Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 37)

Nominal voltage of the
supply system
( ≤ rated insulation
voltage of the
equipment)
a.c. r.m.s.
V
Preferred values of rated impulse withstand
voltage (1,2/50 μs) at 2 000 m
kV
Overvoltage category
IV III II I
Maximum value of
rated operational
voltage to earth
a.c. r.m.s. or d.c.
V
Origin of
Installation
(service
entrance)
level
Distribution
circuit level Load
(appliance,
equipment)
level
Specially
protected
level
300 220/380, 230/400,
240/415, 2607440
277/480
6 4 2.5 1.5
600 347/600, 380/660,
400/690, 415/720
480/830
8 6 4 2.5
1000 - 12 8 6 4
Tab. 2.3-4
Correspondence between the nominal voltage of the supply system and rated impulse withstand voltage
of the device with protection by surge-arrestors according to IEC 60099-1
Excerpt from Table H.1 of IEC 60947-1 ed. 5.0 Annex H
Copyright © IEC, Geneva, Switzerland. www.iec.ch
2.3.4 Short-circuit withstand capacity and short-circuit protection
See also Section 4.1.3 .
Adequate protection against the consequences of a short-circuit is one of the most fundamental
safety measures for electrical equipment. This affects both the protection of persons as well as
of property. For operational reasons it is often desirable that devices survive short-circuits
largely unscathed so that they may become operational again as quickly as possible afterward.
The specification of coordination types for starters is also related to this requirement.
The short-circuit withstand capacity of electrical equipment is usually defined by stating the
largest permitted short-circuit protective device (for example permissible fuse or permissible
circuit breaker). Current limiting fuses and modern current limiting circuit breakers make a major
contribution to the economical rating of devices, as they strongly reduce the thermal and
dynamic loading of devices and equipment connected downstream.
Loading in the event of a short-circuit is defined by the Joule integral (I
2
t value), the cut-off
current (I
D
) and the short-time current (I
cw
).
LVSAM-WP001A-EN-P - April 2009 2-9