° C).
• The 10-AWG copper wire has a peak fusing current of 220,000 amps and can carry 133,000
amps peak, at the same temperature.
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It is insufficient to merely use the green wire ground in a duplex electrical outlet box for grounding of the
antenna discharge unit.