(4) ELECTRICAL SYSTEM DESIGN - PEC - WIRING AND PROTECTIONS (Chapter 2 - Part 1)

Electrical System Design: Wiring and Protection

Introduction

Glossary of Key Terms

• Grounded Conductor: A system or circuit conductor that is intentionally connected to the earth or to some conducting body that serves in place of the earth.

• Branch Circuit: The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

• Feeder: The circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

• Overcurrent Protection: A device such as a fuse or circuit breaker that is designed to interrupt the flow of current when it exceeds a predetermined value.

• Grounding: The act of connecting a system or equipment to the earth or to some conducting body that serves in place of the earth.

• Bonding: The permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.

• Surge Arrester: A protective device for limiting voltage surges on equipment by discharging or bypassing surge current.

• Transient Voltage Surge Suppressor (TVSS): A device designed to limit transient voltage surges in an electrical power system.

• Multi-wire Branch Circuit: A branch circuit that consists of two or more ungrounded conductors that have a potential difference between them, and a grounded conductor that has equal potential difference between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

• GFCI (Ground Fault Circuit Interrupter): A device intended for the protection of personnel that detects ground faults and interrupts the circuit.

• AFCI (Arc Fault Circuit Interrupter): A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.

• Continuous Load: A load where the maximum current is expected to continue for three hours or more.

• Receptacle Outlet: An outlet where one or more receptacles are installed.

• Ampacity: The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

• Demand Factor: The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration.

Lecture by Professor Roger Flores from the Department of Electrical Engineering at Central Mindanao University.Subject: E67 - Electrical System Design, Chapter 2: Wiring and Protection.Reference: Philippine Electrical Code, Edition 2017.

Chapter Overview

Key Topics:

• Identification of Grounded Conductors: Understanding the importance and methods for accurately identifying grounded conductors to maintain safety in electrical installations.

• Circuit Definitions:Detailed explanations of various circuit types including run circuits, feeders, and branch circuit feeders, emphasizing their roles in the overall electrical system.

• Service Calculations:Comprehensive calculations for branch circuits and feeders, as well as overall service requirements to ensure adequate power distribution.

• Overcurrent Protections:Discussion on various methods of overcurrent protection, including circuit breakers and fuses, and their critical role in preventing equipment damage and fire hazards.

• Grounding and Bonding:Essential principles of grounding and bonding to ensure electrical safety and system reliability, including effective grounding techniques.

• Surge Arrestors:Application and importance of surge arrestors for systems exceeding 1000 volts to protect against voltage spikes caused by lightning or switching surges.

• Transient Voltage Protection:Strategies to safeguard electrical systems from transient voltage sources, ensuring consistent operational integrity.

Grounded Conductors

Definition:

A grounded conductor is intentionally connected to the ground to ensure safety by providing a low-resistance path to divert fault currents.

Identification Methods

• Use of Tape/Paint: Utilize white or gray tape or paint to signify grounded conductors effectively.

• Size Specifications: For grounded conductors of size 14 mm squared or smaller:

  • Continuous white or gray outer finish

  • Three continuous white stripes on the insulation of the wire to facilitate easy identification

• Larger Conductors: Grounded conductors larger than 14 mm squared must also adhere to these identification rules.

Flexible Cords

• Insulated conductors for grounding must be distinctly marked to avoid confusion with non-grounded conductors, ensuring safety in usage.

Article 2.10 - Branch Circuits

Scope:

Covers all types of branch circuits in residential and commercial settings, excluding specific provisions for motor loads.

Circuit Ratings:

Settings for branch circuits rated for 15A, 20A, 30A, 40A, and maximum 50A circuits are crucial for meeting various operational demands.

Specification:

Considerations for circuit ratings must align with the capacity and specifications of the associated overcurrent device to prevent failures.

Multi-Wire Branch Circuits

• Permitted configurations originating from the same panel board if correctly managed with a means to simultaneously disconnect all ungrounded conductors.

• Multi-wire branch circuits should primarily supply line-to-neutral loads, with defined exceptions for specific applications, enhancing flexibility and efficiency.

Identification Requirements

• Grounded Conductors: Must be identified according to strict specifications utilizing color coding or marking tape to ensure clear identification.

• Equipment Grounding Conductors: Must also possess identifiable markings to prevent safety incidents.

Voltage Limitations

• Nominal Voltage: Established to not exceed specific values, such as 230 volts for dwelling units, to ensure human safety and equipment protection.

• Special Provisions: Detailed guidance provided for installations at 277 volts to maintain clarity in system design and safety protocols.

Ground Fault Circuit Interrupters (GFCI)

• Required for Receptacles: Essential in areas like bathrooms, garages, basements, kitchens, and outdoor locations to protect users from electrical hazards.

Branch Circuits for Appliances

Requirements:

Specific requirements governing branch circuits supplying lighting and motor appliances, ensuring adequate power distribution for both safety and functionality.

Kitchen Branch Circuits:

• Mandated dedicated branch circuits must be allocated for small appliances, with a minimum rating of 20A, to prevent overloads and enhance usability in kitchen areas.

Arc Fault Circuit Interrupters (AFCI)

• Essential for providing protection against arcing faults, particularly in dwelling units, by detecting arc faults and disconnecting the circuit to prevent fires.

• Installation must adhere to stipulated criteria based on proximity to branch circuit devices to ensure effectiveness.

Receptacle Outlet Requirements

Location:

Strategically placed within proximity for easy accessibility, particularly emphasized in kitchens, bathrooms, and garages.

Minimum Number:

Determined by area size and intended usage, with a greater number of outlets required in kitchens for efficient operation of small appliances.

Conclusion

Emphasizes the critical importance of adhering to the Philippine Electrical Code in ensuring safety and proper installations in all aspects of electrical wiring and system design, promoting both user safety and equipment reliability.