Basics of Electrical System Desiiign.pdf

Basics of Electrical
System Design

Definition of Terms
● Electrical conductors - materials that offer a very low
resistance to current flow.
○ silver, zinc, copper, aluminum, platinum, lead
● Insulators - materials that offer a very high resistance to
current flow.
○ rubber, asbestos, porcelain, paper, dry air, mica, glass

Definition of Terms
● Wire - In electrical
jargon, the term
“wire” is used to
indicate the
conductor.

Definition of Terms
● Wires - Either solid or stranded.
● All electrical wires carry a cover of insulation material such as
PVC or rubber to prevent contact between the wires.

Definition of Terms
● Cables - in electrical jargon, it simply means a wire or a
conductor with an insulation cover.

Definition of Terms
● Other types of cables

Types of Electric Cable
Trade Name / Characteristics
Code/Type Letter and
Maximum Operating
Temperature
Application Provisions
● Flame retardant
● Moisture and Heat
Resistant Thermoplastic
insulation
THW / 75 OC
● Dry and Wet Location
● Building wiring, feeder and
branch circuit
● Internal secondary
industrial distribution
● Flame retardant
● Heat Resistant
Thermoplastic insulation
THHN / 90 OC
● Dry Location
● Wiring of machine tools,
control circuits or on
certain appliances.

Types of Electric Cable
Trade Name / Characteristics
Code/Type Letter and
Maximum Operating
Temperature
Application Provisions
● Flame retardant
● Moisture - Resistant
Thermoplastic insulation
TW / 60 OC
● Building wiring, feeder and
branch circuit
● Internal secondary
industrial distribution
● Flame retardant
● Moisture and Heat
Resistant Thermoplastic
insulation
THWN / 75 OC
● Installation of in conduit,
machine tools, controlled
circuits, or other general
purpose wiring

What is Cable Raceway
● It provide a surface-mounted pathway for wiring that
completely encloses the cables and protects them from
heat, dust, light and even moisture.
● A great tool for routing wiring and for concealing cables
that would otherwise be exposed.

What is Cable Raceway
● These are also sometimes referred to as a latching duct
solution, as the raceway itself acts as a duct, and the 360
enclosure around the wire can have a latching mechanism
to securely hold all wiring in place.

Types of Cable Raceways
● Latching - also known as surface
raceways and latching ducts, most
common and widely used raceways.
Used for wiring enclosures in many
residential and office settings where
new wiring has been installed on
the outside of a wall.

● Corner Duct - These are ideal for
residential use, as corner duct
raceways mimic the look of crown
molding and make for an attractive
cable management setup.

● Overfloor - protect cables and wires
from being tripped over or
unplugged. They are usually flatter
and more low profile to avoid
creating an unnecessary tripping
hazard.

● Exterior Wire Guards - these are
commonly found at outdoor
concerts or festivals and cover and
protect the large cables that are run
along the ground.

● Flexible Wire Duct - these cable
raceways are a versatile wiring
enclosure that can be used in both
industrial and commercial
applications.

Cable Raceway Benefits
● Easy to install - Most varieties are surface raceways and can
be easily affixed to any wall in just a couple of steps.
● Streamlined cable management - With electrical raceways,
all of your cables and wires can be fed through the plastic
duct and kept out of sight and out of mind.
● Promotes safety - Using cable raceways makes everyone
safer and ensures that all cables and wires are protected.

What is an electrical conduit?
● Electrical conduit is a raceway used to house and protect
electrical wires within a building or structure.
● The specified conduit for your project may be rigid or
flexible and will offer varying degrees of protection from
impact, corrosion, gases and vapors, moisture, fire, and
even electromagnetic interference, depending on the
needs of the installation environment.

Types of Electrical Conduits
• Rigid Metal Conduit (RMC)
• Galvanized Rigid Steel Conduit (GRC)
• Intermediate Metal Conduit (IMC)
• Electrical Metallic Tubing (EMT)
• Rigid Nonmetallic Conduit (RNC)
• Reinforced thermosetting resin conduit (RTRC)
• PVC Conduit
• Electrical Nonmetallic Tubing (ENT)

Types of Junction Box
● Standard
residential
junction box

● Round Pan
Electrical
boxes

● Octagon
Junction Boxes

● Gang Boxes

● Outdoor
Junction Boxes

Circuit Breaker
● switching device
● offers protection by tripping & cutting off the supply to
load in case of fault (overload, short circuit)

What is an Electrical Plan?
● sometimes called as electrical drawing or wiring diagram
● a type of technical drawing that delivers visual
representation and describes circuits and electrical
systems
● an electrical plan describes the position of all the
electrical apparatus

An electrical drawing may include all of these essential
details described below:
● Interconnection of electrical wires and other parts of the
system
● Connection of different components and fixtures to the
system
● Power lines with details such as size, voltage, rating, and
capacity

An electrical drawing may include all of these essential
details described below:
● Power transformers and also their winding connections
● The main switches, tiebreaker, and fused switches
● Other essential equipment such as solar panels, batteries,
generators, air conditioning, and so on

Why is there a need to have an electrical
plan or drawing?
The purposes of an electrical plan are as follows:
● These drawings are vital for documenting, communicating
information, and troubleshooting your power systems on-
site.
● Accurate and updated drawings keep your building in
compliance with all the code regulations.

plan or drawing?
The purposes of an electrical plan are as follows:
● It is a thorough planning tool because it gives an in-depth
view of your building's electrical and wiring system.
● It helps to distribute power to various appliances and
equipment through accurate operation and installation of
elements.

plan or drawing?
Benefits of an Electrical Plan
● A plan highlights all the potential risks to make
amendments quickly before the occurrence of any
substantial damage.
● It helps to ensure that your system runs safely, efficiently,
and smoothly.

Parts of an Electrical Plan
● Location and Site Plans
● General Notes and/or Specifications
● Legend or Symbols (Electrical Symbols)
● Electrical Layout (i.e. Lighting, Power Layout)
● Load Schedule
● Design Analysis
● Panel Board Details or Single Line Diagram

Legend or Symbols in an Electrical Plan
Power Symbols
Duplex Outlet
Triplex Outlet
Simplex Outlet

Power Symbols
Weatherproof Duplex
Outlet
Ground Fault Circuit
Duplex Outlet
Duplex Outlet - One Receptacle
Controlled by Switch

Power Symbols
Duplex Outlet on
Emergency Branch
Double Duplex Outlet
(a.k.a Quad Outlet)
Switch
3-Way Switch

Power Symbols
Switch with built-in
Dimmer
Power Panel
Lighting Panel

Power Symbols
Junction Box
Recessed Floor
Box

Lighting Symbols
2x2 Recessed
Light
Recessed
Linear Light
2x4 Recessed
Light

Lighting Symbols
Track Lighting
Wall Mounted
Light

Branch Circuit Load Calculations
● General Lighting Loads
● Small Appliance Branch Circuits
● Receptacles

Single Dwelling Unit
Plot Area: 120 m2 (1 Floor only)
Floor: 1
Appliances
● Typical Household
Appliances
● 1- Electric Range - 6KW
● 1- Electric Dryer - 4KW
● 1-Water Heater - 4.5KW
● 1-Booster Pump - 1.5HP
● 1-ACU - 3HP
● 3-ACU - 1HP

2.20.2 Branch Circuit Calculations
2.20.2.1 General. Branch-circuit loads shall be calculated as
shown in 2.20.2.3, 2.20.2,5, and 2.20.2.7.
2.20.2.3 Lighting Load for Specified Occupancies
2.20.2.5 Other Loads - For All Occupancies
2.20.2.7 Loads for Additions to Existing Installations

2.20.2 Branch Circuit Calculations
2.20.2.3 Lighting Load for Specified Occupancies. A unit
load of not less than that specified in Table 2.20.2.3 for
occupancies specified shall constitute the minimum lighting
load. The floor area for each floor shall be calculated from the
outside dimensions of the building, dwelling unit, or other
area involved. For dwelling units, the calculated floor area
shall not include open porches, garages, or unused or
unfinished spaces not adaptable for future use.

Total Area = 73 m2
Total Volt-Ampere = 24 x 73 = 1,752 VA
Total Amperes = 1,752 / 230 = 7.62 A
Therefore, at least one 15 Ampere-rated
branch circuit is required.

Layout of the lighting and switches
● 2.10.3.21 Lighting Outlets Required
● 2.10.1.11(C)1 through 4 Dwelling Units
Branch Requirements
Minimum number of branch circuit: at least
one 15 Ampere-rated.
However, it is permissible to have two or
more 15 Ampere-rated, or 20 Ampere-rated
branch circuits for this layout.

For the Receptacle/Outlet Layout and Other
Loads:
2.20.2.5 Other Loads - All Occupancies. In all
occupancies, the minimum load for each outlet
for general-use receptacles and outlets not used
for general illumination shall not be less than
that calculated in 2.20.2.5(A) through (L), the
loads shown being based on nominal branch-
circuit voltages.
2.10.3.3(A)(1) - Required Outlets for Dwelling
Units.
2.10.1.8 - GFCI for Personnel Protection
4.6.1.9 - Receptacles in Wet and Damp
Location
2.10.1.11(C)1 through 4 Dwelling Units Branch

2.10.2.2 Conductors - Minimum Ampacity and
Size
(A)Branch Circuits Not More than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity
not less than the maximum load to be served. Conductors
shall be sized to carry not less than the larger of
2.10.2.2(A)(1)(a) or (b).
(a) Where a branch circuit supplies continuous loads or any
combination of continuous and noncontinuous loads,
the minimum branch circuit conductors size shall have
an allowable ampacity not less than the noncontinuous
load plus 125 percent of the continuous load.

Size
Sample Problem
A branch circuit has a continuous load of 8 amperes and a
noncontinuous load of 10 amperes. What will be the minimum size
of the conductor? (noncontinuous load plus 125 percent of the continuous load)
10 + (8*1.25) = 20 Amperes
Conductor must be sized to have an ampacity of not less than 20
Amperes.

Size
(b) The minimum branch-circuit conductor size shall have
an allowable ampacity not less than the maximum load to be
served after the application of any adjustment of correction
factors.

Size
(b) The minimum branch-circuit conductor size shall have
an allowable ampacity not less than the maximum load to be
served after the application of any adjustment of correction
factors.
All conductors installation and application is not more than
three current-carrying conductors in a conduit, and the
ambient temperature is 30oC. Hence, adjustment factor and
correction is 100%.

2.10.2.3 Overcurrent Protection
Branch-circuit conductors and equipment shall be protected by
overcurrent protective devices that have a rating or setting that
complies with 2.10.2.3(A) through (D).
(A)Continuous and Noncontinuous Loads. Where a branch
circuit supplies continuous loads or any combination of
continuous and noncontinuous loads, the rating of the
overcurrent device shall not be less than the
noncontinuous load plus 125 percent of the continuous
load.

Sample Problem
A branch circuit has a continuous load of 8 amperes and a
noncontinuous load of 10 amperes. What will be the minimum
size of the conductor? (noncontinuous load plus 125 percent of the continuous load)
10 + (8*1.25) = 20 Amperes
Conductor must be sized to have an ampacity of not less than
20 Amperes. Therefore the overcurrent protective device
shall not be less than 20 Amperes

As shown above, the overcurrent protective device shall be
20 Ampere Trip or 20 AT.

2.50.6.13 Size of Equipment Grounding
Conductors
(A)General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall be
smaller than shown in Table 2.50.6.13, but in no case shall
they be required to be larger than the circuit conductors
supplying the equipment. Where a cable tray, a raceway,
or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 2.50.6.9 and
2.5.7.5(A), it shall comply with 2.50.1.4.(A)(5) or (B)(4).

Sample Problem
10 + (8*1.25) = 20 Amperes
Conductor must be sized to
have an ampacity of not less
than 20 Amperes.
Therefore the overcurrent
protective device shall not
be less than 20 Amperes.
Hence, the size of EGC is
3.5mm2.

Branch Circuit #1: 1,752 VA (continuous load)
(1,752/230)=7.62 A, hence, 7.62A x 1.25 = 9.52 A
Conductor size is 2.0 mm2 - Table 3.10.2.6(B)(16)
CB size is 15 Ampere Trip or 15 AT - Table 2.40.1.6(A)
EGC size is 2.0 mm2 - Table 2.50.6.13

2.20.3.13 Small-Appliance and Laundry
Loads - Dwelling Unit
(A)Small-Appliance Circuit Load. In each dwelling unit, the
load shall be calculated at 1500 volt-amperes for each 2-
wire small appliance branch circuit as covered by
2.10.1.11(C)(1). Where the load is subdivided through two or
more feeders, the calculated load for each shall include
not less than 1500 volt-amperes for each 2-wire small-
appliance branch circuit. These loads shall be permitted to
be included with the general lighting load and subjected
to the demand factors provided in Table 2.20.3.3.

(C) Dwelling Units.
(1) Small-Appliance Branch Circuits. In addition to the
number of branch circuits required by other parts of
this section, one or more 20-ampere small-appliance
branch circuits shall be provided for all receptacle
outlets specified by 2.10.3.3(B).

Branch Circuit #2 and #3: 1,500 Volt-Amperes
Conductor size: 3.5 mm2 - Table 3.10.2.6(B)(16)
EGC size: 3.5 mm2 - Table 2.50.6.13

(B) Laundry Circuit Load. A load of not less than 1500 volt-
amperes shall be included for each 2-wire laundry branch
circuit installed as covered by 2.10.1.11(C)(2). This load shall be
permitted to be included with the general lighting load and
subjected to the demand factors provided in Table 2.20.3.3.

2.10.1.11(C)(2)
(2) Laundry Branch Circuits. In addition to the number of
branch circuits required by other parts of this section, at least
one additional 20-ampere branch circuit shall be provided to
supply the laundry receptacle outlet(s) required by 2.10.3.3(F).
This shall have no other outlets.

2.10.1.11(C)(3) & (4)
(3) Bathroom Branch Circuits. In addition to the number of
one additional 230-volt, 20-ampere branch circuit shall be
provided to supply bathroom receptacle outlet(s). Such
circuits shall have no other outlets.

2.10.1.11(C)(3) & (4)
(4) Garage Branch Circuits. In addition to the number of
one 230 or 115-volt, 20-ampere branch circuit shall be
installed to supply receptacle outlets inn attached garages
and in detached garages with electric power. This circuit
shall have no other outlets.

What are those receptacle outlets
covered in 2.20.2.5(J) and (K)?
2.20.2.5(J)
(J) Dwelling Occupancies. In one-family, two-family and
multifamily dwellings, and in guest rooms or guest suites of
hotels and motels, the outlets specified in (J)(1), (J)(2), and
(J)(3) are included in the general lighting load calculations of
2.20.2.3. No additional load calculations shall be required for
such outlets.

Recap
● General Lighting Loads for
Dwelling Unit Includes:
○ General Areas
○ Bathroom
○ Garages
○ Lightings
No additional calculation
required for the outlets
installed in these areas.
● Small Appliance Branch
Circuits should be calculated
at least 1500 Volt-Amperes
○ Kitchen
○ Pantry
○ Breakfast Room and similar
areas
The 180 VA rating for each
receptacle outlet does not apply
to all type of dwelling units.

Branch Circuit Load Calculations
● Electric Cooker/Ranges
● Electric Clothes Dryer
● Water Heater
● Motor Loads and AC Units

Article 4.22 - Appliances
4.22.2.4 Storage-Type Water Heaters. A fixed storage type
water heater that has a capacity of 450 L or less shall be
considered a continuous load for the purposes of sizing
branch circuits.
4.5kw Storage Type Water Heater
(4500/230)x1.25 = 24.46 Amperes

4.22.2.4 Storage-Type Water Heaters. A fixed storage type
water heater that has a capacity of 450 L or less shall be
considered a continuous load for the purposes of sizing
branch circuits.
(4500/230)x1.25 = 24.46 Amperes

(E) Single Non-Motor-Operated Appliance. If the branch
circuit supplies a single non-motor-operated appliance, the
rating of overcurrent protection shall comply with the
following:
(1) Not exceed that marked on the appliance.
(2) Not exceed 20 amperes if the overcurrent protection
rating is not marked and the appliance is rated 13.3 amperes
or less; or

(3) Not exceed 150 percent of the appliance rated current if
the overcurrent protection rating is not marked and the
appliance is rated over 13.3 amperes. Where 150 percent of
the appliance rating does not correspond to a standard
overcurrent device ampere rating, the next higher standard
rating shall be permitted.

(4500/230)x1.25 = 24.46 Amperes
(4500/230) = 19.57 Amperes
Maximum Overcurrent Protection = 19.57 x 1.5 = 29.36 A

2.20.3.15 Electric Clothes Dryers -
Dwelling Unit
The load for household electric clothes dryers in a dwelling unit(s)
shall be either 5000 watts (volt-amperes) or the nameplate rating,
whichever is larger, for each dryer served. The use of the demand
factors in Table 2.20.3.15 shall be permitted. Where two or more
single-phase dryers are supplied by a 3-phase, 4 wire feeder or
service, the total load shall be calculated on the basis of twice the
maximum number connected between any two phases. Kilovolt-
amperes (kVA shall be considered equivalent to kilowatts (kW) for
loads calculated in this section.

2.20.3.16 Electric Cooking Appliance in Dwelling
Units and Household Cooking Appliances Used in
Instructional Programs
The load for household electric ranges, wall-mounted overs,
counter-mounted cooking units, and other household
cooking appliances individually rated in excess of 1 ¾ kW
shall be permitted to be calculated in accordance with Table
2.20.3.16. Kilovolt-amperes (kVA shall be considered
equivalent to kilowatts (kW) for loads calculated in this
section.

4. Branch-Circuit Load. It shall be permissible to calculate the
branch-circuit load for one range in accordance with Table
2.20.3.16. 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 calculated by adding the nameplate
rating of the individual appliances and treating this total as
equivalent to one range.

6kw Electric range
(6000/230) = 26.09 Amperes

2.10.2.2 Conductors - Minimum
Ampacity and Size
(A)Branch Circuits Not More Than 600 Volts.
(4) Other Loads. Branch-circuit conductors that supply loads
other than those specified in 2.10.1.3 and other than cooking
appliances as covered in 2.10.2.2(A)(3) shall have an ampacity
sufficient for the loads served and shall not be smaller than
2.0 mm2 (1.6 mm dia).

Since the electric clothes dryer is not
included on the list, hence, the
computation would be as follow:
5000/230 = 21.74 Amperes
Conductor size: 5.5 mm2 - Table
3.10.2.6(B)(16)
CB size is 25 Ampere Trip or 25 AT -
Table 2.40.1.6(A)

1.5 HP Booster Pump
Full-Load Current: 10 Amperes

4.30.2 Motor Circuit Conductors
4.30.2.2 Single Motor. Conductors that supply a single motor
used in a continuous duty application shall have an ampacity
of not less than 125 percent of the motor full-load current
rating, as determined by 4.30.1.6(A)(1) or not less than
specified in 4.30.2.2(A) through (G).
1.5 HP Booster Pump
10 x 1.25 = 12.50 Amperes

1.5 HP Booster Pump
10 x 2.5 = 25 Amperes

1.5 HP Split Type AC
10 x 1.25 = 12.50 Amperes

Article 4.40.3 - Branch-Circuit Short-Circuit
and Ground-Fault Protection
4.40.3.2 Application and Selection.
(A) Rating or Setting for Individual Motor-Compressor. The motor-compressor
branch-circuit short-circuit and ground-fault protective device shall be capable of
carrying the starting current of the motor. A protective device having a rating or setting
not exceeding 175 percent of the motor-compressor rated-load current or branch-
circuit selection current, whichever is greater, shall be permitted, provided that, where
the protection specified is not sufficient for the starting current fo the motor, the rating
or setting shall be permitted to be increased but shall not exceed 225 percent of the
motor rated-load current or branch circuit selection current, whichever is greater.
Exception: The rating of the branch-circuit short-circuit and ground-fault protective
device shall not be required to be less than 15 amperes.

10 x 1.25 = 12.50 Amperes
10x1.75 = 17.5 Amperes
8 x 1.25 = 10 Amperes
8x1.75 = 14 Amperes

Feeder and Service Load Calculations
● Feeder Load Calculations
● Service Entrance Conductor
● Service Equipment Sizing Determination
● Ground Rod Sizing Determination
● Grounding Conductors

2.20.3 Feeder and Service Load Calculations
2.20.3.1 General. The calculated load of a feeder or service shall
not be less than the sum of the loads on the branch circuits
supplied, as determined by Part 2.20.2, after any applicable
demand factors permitted by Part 2.20.3 or 2.20.4 or required by
Part 2.20.5 have been applied.
Section 2.20.2 - Branch Circuit Load Calculation
Section 2.20.3 - Feeder and Service Load Calculation
Section 2.20.4- Optional Feeder and Service Load Calculation
Section 2.20.5 - Farm Load Calculation

2.20.3.3 General Lighting
The demand factors specified in Table 2.20.3.3 shall apply to
that portion of the total branch-circuit load calculated for
general illumination. They shall not be applied in determining
the number of branch circuits for general illumination.

(A)Small-Appliance Circuit Load. In each dwelling unit, the load
shall be calculated at 1500 volt-amperes for each 2-wire small
appliance branch circuit as covered by 2.10.1.11(C)(1). Where the
load is subdivided through two or more feeders, the calculated
load for each shall include not less than 1500 volt-amperes for
each 2-wire small-appliance branch circuit. These loads shall
be permitted to be included with the general lighting load and
subjected to the demand factors provided in Table 2.20.3.3.

2.20.3.14 Appliance Load - Dwelling
Unit(S)
It shall be permissible to apply a demand factor of 75 percent
to the nameplate rating load of four or more appliances
fastened in place*, other than electric ranges, clothes dryers,
space-heating equipment, or air-conditioning equipment, that
are served by the same feeder or service in a one-family, two-
family, or multifamily dwelling.
*fastened in place - garbage disposals, dishwashers, electric
water heaters, and similar fixtures.

2.20.3.16 Electric Cooking Appliance in Dwelling
Units and Household Cooking Appliances Used in
Instructional Programs
The load for household electric ranges, wall-mounted overs, counter-
mounted cooking units, and other household cooking appliances
individually rated in excess of 1 ¾ kW shall be permitted to be calculated
in accordance with Table 2.20.3.16. Kilovolt-amperes (kVA shall be
considered equivalent to kilowatts (kW) for loads calculated in this
section.
Where two or more single-phase ranges are supplied by a 3-phase, 4-wire
feeder or service, the total load shall be calculated on the basis of twice
the maximum number connected between any two phases.

Minimum Conductor Ampacity
Feeder and Service Entrance Conductors
Total Demand Load = 28,558.20 VA
Highest Rated Motor Rating = 1.5 HP Booster Pump

Feeder and Service Entrance Conductors

Hence, use 60mm2 (THW or
THHN)

Service Equipment Rating and Main Feeder
Protection
Minimum Conductor Ampacity

Equipment Grounding Conductor
Use 14mm2 (THW or THHN)

2.50.3.17 Size of Alternating-Current
Grounding Electrode Conductor
The size of the grounding electrode conductor at the service,
at each building or structure where supplied by a feeder(s) or
branch circuit(s), or at a separately derived system of a
grounded or ungrounded ac system shall not be less than
given in Table 2.50.3.17, except as permitted in 2.50.3.17(A)
through (C).

Basics of Electrical System Desiiign.pdf

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