A journeyperson is connecting a 120/208 V, 3-phase, 4-wire transformer in a commercial building. Before connecting the secondary conductors to the panelboard, the electrician must verify the phasing. What is the safest and most accurate method to do this?

Question: A journeyperson is connecting a 120/208 V, 3-phase, 4-wire transformer in a commercial building. Before connecting the secondary conductors to the panelboard, the electrician must verify the phasing. What is the safest and most accurate method to do this?

Answer options:

• Momentarily flash the secondary leads to check for arc intensity. ✅ Use a phase rotation meter or multimeter to confirm phase sequence and voltage between phases and to neutral.
• Observe the rotation of a small test motor connected to the secondary side.
• Consult the transformer's nameplate and assume the outgoing phases are correctly sequential.

Correct answer: Use a phase rotation meter or multimeter to confirm phase sequence and voltage between phases and to neutral.

Explanation: Using a phase rotation meter or multimeter is the safest and most accurate method to verify phase sequence and voltage without creating dangerous conditions. "Flashing" leads is extremely dangerous. Observing a test motor's rotation is less precise and still involves connecting to energized components. Assuming correct sequencing based on a nameplate can lead to costly and dangerous errors if wiring is not verified.