24.12.2012 Views

standards and guidelines for communication sites - Radio And ...

standards and guidelines for communication sites - Radio And ...

standards and guidelines for communication sites - Radio And ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

GROUNDING (EARTHING) ROOF-MOUNTED ANTENNA MASTS AND METAL SUPPORT STRUCTURES CHAPTER 4: EXTERNAL GROUNDING (EARTHING)<br />

IMPORTANT: In ice prone areas, if isolating the cable bridge/ice bridge from the tower creates an<br />

unprotected area on the RF transmission lines, some type of ice shield shall be installed above the<br />

isolation point in order to protect the RF transmission lines. The ice shield shall be bonded to the tower<br />

only.<br />

4.7.11 METALLIC BUILDING SIDING GROUNDING (EARTHING)<br />

Although metallic building siding is not required to be grounded by this st<strong>and</strong>ard, grounding the<br />

metallic siding can provide additional safety at the site (NFPA 70-2005, Article 250.116-FPN). It is<br />

recommended to bond the metallic building siding in at least one location on the building, preferably<br />

near the electrical service entrance.<br />

4.8 GROUNDING (EARTHING) ROOF-MOUNTED ANTENNA<br />

MASTS AND METAL SUPPORT STRUCTURES<br />

All roof-mounted antenna masts <strong>and</strong> metal support structures shall be grounded (earthed) (NFPA 70-<br />

2005, Article 810.15).<br />

NOTE: Rooftop mounted towers are not covered in this section. See “Grounding (Earthing) Rooftop Mounted<br />

Tower Structures” on page 4-79 <strong>for</strong> in<strong>for</strong>mation about rooftop tower grounding requirements.<br />

In new construction, provisions shall be engineered into the building design <strong>for</strong> effective roof-mounted<br />

antenna mast <strong>and</strong> support structure grounding. Typically this will include a grounding point, or multiple<br />

grounding points, with at least two direct connections to the building's grounding electrode system. The<br />

direct connection to the building's grounding electrode system may be made using effectively grounded<br />

structural building steel (preferred) <strong>and</strong>/or down-conductors. Other engineered antenna mast <strong>and</strong><br />

support structure grounding systems may include metallic antenna support structures that are directly<br />

<strong>and</strong> effectively bonded to effectively grounded structural building steel.<br />

When a lightning protection system is installed on the building, roof-mounted antenna masts <strong>and</strong><br />

support structures shall be bonded to the lightning protection system (IEC 61024-1-2 <strong>and</strong> NFPA 780-<br />

2004, section 4.17). The conductor shall be of the same size as the Main Roof Perimeter Lightning<br />

Protection Ring (FAA STD-019d-2002, section 3.7.9.4). Conductor bonding shall be made using<br />

exothermic welding, listed irreversible high-compression fittings, or other fittings listed <strong>for</strong> use in<br />

lightning protection systems. See “Bonding to the External Grounding (Earthing) Electrode System” on<br />

page 4-40. No additional grounding shall be required of roof-mounted antenna masts <strong>and</strong> support<br />

structures when bonded to a lightning protection system.<br />

4-74 68P81089E50-B 9/1/05

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!