USCG Exam PracticeElectrical fundamentals — DC/AC, motors, distribution
On a vessel with an aggregate generating capacity below 1500 kW, what is the assumed maximum short-circuit current for a DC system under 46 CFR §111.51-3?
- A. 8 times aggregate rated generator currents plus 3 times aggregate rated motor currents.
- B. 10 times aggregate rated generator currents plus 4 times aggregate rated motor currents.
- ✓ 10 times aggregate rated generator currents plus 6 times aggregate rated motor currents.Correct
- D. 8 times aggregate rated generator currents plus 6 times aggregate rated motor currents.
Why C is correct
46 CFR §111.51-3(a) specifies that the maximum short-circuit current for a DC system is 10 times the aggregate normal rated generator currents plus 6 times the aggregate normal rated currents of all motors that may be in operation. The 8× and 3× multipliers apply to the average asymmetrical AC short-circuit current under §111.51-3(c).
Cited:46 CFR §111.51-3