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ELECTRIC CIRCUITS IN BUILDINGS
ELECTRIC CIRCUITS IN BUILDINGS
SERVICE ENTRANCE
• 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.
• The conductor and equipment for delivering energy from the electricity supply system to the wiring system of the premises served.
SERVICE ENTRANCE
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.
SERVICE ENTRANCE
TYPES:
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.
SERVICE - ENTRANCE CONDUCTORS
SIZE AND RATING: Service entrance conductors shall be of sufficient size to carry the computed loads.
Ungrounded conductors shall not be smaller than:
1. 100 A ---- For one family dwelling with six or more 2-wire branch circuits.
2. 60 A ---- For one family dwelling with an initial computed load of 10 kVA above.
3. 40 A ---- For other loads.
SERVICE - ENTRANCE CONDUCTORS
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. Type IGS cable
INSTALLATION OF SERVICE CONDUCTORS
3. Rigid Metal Conduit (RMC)
4. Intermediate Metallic Tubing (IMT)
5. Electrical Metallic Tubing (EMT)
6. Electrical Nonmetallic Tubing (ENT)
7. Service-Entrance Cables
8. Wireways
9. Busways
10. Auxiliary gutters
INSTALLATION OF SERVICE CONDUCTORS
11. Rigid Non-Metallic Conduit (RNMC)
12. Cable Bus
13. Mineral-Insulated Metal-Sheated Cable
14. Type MC Cables
15. Liquidtight flexible nonmetallic conduit
INSTALLATION OF SERVICE CONDUCTORS16. Flexible metal conduit not over 1 800 mm long or
liquidtight flexible metal conduit not over 1 800 mm long between raceways, or between raceway and service equipment, with equipment bonding jumper routed with the flexible metal conduit or the liquidtight flexible metal conduit according to the provisions
INSTALLATION OF SERVICE CONDUCTORSPROTECTION:
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 MEANSGENERAL:
The service-disconnecting means shall be provided to disconnect all conductors in a building or other structures from the service-entrance conductor.
THE SERVICE EQUIPMENT-DISCONNECTING MEANSNUMBER 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.
THE SERVICE EQUIPMENT-DISCONNECTING MEANSLOCATION:
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
THE SERVICE EQUIPMENT-DISCONNECTING MEANSRATING:
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.
THE SERVICE EQUIPMENT-DISCONNECTING MEANS3. 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.
ELECTRIC SERVICE METERING
Electric Meter
Generally installed outside the building at the property line wall, or electric post for ready access to meter reader, making it more difficult to tamper or install jumpers.
FEEDER
• All circuit conductors between the service equipment or the generator switchboard of an isolated plant, and the final branch circuit overcurrent device.
Considerations on installing feeders
1. On large installation, each floor is provided with one feeder.
2. In small installations, 1 or 2 feeders is satisfactory.
3. Feeder for electrical motor must be separate and independent from the light circuits.
Considerations on installing feeders
4. Feeders requiring more than 50 mm diameter conduit should not be used.
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.
Considerations on installing feeders
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.
Main
• Feeder interior wiring extending from the service switch, generator bus, or converter bus, to the main distribution center or electric service equipments.
GROUND
➢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.
➢purpose is to fix permanently a zero voltage point in the system.
➢grounded line of a circuit should not be broken nor fused to maintain a solid and uninterrupted connection to the ground.
GROUNDING PROTECTION
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.
Reasons for Grounding the Circuit System1. Prevent a sustained contact between the low voltage
secondary line and the high voltage primary line in case of insulation fire
2. To prevent single grounds from being unnoticed or detected until a second ground occurs which could totally disable the secondary line.
Reasons for Grounding the Circuit System3. To facilitate in locating ground faults
4. To protect against a short sudden rush of electric current in the circuit
5. To establish a neutral at zero potential not to be interrupted by switches or other devices
6. To connect the service entrance to ground only at one point and to use colored wires for easy identification
Circuit Safe Load
How to determine the types of wire to be used, their sizes and other appurtenances relative to installation
1. Wirings for electric circuitry shall be of types RHW, T, THW, TW, THWN, XHHW in a raceway
2. A single appliance shall not draw a maximum load of 12 A on a 15 A circuit
Circuit Safe Load
3. A single appliance shall not draw current in excess of 16 A on a 20 A circuit
4. If a branch circuit is combined with lighting or portable appliances, any fixed appliance shall not be allowed to draw more than 7.5 amperes on a 15 amperes circuit and 10 amperes on a 20 amperes circuit.
Circuit Safe Load
5. On a 30 amperes circuit, a single appliance draw shall not exceed 24 amperes.
6. A heavy lamp holder shall not be rated not less than 750 watts.
7. A 30, 40, and 50 amperes circuit shall not be used for fixed lighting in residences.
Circuit Safe Load
8. When loads are connected for a long period of time, its actual load shall be computed not to exceed 80% of the fuse rating.
9. A continuous type load shall be considered at 125% of the actual load in all load calculations.
10. A single receptacle on individual branch circuit shall have a rating of not less than the circuit.
Circuit Safe Load
11. Receptacles feeding portable and/or steady appliance shall be limited to loads of 80% of their rating.
12. The number of outlets shall be limited to:
6 outlets on a 15 ampere circuit
8 outlets on a 20 ampere circuit
WIRING CALCULATIONS
WIRING CALCULATIONS FOR SINGLE
FAMILY DWELLING UNIT
Conduit Size (mm)
Wire
Size
Number of wire in One Conduit
1 2 3 4 5 6 7 8 9
14 13 13 13 20 20 25 26 27 28
12 13 13 20 20 20 25 25 25 32
10 13 20 20 25 25 25 32 32 32
8 13 20 25 25 25 32 32 32 32
6 13 25 32 32 38 38 50 50 50
5 20 32 32 32 38 50 50 50 50
4 20 32 32 38 50 50 50 50 63
3 20 32 32 38 50 50 50 63 63
2 20 32 38 38 50 50 63 63 63
1 20 38 38 50 50 63 63 75 75
Lighting Load
NEC:
“100 watts shall be the maximum load for each
household lighting outlet.”
“Ampacity of the connected load shall not
exceed 80% of the average capacity of the
conductor and the fuse.”
Lighting Load
A single family dwelling is to be circuited with 8 lighting outlets. Consider a 230 V Service, Single Phase 2 wire 60Hz
Determine the:
a) size of the branch circuit wire for lighting outlets
b) size of the conduit pipes
c) size or rating of the fuse protective device
Small Appliance Load
• NEC:
“For each single receptacle shall be considered at no less than 180 watts rating.”
Example
Solve for
Total Estimated Load
Max Expected Current Load
Size of Conductor Wire
Size of Conduit Pipe
Overcurrent fuse protection
Other Loads
If the other loads are a 1.1kW electric stove and a 2.5 kW water heater, determine:
a) Size of the conductor wire
b) Size of conduit pipe
c) Rating of the overcurrent protection
Service Entrance
“Use 8.0 mm2 or No. 8 AWG conductor as the minimum size for service entrance.”
*Demand factor must be considered.
Activity
Circuit 1: 10 light outlets
Circuit 2: 9 light outlets
Circuit 3: 6 convenience outlets
Circuit 4: 8 convenience outlets
Circuit 5: 8 kW Range
Circuit 6: 2.5 kW Water Heater
Circuit 7: 1 HP Aircon
Circuit 8: 0.5 HP Aircon
Compute for each circuit wire size, conduit size and OCP
Determine the conductor size of the main feeder, conduit size and main breaker rating
