Technical information

STEP 3
Determine the overall short circuit current rating of the panel as specified in
SB4.4.
The short circuit current ratings of the individual components are compared to
their branch circuit protective device.The smaller of the two ratings are applied
to the line side of the branch circuit protective device. If a control circuit is
located in a branch, then the overcurrent protective device for the control circuit
must also be considered.
The guidelines for determining the short circuit current ratings of the complete
panel can be found in SB4.4.4. For control panels with single branch circuits, the
short circuit current rating of the panel is the rating of the branch.
Control panels with multiple branch circuits and feeder components are covered
in clause c) The lowest short circuit current rating of all branch circuits, feeder
components and control circuit overcurrent protective devices, connected to the
feeder will determine the panel short circuit current rating.
In this example, the lowest short circuit current rating of all branch circuits,
feeder components and control circuit overcurrent protective devices connected
to the feeder is 65kA.Therefore, the overall panel short circuit current rating is
65kA rms symmetrical at 480V.
* Values represent overcurrent protective device with fuses
INDUSTRIAL MACHINERY
98
The short circuit current ratings of the
individual components are compared to
their branch circuit protective device
The smaller of the two ratings, (highlighted
in yellow) are applied to the line side of
the branch circuit protective device
Available Fault:
40kA at 480V
Available Fault:
40kA at 480V
1
00kA*
1
00kA*
100kA*
100kA*
100kA
65kA
70kA
100kA*
65kA 65kA
70kA*
65kA
65kA
Panel Short Circuit Current Rating is
65kA rms symmetrical @ 480V
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