E L E C T R I C A L D E S I G N 1
THIS COURSE DEALS WITH THE STUDY OF ELECTRICAL SYSTEM DESIGN, INSTALLATION AND COST ESTIMATION FOR SINGLE AND MULTI-FAMILY DWELLING UNITS GUIDED BY THE PROVISIONS OF THE PHILIPPINE ELECTRICAL CODE (PEC) AND OTHER RELEVANT LAWS AND STNDARDS.
BASIC CONCEPT IN ELECTRICAL DESIGN
RECEPTACLES AND WIRING DEVICES
ELECTRICAL CONDUCTORS AND INSULATORS
Electrical Conductors are substances that offer a very low resistance to current flow. Insulators are substances that offer a very high resistance to current flow.
List of some good electrical conductors:
Silver Zinc Copper Platinum Aluminum Iron Nickel Tin Brass Lead
List of some insulating materials: Rubber Asbestos Porcelain Thermoplastics Varnish Paper Slate Oils Glass Wax Mica
Dry air Latex
WIRES AND CABLES
Wires are those electrical conductors which are 8 mm2 (AWG no. 8) or smaller, while cables are
those larger than the wires. They are either solid or stranded.
Stranded wire - consists of a group of wires twisted to form metallic string. The total circular-mil
area of a stranded wire is found by multiplying the circular mil area of each strand by the total number of strand.
Cord is the term given to an insulated stranded wire.
CIRCULAR MIL. This is the unit of cross section in the American wire gauge. The term “mil” means one-thousandth of an inch (0.001 in.). It is the area of a circular wire having a diameter of one mil. To find the number of circular mils in a circle of a given diameter, we have to square the number of mils in the diameter.
Area in circular mil = ( diameter in mils )2
1 inch = 1,000 mils
MCM = 1,000 circular mils
SQUARE MIL. It is the area of a square having its side equal to 1 mil.
Square mil = ( sides )2 = ( 1 mil )2 = ( 0.001 in.)2 = 1 x 10-6in.2
Square mil = 0.7854 x circular mils CONDUCTOR AREAS:
CONVERSION FACTOR
Square inch = square mil x 0.000001 Square mil = square inch x 1,000,000
Square mil = circular mils x 0.7854 Circular mil = square mils x 1.273
Millimeter = inches x 25.4
DIFFERENT TYPES OF CABLES
1. Armored Cable. This type of cable, the type AC is a fabricated assembly of insulated conductors enclosed in flexible metalsheath. Armored cable is used in both exposed and concealed work.
2. Metal Clad Cable. Cable of the type MC is a factory assembled cable of one or more
conductors, each individually insulated and enclosed in a metallic sheath of interlocking tape, or a smooth or corrugated tube. This type is used specifically for services, feeders, branch circuits, either exposed or concealed and for indoor or outdoor work.
3. Mineral Insulated Cable. This type of cable, type MI, is a factory assembly of one or more conductors insulated with a highly compressed refractory mineral insulation and enclosed in liquid-tight and gas-tight continuous copper sheath. The type MI is used in dry, wet or continuously moist location as service, feeders or branch circuit.
4. Nonmetallic Sheathed Cable. Types NM and NMC are factory assembled two or more insulated conductors having a moisture-resistant outer sheath, flame-retardant and non-metallic material. These types are used specifically for one or two dwelling not exceeding 3 storey buildings.
5. Shielded Nonmetallic Sheathed Cable. This type of cable, the type SNM, is a factory assembly of two or more insulated conductors in an extruded core or moisture-resistant and
flame-retardant material, covered with an overlapping spiral metal tape. This type is used in hazardous locations and in cable trays or in raceways.
6. Service Entrance Cable. This is a single conductor or multiconductor assembly provided with or without an over-all covering, primarily used for services and of the types SE and USE.
7. Underground Feeder and Brach Circuit Cables. This type of cable, the type UF cable is a moisture-resistant cable used for underground, including direct burial in the ground, as feeder or branch circuit.
8. Power and Control Tray Cable. Type TC cable is a factory assembly of two or more insulated conductors with or without associated bare or covered grounding under a metallic sheath. This is used for installation in cable trays, raceways or where supported by a messenger wire.
9. Flat Cable Assemblies. This is an assembly of parallel conductors formed integrally with an insulating material web designed specifically for field installation in metal surface raceway. Cables of this type are the types FC.
10. Flat Conductor Cable. This type of cable, type FCC consists of three or more flat conductors placed edge to edge, separated and enclosed within an insulating assembly. This used for general purpose, appliance branch circuits and for individual branch circuits specifically on hard,
12.Medium Voltage Cables. MV cable is a single or multiconductor solid dielectric insulated cable rated 2,001 volts or higher and is used for power systems up to 35,000 volts. The MV cables are of different types and characteristics.
RACEWAYS
Raceways are channels designed for holding wires, cables or bus-bars, which are either made of
metal or insulating materials. The common types of raceways in household wiring are the a)
conduits, b) connectors, and c) others.
a) Conduits
Conduits, pipes or tubings are the most common electrical raceway.
According to the type of materials used, conduit maybe classified as either metallic such as steel pipes or nonmetallic such as PVC, and the like.
According to its make, conduits maybe classified as: rigid metal, flexible metal, rigid nonmetal and flexible nonmetal.
b) Connectors
A connector is a metal sleeve usually made of copper that is slipped over and secured to the butted ends of conductors in making joint. A connector is also called a splicing sleeve.
c) Other Raceways
Aside from the conduits and connectors there are still numerous types and kinds of raceways, among these are the a) conduit couplings, elbows and other fittings; b) conduit supports, such as
clamps, hangers,etc; c) cable trays, cablebus; d) metal raceways;e) nonmetal raceways.
OUTLETS, RECEPTACLES and other WIRING DEVICES
OUTLETS. An outlet is a point in the wiring system at which current is taken to supply
utilization equipment. The kinds of outlets are: convenience outlet or attachment cap, lighting outlet, and receptacle outlet.
A convenience outlet or attachment cap is a device which by insertion in a receptacle, establishes connection between the conductor of the flexible cord and the conductors connected permanently to the receptacle.
A lighting outlet is an outlet intended for direct connection of a lampholder, a lighting fixture, or a pendant cord terminating in a lampholder.
A receptacle outlet is an outlet where one or more receptacles are installed.
TYPES OF WIRES
A. TYPES T, TW, THW
The most ordinary type of plastic insulated wire is the “type T”. It may be used only in dry locations. Some manufactures no longer make the ordinary Type T, instead produce Type TW, which is identical in appearance, but may be used in wet or dry locations. Also available is Type THW, is similar to Type TW but withstand a greater degree of heat, and consequently has a higher ampacity rating in the larger sizes.
B. TYPES THHN, THWN
These are comparatively new types of wire, consisting of the basic Type THH and THW but with less thermoplastic insulation, and with a final extruded jacket of nylon. Nylon has exceptional insulating qualities and great mechanical strength, all of which results in a wire which is smaller in diameter than ordinary Types T, TW, TW of corresponding size.
C. TYPE XHHW
In appearance, it resembles Types T, TW, THW but because of somewhat thinner layer of insulation, the over-all diameter is smaller. The insulation is “cross-linked synthetic polymer,” which has an extraordinary properties as to insulating value, heat resistance, and moisture resistance. It may be used in dry or wet locations. While at present, it is an expensive wire, it would be no surprise if in due course of time, this one single type will replace all the many types and subtypes of Type T or R now recognized by the Code.
D. RUBBER-COVERED WIRE
It consists of copper conductor, tinned to make it easier to remove the insulation, and for easy soldering. Over the copper is a layer of rubber, the thickness of which depends on the size of the wire. Then follows an outer fabric braid which is saturated with moisture-and-fire-resistant compounds; if it is set on fire with a blowtorch, the flame dies out when the torch is removed. E. OTHER TYPES
Other types such as the basic Type R, which is suitable for only in dry locations, is no longer being made. The most ordinary kind is Type RHW, which may be used for dry or wet locations. Types RH and RHH have insulation which withstands more heat and therefore have a higher ampacity in the larger size. They may be used only in dry locations.
KINDS OF LOCATIONS
DAMP LOCATION
Partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subjected to moderate degree of moisture, such as some basements, some barns, and some cold-storage warehouses.
DRY LOCATION
A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.
WET LOCATION
Installations underground or in concrete slabs or masonry in direct contact with the earth, and location subject to saturation with water or other liquids, such as vehicle washing areas, and locations exposed to weather and unprotected.
HAZARDOUS (CLASSIFIED) LOCATIONS
Locations where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitible fibers or flyings.
1. Class I Locations. Class I locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitible mixtures.
a) Class I, Division 1. A Class I, Division 1 location is a location: I) in which igntible
concentrations of flammable gases or vapors can exist under normal operating conditions; or ii) in which ignitible concentrations of such gas vapors may exist frequently because of repair or maintenance operations or because of leakage; or iii) in which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.
b) Class I, Division 2. A Class I, Division 2 location is a location: I) in which volatile flammable liquids or flammable gases are handled, processes, or used, but in which the liquids, vapors, or gases will normally be confines within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in case of abnormal operation of equipment; or ii) in which ignitible concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operation of the ventilating equipment; iii) that is adjacent to Class I, Division 1 location, and to which ignitible concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.
Class II Locations. Class II locations are those that are hazardous because of the presence of combustible dust.
a) Class II, Division 1. A class II, Division 1 location is a location: I) in which combustible dust is in the air normal operating conditions in quantities sufficient to produce explosive or ignitible mixtures; or ii) where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitible mixtures to be produced, and might also provide a source of ignition through simultaneous failure of electric equipment, operation devices, or from other causes; or iii) in which combustible dusts of an electrically conductive nature may be present in hazardous quantities.
b) Class II, Division 2. A Class II, Division 2 location is a location where combustible dust is not normally in the air in quantities sufficient to produce explosive or ignitible mixtures, and dust accumulations are normally insufficient to interfere with the normal operation of electrical equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment and where combustible dust accumulations on, in, or in the vicinity of the electrical equipment may be sufficient to interfere with the safe dissipation of heat from electrical equipment or may be ignitible by abnormal operation or failure of electrical equipment.
3. Class III Locations. Class III locations are those that are hazardous because of the presence of easily combustible fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitible mixtures.
a) Class III, Division 1. A Class III, Divisions 1 location is a location in which easily ignitible fibers or materials producing combustible flyings are handled, manufactured, or used.
b) Class III, Division 2. A Class III, Division 2 location is a location in which easily ignitible fibers are stored or handled.
ELECTRIC CIRCUITS IN BUILDING
* SERVICES *
No. of Service:
A building or other structure served shall be supplied by only one service.
*EXCEPTIONS*
1. For fire pump where a separate service is required.
3. Multiple-Occupancy building
4. Capacity Requirements. Two or more services shall be permitted:
a) Where the capacity requirements are in excess of 2,000 amperes at a supply voltage of 600 volts or less; or
b) Where the load requirements of a single-phase installation are greater than the serving agency normally supplies through one service; or
5. Building of Large Area ( 10,000 m2 or more Total Area ).
6. For different voltage characteristics, such as for different voltage, frequencies, or phases, or for different uses, such as for different rate schedules.
THE OVERHEAD SERVICE-DROP CONDUCTOR
This is the overhead service conductor from the last pole or other aerial support to and including the splices if any, connecting the service entrance conductors at the building or other structure.
SIZE AND RATING:
a) General. Service drop shall have sufficient ampacity to carry the load without a temperature rise detrimental to the covering or insulation of the conductors and shall have adequate
mechanical strength.
b) Minimum Size. The conductors shall not be smaller than 8 mm2 copper, 14 mm2 aluminum or copper-clad aluminum.
CLEARANCES:
a) Above Roofs. Conductors shall have a vertical clearance of not less than 2,500 mm from the roof surface.
b) Vertical Clearance from Ground.
3,100 mm - at the electric service entrance to buildings, or at the drip loop of the building electric
entrance, or above areas or sidewalks
3,700 mm - for those areas listed in the 4,600 mm classification when the voltage is limited to
600 volts to ground.
4,600 mm - over residential property and driveways, and those commercial areas not subject to
5,500 mm - over public streets, alleys, roads, parking areas subject to truck traffic, driveways on
other than residential property, and other land transversed by vehicles such as cultivated, grazing, forest, and orchard.
UNDERGROUND SERVICE-LATERAL CONDUCTOR
This is the underground service conductor between the street main, including any risers at a pole or other structure or from transformers, and the first point of any connection to the service-entrance conductors in a terminal box or meter or other enclosure with adequate space, inside or outside the building wall.
INSULATION. Service-lateral conductor shall withstand exposure to atmospheric and other conditions of use without detrimental leakage of current.
*EXCEPTIONS*
A grounded conductor shall be permitted to be uninsulated as follows:
a) Bare copper used in a raceway.
b) Bare copper for direct burial where bare copper is judged to be suitable for the soil conditions.
c) Bare copper for direct burial without regard to soil conditions where part of cable assembly identified for underground use.
d) Aluminum or copper-clad aluminum without insulation or covering where part of a cable assembly identified for underground use in a raceway or for direct burial.
SIZE AND RATING
a) General. Service lateral conductors shall have sufficient ampacity to carry the current for the load and shall have adequate mechanical strength.
b) Minimum Size. The conductors shall not be smaller than 5.5 mm2 copper or 8.0
mm2 aluminum or copper-clad aluminum.
Where two to six service disconnecting means in separate enclosures supply separate loads from one service drop or lateral, one set of service entrance conductors shall be permitted to supply each or several such service equipment enclosures.
EXCEPTION: For installations to supply only limited loads of a single branch circuit such as small polyphase power, controlled water heaters and the like, they shall not be smaller than 3.5 mm2 copper or 5.0 mm2 aluminum or copper-clad aluminum.
SERVICE ENTRANCE
Service is defined as the portion of the supply which extends from the street main duct or transformer to the service switch or switchboard of the building supply.
-it is the conductor and equipment for delivering energy from the electricity supply system to the wiring system of the premises served.
TYPES:
1. Overhead Service Entrance
The most common type of service entrance employed by the power companies supplying electricity which is either a 2, 3 or 4-wire connection. Generally, the overhead service cable between the building property line and the supply point is supplied by electric company to a limit of 30 meters.
2. The Underground Service Entrance
The underground service entrance consists of a raceway conduit extending from the building to the property line where it is tapped to the main. The type of cable recommended is the
underground service entrance cable commonly referred to as USE.
SERVICE - ENTRANCE CONDUCTORS
No. of Service-Entrance Conductor Sets
Each service drop or lateral shall supply only one set of service-entrance conductors.
*EXCEPTIONS:
1. Buildings with more than one occupancy.
2. Where two to six service disconnecting means in a separate enclosures are grouped at one location and supply separate loads from one service drop or lateral.
SIZE AND RATING: Service entrance conductors shall be of sufficient size to carry the computed loads.
Ungrounded conductors shall not be smaller than:
2. 60 A ---- For one family dwelling with an initial computed load of 10 kVA above. 3. 40 A ---- For other loads.
EXCEPTIONS:
1. For loads consisting of not more than 2 - wire branch circuits, 5.5 mm2 copper or 8.0
mm2 aluminum or copper-clad aluminum.
2. By special permission, for loads limited by demand or by the source of supply, 5.5 mm2 copper or 8.0 mm2 aluminum or copper-clad aluminum.
3. For limited loads of single branch circuit, 3.5 mm2 copper or 5.5 mm2 aluminum or copper-clad aluminum.
INSTALLATION OF SERVICE CONDUCTORS
Service entrance conductors shall be installed in accordance with the applicable requirements of this Code covering the type of wiring method used and limited to the following methods:
1. Open-wiring on insulators 2. Rigid Metal Conduit (RMC)
3. Intermediate Metallic Tubing (IMT) 4. Electrical Metallic Tubing (EMT)
5. Service-Entrance Cables
6. Wireways 7. Busways
8. Auxiliary gutters
9. Rigid Non-Metallic Conduit (RNMC)
10. Cable Bus
11. Mineral-Insulated Metal-Sheated Cable
PROTECTION:
Service entrance conductors subjected to physical damage shall be protected in any of the following ways or methods:
1. By RMC
2. By IMC
3. By RNMC suitable for the location
4. By EMT
5. Type MC cable or other approved means
THE SERVICE EQUIPMENT-DISCONNECTING MEANS
GENERAL:
The service-disconnecting means shall be provided to disconnect all conductors in a building or other structures from the service-entrance conductor.
NUMBER OF DISCONNECTING MEANS:
The service disconnecting means for each set or each subset of service entrance conductor shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, or in a switchboard.
LOCATION:
The service disconnecting means shall be installed either inside or outside the building or other structure at a readily accessible location nearest the point of entrance of the service entrance conductor
RATING:
The service disconnecting means shall have a rating of not less than the load to be carried. In no case shall the rating be lower than specified through:
1. One circuit installation -- The service disconnecting means shall have a rating of not less than 15 amperes.
2. Two circuit installation -- The service disconnecting means shall have a rating of not less than 30 amperes.
3. One family dwelling -- The service disconnecting means shall have a rating of:
60 A -- where the initial computed loads is 10 kVA or more
100 A -- where the initial installations consist of six or more 2-wire branch circuit.
4. Others -- For all other installations, the service disconnecting means shall have a rating of not less than 40 amperes.
NOTES:
The service disconnecting means shall simultaneously disconnect all ungrounded conductors and shall be capable of being closed on a fault equal to or greater than the maximum available short-circuit current.
Service entrance conductor shall have a short-circuit protective device in each ungrounded conductors.
Fuses shall have an Interrupting Rating no less than the maximum available short circuit current in the circuit at their supply terminals.
Circuit breakers shall be free to open in case the circuit is closed on an overload. Circuit breakers shall have an interrupting rating not less than the maximum available short-circuit current at its supply terminals.
THE CIRCUIT BREAKER AND THE FUSE
A circuit breaker is an overcurrent protective device also designed to function as a switch. It is equipped with an automatic tripping device to protect the branch circuit from overload and ground fault.
A fuse is also an overcurrent protective device with a circuit opening fusible element which opens when there is an overcurrent in the circuit. It is considered as the simplest and the most common circuit protective device used into the house wiring connection.
Advantages of circuit breaker over a fuse
2. When there is an overcurrent, the circuit breaker trips automatically and after correcting the fault, it is ready to be switched on again, unlike the fuse which has to be discarded and replaced after it is busted.
Advantages of fuse over a circuit breaker
1. One of its major advantage is its reliability and stability. It can stay on its position for years and act when called on to act as designed, unlike the circuit breaker which requires proper maintenance and periodic testing to keep it into a tip-top condition.
2. The cost of a fuse is less than that of a circuit breaker.
Standard Ampere Ratings of Fuses and Inverse time circuit breakers
15, 20, 25, 30, 40, 45, 60, 70, 80, 90, 100, 110, 125, 150, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000 and 6000
Fuses, circuit breakers or combinations shall not be connected in parallel.
Exception: Circuit breakers or fuses, factory assembled in parallel, and approved as a unit.
Position of Knife Switches
a) Single-throw Knife Switches. Single-throw knife switches shall be so placed that gravity will not tend to close them. Single-throw knife switches, approved for use in the inverted position, shall be provided with a locking device that will ensure that the blades remain in the open position when so set.
b) Double-throw Knife Switches. Double-throw knife switches shall be permitted to be mounted so that the throw will be either vertical or horizontal. Where the throw is vertical, a locking device shall be provided to hold the blades in the open position when so set.
FEEDERS AND MAIN
Essential considerations being adapted or followed.
1. On large installation, one feeder is provided for each floor.
2. In small installations, one or two feeders is satisfactory.
3. Feeder for motor must be separate and independent from the light circuits.
5.Feeders should be subdivided if there are several bends or offsets because a 50 mm conduit is the largest that could be economically used.
6. Feeders radiating from the distributing panel should be provided each with a properly rated switch and circuit breaker.
7. Good practice dictates that feeders and main shall be installed inside a conduit pipe as it carries high voltage that should be well protected.
GROUNDING PROTECTION
A ground is an electrical connection which may either be intentional or accidental between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth. The purpose of grounding a circuit is to fix permanently a zero voltage point in the
system. The grounded line of a circuit should not be broken nor fused to maintain a solid and uninterrupted connection to the ground.
Grounding could be accomplished in the following manner:
1. Connection to a buried cold water main.
2. Connection to a rod or group of rods. 3. Connection to a buried ground plate.
THE PANELBOARD
A panelboard is a single panel or group of panel units designed for assembly in the form of a single panel. This includes buses, automatic overcurrent protective devices, and with or without switches for the control of light, heat or power circuit. It is designed to be placed in a cabinet or cutout box placed in or against a wall or partition and accessible only from the front.
Principles applied in installing panel board
1. The approach should be accessible and convenient.
2. The panelboard must be centrally located to shorten the home wiring runs.
3. It must be installed near the load center. As in most cases, panelboard is installed near the kitchen and the laundry where heavy loads are expected.
MAIN- is the feeder interior wiring extending from service switch, generator bus, or converter bus to the main distribution.
BRANCH CIRCUIT- is defined as the circuit conductors between the final overcurrent device protecting the circuit and the outlets. This means that the branch circuit is only the wiring between the circuit overcurrent protection device such as fuses or circuit breaker and the outlets. However, it is a common knowledge and practice that the branch circuit comprises the entire circuit including the outlet receptacles and other wiring devices.
PROTECTION OF THE BRANCH CIRCUIT
Any current in excess of the rated current capacity of the equipment or the rated ampacity of the conductor is calledovercurrent.
The causes of overcurrent are:
1. Overload in the equipment conductors. 2. Short circuit or ground fault
As per PEC requirement, conductors shall be protected against overcurrent in accordance with their ampacities (Art. 4.5.1.3)
Ampacity - is the current-carrying capacity of an electric conductor.
CIRCUITRY DESIGN
Circuitry design varies according to the number of designers. However, good circuitry design is based on the following considerations:
flexibility of the circuit
It means that the installation can accommodate all probable pattern arrangements and location of the loads for expansion, or future development
· reliability and efficiency of service
It means to have a continuous service and supply of power that are all dependent on the wiring system. Reliability of electric power in a facility is determined by two factors:
o utility service
o building electric system · safety of the circuitry
SAFETY means that independent service can be used in lieu of emergency equipment as backup for normal services. For reliability of the circuitry, the following principles should be considered:
o to provide double emergency power equipment at selected weak points in the system
o that the electrical service and the building distribution system must act together so that the power can reach the desired point of service
o critical loads within the best way to serve them by providing a reliable power either from the outside source, or by standby power package for them
o the system design must readily detect any equipment failure and to be corrected automatically, · economy as to cost
ECONOMY refers to the initial cost as well as the operating costs. These two cost-factors stand in inverse relationship to one another. OVER DESIGN is as bad as under design. It is wasteful both on initial and operating costs.
The effect of acquiring low cost equipment: o high energy cost
o higher maintenance cost o shorter life
· energy consideration
It is a complex one considering the following factors: o energy laws and codes
o budget
o energy conservation technique o energy control
· space allocation
It must consider the following: o easy maintenance
o ventilation o expandability o centrality
o limitation of access
BRANCH CIRCUIT
The branch circuit is classified into: General purpose branch circuit
It supplies outlets for lighting and appliances, including convenience receptacles
Appliance branch circuit
It supplies outlets intended for feeding appliances.
Individual branch circuit
It is designed to supply a single specific item.
CIRCUITING GUIDELINES:
There are many ways of doing circuitry but there is no optimum or perfect way of doing it. However, there are certain rules and guidelines promulgated by the NEC for
flexibility, economical, and convenient way of installing a circuitry.
1. The Code requires sufficient circuitry to supply residential load of 30 watts per square meter in buildings excluding porches, garages, and basements.
2. The requirement of 30 watts per square meter is up to 80 sq. m for a 20 amperes circuit (2400 watts) or 60 sq. m for 15 ampere circuit (1800 circuit).
3. Good practice suggests that the load should not exceed 1600 watts for a 20 amperes circuit and 1200 watts for a 15 amperes circuit.
a. Observe a minimum load of 1200 watts on a 15 amperes circuit with a maximum area of 40 sq. m
4. The Code requires a minimum of 20 amperes application branch circuit to feed all small appliance outlets in the kitchen, pantry, dining, and family room
5. The general purpose branch circuit shall be rated at 20 amperes circuit, wired with No. 12 AWG being the minimum size of conductor wire required for all convenience outlets. 6. Plug outlets or convenience receptacles shall be counted in computing the load if it is not included in the load for general lighting circuit. To find the number of outlets for 9 and 12 A loading on a 20 A circuit respectively, we have:
a. For 15 A ckt : 91.5 = 6 outlets b. For 20 A ckt : 121.5 = 8 outlets
7. Convenience receptacles should be planned properly, so that in case of failure by any one of the circuitry, the entire area will not be deprived of power supply.
8. All kitchen outlets should be fed from at least two of these circuits
9. The Code further stipulated that: “all receptacles are potential appliance outlet and at least two circuits shall be supplied to serve them.”
10. Certain outlets in the room should be designed as appliance outlet like: a. All kitchen receptacles
b. Dining room receptacles c. One in the living room
11. The Code requires that, “at least one 20 A ckt. Supply the laundry outlets.”
OTHER GOOD PRACTICES IN CIRCUITING
1. Lighting and receptacles should not be combined in a single circuit.
2. Avoid connecting all building lights on a single circuit
3. Lighting and receptacles should be supplied with current from at least 2 ckt. so that if a single line is out, the entire area is not deprived of power.
4. Do not allow combination switch and receptacle outlets
5. Provide at least one receptacle in the bathroom, and one outside the house. Both must be Ground Fault Circuit Interrupter (GFCI) type
6. Provide switch control for closet lights. Pull chain switch is nuisance
7. Convenience outlet though counted as part of the general lighting load shall be limited to 6 convenience outlets on a 15 A ckt and 8 convenience outlet on a 20 A ckt.
8. The Code requires that, at least one 20 A ckt supply shall be installed to the laundry outlets
9. Convenience outlet shall be laid out in such a manner that no point on a wall is more than 2 meters from an outlet. Use a grounding type receptacle only
PEC REQUIREMENTS FOR ADEQUATE WIRING IN SINGLE AND MULTI-FAMILY DWELLING UNIT
GENERAL LIGHTING LOADS BY OCCUPANCIES
(Table 1.1)* All receptacle outlets of 20-ampere or less in one-family, two-family and multifamily dwellings and in guest rooms of hotels and motels shall be considered as outlets for general illumination, and no additional load calculations shall be required for such outlets.
** In addition a unit load of 8 volt-amperes per square meter shall be included for general purpose receptacle outlets when the actual number of general purpose receptacle outlets is unknown.
FEEDER DEMAND FACTORS FOR GENERAL LIGHTING LOAD AND SMALL
APPLIANCE LOAD
*The demand factors of this table shall not apply to the computed load of feeders to areas in hospitals, hotels, and motels where the entire lighting is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms.
DEMAND FACTOR FOR HOUSEHOLD ELECTRIC CLOTHES DRYER
DEMAND LOADS FOR HOUSEHOLD ELECTRICRANGES,
WALL-MOUNTED OVENS, COUNTER-MOUNTED COOKING UNITS, AND
OTHER HOUSEHOLD COOKING APPLIANCES OVER 1.75 KW RATING.
COLUMN A TO BE USED IN ALL CASES EXCEPT AS
OTHERWISE PERMITTED ON NOTE 3 BELOW
(Table 4.1)
Note: Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column A shall be increased 5 % for each additional kW of rating of major fraction thereof by which the rating of individual ranges exceeds 12 kW.
Note 2: Over 8.75 kW through 27 kW ranges of unequal ratings. For ranges individually rated more than 8.75 kW and of different ratings but no exceeding 27 kW, an average of value of rating shall be computed by adding together the ratings of all ranges to obtain the total connected load (using 12 kW for any range rated less than 12 kW) and dividing by the total number of
ranges; and then the maximum demand in column A shall be increased 5 percent for each kW or major fraction thereof by which this average value exceeds 12 kW.
Note 3: Over 1.75 kW through 8.75 kW. In lieu of the method provided in column A, it shall be permissible to add the nameplate ratings of all ranges rated more than 1.75 kW but not more than 8.75 kW and multiply the sum by the demand factors specified in column B or C for the given numbers of appliances.
Note 4: Branch circuit load. It shall be permissible to compute the branch-circuit load for one range In accordance with Table 3.3.2.10. the branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be computed by adding the nameplate ratings of the individual appliances and treating this total as equivalent to one range.
Note 5: This table also applies to household cooking appliances rated over 1.75 kW and used in instructional programs.
FULL LOAD CURRENT IN AMPERES
SINGLE PHASE ALTERNATING - CURRENT MOTORS
(Table 4.1)
FULL-LOAD CURRENT
TWO-PHASE ALTERNATING CURRENT MOTORS (4-WIRE)
(Table 5.1)
FULL-LOAD CURRENT
THREE-PHASE ALTERNATING-CURRENT MOTORS
CONVERSION TABLE OF LOCKED-ROTOR CURRENTS
FOR SELECTION OF DISCONNECTING MEANS AND CONTROLLERS
AS DETERMINED FROM HORSEPOWER AND VOLTAGE RATING
MAXIMUM RATING OR SETTING OF MOTOR BRANCH-CIRCUIT
SHORT-CIRCUIT AND GROUND-FAULT PROTECTIVE DEVICES
ALLOWABLE AMPACITIES OF INSULATED CONDUCTORS
RATED 0-2000 VOLTS, 60º C TO 90ºC
NOT MORE THAN THREE CONDUCTORS IN RACEWAY OR CABLE OR
EARTH (DIRECTLY BURIED), BASED ON AMBIENT
TEMPERATURE OF 30ºC
AMPACITY CORRECTION FACTORS
(Table 10.1)
ALLOWABLE AMPACITIES OF SINGLE INSULATED
BASED ON AMBIENT AIR TEMPERATURE OF 30ºC
(Table 11.1)
AMPACITY CORRECTION FACTORS
+ Unless otherwise specifically permitted elsewhere in this Code, the over current protection for conductor types marked with an obelisk (+) shall not exceeds 15 amperes for 2.0 mm2,20
amperes for 3.5 mm2, and 30 amperes for 5.5 mm2 copper; or 15 amperes for 3.5 mm and 25
amperes for 5.5 mm2aluminum and copper clad aluminum.
ALLOWABLE AMPACITIES OF THREE SINGLE INSULATED
CONDUCTORS, RATED 0-2000VOLTS, 150º TO 250ºC, IN RACEWAY OR CABLE BASED ON AMBIENT AIR TEMPERATURE OF 40ºC
AMPACITY CORRECTION FACTORS
ALLOWABLE AMPACITIES FOR SINGLE INSULATED
CONDUCTORS, RATED 0-2000VOLTS, 150º TO 250ºC, IN
FREE AIR BASED ON AMBIENT AIR
TEMPERATURE OF 40ºC
(Table 15.1)
AMPACITY CORRECTION FACTORS
EXCEPTIONS (based on PEC requirements)
1. The small appliance appliance branch circuit required in a dwelling unit shall supply only the receptacle outlets specified in that section.
(b.) 25- and 30-Ampere Branch Circuits. A 25- or 30-ampere branch circuit shall be permitted to supply fixed lightning units with heavy-duty lamp holders in other dwelling unit(s) or appliances shall not exceed 80 percent of the branch-circuit ampere rating.
(c.) 40- and 50-Ampere Branch Circuits. A 40- and 50-ampere branch circuit shall be permitted to supply fixed lighting units with heavy-duty lamp holders or infrared heating units in other than dwelling units or cooking appliances that are fastened in place in any occupancy.
Receptacle Outlets required
(a) General. where flexible cords are used.
2. where flexible cords are specifically permitted to be permanently connected, and are so connected in boxes or fittings approved for the purpose, it shall be acceptable to omit receptacles on such equipment. (b) Dwelling units. In every kitchen, family room, dining room, breakfast room, living room, parlor, library, den, sun room, bedroom, recreation room, or similar rooms, receptacle outlets shall be installed so that no point along the floor kine in any wall space is more than 1800 mm, measured horizontally, from an outlet in that space, including any wall space 600 mm or more in width and the wall space occupied by sliding panels in exterior walls. The wall space afforded by fixed room dividers, such a free-standing bar type counters, shall be included in the 2 meter measurement.
In kitchen and dining areas, a receptacle outlet shall be installed at each counter space wider than 300 mm. Counter top spaces separated by range tops, refrigerators, or sinks shall be considered as separate counter top spaces. Receptacles rendered inaccessible by appliances fastened in place or appliances occpying dedicated space shall not be considered as these requires outlets.
Receptacles outlets shall, in so far as practicable, be spaced equal distances apart. Receptacle outlets in floors shall not be counted as part of the required number of receptacle outlet unless located close to the wall.
At least one wall receptacle shall be installed in the bathroom adjacent in the basin location. For a one-family dwelling, at least one receptacle outlet shall be installed outdoors.
For a one-family dwelling, at least one receptacle outlet in addition to any provided for laundry equipment, shall be installed in each basement and in each attached garage.
Outlets in other section of the dwelling unit for special appliances, such as laundry equipment, shall be placed within 1800 mm of the intended location of the appliance.
At least one receptacle outlet shall be installed for the laundry.
3. In a dwelling unit that is an apartment or living area in a multifamily dwelling where laundry facilities are provided on the premises that are available to all building occupancies, a laundry receptacle shall not be required.
4.In other than one-family dwellings where laundry facilities are not be installed or permitted, a laundry receptacle shall not be required.
As used in this section, a "wall space" shall be considered a wall unbroken along the floor line by doorways, fireplaces, and similar openings. Each wall space 600 or more mm wide shall be treated individually and separately from the other wall spaces within the room. A wall space shall be permitted to include two or more walls or a room(around corners) where unbroken at the floor line.
The receptacle outlets required by this section shall be in addition to any receptacle that is part of any lighting fixture or appliances, located within cabinet or cupboard, or located over 1600 mm above the floor.
5. Permanently installed electric baseboard heaters equipped with factory installed receptacle outlets, or outlets provided as a separate assembly by the manufacture, shall be permitted as the required outlet or outlets for the wall space utilized by such permanently installed heaters. Such receptacle outlets shall not be connected to the heater circuits.
Lighting Outlets Required:
(a) Dwelling units: At least one wall switch controlled lighting outlet shall be installed in every habitable room, in bathrooms, hallways, stairways and attached garage: and at outdoor entrances
At least one lighting outlet shall be installed in an attic, underfloor space, utility room and basement only wher these spaces are used for storage or containing equipment requiring servicing.
6. In habitable rooms, other than the kitchen, one or more receptacles controlled by a wall switch shall be permitted in lieu of light outlets
7. In hallways, stairways, and at outdoor entrances remote, central, or automatic control of lighting shall be permitted.
FEEDERS:
Minimum size or rating. Feeder conductors shall have an ampacity not lower than required to supply the load . The minimum sizes shall be as specified in (a) and (b) below under the conditions stipulated. Feeder conductors for a one family dwelling or amobile home need not be larger than service entrance
conductors.
supplied consists of the following number and types of circuits: (1) Two or more 2-wire branch circuits supplied by a 2-wire feeder. (2) MOre than two 2-wire branch circuits supplied by a 3-wire feeder (3) Two or more 3-wire branch circuits supplied by a 3-wire feeder
(b) ampacity relative to service entrance conductors. The feeder conductor ampacity shall not be lower than that of the service-entrance conductors 14 square mm or smaller.
(c) Overload feeders. Where at any time feeder conductors are or will be overloaded the feeder conductors shall be increased in ampacity to accommodate the ctual load served.
OPTIONAL CALCULATION - MULTIFAMILY DWELLING
(a) It shall be permissible to compute the feeder or service load of a multifamily dwelling where all the following conditions are met:
(1) No dwelling unit is supplied by more than one feeder
(2) Each dwelling unit is equipped with electric cooking equipment.
EXCEPTION: When the computed load for multifamily dwelling under the section without cooking load exceeds that computed under this section for the identical load plus electric cooking exceeds that computed for the identical load plus the electric cooking, the lesser of the loads may be used. (3) Each dwelling unit is equipped with either electric space heating or air conditioning or both
Feeders and service-entrance conductors whose demand load is determined by this optional calculation shall be permitted to have the neutral load determined by this section
the connected load to which the demand factors apply shall include the following:
(1)1500 watts for each 2-wire, 20 A small appliance branch circuit and each laundry branch circuit (2) 24 watts per square meter for general lighting and general use receptacles
(3) The nameplate rating of all appliances that are fastened in place, permanently connected or located to be on a specific circuit, ranges, wall mounted ovens, counter-mounted cooking units, clothes dryer, water heaters and space heaters
If water heater elements are so interlocked that all elements cannot be used at the same time, the maximum possible load shall be considered the nameplate load.
(4)The nameplate A or kVA rating of all motors and of all low-power factor load. (5) The larger of the air conditioning load or the space heating load.
WIRING CALCULATIONS FOR SINGLE FAMILY DWELLING UNIT
SINGLE FAMILY DWELLING
Type of Service - 230 V Single Phase 2 wire 60 Hz Line to ground Current system
PROBLEM:
A single family dwelling is to be circuited with the following requirements as shown on the figure above. Determine the:
size of the branch circuit wire for lighting outlets size of the conduit pipes
size or rating of the fuse protective device
SOLUTION
A. Circuit - 1 for lighting load
1. From the Figure above, determine the number of lighting outlets. By direct counting, there are 8 light outlets.
The National Electrical Code provides that:
"100 watts shall be the maximum load for each household lighting outlet." Adopting the 100 watts per lighting outlet we have:
8 outlets x 100 = 800 watts
2. Determine the Total Current load 800 watts/230 volts = 3.48 amperes
3. Determine the size of conductor wire for circuit - 1 . Refer to Table 9.1 or 11.1. use 2 pieces 2.0 mm2 or No. 14 TW copper wirehaving an ampacity of 15 amperes that is much largr than the 3.48 amperes computed maximum load.
4. Determine the size of the Conduit Pipe. Refer to Table . The smallest diameter of a conduit pipe that could accommodate up to 3 pieces of No.14 TW conductor wire is 13 mm diameter. therefore, specify13 mm diameter conduit pipe.
5. determine the size or rating of the fuse protective device. Refer to Table . Use 15 amperes fuse The National Electrical Code provides that:
"Ampacity of the connected load shall not exceed 80% of the amperage capacity of the conductor and the fuse."
In Table , the maximum ampacity load of a or 2.0 mm2 No.14 AWG copper wire is 15 amperes. 80 % of 15 is 12, the maximum allowable load of the circuit sufficient enough to carry the 3.48 amperes computed load for a maximum 100 watts per light outlet. therefore the use of 2.0mm2 or No.14 TW is safe.
SOLUTION
The National Electrical Code provides that:
"For each single receptacle shall be considered at no less than 180 watts rating."
It simply mean that, each convenience outlet, is considered to have a maximum load of not less than 180 watts per plug or gang. thus:
1. From Figure above, there are 6 convenience receptacles for small appliance load. considering that there are two plug outlet, the total number of plug will be:
6 outlets x 2 plug = 12 pieces
2. Solve for the Total Estimated Load 12 x 180 watts per outlet = 2,160 watts
3. Determine the Maximum Expected Current Load: 2,160 watts / 230 volts = 9.39 amperes
4. Determine the Size of the Conductor wire . Refer to Table 9.1 or 11.1. For 9.39 amperes, use 2 pieces 3.5 mm2 or No. 12 TW copper wire for Circuit no.2
5. Determine the Size of the conduit pipe. for the 2 - No. 12 TW wire, refer to Table . Use 13 mm conduit pipe.
6. Determine the Over Current fuse protection. Refer to Table . under the column of fuse and breaker rating, the 20 amperes fuse can safely carry a maximum load of 16 amperes the 80 % of 20 amperes fuse can safely carry a maximum load of 16 amperes the 80% of 20 amperes load permitted by the National Electrical Code on No. 12 circuit wire.
COMMENT:
1. On convenience outlet receptacle, the National Electrical Code provides that, " Each single receptacle shall be considered at no less than 180 watts rating."
2. Examining the values given on Table , the 2.0 mm2 or No. 14 AWG TW copper wire has an allowable ampacity rating of 15 amperes. Granting that only 80 % of this 15 amperes is considered the derated value, still 12 amperes is very much larger than the 9.36 amperes computed as maximum load for 6-convenience outlet. Why specify a bigger 3.5 mm2or No. 12 AWG conductor wire?
3. Although the 2.0 mm2or No. 14 AWG wire conductor could safely carry the 9.36 amperes computed load, considering its 15 amperes ampacity rating,yet, we cannot do so because the Code specifically
mandated the use of 3.5 mm2or No. 12 AWG copper wire as the minimum size for all types of
convenience outlet wiringexcept, for an appliance with limited load wherein a 2.0 mm2or No.14 AWG wire is permitted.
C. Circuit - 3 for other loads SOLUTION
1. Examining Figure above, other loads are: 1 - unit electric stove at 1.1 kw = 1,1oo watts 1 - unit water heater at 2.5 kw = 2,500 watts Total Load...3,600 watts
2. Compute for the current load. Divide: 3,600 watts / 230 volts = 15.65 amperes
3. Determine the size of the service conductor wire. Refer to Table 9.1 or 11.1. 4. For the 15.65 amperes load, use 2 pieces 3.5mm2or No.12 AWG TW copper wire
5. Determine the Size of the Conduit Pipe (if reqd) to Table. Two pieces No. 12 AWG wire can be accommodated comfortably in a 13 mm diameter conduit pipe. Specify 13 mm diameter conduit pipe. 6. Determine the size or rating of the Over-current Protection. Refer to Table . For the 15.65 amperes load use 20 amperes fuse rating.
COMMENTS:
The fuse rating is 20 amperes. Granting that it will be derated at 80 % x 20, the 16 amperes derated value is still higher than the computed load of 15.65 amperes. Therefore, the 20 amperes fuse over current protection is accepted.
FINDING THE SIZE OF SERVICE ENTRANCE
The size of service entrance being the supply conductor and equipment for delivering energy from the electricity supply to the wiring system of the building, is also computed based on the total load supplied by the branch circuit. Continuing the solution, we have the following:
1. Solve for the total load of circuit 1 to circuit 3.
Total current load = Total connected load / voltage rating = (800 W + 2,160 W + 3,600 W) / 230 V
= 28.52 amperes
2. Apply 80% demand factor as permitted by the National Electrical Code. 28.52 x .80 = 22.8 amperes
3. Find the Size of the Service Wire. Refer 22.8 amperes to Table . Use 2- 8.0 mm2or No.8 TW copper wire
4. Determine the size of conduit pipe for the service wire. Refer Table , for No.8 TW copper wire, use 20 mm diameter conduit pipe.
COMMENT:
1. A demand factor of 80% was applied considering that not all receptacles and outlets are being used
simultaneously.
2. These type of loads are classified as non-continuous load. From Table 9.1, the 5.5 mm2or No.10 AWG copper wire conductor has 30 amperes ampacity which is bigger than 22.8 amperes as
computed. However, we do not specify the use of No.10 AWG wire because the code limits the use of
8.0mm2or No.8 AWG, conductor as minimum size for Service Entrance.
3. The National Electrical Code on Service Entrance provides that:
" Service entrance shall have sufficient ampacity to carry the building load. They shall have the
adequate mechanical strength and shall not be smaller than 8.0 mm2or 3.2 mm diameter except for
installation to supply limited load of a single branch circuit such as small poly-phase power, controlled water heaters and the like and they shall not be smaller than 3.5 mm2or 2.0 mm diameter copper or equivalent.
THE MAIN DISCONNECTING MEANS OR SAFETY SWITCH Find the total computed load
Circuit - 1 ... 3.48 amperes Circuit - 2 ...9.39 amperes Circuit - 3 ...15.65 amperes TOTAL...28.52 amperes
2. Use 2 pieces 30 amperes fuse parallel connection 60 amperes 2 pole single throw (PST) 250 volts safety switch
3. Provide 2-double branch circuit cut out with two 15 and 2-20 amperes fuse respectively.
MULTI-ground system and line to line service
The protection of branch circuit is tapped to the hot line of live wire. The grounded line being in neutral zero voltage is not protected with fuse. this is one advantage of the MULTI-GROUND SYSTEM being adopted by the electric cooperative implemented by the RURAL ELECTRIFICATION PROGRAM of the government. The branch circuit and cutout should be doubled because the engaged voltage in the line is only 230 V while the other is zero being grounded ( see figure)
Other electric service system on the other hand, are classified as LINE TO LINE SERVICE wherein the engaged voltage is 115/230 volts which requires FUSE PROTECTIO FOR BOTH LINES.
NOTE:
The quantity of materials is subject to change depending upon the area and the choice of the designing engineers. For open onstallation, conduit pipe can be changed to split knobs or PDX wires.
SINGLE FAMILY DWELLING
Type of Service - 115/230 V Single Phase 3 wire 60 Hz Line to Line system
SOLUTION:
Examining the lighting plan of the above figure, there are 19 lighting outlets. Split the 19 outlets into two circuits A and B.
A. Circuit - 1 Lighting Load (10 light outlets)
1. The PEC provides that 100 watts be the maximum load per light outlet. thus, for 10 light outlets at 100 watts, multiply:
10 outlets x 100 watts = 1000 watts 2. Compute The Current Load 1000 watts/230 volts = 4.35 amperes
3. Find the size of Branch circuit wire. Refer to Table 9.1 or 11.1. For 4.35 amperes, use 2.0 mm2 TW copper wire.
4. Find the rating of overcurrent protection. Refer to Table. for 4.35 A, use 15 amperes trip breaker. 5. Determine the size of conduit pipe. Refer to Table , for No. 14 TW copper wire, use 13 mm conduit pipe. B. Circuit - 2 Lighting Load (9 light outlets)
1. For 9 outlets, find the Total load in watts. 9 outlets x 100 watts per outlet = 900 watts Divide : 900 watts/230 volts = 3.91 amperes
2. Determine the Size of the Branch circuit Wire. Refer to Table 9.1 or 11.1. For 3.91 A load, use 2.0 mm2or No.14 TW copper wire.
3. Determine the size of the conduit pipe. Refer to Table. For 2 pieces No. 14 TW copper wire, use the 13 mm minimum size of conduit pipe.
4. Determine the size or rating of the overcurrent Protection. Refer to Table. For 3.91 A load, use 15 A load fuse of trip breaker.
C. Circuit - 3 For small appliance load
Section 3.3.1.2 of the the PEC specif 180 watts load limit per convenience outlet. Thus, 1. Find the number of appliance load outlet and the current load.
6 outlets x 2 gang per outlet x 180 watts 12 x 180 = 2,160 watts
Divide: 2160 watts/230 volts = 9.39 A
the minimum wire gauge for convenience outlet. 2 pieces 3.5 mm2or No.12 TW copper wire
3. Determine the Size of the conduit pipe. Refer to Table. For 2 pieces No.12 TW copper wire. Use 13 mm diameter conduit pipe.
4. Solve for the Size or Rating of the Over current Protection. Refer to Table. For 9.39 A on No. 12 TW copper wire specify:
20 A fuse or trip breaker.
D. Circuit- 4 for Small Appliance Load
1. The load of circuit 4 is identical with circuit . Use the same size of wire, conduit, and wire protection rating.
E. Circuit - 5 for Range Load
1. Range load (appliance rating) at 8.0 kW = 8000 watts 2. Solve for the Line current.
8000 watts / 230 V= 34.78 A
3. Refer to Table , apply 80% demand load factor . 34.78 x .80df = 27.82 A
4. Determine the Size of the Branch Circuit wire. Refer to Table 9.1 or 11.1. For the 27.82 A, use 8.0 mm2 or No. 8 TW copper wire.
5. Determine the Size of Conduit pipe. Refer to Table. For 2 pieces No.8 wire use 200 mm diameter pipe. 6. Find the Size or Rating of the Fuse or Trip Breaker. Refer to Table. For appliance load, use 40 A fuse or trip breaker.
F. Circuit - 6 for Water heater Load
1. one unit water heater at 2.5 kW = 2500 watts 2. The current load will be:
2500 watts/230 volts = 10.86 A
3. Solve for the Size of the Branch circuit wire. Refer to Table 9.1 or 11.1 . For 10.86 A convenience outlet use 2 pcs 3.5 mm2 or No. 12 TW copper wire.
4. Determine the Size of the conduit pipe. Refer to Table. For 2 - No.12 Tw copper wire, use 13 mm conduit pipe.
5. Find the Size or Rating of the Over Current Protection. For the 10.86 A load, use 20 A fuse fuse or trip breaker.
G. Circuit 7 and 8 with 1 - unit ACU each 1. One unit ACU at 1.5 Hp is
Article 6.7 of the Philippine Electrical Code provides that: "BRANCH CIRCUIT CONDUCTOR SUPPLYING A MOTOR SHALL HAVE AN AMPACITY NOT LESS THAN 125% OF THE FULL LOAD CURRENT."
2. Current Load: 1119 watts/230 V = 4.86 A 4.86 A x 125% = 6.07 A
3. Find the Size of the Branch circuit service wire. Refer to Table. The 6.7 A can be served by a 2.0 No.14 TW copper wire, but the Code limits the size of convenience outlet to No. 12 AWG copper wire.
SpecifyNo.12 THW copper wire for circuit 7 and 8.
4. Find the Size of the conduit pipe. Refer to Table. For two No.12 wire, use 13 mm conduit pipe. 5. Find the Size and Rating of the Branch Circuit Protection. The Code on branch circuit protection for a single motor provides that" It shall be increased by 250% of the full load current of the motor." thus, 4.86 x 250% = 12.15 A. From Table for a continuous load use 2-30 AT breaker.
CALCULATING THE AMPACITY OF THE SERVICE
ENTRANCE CONDUCTOR AND THE MAIN DISCONNECTING MEANS
1. Find The total current load of circuit 1 to circuit 8: lighting load Ct. 1 and Ct.2 ...1900 watts small appliance load Ct. 3 and Ct. 4...4320 watts other loads Ct.5 and Ct 6.,...10500 watts TOTAL LOAD(except the ACU)....16720 watts
2. From Table , OPTIONAL CALCULATION for dwelling Unit, apply demand factor. for the first 10000 w at 100%(df)...10000 watts
subtract: 16720 - 10000 = 6720 watts for other load, multiply by 40%
6720 x .4 ...2688 watts Aircon unit at 100% demand factor
2-units at 1119 watts...2238 watts TOTAL ...14, 926 watts
TOTAL CONNECTED LOAD PLUS 25% OF THE LARGEST MOTOR 1. Ampere I = 14.926w + (25% of 1.119w)/230 V
= 63.37 A
2. Find the Size of Main feeder and the Neutral line. - Use 2 - 3.8 mm2 TW copper wire
70% of the ungrounded(live wire) conductor or TWO TRADE SIZE SMALLER SIZE THAN THE UNGROUNDED CONDUCTOR. (PEC specs) Therefore use1- 22 mm2 Tw copper wire for the Neutral line.
4. Determine the Size of the Conduit pipe. Refer to Table , use 32 mm diameter pipe.
5. For main Breaker, refer to Table . Use 2 - 100 A 2 - wires 250 V, 2 pole molded air circuity breaker. COMMENT:
The total computed load is 63.37 A. The 30 mm2 copper wire could be used considering its 90 A capacity. However, The NEC provides that:
" If the computed load exceeds 10000 watts, the conductor and overcurrent protection shall be rated not less than 100 A.
THEREFORE USE 2 - 38 mm2 TW WIRE FOR THE MAIN FEEDER AND 2 - 100 A FOR THE MAIN BREAKER.
Small Family Dwelling
Type of Service - 230 volts; two wire Line to Ground system
A single family dwelling with a floor area of 80 square meters has the following receptacles and outlets load.
LIGHTING:
7 pcs. - 40 watts fluorescent lamps 2 pcs. - 20 watts Incandescent lamps CONVENIENCE OUTLET:
1 - Electric Iron ... 1000 watts 1 - Electric stove... 1100 watts 2 - Electric fan ... 500 watts 1 - 7 cu. ft Refrigerator ... 175 watts 1 - Portable stereo ... 100 watts 1 - 20" TV set ... 300 watts
SOLUTION:
A. Circuit 1 - Lighting Load by the Area method
1. Determine the wattage required per square meter area. From, the wattage required per square meter for dwelling units is 24 watts. Multiply:
2. Determine the current load. Divide: 1920 watts/ 230 volts = 8.35 A
3. Compute the actual lighting load. Multiply: 7 - Fluorescent lamps x 40 watts = 280 watts 2 - Incandescent bulb x 60 watts = 120 watts TOTAL... 400 watts
4. Solve the actual current load. Divide: 400 watts/230 volts = 1.74 A
5. Determine th Size of the Branch Circuit wire. From , the 1.74 A is very small load to be carried by 2.0 mm2 or No. 14 TW copper wire. Therefore, the No. 14 wire is safe.
6. Determine the Size of the conduit pipe. Refer to table, for 2- No.14 wire, use 13 mm conduit pipe. 7. Determine the size or rating of the branch circuit protection. Refer to table. For 2.0 mm2 or No.14 copper wire conductor, use 15 A fuse or trip breaker.
B. Circuit - 2 For small appliance load 1. Solve for the total appliance current load.
LOAD CURRENT = ( 1000 + 1100 + 500 + 175 + 300 + 100) / 230 volts = 3175 watts/230 volts
= 13.81 A
2. Determine the size of the Branch circuit wire conductor. Refer to Table. For a convenience load of 13.81 A specify 3.5 mm2 or No. 12 TW copper wire, the minimum size required for convenience outlet.
3. Find the size of the conduit pipe. Refer to Table, for 2 pieces No.12 TW copper wire, use 13 mm diameter pipe.
4. Find the Size or rating of the Protection device. See Table, for 13.81 A, use 1 - 20 A fuse. COMMENT:
It is interesting to note that only one 20 A fuse protection was used because the current is a LINE TO GROUND OR MULTI-GROUND SYSTEM where one line is zero voltage being grounded. Unlike the LINE TO LINE SYSTEM of current supply, it is necessary to provide 2 fuses to protect the two line branch circuit.
FINDING THE SIZE OF THE SERVICE ENTRANCE OR FEEDER 1. Get the sum total of connected load. Add:
Lighting Load... 1920 watts Small appliance load ... 3175 watts TOTAL... 5095 watts
5095 watts/230 volts = 22.15 A
3. Find the size of Service Entrance. Refer to Table. For 22.15 A, useNo. 8 TW copper wire, the minimum size for service entrance.
4. For Main Protection, use 1-safety switch, 2 pole, 2 wires, 250 volts.
Under the preceding set-up, one safety switch could supply both lighting and convenience outlet at different branch circuit without the use of fuse cutout. This is only applicable to the line to ground or multi-ground system being used by the electric cooperative.
ILLUMINATION CALCULATION AND DESIGN FOR SINGLE FAMILY DWELLING
PRINCIPLES OF ILLUMINATION
6 – 1 INTRODUCTION
Illumination is defined as the intensity of light per unit area. When we talk of illumination, or simply lighting, we are referring to man made lighting. Daylight being excellent is not included, thus, we assume a night time condition.
Electric Illumination is the production of light by means of electricity and its applications to
provide efficient, comfortable and safe vision. Specifically, when one speaks of lighting design, he refers to only two things:
1.The quantity of light 2.The quality of light
Quantity of Light – refers to the amount of illumination or luminous flux per unit area.
Quantity of light can be measured and easily handled because it deals with the number of light fixtures required for a certain area.
Quality of Light – refers to the distribution of brightness in the lighting installation. It deals with the essential nature or characteristics of light. In short, quality of light is the mixture of all the items related to illumination other than the quantity of light which includes several elements such as:
1.Brightness
3.Glare 4.Diffuseness
5.Color
6.Aesthetics
7.Psychological reaction to color and fixtures
8.Economics
There are four factors that affect illumination, namely:
1.Brightness 2.Glare
3.Contrast 4.Diffuseness
Brightness is the light that seems to radiate from an object being viewed. Brightness or luminance is the luminous flux (light) emitted, transmitted or reflected from a surface.
Contrast is the difference in brightness or the brightness ratio between an object and its background. The recommended brightness ratio between an object being viewed and its background is normally 3:1.
If a print on a white paper can be clearly seen on a light background, it is due to the effect
called contrast. Likewise, if a light object is placed on a dark background, the light object reflects more light and looks brighter although bought have equal illumination. It is for this reason that office furniture are generally light colored, tan or light green for eye comfort.
Glare is a strong, steady, dazzling light or reflection. There are two types of glare:
1.Direct Glare is an annoying brightness of light in a person’s normal field of vision.
2.Indirect or Reflected Glare is much more serious and difficult to control. Technically,
reflected glare is a glossy object.
Diffuseness refers to the control of shadows cast by light. Diffuseness is the degree to which light is shadowless and is therefore a function of the number of directions to which light collides with a particular point and the comparative intensities.
Perfect Diffusion is an equal intensities of light clashing from all directions producing no shadows. A single lamp will cast sharp and deep shadows. A luminous ceiling provides a satisfactory diffuse illumination and less shadows.
The color of lighting and the corresponding color of the object within a space is an important consideration in producing a quality of light.
There are three characteristics that define a particular coloration. They are:
a.Hue – is the quality attribute by which we recognize and describe colors as red, blue, yellow, green, violet and so on.
b.Brilliance or Value – is the difference between the resultant colors of the same hue, such as: white is the most brilliant of the neutral colors while black is the last.
c.Saturation or Chroma – is the difference from the purity of the colors. Colors of high saturation must be used in well lit spaces.
6 – 2 ESTIMATING ILLUMINATION AND BRIGHTNESS
In many respect, it is more important to know luminance measurements than illumination because the eye is more sensitive to brightness than simple illumination. However, it is more difficult to measure luminance than illumination.
There are three types of luminance meter, namely:
1.The Comparator type which requires the operator to make a brightness equivalence judgment between the target and the background.
2.The Direct Reading type is basically an illumination meter equipped with a hooded cell arranged to block oblique light.
3.The Accurate Laboratory Instrument which unsuitable for field work.
The quantity of light level of illumination can be easily measured or calculated with the aid of portable foot candle meter.
Footcandle (fc) is the amount of light flux density. It is the unit of measure used when describing the amount of light in a room and is expressed in lumens per square foot.
Footlambert (fl) is defined as “the luminance of a surface reflecting. Transmitting or emitting one lumen (lm) of illumination per square foot of area in the direction being viewed or the conventional unit of brightness or luminance. In the same manner, the lumens (lm) is the light output generated continuously by a standard wax candle