FE Electrical & Computer Practice Question Solution included after investigation
CASE E-029 · FE

The Motor Load That Drew More Current Than the kW Suggested

The load was only 30 kW, but the feeder current was much higher than the kW-only calculation predicted.

▶ INTERACTIVE CASE FILE • 5–10 MIN • CLICK TO INVESTIGATE

Inspect, commit, prove, fix, and sign off.

Case E-029 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field — in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A balanced 480 V three-phase motor load consumes 30 kW at 0.75 power factor. A feeder review estimates current as 30,000/(√3×480) = 36.1 A. In operation, current is about 48 A. Diagnose the missing term, calculate the actual line current, and determine the current after correcting power factor to 0.95.

Power Systems Electrical & Computer Design Verification Root Cause Analysis Safe Correction
E-029
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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DEBRIEF (LOCKED)

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Find the root cause, confirm the fix, and see how this connects to the exam.

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🔒Exam takeawayComplete the case
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

The feeder current was underestimated.

What was assumed

The load was treated as unity power factor.

Corrected model

Use P = √3 V_L I_L pf.

QUICK ANSWER

For a balanced three-phase load, P = √3 V_L I_L pf. At 30 kW, 480 V, and pf = 0.75, the line current is about 48.1 A. Omitting power factor gives only 36.1 A.

ENGINEERING TAKEAWAY

For a balanced three-phase load, P = √3 V_L I_L pf. Lower power factor requires more line current for the same kW and voltage.

CASE QUESTIONS

Questions this case should settle.

How do you calculate three-phase current from kW and power factor?

Use I = P/(√3 V_L pf).

Does improving power factor reduce current?

Yes. For fixed real power and line voltage, higher power factor reduces line current.

NEXT FE PRACTICE QUESTION

The 8 Ohm Load That Became 128 Ohms

Power Systems · 5–10 min

Continue Practice →
WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

Most cases are designed for a focused 5–10 minute investigation.

Are the cases aligned with engineering exams?

Each case is mapped to a verified exam, subject, topic, and misconception before publication.

What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.