Siemens NEC Article 409 - SB4.4 - SCCR Calculation of the Industrial Control Panel

Basic steps for calculating the SCCR of a control panel
4.3 SB4.4 – SCCR calculation of the industrial control panel
Short-circuit current rating (SCCR) of industrial control panels
Reference Manual, 06/2013, A5E31896849002A/RS-AA/001
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4.3
SB4.4 – SCCR calculation of the industrial control panel
The SCCR of the industrial control panel is calculated with limitation to the lowest value of a
component or a circuit according to SB4.2 or SB4.3.
Example
The first calculation is based on SB4.2 and looks as the individual SCCR values with which
the components are marked or that appear on the list of unmarked components.
Industrial control panel
Components
No.
Power circuit
①
Circuit breaker
②
Contactor
③
Overload relays
④
Fuses on the primary side of the
control transformer
No.
Control circuit
⑤
Control transformer
⑥
Control relay
⑦
Terminal blocks
⑧
Display lamp
⑨
HAND-OFF-AUTO selector switch
The components listed under control circuit do not have to be included in the SCCR
calculation for the industrial control panel.
The individual SCCR values of the individual power circuit components are as follows:
No.
Power circuit
SCCR at 480 V
①
Circuit breaker 25 kA
②
Contactor 5 kA
③
Overload relays 5 kA
④
Fuses on the primary side of the control
transformer
200 kA
Both the contactor and the overload relay have an SCCR of 5 kA at 480 V. If no further
information is available, this industrial control panel would be marked with an SCCR of 5 kA
at 480 V AC.