Insulators shall comply with NEMA HV 2 for general requirements.
Suspension insulators shall be used at corners, angles, dead-ends, other
areas where line insulators do not provide adequate strength, and as
indicated. Mechanical strength of suspension insulators and hardware shall
exceed the rated breaking strength of the attached conductors.
2.9.1
Medium-Voltage Line Insulators
**************************************************************************
NOTE: Specify the first value for dry areas or
limited fog areas with moderate industry
contamination. Specify the second value for more
heavily contaminated areas.
**************************************************************************
Medium-voltage line insulators shall comply with ANSI C29.2, ANSI C29.5,
and ANSI C29.6, and as applicable. Ratings shall not be lower than the
ANSI classes indicated in TABLE I. Horizontal line-post insulators shall
be used for armless construction and shall have the same mechanical and
electrical ratings as vertical line-post insulators for the ANSI class
indicated, but shall be modified to be suitable for horizontal
installation. Where line-post insulators are used for angles greater than
15 degrees, clamp-top fittings shall be provided as well as for other
locations shown. Conductor clamps for use with clamp-top, line-post
insulators shall be hot-dip galvanized malleable iron for copper conductors
and aluminum alloy for aluminum-composition conductors. Either line-post
or pin insulators may be used for crossarm construction. Pin insulators
for use on voltages in excess of 6 kV phase-to-phase shall be
radio-interference-freed or else line-post insulators shall be used.
TABLE I
MINIMUM ANSI RATING OF MEDIUM-VOLTAGE INSULATORS BY CLASS
Voltage Level
Line-Post
Pin
Suspension
Up to 5 kV
57-1 or 11
55-3
One 52-1
57-1 or 11
55-5
Two 52-1
6 kV to 15 kV
57-1 or 11
55-5
Two 52-2
57-2 or 12
56-3
Two 52-3 or 4
16 kV to 25 kV
57-2 or 12
56-3
Two 52-3 or 4
57-3 or 13
56-4
Three 52-3 or 4
26 kV to 35 kV
57-3 or 13
56-4
Three 52-3 or 4
57-4 or 14
56-5
Four 52-3 or 4
2.9.2
Low-Voltage Line Insulators
Low-voltage line insulators shall comply with ANSI C29.2 and ANSI C29.3 as
applicable. Spool insulators for use on low-voltage lines shall be mounted
on clevis attachments or secondary racks and shall be not smaller than
Class [53-2] [53-3]. For No. 4/0 AWG and larger conductors, Class [53-4]
[53-5] shall be used. Suspension insulators on clevis attachments used at
dead-ends shall be not smaller than Class 52-1.
SECTION 16370A
Page 20
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