Siemens UL 508A Reference Manual - Page 21

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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

Examples

The following two examples show a fuse as the feeder circuit protective device. The

procedure described also applies if a circuit breaker according to UL489 is used as the

feeder circuit protective device.

Example 1

⇒ SCCR 35 kA since the circuit breaker is only suitable for 35 kA.

The contactor and overload relays are protected by the fuse in the feeder circuit since 5 kA

(SCCR of contactor and overload relays) is > 3 kA (let-through value of the fuse).

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

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

Basic steps for calculating the SCCR of a control panel