Page 391 - Industrial Power Engineering and Applications Handbook

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50 Hz system
Fault level
50kA, 1 sec
________-___
I 1

[Not a recommended practice
when high rupturing capacity
interrupters are available.]
-

. _ . _ . -. _ .
l~ < 8.5kA
i
impedance) I.

< 50kA, 1 sec. 1 sec.
-
All OIG
All OIG feeders
feeders
< 50kA << 5kA

1 1

Figure 13.29 A power distribution scheme illustrating the procedure to assign fault level to a device, component or a bus system

The maximum it can operate is under a locked rotor components or devices used in the circuit. Hence it is
condition of a motor, in which case the maximum not considered in the table.
current may not exceed six to seven times its rated 4 Diversity factor: this applies to column 7 of Table
current, which is moderate and far less than a short- 13.13. Whenever a bus section has to feed a number
circuit condition. Hence, it is not considered in Table of outlets, one can apply the diversity factor as
13.13. discussed in Section 13.4.1(4) to optimize on the size
3 Similarly, a contactor is a simple circuit making and of busbars and also the size of the main incoming
breaking device, and is protected by other protective feeder (Example 13.1).
devices used in association with it. It has no role in 5 Service conditions: on all the ratings so determined,
the decision making for the current rating of other one may apply the applicable service factors as noted