Siemens NEC Article 409 - Current-Limiting Fuses

Basic steps for calculating the SCCR of a control panel
4.2 SB4.3 – Adaptation of the available short-circuit current rating based on the peak let-through currents when
using current-limiting devices in the feeder circuit
Short-circuit current rating (SCCR) of industrial control panels
20 Reference Manual, 06/2013, A5E31896849002A/RS-AA/001
4.2.3
Current-limiting fuses
Only fuses from UL508A, Tab. SB4.2 may be used as current-limiting fuses. This table
shows the relevant peak let-through currents (see column I
p
x 10³).
Figure 4-9 Table SB4.2
The SCCR of the assembly is the breaking capacity of the fuse in the feeder circuit under the
following conditions:
● The SCCR of all individual components in the branch circuit is not lower than the peak let-
through current of the fuse in the feeder circuit.
● The breaking capacity of all branch circuit protective devices or the SCCR of all
combination motor controllers is not lower than the breaking capacity of the fuse in the
feeder circuit.
⇒ The SCCR of the assembly is the lowest breaking capacity of a branch circuit protective
device or combination motor controller connected on the load side of the fuse in the feeder
circuit if this is smaller than the breaking capacity of the fuse in the feeder circuit.
⇒ The SCCR of the assembly is the lowest SCCR of each branch circuit on the load side of
the fuse if the above conditions do not apply.