Three-phase integrated

1. Read the nameplate/service label: 208Y/120? 480Y/277? 480 Δ?
2. Meter L-L and L-N; confirm √3 story.
3. Clamp three lines on the problem motor; check balance and rotation.
4. If PF or feeder loading is the complaint, measure kW/kVAR; consider capacitor stages.
5. If generation is involved, separate kW and kVAR sharing issues.
6. Document values so the next tech inherits a baseline.

• Capacitors and XC explain what PF banks are doing
• RLC/resonance explain why banks and VFDs sometimes fight
• Transformers (next courses) will reconnect wye and delta again at larger scale

• Why is 120 V L-N giving 208 V L-L, not 240?
• When is ILine equal to IPhase, and when is it √3 larger?
• What changes if PF rises from 0.7 to 0.95 at fixed kW?
• What do you measure to catch single-phasing?
• What paralleling conditions must match before closing?

If you can answer without notes, Unit 27 landed.

Final drill:

1. 277 L-N → expected L-L? (480)
2. Delta ILine=34.64 A → IPhase? (20 A)
3. 480 V, 10 A, PF 0.9 → P? (~7.48 kW)
4. Single-phasing: which meter catches it fastest? (clamp)
5. Caps online at light load risk? (leading PF)

“This is a 480Y/277 wye. Motors see 480 L-L. L-N lighting lands on 277. Line current equals phase current in the supply wye. Power is √3 EI PF. If we add PF caps, amps should drop at the same kW unless we overcorrect.”

Deliver that cleanly and the course did its job.

Transformers will reconnect these same wye/delta ideas on primary and secondary windings. Keep the pocket table.

Situation. New helper orientation at a 480Y/277 V plant: correctly predicts 480 L-L and 277 L-N, clamps a delta-connected motor expecting ILine as nameplate FLA, and explains why adding a PF bank should drop feeder amps without reducing shaft work.

What happened. Topology + power + correction language used together.

Applied lesson. Integration is fluent use of the pocket table on live equipment.

### Teaching pause — say this out loud

Before you leave this lesson, explain the main idea to an imaginary first-month helper in under one minute. If you need the book open to do it, reread How it works once more. Field diagnosis only helps after the concept is yours.

Also sketch the key diagram from memory (triangle, wye/delta, filter shape, or charge curve — whichever this lesson used). Labels beat artistic skill.

### Why this lesson matters on Monday morning

Three-phase integrated is not trivia. You will meet it when a meter reading looks “impossible,” when a replacement part is almost right, or when a helper asks why the book uses √3 or lead/lag. Master the model here so the next call is pattern recognition, not panic.

Common Monday uses: verify a nameplate against clamps, explain a PF or capacitor change to a customer, or catch a miswired series/parallel or wye/delta assumption before energizing.