Pfannenberg PWS Series - Manual (Page 13)

10
9.2 SCCR Determination
Article 409 of the 2005 National Electric Code (NFPA
70) requires Industrial Control Panels (electrical
panel enclosures) to be marked with a short
circuit current rating. As specified in the National
Electric Code, the Standard for Industrial Control
Equipment, UL508A-2001, Supplement SB, provides
an accepted method for determining the short
circuit current rating of the control panel. The link
to spreadsheets provide guidance for industrial
control panel manufacturers who purchase the
discreet components and assemble combination motor controllers within their panels to achieve a
combination short circuit rating that is higher than
the lowest rated individual component.
Using the technical data sheet and the information
on the cooling unit ID plate, identify the full load
current conditions for the appropriate voltage. The
installation of the cooling unit should be calculated
as a dedicated branch circuit for determining the
SCCR value. All selections should be evaluated based
on the current UL standards for UL508a.
Table 1
Room cooling units rated-Load Current, Amperage
Single Phase 3 3 Phase 3 50 KA 100 KA 200 KA
110 - 120 V 200 - 208 V 220 - 240 V 254 - 277 V 440 - 480 V
Peak
Let-thru
Current 2
Max
Fuse 1
I
p
x 10 3
Max
Fuse 1
I
p
x 10 3
Max
Fuse 1
I
p
x 10 3
9.9 16.0 5.4 8.8 5.0 8.0 6.65 Less 1.8 Less 1000 15 50 KA n/a n/a
16.1 34.0 8.9 18.6 8.1 17.0 --- --- --- --- 2000 30 50 KA 15 100 KA n/a
--- --- --- --- --- --- --- --- Over 1.8 5000 15 50 KA 30 100 KA 30 200 KA
1 Maximum CC class Fuse size that can achieve this branch circuit SCCR value. Smalller values may be used and still achieve equal rating.
2 Circuit capacity amperes based on UL 484 table 52.1
3 Individual units running amperes can be obtained on each unit's technical data sheet.
Example 2: DTS 35xx 460V units has a 5KA IR value
based on UL 484 table 52.1 (see Table 1) and the
amp draw of the unit. If a 15amp Class CC current
limiting feeder circuit is used in combination with
the DTS35xx 460V unit, the maximum allowable
Ipeak of the 15 amp Class CC fuse at an available RMS
fault current of 200 kA is 1700 amps (figure 2). This
value does not exceed the allowable Ipeak of this
unit based on UL SCCR value of Table 52.1. Therefore,
the individual branch circuit SCCR value of this series
combination can support 200 kA IR. (See figure 1.)
Figure 2