When checking a 3-phase panel, you read 120V from Phase A to Neutral, 120V from Phase B to Neutral, and 208V from Phase C to Neutral. What type of electrical system are you testing?
Answers
AA 240/120V 3-phase, 4-wire high-leg delta system
BA 208/120V 3-phase, 4-wire wye system
CA 480/277V 3-phase, 4-wire wye system
DA corner-grounded 240V delta system
Correct answer: A — A 240/120V 3-phase, 4-wire high-leg delta system
In a high-leg (or wild-leg) delta system, the center tap of one transformer is grounded, making the voltage from the high leg (typically Phase C) to neutral exactly √3 * 120V = 208V.
MIFOTRA exam practicealigned to NFPA 70 / IEC 60364·4 marks·Hard