Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingEasy
A client has a 3-phase, 4-wire, 208Y/120V electrical service. What is the phase-to-phase voltage between any two of the ungrounded (hot) conductors?
- A208 V
- B120 V
- C240 V
- D277 V
Show answer & explanationAnswer & explanation
Correct answer: A. 208 V
In a 3-phase, 4-wire, Wye (Y) system, the service voltage designation '208Y/120V' means that 208V is the phase-to-phase voltage (voltage between any two hot conductors), and 120V is the phase-to-neutral voltage (voltage between any hot conductor and the neutral).
Why the other options are wrong
- B. 120V is the phase-to-neutral voltage in this system.
- C. 240V is typically found in a Delta system or a single-phase system, not a 208Y/120V Wye system.
- D. 277V is the phase-to-neutral voltage in a 480Y/277V system.
Wye (Y) System Voltages
A 3-phase Wye (star) electrical distribution system provides both phase-to-phase and phase-to-neutral voltages.
- Phase-to-phase voltage (V_LL) = √3 × Phase-to-neutral voltage (V_LN).
- Phase-to-neutral voltage (V_LN) = V_LL / √3.
- Common Wye systems are 208Y/120V and 480Y/277V.
Memory trick: Y-system: Your hot-to-hot is bigger by root 3.