REE: Circuits, Machines, and Power Systems

REE circuits and machines is the heart of the Registered Electrical Engineer licensure exam. Electrical Engineering Professional Subjects — worth 45% of your rating on its own — pulls heavily from circuit analysis, electric machines, and power systems. It's the longest paper (six hours), the most calculation-heavy, and the one that most determines whether your general weighted average clears 70%. Reviewers who memorise without practising live calculations come unstuck under exam pressure.

PRC held the 2026 Registered Electrical Engineers exams on April 21–22 and September 5–6, 2026. The national pass rate was 57.49% in April and 49.31% in September (1,676 of 3,399), after 61.37% in April 2025 and 38.92% in August 2025. About 9,900 examinees sat the REE across 2025. The next REE is expected around April 2027 — PRC has not yet published its 2027 schedule.

What the Paper Covers

The REE has three subject groups: Mathematics (25%), Engineering Sciences and Allied Subjects (30%), and Electrical Engineering Professional Subjects (45%). From the September 2026 sitting, PRC changed the order: Day 1 is Engineering Sciences and Allied Subjects (8 AM–12 NN) then Electrical Engineering Professional Subjects (1–7 PM); Day 2 is Mathematics (8 AM–1 PM). Check the programme for your sitting.

PRC's programme lists the professional subjects' topics but not item counts. Group them like this:

• DC and AC circuit analysis — Kirchhoff's laws, mesh and nodal, AC steady state, transients, three-phase.
• Transformers — single-phase, three-phase, equivalent circuit, regulation, efficiency.
• Induction motors — equivalent circuit, slip, torque-speed, starting, control.
• Synchronous machines — generators and motors, voltage regulation, parallel operation.
• DC machines — generators and motors, characteristics, control.
• Power systems — transmission, distribution, interconnection, substation design, fault analysis, per-unit system.
• Protection and control — relays, circuit breakers, coordination.
• Illumination and wiring design for buildings.
• Power and industrial electronics — diodes, thyristors, converters.

The Recurring Problem Archetypes

Three-Phase Circuit Analysis

Wye-wye, wye-delta, delta-delta connections. Line vs phase quantities. Power calculations using line values. The trap is forgetting the √3 factor when converting between line and phase.

Single-Phase Transformer Equivalent Circuit

Open-circuit and short-circuit tests. Calculate equivalent resistance and reactance referred to primary or secondary. Voltage regulation at given power factor. Drill the per-unit conversion as well.

Three-Phase Transformer Banks

Wye-delta, delta-wye connections. Phase shift between primary and secondary.

Induction Motor Performance

Slip given. Calculate rotor frequency, rotor current, developed torque, efficiency. The torque-slip curve. Memorise the equivalent circuit and the relationship between slip and rotor copper losses.

Synchronous Generator Voltage Regulation

Synchronous reactance given. Calculate excitation EMF for a given load. Voltage regulation.

Transmission Line Parameters

Series impedance and shunt admittance per unit length. Short, medium, long line classifications. ABCD parameters.

Symmetrical Fault Analysis

Three-phase fault on a power system. Per-unit conversion. Fault current calculation.

Where Reviewers Leak Points

• Per-unit base mismatch — using one MVA base for the system but forgetting to convert transformer reactance to that base. Common trap.
• Power factor sign convention — leading vs lagging. Capacitive vs inductive. Sketch the phasor on every problem.
• Slip calculation — synchronous speed minus mechanical speed, divided by synchronous speed. Easy to slip the sign under pressure.
• PEC references — drill from the current Philippine Electrical Code edition, not older ones.

An 8-Week Plan

1. Weeks 1–2 — DC and AC circuit fundamentals. Three-phase systems. 80 problems.
2. Week 3 — Transformers. Single-phase and three-phase. 50 problems.
3. Week 4 — Induction motors. 50 problems.
4. Week 5 — Synchronous and DC machines. 50 problems.
5. Week 6 — Power systems. Transmission, fault analysis, per-unit. 50 problems.
6. Week 7 — Protection, illumination, wiring design, electronics. 60 problems.
7. Week 8 — Full practice papers (six hours for the professional subjects). Two minimum.

The Per-Unit System

Master this. Power system and transformer problems hinge on per-unit conversion done correctly.

Why Per-Unit

It normalises calculations across multiple voltage levels in a power system. A transformer's per-unit impedance is the same on either side. Per-unit fault currents simplify cross-system analysis.

The Conversion Rules

• Choose a base MVA and base voltage on one side of the system.
• Base current = base MVA / (√3 × base voltage line) for three-phase.
• Base impedance = base voltage line² / base MVA.
• Per-unit impedance = actual impedance / base impedance.
• To convert per-unit between bases, multiply by (new MVA / old MVA) and (old kV / new kV)².

Drill the conversion until automatic. Problems often present a transformer rated on one MVA base and ask for fault current on a different system base.

Power System Protection

The high-yield topics:

• Overcurrent relays — definite-time, inverse-time, instantaneous. Coordination with downstream relays.
• Differential protection — for transformers and generators. Restraining and operating coils.
• Distance protection — for transmission lines. Zone reach and timing.
• Circuit breaker ratings — interrupting capacity, BIL, voltage class.

Illumination, Wiring Design and the PEC

Illumination and wiring design for buildings are listed under the professional subjects; the Philippine Electrical Code (Parts 1 and 2) is listed under Engineering Sciences and Allied Subjects. Cover them together:

• Conductor sizing — ampacity tables, voltage drop calculations.
• Branch circuits and feeders — load calculations.
• Grounding — equipment grounding, system grounding.
• Motor circuits — overload and short-circuit protection.
• Illumination — lumen method, point-by-point method, recommended levels.

How This Subject Connects to the Other REE Subjects

Mathematics covers algebra through differential equations, Fourier series and Laplace transforms. Engineering Sciences and Allied Subjects covers chemistry, physics, engineering mechanics, thermodynamics, fluid mechanics, engineering economics, EE law and ethics, contracts and specifications, computer fundamentals and the PEC. The professional subjects build on both.

Cross-references matter. Complex numbers and Laplace transforms from Mathematics feed AC steady-state and transient analysis. Mechanics and thermodynamics feed prime movers and energy conversion. Drill in parallel.

You pass with a 70% general weighted average and no subject group below 50% (RA 7920). With 45% of the rating, the professional subjects move your average more than anything else.

Where REE Differs From Other Engineering Boards

REE puts almost half its weight on one subject group. The CELE has heavier individual structural problems, the ME blends thermodynamics with design, and the ECE blends communications theory with applications. REE is sustained calculation across circuits, machines, and power systems — and the per-unit system threads through everything.

That makes pacing critical. Once you see the paper, set a per-item time budget, let the quick circuit items bank time, and cap the harder transformer and machine problems. Drill full practice papers under timed conditions.

Related Guides

For broader context, see the engineering board review pillar. Electronics reviewers can compare the AC analysis block with the ECE electronics systems guide. Mechanical reviewers can cross-reference materials topics with the ME machine design guide. PRC posts the exam programme for each sitting on prc.gov.ph — confirm the subjects and schedule before you sit.

FAQ

How heavy is per-unit on the paper?

PRC doesn't publish a topic split, but per-unit threads through the power systems and transformer problems. Drill it cold.

Is the PEC tested in detail?

The Philippine Electrical Code, Parts 1 and 2, is named in the programme. Cover conductor sizing, voltage drop, motor circuits and grounding, and read the current edition once.

Are electronics fundamentals heavy?

Power electronics and industrial electronics are named in the professional subjects. Cover diodes, thyristors, converters and op-amps at a practical level, but don't over-prep.

What's the worst trap?

Per-unit base mismatch. The cleanest path is to set the base, convert all impedances at the start, then run all calculations in per-unit.

What to Do This Week

• Engineering Board Review Pillar
• ECE Electronics Systems Strategy
• ME Machine Design Strategy
• REE Exam Overview