chapter 3

• Electric Circuit


  The complete path traversed by an electric current. The entire house wiring installation.
• Branch Circuit


  The circuit conductors between the final over current protective device (fuse or circuit breaker) and the outlets.
• What a branch circuit comprises

  • The source of voltage
  • The wiring
  • The load
• Considerations for good circuitry design

  • Flexibility of the circuit
  • Reliability and efficiency of service
  • Safety of the circuitry
  • Economy as to cost
  • Energy consideration
  • Space allocation
• Flexibility of the circuit

  The installation can accommodate all probable pattern arrangements and location of the loads for expansion, or future development.
• Reliability and Efficiency of Service


  To have a continuous service and supply of power that are all dependent on the wiring system.
• Factors determining reliability of electric power in a facility


  • The utility service
  • Building electric system
• Safety


  Independent service can be used in lieu of emergency equipment as backup for normal services.
• Principles to consider for reliability of the circuitry

  • Provide double emergency power equipment at selected weak points in the system
  • The electrical service and the building distribution system must act together so that the power can reach the desired point of service
  • Critical loads within the facility must be pinpointed to determine the best way to serve them by providing a reliable power either from the outside source, or by standby power package for them
  • The system design must readily detect any equipment failure and to be corrected automatically
• Economy


  Refers to the initial cost as well as the operating costs. These two cost-factors stand in inverse relationship to one another.
• Effects of acquiring low cost equipment

  • High energy cost
  • Higher maintenance cost
  • Shorter life
• Factors to consider for Energy Consideration

  • Energy laws and codes
  • Budget
  • Energy conservation technique
  • Energy control
• Factors to consider for Space Allocation

  • Easy maintenance
  • Ventilation
  • Expandability
  • Centrality
  • Limitation of access
• Types of Branch Circuits

  • General purpose branch circuit
  • Appliance branch circuit
  • Individual branch circuit
• General purpose branch circuit

  Supplies outlets for lighting and appliances, including convenience receptacles.
• Appliance branch circuit


  Supplies outlets intended for feeding appliances. Fixed lighting however, is not supplied.
• Individual branch circuit


  Designed to supply a single specific item.
• Electrical circuitry


  • No optimum or perfect way of doing it
  • Certain rules and guidelines promulgated by the National Electrical Code (NEC) for flexibility, economical and convenient way of doing circuitry
• NEC requirements for residential load

  1. Sufficient circuitry to supply 30 watts per square meter in buildings excluding porches, garages and basements

  2. Requirement of 30 watts per square meter up to 80 sq. m. for a 20 amperes circuit (2,400 watts) or 60 sq. m. for 15 amperes circuit (1,800 watts)
• Good practice guidelines for load

  • Load should not exceed 1,600 watts for a 20 amperes circuit and 1,200 watts for a 15 amperes circuit
  • Minimum load of 1,400 watts on a 15 amperes circuit with a maximum area of 40 square meters
  • Maximum load of 1,600 watts on a 20 amperes circuit with a maximum area of 53 square meters
• NEC requirements for kitchen and other appliance circuits

  1. Minimum of 20 amperes appliance branch circuit to feed all small appliance outlets in the kitchen, pantry, dining and family room

  2. General purpose branch circuit shall be rated at 20 amperes, wired with No. 12 AWG being the minimum size of conductor for all convenience outlets
• Calculating number of outlets for 15 and 20 amperes circuits

  1. For 15 amp circuit: 9 amps / 1.5 amps per outlet = 6 outlets

  2. For 20 amp circuit: 12 amps / 1.5 amps per outlet = 8 outlets
• Convenience receptacles planning


  • Each area should be provided approximately with different circuits for reliability of service
  • All kitchen outlets should be fed from at least two circuits
  • All receptacles are potential appliance outlets and at least two circuits shall be supplied to serve them
• Certain outlets designed as appliance outlets

  • All kitchen receptacles
  • Dining room receptacles
  • One in the living room
• NEC requirements for laundry outlets

  At least one 20 amperes circuit supply the laundry outlets
• If air conditioner is anticipated, provide a separate circuit for this particular appliance
• Good practices in circuiting

  • Lighting and receptacles should not be combined in a single circuit
  • Avoid connecting all building lights on a single circuit
  • Lighting and receptacles should be supplied with current from at least two circuits so that, if a single line is out, the entire area is not deprived of power
  • Do not allow combination switch and receptacle outlets
  • Provide at least one receptacle in the bathroom, and one outside the house, both must be Ground Fault Circuit Interrupter (GFCI) type
  • Provide switch control for closet lights, pull chain switch is a nuisance
  • Convenience outlets limited to 6 on a 15 amperes circuit and 8 on a 20 amperes circuit
  • Convenience outlets shall be laid out so that no point on a wall is more than 6.00 meters from an outlet, use a grounding type receptacle only
• Clearing


  The action of the over current protective device that clears the circuit of the fault or over current load
• What over current protective devices protect

  • The wiring
  • The transformer
  • The lights
  • Appliances and other equipment
• Conductors shall be protected against over current in accordance with their ampacities
• Over Current


  Any current in excess of the rated capacity of the equipment or the rated ampacity of the conductor
• Fuse


  An over current protective device with a circuit opening fusible element which opens (breaks) when there is an over current in the circuit
• Fuse types

  • Cartridge type enclosed in an insulating fiber tube
  • Plug Fuse type enclosed in a porcelain cap
• Circuit Breaker


  An over-current protective device designed to function as a switch, equipped with an automatic tripping device to protect the branch circuit from overload and ground fault
• Advantages of Circuit Breaker over Fuse

  • The circuit breaker acts as a switch aside from being an over current protective device
  • Unlike the fuse that has to be discarded after it was busted due to an over current flow, the circuit breaker trips off automatically and after correcting the fault, it is again readily available for switch on
• Trip or Tripping


  The cutting-off or disconnection of the current supply
• Panelboard


  The box wherein the protective devices are grouped from which they are fed, called Fuse Panel if the devices are fuses, and Breaker Panel if the devices are circuit breakers
• Electric Circuit


  The complete path traversed by an electric current. The entire house wiring installation.
• Branch Circuit


  The circuit conductors between the final over current protective device (fuse or circuit breaker) and the outlets.
• Components of a Branch Circuit

  • The source of voltage
  • The wiring
  • The load