Electrical Design Principles

• The text discusses building electrical design principles, focusing on standards to ensure safety for people and buildings.

Electrical Codes, Licenses, and Permits

• Electrical codes specify minimum safety provisions for people and property regarding electricity and electrical equipment, applying to both manufacturing and installation.
• The National Electrical Code (NEC) is a model code established in 1887, sponsored by the National Fire Protection Association (NFPA) since 1911.
• The Philippine Electrical Code (PEC) is used nationally to protect persons and buildings from electrical hazards, with provisions necessary for safety and legal enforcement.
• PEC's primary objective sets standards for materials, quality, and electrical works for the safe use of electricity in various applications.
• The purpose of PEC includes practical safeguarding, adequacy of safety measures (Fine Print Notes included), and serving as a design specification for licensed practitioners.
• Municipalities require licenses for individuals installing electrical systems.
• Licensed electrical practitioners, such as RMEs and REEs approved and sealed by a PEE, are required for electrical installations.
• Municipalities require permits before any electrical installations or changes.
• Owners or licensed practitioners must obtain electrical permits from building officials.
• Complete electrical plans are needed for review and approval before installation, checked by electrical inspectors during scheduled visits before wiring concealment.

Electrical Construction Drawings

• Shows the layout and design of an electrical installation.
• A complete set of construction drawings and specifications are required.
• Construction drawings and details generally required:
• Complete plans and specifications of all electrical work
• Labeling criteria for all electrical equipment
• Lighting floor plans
• Power floor plans
• Exit sign/means of egress lighting location and power supply
• Panelboard schedule
• Lighting fixture schedule
• Symbol schedule and diagrams

Review of Design Requirements

• Location plans guide electrical design engineers, inspectors, bidders, and others.
• Electrical layouts show the interconnection of service components and occupancies.
• Legends or symbols are used in electrical plans to indicate electrical components.

General Notes and Specifications

• Show nature of electrical service including:
• Number of phases
• Number of wires
• Voltage and frequency
• Examples of electrical service:
• 230V, 60Hz, single phase, 2W (common in provinces)
• 120/240V (split-phase), 60Hz, single phase, 3W+1N (used in cities)
• 230V/400V, 60Hz, three phase (used in commercial buildings)
• Types of wiring:
• Cleat wiring (temporary, rarely used)
• Casing and capping wiring(cables carried through wooden casing enclosure)
• Batten wiring
• Lead sheathed wiring
• Conduit wiring
• Surface wiring (conduits on walls or roofs)
• Concealed conduit wiring (conduits hidden in walls)
• Indication of special equipment, is needed for the:
• Rating
• Hertz
• Number of Poles
• KAIC Rating
• Types of grounding in building electrical systems:
• System grounding (provides protection against electric shock, lightning, and fires)
• Equipment grounding (bare or green-colored conductor used in appliances).
• Clearance and mounting height for electrical panels:
• Panels must be at least 4 feet off the ground (max 6 feet)
• Allow for at least a 90-degree panel door opening
• Mounting Height of devices:
• Switches: 48 inches
• Outlets: 12 inches

Other Elements of Note

• Schedules of Loads: a load tabulation indicates branch circuits, ratings, power source, and wiring details.
• Single Line or Riser Diagram: indicates service interconnection, sizes, ratings, and voltage drops.
• Title Block: strip containing installation details, owner information, engineer details, sheet contents, scale, and sheet number.
• Design Analysis: this is a selection of the following:
• Wire and conduit sizes for circuit types
• Overload protective device ratings and trip settings
• Short circuit current and interrupting capacity
• Design Process: starts from architectural layouts.
• Preparations: development of electrical design, arrangement of electrical plan to avoid overcrowding in the electrical plan.

Design Example

• Dwelling Unit: 100 sq.m. with three 20A small appliance branch circuits, one 20A laundry circuit, 10kW electric range, a 5kW clothes dryer and two ¾ HP and one 1.5HP air conditioning units.
• Branch Circuits:
• Lighting Loads
• Small Appliance Loads
• Laundry Loads
• 10kW Electric Range
• and more

Computation of Loads for a Typical Residential Unit

• Calculation of general lighting, small appliance, and laundry circuit loads. Including wire sizes, conduit types, and circuit breaker specifications.
• Calculating the ampacity of wire and branch circuit protection for air conditioning units, with code references.

Design example load computations:

• General lighting: 3,300 VA, using a 20-ampere breaker with 2-3.5 mm² THHN copper wire
• Small appliance load: 4,500 VA, three 20-ampere breakers, 2-3.5 mm² THHN copper wire.
• Laundry circuit load: 1,500 VA, one 20-ampere breaker, 2-3.5 mm² THHN copper wire.
• Clothes dryer: 5,000 VA, one 30-ampere breaker, 2-5.5 mm² THHN copper wire.
• Calculations for determining total computed load using demand factors.

Demand Factors and Service Equipment

• First 3,000 Volt-Amperes @ 100% Demand Factor
• Remainder @ 35% Demand Factor, = (11,300 VA x 0.35)
• Current rating for protective devices using non-time delay fuses.

Project Requirements:

• Lighting Layout
• Power Layout
• Schedule of Loads
• Riser Diagram
• Branch Circuit Computations
• Location