Siemens UL 508A Reference Manual - Page 20

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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

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

Figure 4-9

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.

Table SB4.2

x 10³).

Short-circuit current rating (SCCR) of industrial control panels

Reference Manual, 06/2013, A5E31896849002A/RS-AA/001