UFC 3 -520-01
June 10, 2002
Finally, as an ongoing maintenance consideration, the ATS continuous duty capability
should be achievable with minimal maintenance.
13-5.3.1.3 To meet the above continuous duty requirements, the ATS contact
temperature rise must be well below that established for an 8 -hour rated device. Select
an ATS capable of carrying the maximum continuous load current. Momentary inrushes
need not be included in the continuous load requirement, provided that the ATS is rated
for the inrush. Table 13-3 shows typical ATS continuous current rating s:
Table 13-3. Typical ATS Continuous Current Ratings
Current Ratings
(amperes)
30
600
40
800
70
1000
80
1200
100
1600
150
2000
225
3000
260
4000
400
13-5.3.1.4 Consider oversizing the ATS to be as large in current carrying capability as
its upstream protective device. Although oversizing an ATS will add to the system cost,
it ensures that the ATS does not become the limiting component if loads are added to
the system.
13-5.3.2 Fault Current Withstand Rating.
13-5.3.2.1 An ATS has to be capable of withstanding the stresses and dissipate the
heat energy generated during short circuit currents. ATS withstand current ratings vary
with switch size and type as shown in Table 13-4. An ATS has to be rated for 1) the
available fault current at its location in the electrical system and 2) the expected
duration that the fault current will be present before an upstream overcurrent device (or
the ATS if it has integral overcurrent protection) clears the fault; both design features
are important.
13-17
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