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11.1 PEC Equipment Installation & Wiring Methods
PRC Registered Electrical Engineer REE
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1 Chapter 1: Overview, RA 7920 & Electrical Engineering Ethics
1.1 PRC Board of Electrical Engineering & REE Examination Overview 1.2 Republic Act No. 7920 (New Electrical Engineering Law) & License Classes 1.3 Code of Ethics & Professional Practice for Electrical Engineers
2 Chapter 2: Math — Algebra, Trig & Geometry
2.1 Algebraic Equations, Polynomials & Complex Numbers 2.2 Trigonometry — Identities, Triangles & Spherical Trig 2.3 Analytic & Solid Geometry
3 Chapter 3: Engineering Mathematics — Calculus & Differential Equations
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4 Chapter 4: Engineering Mathematics — Advanced Math & Transform Methods
4.1 Laplace Transforms, Inverse Transforms & Circuit Applications 4.2 Fourier Series, Fourier Transforms & Frequency-Domain Analysis 4.3 Vector Analysis, Linear Algebra, Matrices & Complex Analysis
5 Chapter 5: Engineering Mathematics — Probability, Statistics & Engineering Data Analysis
5.1 Probability Theory, Counting Techniques & Bayes' Theorem 5.2 Engineering Data Analysis I — Descriptive Statistics & Probability Distributions 5.3 Engineering Data Analysis II — Confidence Intervals, Hypothesis Testing & Regression
6 Chapter 6: Engineering Mathematics — Numerical Methods & Analysis
6.1 Numerical Root-Finding & Solution of Linear Systems 6.2 Interpolation, Numerical Integration & Numerical Solution of ODEs
7 Chapter 7: ESAS — Physics, Chemistry & Computer Fundamentals
7.1 Physics for Engineers 7.2 General Chemistry & Materials Science 7.3 Computer Fundamentals, Programming & Data Logic 7.4 Logic Circuits, Switching Theory & Microprocessor Systems
8 Chapter 8: ESAS — Mechanics & Thermal-Fluid Engineering
8.1 Engineering Mechanics — Statics & Dynamics 8.2 Strength of Materials & Mechanics of Deformable Bodies 8.3 Thermal-Fluid Engineering — Thermodynamics & Fluid Mechanics
9 Chapter 9: ESAS — Engineering Economics, Management & Contracts
9.1 Engineering Economics & Depreciation 9.2 Engineering Management & Ethics 9.3 Philippine Electrical Engineering Law, Code & Contracts 9.4 Technopreneurship 101 & Management of Engineering Projects
10 Chapter 10: PEC 1 — Safety, Sizing & Protection
10.1 PEC Fundamentals, Safety Standards & Grounding/Bonding 10.2 Conductor Sizing, Ampacity Adjustment & Voltage Drop 10.3 Overcurrent Protection, Branch Circuit & Feeder Sizing 10.4 Basic Occupational Safety & Health (BOSH) and Electrical Safety Standards
11 Chapter 11: PEC 1 & 2 — Equipment & Utility Systems
11.1 PEC Equipment Installation & Wiring Methods 11.2 Utility Systems, Transformers & Switchgear 11.3 Special Occupancies & Hazardous Locations
12 Chapter 12: Electrical Professional — DC & AC Circuit Fundamentals
12.1 DC Circuit Analysis & Network Theorems 12.2 Single-Phase AC Circuits & Phasor Analysis 12.3 Balanced & Unbalanced Three-Phase AC Circuits
13 Chapter 13: Electrical Professional — EM Fields & Transients
13.1 Electrostatics, Magnetostatics & Maxwell's Equations 13.2 Electromagnetic Waves & Transmission Line Fields 13.3 First-Order & Second-Order Circuit Transients
14 Chapter 14: Electrical Professional — Electronics, Industrial Electronics & Communications
14.1 Electronics 1 & 2 — Semiconductor Devices & Analog Circuits 14.2 Electrical Apparatus & Devices — Industrial Electronics & Power Converters 14.3 Fundamentals of Electronic Communications
15 Chapter 15: Electrical Professional — Transformers & DC Machines
15.1 Single-Phase & Three-Phase Transformers 15.2 Transformer Connections & Special Transformers 15.3 DC Generators & DC Motors
16 Chapter 16: Electrical Professional — AC Synchronous & Induction Machinery
16.1 Synchronous Generators (Alternators) 16.2 Synchronous Motors & Special AC Machines 16.3 Three-Phase & Single-Phase Induction Motors
17 Chapter 17: Electrical Professional — Power Plants & Energy Conversion
17.1 Hydroelectric, Thermal & Combined Cycle Power Plants 17.2 Renewable Energy Systems & Geothermal Power Plants 17.3 Power Plant Economics, Load Curves & Energy Conversion
18 Chapter 18: Electrical Professional — Transmission & Distribution
18.1 Transmission Line Parameters & Performance Models 18.2 Mechanical Overhead Line Design, Underground Cables & Insulators 18.3 Distribution Systems, Substation Layouts & Power Flow Control
19 Chapter 19: Electrical Professional — Power System Analysis
19.1 The Per-Unit System, Base Conversion & Impedance Diagrams 19.2 Symmetrical Components & Unbalanced Fault Analysis 19.3 Load Flow, Economic Dispatch & Power System Stability
20 Chapter 20: Electrical Professional — Protection, Control, Instrumentation & Illumination
20.1 Power System Protection & Protective Relaying 20.2 Industrial Motor Control, Logic Circuits & PLC Automation 20.3 Electrical Instrumentation, Transducers & Measurement Systems 20.4 Illumination Engineering, Lighting Design & Photometrics 20.5 Feedback Control Systems & Research Methods
11.1 PEC Equipment Installation & Wiring Methods
Key Takeaways Explain This Topic AI
Conductor fill limits for conduit and raceways are strictly capped by PEC Part 1 at 53% for 1 conductor, 31% for 2 conductors, and 40% for 3 or more conductors to ensure effective thermal dissipation and prevent insulation damage during pulling.
Motor branch-circuit conductors must be sized for a minimum continuous ampacity of 125% of the motor's Full-Load Current (FLC), while motor feeder conductors must be sized for 125% of the largest motor's FLC plus 100% of the FLC of all other motors connected to the feeder.
Panelboard working space requires a minimum depth of 0.9 m 0.9\ \text{m} 0.9 m (Condition 1), 1.0 m 1.0\ \text{m} 1.0 m (Condition 2), or 1.2 m 1.2\ \text{m} 1.2 m (Condition 3) for nominal voltages of 0– 600 V 600\ \text{V} 600 V , a minimum width of 750 mm 750\ \text{mm} 750 mm or the equipment width (whichever is greater), and headroom of at least 2.0 m 2.0\ \text{m} 2.0 m .
Rigid Metal Conduit (RMC) and Electrical Metallic Tubing (EMT) must be securely fastened within 900 mm 900\ \text{mm} 900 mm of every box, cabinet, or fitting, with maximum support intervals of 3.0 m 3.0\ \text{m} 3.0 m for EMT and up to 6.0 m 6.0\ \text{m} 6.0 m for larger rigid metal conduit sizes.
Equipment Grounding Conductors (EGCs) are sized based on the ampere rating of the upstream overcurrent protective device per PEC Table 2.50.6.13 to provide a low-impedance ground-fault return path capable of rapidly opening overcurrent devices.
Last updated: August 2026
11.1 PEC Equipment Installation & Wiring Methods
The Philippine Electrical Code (PEC Part 1) establishes safety rules and standards for building electrical installations, wiring methods, equipment sizing, and protective grounding. For candidates preparing for the PRC Registered Electrical Engineer (REE) Licensure Examination, mastering PEC wiring methods, raceway fill limits, motor circuit sizing, panelboard clearances, and grounding requirements is vital for both the exam and professional engineering practice.
1. Raceways, Cable Trays, and Conductor Installation
Raceways shield insulated electrical conductors from mechanical damage, environmental degradation, and fire hazards. The choice of raceway depends on location (exposed, concealed, dry, wet, or hazardous).
Types of Common Raceways
Rigid Metal Conduit (RMC): Heavy-wall threaded steel conduit providing maximum mechanical protection in exposed outdoor or harsh industrial environments.
Intermediate Metal Conduit (IMC): Steel raceway with thinner walls than RMC but greater strength than EMT, suitable for outdoor and indoor industrial applications.
Electrical Metallic Tubing (EMT): Unthreaded thin-wall metallic raceway widely installed in commercial and residential concealed or exposed indoor locations.
Flexible Metal Conduit (FMC) & Liquidtight FMC (LFMC): Flexible raceways used to connect vibrating equipment (such as motors and transformers) to fixed conduit systems.
Rigid Nonmetallic Conduit (PVC / HDPE): Flame-retardant, sunlight-resistant, non-metallic raceways ideal for underground direct burial or corrosive chemical atmospheres.
Raceway Conductor Fill Percentages
To prevent excessive heat buildup from conductor resistance losses and avoid stretching or damaging wire insulation during wire pulling, PEC Part 1 (Table 10.1.1.1 / Chapter 9 Table 1) limits the total cross-sectional area of conductors enclosed inside a raceway:
- Number of Conductors Maximum Allowable Fill (All Conductor Types) Lead-Covered Cable Fill
- 1 Conductor 53 % 53\% 53% 55 % 55\% 55%
- 2 Conductors 31 % 31\% 31% 30 % 30\% 30%
3 or More Conductors 40 % 40\% 40% 40 % 40\% 40% Total Conductor Area = ∑ i = 1 n A cond , i ≤ Allowable Fill % × A conduit, internal \text{Total Conductor Area} = \sum_{i=1}^{n} A_{\text{cond},i} \le \text{Allowable Fill \%} \times A_{\text{conduit, internal}} Total Conductor Area = i = 1 ∑ n A cond , i ≤ Allowable Fill % × A conduit, internal
Important PEC Rule: When calculating conduit fill for combinations of phase conductors, neutral conductors, and equipment grounding conductors (EGC), all conductors (including grounding conductors) occupying space within the conduit must be included in the total cross-sectional area calculation.
Support Intervals for Metallic Raceways
EMT Support: Must be securely fastened in place within 900 mm 900\ \text{mm} 900 mm (3 ft) of each outlet box, junction box, cabinet, or fitting, and supported at intervals not exceeding 3.0 m 3.0\ \text{m} 3.0 m (10 ft).
RMC / IMC Support: Must be supported within 900 mm 900\ \text{mm} 900 mm of each box or fitting. Straight runs with threaded couplings may extend support spacing up to 3.0 m 3.0\ \text{m} 3.0 m (for 16 – 20 mm 16\text{--}20\ \text{mm} 16 – 20 mm trade size), 4.5 m 4.5\ \text{m} 4.5 m (for 25 – 32 mm 25\text{--}32\ \text{mm} 25 – 32 mm size), and up to 6.0 m 6.0\ \text{m} 6.0 m (for 40 – 50 mm 40\text{--}50\ \text{mm} 40 – 50 mm or larger trade sizes).
Cable Tray Systems
Cable trays provide rigid structural support for multi-conductor cables and single conductors in commercial and industrial facilities. Types include ladder, ventilated trough, ventilated channel, and solid-bottom trays.
Cable Spacing & Ampacity Derating: Single-layer ladder tray spacing maintains 100 % 100\% 100% conductor ampacity. When multi-conductor cables are installed in unspaced single layers, ampacity is derated to 80 % 80\% 80% of allowable free-air rating, or calculated per PEC ampacity tables.
Continuous Grounding: Metal cable trays must be bonded together across joints with bonding jumpers and connected to the main grounding electrode system to serve as an equipment grounding conductor.
2. Panelboards, Switchboards, and Equipment Working Clearances
Proper working space around electrical equipment ensures that maintenance personnel can inspect, adjust, service, and repair energized equipment safely without risk of arc flash or electrocution.
Equipment Working Space Clearances (PEC Article 1.10 / 0–600 V Systems)
Working space width must be at least 750 mm 750\ \text{mm} 750 mm ( 30 in 30\ \text{in} 30 in ) or the width of the equipment, whichever is greater. Doors or hinged panels must open at least 90 ∘ 90^\circ 9 0 ∘ . The clear headroom above the workspace must be a minimum of 2.0 m 2.0\ \text{m} 2.0 m ( 6.5 ft 6.5\ \text{ft} 6.5 ft ) or the height of the equipment.
Depth of working space measured perpendicular to energized live parts depends on the exposure environment:
Nominal Voltage to Ground Condition 1 (Exposed live parts on one side, non-conductive on other) Condition 2 (Exposed live parts on one side, grounded surface on opposite side) Condition 3 (Exposed live parts on both sides of workspace)
0 – 150 V 0.9 m 0.9\ \text{m} 0.9 m ( 3.0 ft 3.0\ \text{ft} 3.0 ft ) 0.9 m 0.9\ \text{m} 0.9 m ( 3.0 ft 3.0\ \text{ft} 3.0 ft ) 0.9 m 0.9\ \text{m} 0.9 m ( 3.0 ft 3.0\ \text{ft} 3.0 ft )
151 – 600 V 0.9 m 0.9\ \text{m} 0.9 m ( 3.0 ft 3.0\ \text{ft} 3.0 ft ) 1.0 m 1.0\ \text{m} 1.0 m ( 3.5 ft 3.5\ \text{ft} 3.5 ft ) 1.2 m 1.2\ \text{m} 1.2 m ( 4.0 ft 4.0\ \text{ft} 4.0 ft )
Condition 1: Exposed live parts on one side and no live or grounded parts on the opposite side of the working space.
Condition 2: Exposed live parts on one side and grounded parts on the opposite side (e.g., concrete wall, grounded metal enclosure, masonry, or tile).
Condition 3: Exposed live parts on both sides of the working space with the operator positioned between them.
Panelboard Sizing and Overcurrent Protection
Maximum Overcurrent Device Limit: A lighting and appliance branch-circuit panelboard shall not contain more than 42 overcurrent protective devices (excluding main breaker) in a single cabinet.
Overcurrent Protection Rating: Panelboards must be protected by an upstream or main overcurrent protective device rated not greater than the nominal ampacity of the panelboard busbars.
3. Wiring Methods for Motors, Generators, and HVAC Equipment
Motors present unique electrical characteristics due to high locked-rotor inrush currents (typically 5–6 times full-load current) during starting.
Motor Branch-Circuit Conductor Ampacity
Branch-circuit conductors supplying a single motor operating on continuous duty must have an ampacity of not less than 125 % 125\% 125% of the motor full-load current ( I FLC I_{\text{FLC}} I FLC ) listed in PEC motor tables: I branch, min = 1.25 × I FLC I_{\text{branch, min}} = 1.25 \times I_{\text{FLC}} I branch, min = 1.25 × I FLC
Motor Feeder Conductor Ampacity
Feeder conductors supplying a group of two or more motors must have an ampacity not less than 125 % 125\% 125% of the highest rated motor's FLC plus the sum of the full-load currents of all other motors in the group: I feeder, min = ( 1.25 × I FLC, max ) + ∑ i = 1 n − 1 I FLC , i I_{\text{feeder, min}} = (1.25 \times I_{\text{FLC, max}}) + \sum_{i=1}^{n-1} I_{\text{FLC}, i} I feeder, min = ( 1.25 × I FLC, max ) + i = 1 ∑ n − 1 I FLC , i
Motor Disconnecting Means
Must be located in sight from the motor location and driven machinery (within 15 m 15\ \text{m} 15 m / 50 ft and visible).
Must be readily accessible and have a continuous horsepower rating or ampacity rating not less than 115 % 115\% 115% of the motor full-load current.
Generator Conductor Sizing
Conductors carrying current from generator terminals (excluding neutral) must have an ampacity of not less than 115 % 115\% 115% of the nameplate current rating of the generator.
4. Grounding, Bonding, and Equipment Grounding Conductors (EGC)
Grounding prevents dangerous transient voltages on exposed metal frames and creates a low-impedance path to return fault current to the system source, prompting overcurrent devices to open rapidly.
Equipment Grounding Conductor (EGC) Selection
EGCs are sized according to the rating or setting of the automatic overcurrent protective device (fuse or circuit breaker) protecting the circuit upstream, per PEC Table 2.50.6.13:
OCPD Rating / Setting (Amperes) Minimum Copper EGC Size ( mm 2 \text{mm}^2 mm 2 ) Minimum Aluminum / Copper-Clad EGC Size ( mm 2 \text{mm}^2 mm 2 )
- 15 A 2.0 mm 2 2.0\ \text{mm}^2 2.0 mm 2 (#14 AWG) 3.5 mm 2 3.5\ \text{mm}^2 3.5 mm 2 (#12 AWG)
- 20 A 3.5 mm 2 3.5\ \text{mm}^2 3.5 mm 2 (#12 AWG) 5.5 mm 2 5.5\ \text{mm}^2 5.5 mm 2 (#10 AWG)
- 30 A 5.5 mm 2 5.5\ \text{mm}^2 5.5 mm 2 (#10 AWG) 8.0 mm 2 8.0\ \text{mm}^2 8.0 mm 2 (#8 AWG)
- 60 A 5.5 mm 2 5.5\ \text{mm}^2 5.5 mm 2 (#10 AWG) 8.0 mm 2 8.0\ \text{mm}^2 8.0 mm 2 (#8 AWG)
- 100 A 8.0 mm 2 8.0\ \text{mm}^2 8.0 mm 2 (#8 AWG) 14 mm 2 14\ \text{mm}^2 14 mm 2 (#6 AWG)
- 200 A 14 mm 2 14\ \text{mm}^2 14 mm 2 (#6 AWG) 22 mm 2 22\ \text{mm}^2 22 mm 2 (#4 AWG)
- 400 A 22 mm 2 22\ \text{mm}^2 22 mm 2 (#3 AWG) 38 mm 2 38\ \text{mm}^2 38 mm 2 (#1 AWG)
- 600 A 38 mm 2 38\ \text{mm}^2 38 mm 2 (#1 AWG) 50 mm 2 50\ \text{mm}^2 50 mm 2 (#2/0 AWG)
- Solved Board Exam Examples
- Example 1: Conduit Sizing & Fill Percentage Calculation
Problem: Four 38 mm 2 38\ \text{mm}^2 38 mm 2 (THHN copper) ungrounded phase conductors and one 14 mm 2 14\ \text{mm}^2 14 mm 2 (THHN copper) equipment grounding conductor are to be installed inside a single Intermediate Metal Conduit (IMC). The overall cross-sectional area (including insulation) is 82.4 mm 2 82.4\ \text{mm}^2 82.4 mm 2 for each 38 mm 2 38\ \text{mm}^2 38 mm 2 conductor and 34.2 mm 2 34.2\ \text{mm}^2 34.2 mm 2 for the 14 mm 2 14\ \text{mm}^2 14 mm 2 conductor. Determine the total conductor cross-sectional area and the minimum nominal trade size of IMC conduit required under PEC Part 1.
Solution:
Compute total cross-sectional area occupied by all 5 conductors: A total = ( 4 × 82.4 mm 2 ) + ( 1 × 34.2 mm 2 ) A_{\text{total}} = (4 \times 82.4\ \text{mm}^2) + (1 \times 34.2\ \text{mm}^2) A total = ( 4 × 82.4 mm 2 ) + ( 1 × 34.2 mm 2 ) A total = 329.6 + 34.2 = 363.8 mm 2 A_{\text{total}} = 329.6 + 34.2 = 363.8\ \text{mm}^2 A total = 329.6 + 34.2 = 363.8 mm 2
Determine the maximum allowable fill percentage for 3 or more conductors: Allowable Fill = 40 % \text{Allowable Fill} = 40\% Allowable Fill = 40%
Calculate minimum internal cross-sectional area of conduit required ( A conduit, min A_{\text{conduit, min}} A conduit, min ): A conduit, min = A total 0.40 = 363.8 0.40 = 909.5 mm 2 A_{\text{conduit, min}} = \frac{A_{\text{total}}}{0.40} = \frac{363.8}{0.40} = 909.5\ \text{mm}^2 A conduit, min = 0.40 A total = 0.40 363.8 = 909.5 mm 2
Check internal area of standard IMC conduit sizes:
Trade Size 32 mm 32\ \text{mm} 32 mm (1-1/4 in): Internal area ≈ 980 mm 2 \approx 980\ \text{mm}^2 ≈ 980 mm 2 . Total 40 % 40\% 40% allowable fill area = 0.40 × 980 = 392 mm 2 = 0.40 \times 980 = 392\ \text{mm}^2 = 0.40 × 980 = 392 mm 2 .
Since 363.8 mm 2 ≤ 392 mm 2 363.8\ \text{mm}^2 \le 392\ \text{mm}^2 363.8 mm 2 ≤ 392 mm 2 , a 32 mm 32\ \text{mm} 32 mm (1-1/4 inch) trade size IMC conduit is the minimum compliant size.
Example 2: Motor Feeder Conductor Ampacity & Disconnect Sizing
Problem: An industrial subpanel feeds three 3-phase, 460 V 460\ \text{V} 460 V squirrel-cage induction motors operating on continuous duty:
- Motor 1: 20 HP 20\ \text{HP} 20 HP ( I FLC = 27 A I_{\text{FLC}} = 27\ \text{A} I FLC = 27 A )
- Motor 2: 30 HP 30\ \text{HP} 30 HP ( I FLC = 40 A I_{\text{FLC}} = 40\ \text{A} I FLC = 40 A )
- Motor 3: 50 HP 50\ \text{HP} 50 HP ( I FLC = 65 A I_{\text{FLC}} = 65\ \text{A} I FLC = 65 A )
Calculate: (a) the minimum ampacity of the motor feeder conductors, and (b) the minimum rating of the main feeder disconnect switch.
Solution:
Identify the largest motor full-load current ( I FLC, max I_{\text{FLC, max}} I FLC, max ): I FLC, max = 65 A ( Motor 3, 50 HP ) I_{\text{FLC, max}} = 65\ \text{A} \quad (\text{Motor 3, } 50\ \text{HP}) I FLC, max = 65 A ( Motor 3, 50 HP )
Calculate minimum feeder conductor ampacity per PEC rules: I feeder, min = ( 1.25 × I FLC, max ) + I FLC,1 + I FLC,2 I_{\text{feeder, min}} = (1.25 \times I_{\text{FLC, max}}) + I_{\text{FLC,1}} + I_{\text{FLC,2}} I feeder, min = ( 1.25 × I FLC, max ) + I FLC,1 + I FLC,2 I feeder, min = ( 1.25 × 65 A ) + 27 A + 40 A I_{\text{feeder, min}} = (1.25 \times 65\ \text{A}) + 27\ \text{A} + 40\ \text{A} I feeder, min = ( 1.25 × 65 A ) + 27 A + 40 A I feeder, min = 81.25 + 27 + 40 = 148.25 A I_{\text{feeder, min}} = 81.25 + 27 + 40 = 148.25\ \text{A} I feeder, min = 81.25 + 27 + 40 = 148.25 A
Calculate minimum disconnect switch rating ( 115 % 115\% 115% of total full-load currents): I total, FLC = 27 + 40 + 65 = 132 A I_{\text{total, FLC}} = 27 + 40 + 65 = 132\ \text{A} I total, FLC = 27 + 40 + 65 = 132 A I disconnect, min = 1.15 × 132 A = 151.8 A I_{\text{disconnect, min}} = 1.15 \times 132\ \text{A} = 151.8\ \text{A} I disconnect, min = 1.15 × 132 A = 151.8 A
Select standard continuous current rating disconnect switch: 200 A 200\ \text{A} 200 A switch.