USCG Exam PracticeElectrical fundamentals — DC/AC, motors, distribution
Under 46 CFR §111.51-3, the average asymmetrical short-circuit current for an AC system below 1500 kW aggregate generating capacity is calculated as:
- A. 10 times aggregate rated generator currents plus 6 times aggregate rated motor currents.
- B. 10 times aggregate rated generator currents plus 4 times aggregate rated motor currents.
- C. 8 times aggregate rated generator currents plus 4 times aggregate rated motor currents.
- ✓ 8 times aggregate rated generator currents plus 3 times aggregate rated motor currents.Correct
Why D is correct
46 CFR §111.51-3(c) specifies that the average asymmetrical short-circuit current for an AC system is 8 times the aggregate normal rated generator currents plus 3 times the aggregate normal rated motor currents. The 10× generator and 4× motor multipliers apply to the maximum asymmetrical AC value under §111.51-3(b).
Cited:46 CFR §111.51-3