UFC 3 -520-01
June 10, 2002
interior electrical systems. For purposes of this manual, high voltage refe rs to any
application rated above 15 kV.
5-4
MEDIUM VOLTAGE SWITCHGEAR .
5-4.1
Ratings.
5-4.1.1 Switchgear. Use metal-enclosed, manually operated, fusible load interrupter
switches or power circuit breakers with copper bus . Table 5 -1 indicates the most
commonly used voltages; the standard voltages shown without parentheses are
preferred.
Table 5-1. Medium Voltage Switchgear Voltage Ratings
Standard Nominal
Associated Non-Standard
System Voltages
Nominal System Voltages
7.2 kV and under (in kV)
(2.4)
2.2, 2.3
(4.16Y/2.4)
4.16
4.0
(4.8)
4.6
(6.9)
6.6, 7.2
15-kV class (in kV)
(8.32Y/4.8)
12Y/6.93
11, 11.5
12.47Y/7.2
13.2Y/7.62
(13.8Y/7.97)
13.8
14.4
5-4.1.2 Standards. Apply ratings conforming to ANSI C37.06, Preferred Ratings and
Related Required Capabilities for AC High-Voltage Circuit Breakers Rated on a
Symmetrical Current Basis, and ANSI/IEEE C37.04, American National Standard Rating
Structure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis,
in the selection of circuit breakers.
5-4.1.3 Voltage Rating. Determine the voltage rating in terms of three-phase, line -
to-line voltage, including the following considerations:
5-4.1.3.1 Maximum nominal system voltage for which the breaker is intended.
5-4.1.3.2 Maximum operating voltage at which the breaker will be used, taking into
consideration line voltage regulation, machine over -excitation and overspeed, and shunt
5-4
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