USCG Exam PracticeMotor controllers and remote control
In an ungrounded three-phase AC system aboard a vessel, how many motor-running protective devices (overload coil or heater type relay) are required per 46 CFR §111.70-1, and in which conductors 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 any ungrounded conductor
Why B is correct
46 CFR §111.70-1(b) states that in ungrounded three-phase AC systems, only two motor-running protective devices need be used, placed in any two ungrounded conductors, except when a wye-delta or delta-wye transformer is used.
Cited:46 CFR §111.70-1