Download FUNDAMENTALS OF WATER

COMMERCIAL ELECTRICAL
(Chapter 11)
Conduit
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Pathway for wiring that protects conductors
Types
Aluminum
Plastic
Fittings
Size (additional information)
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Depends on number of conductors
Minimum: ½”
COMMERCIAL ELECTRICAL
(Chapter 11)
Conductors
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Types
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Copper
Aluminum
Conductor size (additional information)
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lower sizes are designated by AWG (40 to 0000)
higher sizes are designated by MCM (250 to 2000).
cross-section of a conductor is calculated in circular mils (CM
or cmil)
a circular mil is the area of a circle 0.001 inch (0.001 in = 1 mil)
in diameter
cross-sectional area of round conductor is found out by
squaring its diameter expressed in mils
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cross-sectional area of a conductor 0.005 inch in diameter would
be 5 x 5 = 25 cmil.
COMMERCIAL ELECTRICAL
(Chapter 11)
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Conductor Insulation (additional
information)
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Letter designators
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T = thermoplastic
R = Rubber
H = heat resistant
W = moisture resistant
N = nylon reinforcing
COMMERCIAL ELECTRICAL
(Chapter 11)
Installing conductors
Special conduits
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Cable tray
Busway
Raceway
Under floor duct
COMMERCIAL
ELECTRICAL
Conductor ampacity (additional information)
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current carrying capacity of a conductor
affected by
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the size of a conductor
max. permissible insulation (operating) temperature
ambient temperature
Circuits
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Lighting circuits (additional information)
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Generally protected with 20 A circuit breakers
Feeder circuit
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Branch circuit
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Circuit between an OCPD and utilization equipment (i.e. an equipment that receives power through the
circuit)
Power circuits (additional information)
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Circuit between a service panel or main panel and an OCPD in a sub-panel protecting a branch circuit
For motors, electrical equipment, receptacles
Feeder circuit
Branch circuit
Dedicated circuits and UPS
COMMERCIAL
ELECTRICAL
Panels
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Receives the service electricity and distributes it to branch circuits
Lighting and power panels (additional information)
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Required to sub-divide and protect individual circuits
Contains circuit breakers
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Bus bars in panels facilitate connection of individual circuit breakers
If there is more than one panel board, then the one receiving the supply
from the service entrance may be termed as the main panel (service
panel) and other panels that receive supply from this panel may be
termed as sub-panels
number of circuits required in the building determines the size of a
service panel
number of circuits to be fed by a sub-panel determines its size
the panel(s) may either be surface-mounted or recessed and should be
conveniently located for easy servicing and resetting of circuit breakers
or fuses
Switchgear
COMMERCIAL
ELECTRICAL
Services (additional information)
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Electric service:
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overhead service drop
underground service lateral
3-phase services
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Three hot phase conductors and one neutral conductor
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The neutral only carries unbalanced load for a 3-phase
connection
Delta configuration: for industrial application
Wye configuration: for office buildings and shopping
centers
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In wye systems, phase-to-phase voltage is √3 or 1.73
times the phase-to-neutral connection
COMMERCIAL
ELECTRICAL
Transformers (additional information)
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Used for stepping up or stepping down AC voltages and current
Available in single- or three-phase type
Capacity is rated in kilovolt-amperes (kVA)
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Capacity of a three-phase transformer for a load of 500 A at 480 V =
500x480x1.73 = 415200 VA = 415.2 kVA
Voltage coming into a transformer from a generating plant is the
primary voltage, and voltage leaving the transformer is the
secondary voltage
Transformers operate on the principle of magnetic induction
Coils are wound around a common silicon steel core
Voltage is induced from primary to secondary due to magnetic
induction
The ratio of secondary (Vs) to primary (Vp) voltage is equal to the
ratio of secondary (Ns) to primary (Ns) winding turns of the coils
(i.e. Vs/Vp = Ns/Np).
COMMERCIAL
ELECTRICAL
Service capacity
Service size
 Service disconnects (main disconnect)
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Rated in amperes
Meter (additional information)
required for registering the amount of energy
consumed
 always installed electrically ahead of main
disconnect
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COMMERCIAL ELECTRICAL
(Additional information)
Overcurrent protection device (OCPD)
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a protective device that automatically cuts off power supply
to any circuit, which is overloaded or short-circuited
may either be a (1) fuse or a (2) circuit breaker
The overcurrent protection devices are installed within the
panel boards
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A fuse is a self-destructive device (containing a fusible link) that
melts upon sensing an abnormal current and opens the circuit
in which it is installed. It is rated in amperes.
A circuit breaker acts both as an OCPD and a switch. It
consists of a thermal trip that opens the circuit when there is
high temperature build-up inside the CB (usually due to
overcurrent), and a magnetic trip that provides short-circuit
protection. A CB is also rated in amperes
COMMERCIAL ELECTRICAL
(Additional information)
Receptacle (convenience outlet)
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a contact device installed at an outlet for
connection of an attachment plug
used for plugging in lights and small appliances
Grounding
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Systems grounding: Connecting neutral wire of
wiring systems to earth. It establishes a neutral
wire at zero potential for safety and reference
Equipment grounding: Connecting all non-current
carrying metal parts of wiring system to the earth
ELECTRIC WIRING DESIGN
(Additional information)
Electrical load
Lighting
 HVAC
 Plumbing and sanitary
 Elevators
 Kitchen equipment
 Miscellaneous (e.g. computers,
convenience outlets, etc.)
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ELECTRIC WIRING DESIGN
(Additional information)
Available system voltages
120 V single-phase
 120/240 V single phase
 120/208 V single phase
 120/208 V three-phase
 277/480 V three-phase
 2400/4160 V three-phase
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ELECTRIC WIRING DESIGN
(Additional information)
OCPD
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must be placed on all ungrounded conductors
all 'hot' wires are ungrounded
Branch circuit design
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must be designed for load connected to it +
expected load expansion.
conduit sizes must be a minimum of 1/2".
a general-purpose branch circuit should be 20 A
and wired with #12AWG wire. Circuit load should
not be 64% (@ 25% expansion) for lighting loads
ELECTRIC WIRING DESIGN
(Additional information)
What is meant by % load and % expansion?
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A 20 A branch circuit @ 120 V, single phase may carry an
electrical load of 20x120 =2400W. A general purpose branch
circuit is not allowed to carry more than 80% of this quantity,
provided no future expansion of load is envisaged for this
circuit (i.e. 0% expansion)
Usually an expansion of 25% of current load is envisaged for
a general purpose branch circuit. Under such circumstances,
the actual load of a circuit shall not exceed 64% of the load it
may carry theoretically. In case of a 20 A, 120 V singlephase circuit, this load would be 2,400X0.64=1536 W (say,
1500).
ELECTRIC WIRING DESIGN
(Additional information)
For small offices, there should be
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one receptacle/40 sft. for first 400 sft. subject to a minimum of one
receptacle for every 10 lft. of wall length
One receptacle per 100 sft. for area in excess of 400 sft.
There shall not be more than 6 receptacles to a 20 A circuit in an office.
Corridors should have a 20 A, 120 V receptacle every 50 ft.
Each receptacle is counted as 1.5 A (180 W).
Receptacles behind a counter top shall be 4 ft. o.c.
Provide a min. of 2 circuits @ kitchen counter
Do not connect more than 4 small appliances to a 20 A circuit.
Calculate lighting load @ 125% of actual value.
Provide GFCI type receptacles in bathrooms and outdoors.
Allow 25% spare circuits based on number of poles and load.
Allow 25% spaces based on number of poles.
Calculate spare circuit loads @ the average value of the active circuit loads