Electrical Wiring Design Notes

Electrical Layout (PEC)

  • The number of outlets on a single circuit depends on the circuit's amperage and the type of outlets used.
    • Standard 15-amp circuit: Typically 8-10 outlets, assuming standard 120-volt outlets and no high-power appliances.
    • Standard 20-amp circuit: Usually 10-12 outlets.
  • These are general guidelines. Reduce the number of outlets or dedicate a circuit to heavy-duty appliances (air conditioners, microwaves, refrigerators).
  • Always check local electrical codes or consult an electrician to ensure safety.

Electrical Professionals

  • Licensed Electrical Practitioner for Design:
    • Professional Electrical Engineer (PEE)
  • Licensed Electrical Practitioner for Electrical Installation:
    • Professional Electrical Engineer (PEE)
    • Registered Electrical Engineer (REE)
    • Registered Master Electrician (RME) (NOT EXCEEDING 600 VOLTS AND 500 kVA)

Electrical Plan Requirements for Building Permit

  • Electrical Plan and Forms must be signed and sealed by a Professional Electrical Engineer (PEE).
  • Electrical Plan contents:
    • Electrical layout
    • Design Analysis
    • Schedule of Loads
    • Single Line Diagram
    • Symbol and Legend
    • Complete Electrical Specification
    • Voltage Drop Calculation
    • Short Circuit Test Computation

General Notes

  • LIGHTING MAX. LOAD: 100 Watts per Lighting Outlet
  • CONVENIENCE OUTLET: At least 2 circuit service each single receptacle shall be no less than 180 Watts/gang
    • Example: 6×2×180/230V=9.396 \times 2 \times 180 / 230V = 9.39 AMPS.
  • SMALL APPLIANCES MINIMUM LOAD: 1,500 Watts or 20 Amp Branch Rating Minimum
  • SERVICE ENTRANCE shall not be less than 8 mm sq. (no.8)
  • LAUNDRY OUTLET MIN. CIRCUIT OF 20 AMPS.
  • DEMAND FACTOR FOR TOTAL CURRENT LOAD: 80 %
  • BRANCH CIRCUIT CONDUCTOR SUPPLYING A MOTOR: NOT LESS THAN 125 % AMPACITY (Aircon, Motor pump, etc.)
  • AIRCON UNIT at 100% Demand Factor + 25% of given largest A.C. Wattage

3 Phase A.C. Electricity

  • 3 Phase A.C. Electricity is a triple circuit. It is used in buildings where loads exceed 50 kVA or more bigger load.
  • The neutral conductor only carries the unbalanced current and zero voltage when the loads on 2 sides are balanced.
  • Single Phase A.C. can be 2 or 3 wires plus the neutral wire designated as "N".
  • 2 wires (ceiling & walls) + "N" is commonly used in residential.

Demand Factor for Multiple Dwelling Units

  • 3-5 Dwelling Units: Use 45% Demand Factor
  • 6-7 Dwelling Units: Use 44% D.F.
  • 8-10 D.U.: Use 43% D.F.
  • 14-15 D.U.: Use 40% D.F.
  • 24- 25 D.U.: Use 35% D.F.
  • 28-30 D.U.: Use 33% D.F.
  • 62 & Over: Use 23% D.F.

Circuit Lighting Load by Area Method

  • Table 4.3 GEN.LIGHTINGLOADBYOCCUPANCY
    • Auditorium, assembly halls, & armories: 8 Watts / sq. m.
    • Banks: 40
    • Barber shop/ parlor: 24
    • Churches: 8
    • Clubs: 16
    • Courtrooms: 16
    • Dwelling units: 24
    • Garage/ commercial storage: 4
    • Hospitals: 16
    • Hotels, Motels, Apartments: 16
    • Industrial / Commercial Loft bldg.: 16
    • Lodge room: 12
    • Office bldg.: 40
    • Restaurant: 16
    • Schools: 24
    • Stores: 24
    • Warehouse / storage: 2
    • Halls, corridors, closets: 4

N.E.C. Circuting Guidelines

  • 30 Watts per sq. m. for residential supply load (excluding garage, porch)
  • 30 Watts/ sq. m. up to 80 sq. mts. for a 20 Amps. circuit (2,400W)
  • or 60 sq. mts. for 15 Amps. circuit (1,800W)
  • Minimum load of 1,200W on a 15 Amps. circuit with a max. area of 40 sq. mts.
  • Max. load of 1,600W on a 20 Amps. circuit with a max. area of 53 sq. mts.
  • Minimum size of conductor wire is No.12 AWG for all convenience outlet.
  • To get No. of outlet:
    • 15 AMPS = 9 / 1.5 = 6 OUTLETS (USE NO.14)
    • 20 AMPS = 12 / 1.5 = 8 OUTLETS (USE NO. 12)

Branch Circuit (House wiring installation)

  • National Electric Code provisions:
    1. Wirings for electrical circuitry shall be of the types RHW,T,THW,TW, THWN, XHHW
    2. On a 15 amp. Circuit, a single appliance shall not draw a max. load of more than 12 amps.
    3. On a 20 amp. Circuit, a single appliance shall not draw a max. load of more than 16 amps.
    4. On a 30 amp. Circuit, a single appliance shall not draw a max. load of more than 24 amps.
    5. The no. of outlets in a circuit shall be limited to:
      • 6 outlets on a 15 amp. circuit
      • 8 outlets on a 20 amp. circuit
    6. Elec. motors, AC, & other similar units w/ a continuous loading shall be computed its actual load not to exceed 80% of the fuse rating.
    7. Service entrance shall not be smaller than 8mm sq.(2 - 4 wires) 110/220v for 2-wires.
    8. Demand load factor for Cooking range = 80%
    9. Demand load factor for AC = 125% of the full load current
  • Phil. Electl. Code Article 6.7: Branch circuit conductor supplying a motor shall have an ampacity not less than 125%
  • Ex. 1.5 HP x 746 w = 1,119 watts / 230v = 4.86 amps. X 125% = 6.07 amps.

Load Schedule:

  1. WATER HEATER: 3000 Watts
  2. MOTOR PUMP: 2,300 Watts
  3. REFRIGERATOR: 1,078 Watts
  4. WASHING MACHINE: 1,760 W or 1 HP = 746 W
  5. COOKING RANGE: 5,000 W
  6. AC / SPARE: 6,000 W or 8,000 W
  7. IRON: 1,200 Watts
  8. LIGHTING OUTLET: 100 Watts maximum per outlet
  9. CONVENIENCE OUTLET: Not less than 180 Watts/gang
  10. TV: 300 Watts
  11. ELECT. FAN: 500 Watts

Wire Size & Ampere Capacity:

WIRE SIZE NO. (AWG Conductor)WIRE SECTION mm SQ.AMPERES CAP.CROSS SECTIONAL (Circular Mils Area)
142 mm sq.154110
123.5 mm sq.206530
105.5 mm sq.3010,380
88 mm sq.40-4516,510
614 mm sq.5526,240
422 mm sq.70-8541,740
230 mm sq.9566,360
150 mm sq.125105,600
0067 mm sq.145133,100
00085 mm sq.165167,800
  • Sq.mm=Circularmil×.0005067Sq. mm = Circular mil \times .0005067
  • 00=133,100Cir.mil×.0005067=67mmsq.00= 133,100 Cir.mil \times .0005067 = 67 mm sq.
  • Usage for building wires and cables:
    • THHN, THWN, TW, UF & TF, XHHW, MTW
  • GOOD ELECTL. CONDUCTOR MATERIALS:
    • SILVER, COPPER, BRASS, LEAD, ALUMINUM, NICKEL, ZINC, IRON, TIN, PLATINUM
  • INSULATORS:
    • RUBBER, MICA, GLASS, PORCELAIN, ASBESTOS, LATEX