COMMERCIAL ELECTRICAL (Chapter 11)

Conduit Pathway for wiring that protects conductors Types Aluminum Plastic Fittings Size (additional information)

Depends on number of conductors Minimum: ½”

COMMERCIAL ELECTRICAL (Chapter 11)

Conductors Types

Copper Aluminum

Conductor size (additional information) 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 cross-sectional area of a conductor 0.005 inch in diameter would

be 5 x 5 = 25 cmil.

COMMERCIAL ELECTRICAL (Chapter 11)

Conductor Insulation (additional information)

Letter designators T = thermoplastic R = Rubber H = heat resistant W = moisture resistant N = nylon reinforcing

COMMERCIAL ELECTRICAL (Chapter 11)

Installing conductors

Special conduits Cable tray Busway Raceway Under floor duct

COMMERCIAL ELECTRICALConductor ampacity (additional information)

current carrying capacity of a conductor affected by

the size of a conductor max. permissible insulation (operating) temperature ambient temperature

Circuits Lighting circuits (additional information)

Generally protected with 20 A circuit breakers Feeder circuit

Circuit between a service panel or main panel and an OCPD in a sub-panel protecting a branch circuit Branch circuit

Circuit between an OCPD and utilization equipment (i.e. an equipment that receives power through the circuit)

Power circuits (additional information) For motors, electrical equipment, receptacles Feeder circuit Branch circuit

Dedicated circuits and UPS

COMMERCIAL ELECTRICAL

Panels Receives the service electricity and distributes it to branch circuits Lighting and power panels (additional information)

Required to sub-divide and protect individual circuits Contains circuit breakers

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) Electric service:

overhead service drop underground service lateral

3-phase services Three hot phase conductors and one neutral conductor

The neutral only carries unbalanced load for a 3-phase connection

Delta configuration: for industrial application Wye configuration: for office buildings and shopping

centers In wye systems, phase-to-phase voltage is √3 or 1.73

times the phase-to-neutral connection

COMMERCIAL ELECTRICAL

Transformers (additional information) 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)

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 capacityService sizeService disconnects (main disconnect)

Rated in amperes

Meter (additional information) required for registering the amount of energy

consumedalways installed electrically ahead of main

disconnect

COMMERCIAL ELECTRICAL (Additional information)

Overcurrent protection device (OCPD) 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 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) a contact device installed at an outlet for

connection of an attachment plug used for plugging in lights and small appliances

Grounding 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.)

ELECTRIC WIRING DESIGN (Additional information)

Available system voltages120 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

ELECTRIC WIRING DESIGN (Additional information)

OCPD must be placed on all ungrounded conductors all 'hot' wires are ungrounded

Branch circuit design 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? 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 single-phase circuit, this load would be 2,400X0.64=1536 W (say, 1500).

ELECTRIC WIRING DESIGN (Additional information)

For small offices, there should be 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