USCG Exam PracticeMotor controllers and remote control
In an ungrounded three-phase AC system, how many motor-running protective devices are required per 46 CFR §111.70-1, and where must they be placed?
- A. Three devices, one in each ungrounded conductor
- ✓ Two devices, in any two ungrounded conductorsCorrect
- C. One device, in the grounded neutral conductor
- D. Two devices, one in the grounded conductor and one in an ungrounded conductor
Why B is correct
46 CFR §111.70-1(b) specifies that in ungrounded three-phase AC systems, only two motor-running protective devices need be used, placed in any two ungrounded conductors. This exception does not apply when a wye-delta or delta-wye transformer is used.
Cited:46 CFR §111.70-1