Pfannenberg PWS Series - Manual (Page 14)

PWS Series Air/Water Heat Exchangers
11
Option 1: UL 508a reference SB4.2
According to UL508A Supplement SB, if a panel
contains no current-limiting devices, its SCCR
depends on the “weakest” or lowest rated
component or combination within the panel.
However, Supplement SB also states that if current-
limiting fuses are used in the feeder circuit, and if the
highest instantaneous current reached during the
first half cycle of a fault is less than or equal to the
lowest rated SCCR in any branch circuit, the SCCR
of the current limiting fuse can be applied to the
combination.
When the specified branch circuit protection related
to the high fault short circuit current rating is a Class
CC,G,J,L,RK1, RK5 or T fuse, a fuse of a different class
is able to be used at the same high fault rating where
the peak let through current and I2t of the new fuse
is not greater than that of the specified fuse.
Option 2: UL 508a reference SB4.3
An alternate method of achieving a high short circuit
rating is by applying a power transformer with an
isolated secondary winding, the short circuit current
rating on the line side of the transformer shall be one
of the following:
For a power transformer rated not more than 10
kVA, and where the short circuit current rating of
all components in the secondary circuit are not
less than 5kA, the short circuit current rating of the
primary overcurrent protective device is able to be
assigned to the line side of the power transformer
circuit.
For a power transformer rated not more that 5kVA
and a 120V maximum secondary voltage, and where
the short circuit current rating of all components in
the secondary circuit are not less than 2kA, the short
circuit rating of the primary overcurrent protective
device is able to be assigned to the line side of the
power transformer circuit.
Option 3: UL 508a reference SB4.2
The combinations listed in the linked spreadsheets
(www.ul.com/controlequipment/shortcircuit.html)
may be applied in a manufacturer’s Listed industrial
control panel without further evaluation or specific
documentation in the manufacturer’s UL Procedure
pages.
The spreadsheets cover the application of individual
components, including a disconnecting means, an
over current protective device, motor controller
and motor overload protection, as a combination
motor controller having specified ratings, including
a short-circuit current rating (SCCR). Each of the
individual components is Listed or Recognized to the
requirements in the applicable component Standard.
The specified ratings for the combination motor
controller may be applied to the end-product
equipment only when all of the specific components
listed are provided in the end-product equipment
and installed according to any applicable conditions
of acceptability.
Components other than those identified in the
combination motor controller and connected in the
power circuit of the combination motor controller
will require additional evaluation.
Figure 1