electrical system illumination1tsy201314
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Electrical System
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Ampacity of Conductors
- ability of wire or conductor to carry current
without overheating.
National Electrical Code ( NEC) provides that:
“ Conductor size and rating shall have sufficient
ampacity to carry load. They shall have adequate
mechanical strength and shall not be less thanthe rating of the branch circuit and not less than
the maximum load to be served”
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Conductor Ampacity
- is determined by the maximum operating
temperature that its insulation can withstand
continuously without overheating
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Example:
Size : 2 mm2 ( 14 AWG )
at 600C : Ampacity = 15 ampere
Type of insulation: T , TW
at 750C : Ampacity = 15 amperes
Type of insulation: RHW, THW, THWN
at 900C : Ampacity = 25 amperes
Type of insulation: SA, RHH , THHNat 1100C : Ampacity = 30 amperes
Type of insulation : AVA
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Raceway
- Are channels or wiring accessories so design forholding wires, cables or busbars that are either madeof metal, plastic, or any insulating mediums.
Types for household wiring
1. The conduits
2. The connectors and other accessories
3. Conduit coupling, elbows and other fittings
4. Conduit supports, such as clamps, hanger5. Cable trays, cable bus, etc
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Conduit
- conduit pipe is the most common electric
raceways used in all types of construction.
Classifications:
1. Metallic such as steel pipes, aluminum, etc
2. Non –metallic such as plastics
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Outlet and Receptacles
Outlet - is any point that supplies an electric
load.
- usually consist of a small metal or non metal
box into which a raceway and or cable ends.
- refers only to the box itself
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Different kinds of outlet
1. Convenience outlet or attachment cap
2. Lighting outlet
3. Receptacle outlet
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Receptacles - are contact device installed at the
outlet fro the connection of a single
attachment plug.
A wall convenience receptacles is vertically
mounted between 30 to 45 centimeters above
the finished floor line.
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Branch Circuit ( by NEC)
- the circuit conductors between the final over
current protective device and the outlets
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Protection of the Branch Circuit
As a rule, branch circuit should be protected
from over current
NEC….. “ Conductors shall be protected against
over current in accordance with their
ampacities”
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By definition,
Over Current is any current in excess of the
rated capacity of the equipment or rated
ampacity of the conductor.
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Fuse , Breaker and Panel Board
Fuse - an over all current protected device with acircuit opening fusible element which openswhen there is an over current in the circuit.
- is a single pole , installed on a single wire thatcould only protect a single electric line.
- consist of a fusible link or wire that easilymelt at low temperature classified into two types:
1. Cartridge type - enclosed in an insulating fivertube
2. Plug Fuse type – enclosed in a porcelain cap
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Circuit Breaker
-is 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.
- can be manually tripped ,,acts as circuit
switch.
- multiple pole, 1 , 2, or 3 poles
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Panel Board
NEC …. A single panel or group of panel limits
designed for assembly in the from of a single
panel.
- known as panel or electrical panel
- simply a box wherein the protective
devices are grouped from which they are fed.
- Fuse Panel , Breaker Panel
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Panel board with 100 cm high or less should be
located 135 cm from the floor to the center
line of the box.
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Panel board with boxes over 100 cm high should
be located 75 cm from the floor to the bottom
of the box, except that the highest branch
circuit unit should not be more than 195 cmfrom the floor.
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If necessary, the box maybe lowered to a
distance not less than 45 cm from the floor to
the bottom of the box. However, where a
maximum height of 195 cm above the floor tothe upper circuit or a distance of 45 cm above
the floor cannot be done, the panel should be
divided into two sections.
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If two or more boxes are adjacent on the same
wall, they should be installed with the
horizontal center line of each box equidistance
from the floor. The center line distance of thehigher box controlling the boxes should be
installed with a minimum spacing of 10 com
apart.
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Switchboard and Switchgear
- are free standing assemblies of switches, fuses
and circuit breakers that provide switching
and feeder protection to a number of circuits
connected to the main source.
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FEEDER
NEC …… All circuit conductors between the
service equipment or the generator
switchboard of an isolated plant, and the final
branch circuit over current devices.
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Location of Service Equipment
1. Should be centrally located to shorten all
home runs. Branch circuit run in excess of 30
meters will have an excessive voltage drop.
2. Accessible and convenient to approach
3. In residential houses, it is located near the
heaviest load center such as the kitchen and
laundry area.
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Design of the Electrical System of Residential Building
( 1 storey and 2 storey)
Scale: 1 : 100 m ------ 1 cm - 1 m
1 : 50 m ------ 2 cm – 1 m
Lighting outlet shall be separated from the circuit of convenienceoutlet except in occupancies where the total connected load doesnot exceeds 15 amperes.
For ideal design, the maximum number of outlets per circuit = 12
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Schedule of loads:
Method of Computation:A. Design Load Method
B. Area Method
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Electrical Plan consist of the following:
• Floor Plan layout – Lighting
– Power
• Schedule of Loads
• Riser Single Line Diagram• Design Computations / Analysis
• Location Plan / Site Plan
• Legend
• Optionals: Details
•
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Assignment:
Floor Area : 100 meters up to 150 meters
Draw a floor plans ( 3 identical )1 floor plan: label properly e.g rooms ,
dimension
2 and 3 floor plan: ?????????USE: small tracing paper, 1 inch margin in all
sides
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DESIGN LOAD METHOD
100VA per L.O
200 VA per C.O.180 VA per CO