NFPA 70.
2.7.3
Locks and Key-Lock Operated Switches
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NOTE: Either round key or conventional key type
locks as defined in this specification are
acceptable. Selection should be based on hardware
availability at the time of design and the
requirement for matching locks currently in use at
the site. If the locks do not have to be matched to
locks in use at the site, and the designer has no
preference as to lock type, all brackets may be
removed.
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2.7.3.1
Locks
Locks required to be installed on system enclosures for maintenance
purposes shall be UL listed, [round-key type, with three dual, one
mushroom, and three plain pin tumblers] [or] [conventional key type lock
having a combination of five cylinder pin and five-point three position
side bar]. Keys shall be stamped U.S. GOVT. DO NOT DUP. The locks shall
be so arranged that the key can only be withdrawn when in the locked
position. All maintenance locks shall be keyed alike and only two keys
shall be furnished for all of these locks.
2.7.3.2
Key-Lock-Operated Switches
Key-lock-operated switches required to be installed on system components
shall be UL listed, [with three dual, one mushroom, and three plain pin
tumblers,] [or] [conventional key type lock having a combination of five
cylinder pin and five-point three position side bar]. Keys shall be
stamped U.S. GOVT. DO NOT DUP. Key-lock-operated switches shall be two
position, with the key removable in either position. All key-lock-operated
switches shall be keyed differently and only two keys shall be furnished
for each key-lock-operated-switch.
2.8
MESSENGER SYSTEM
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NOTE: Percent values stated below are based upon
overload factors that apply to Grade B construction.
If the aerial electrical distribution system
construction is a lesser grade (e.g., Grade C, Grade
N, or not graded), differing values will be provided
by the designer in accordance with NESC and actual
requirements.
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A messenger system meeting the requirements of IEEE C2 to support all
aerial cable shall be furnished and installed. The messenger system shall
include all messenger support and attachment hardware and appurtenances
needed to install the messenger system. Messenger tension due to combined
ice and wind loading on the messenger with supported cables shall not
exceed 60 per of the messenger rated breaking strength. Messenger tension
due to extreme wind loading on the messenger with supported cables shall
not exceed 80 percent of the messenger rated breaking strength. Messenger
support and attachment hardware shall have rated strength not less than the
SECTION 16794A
Page 22
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