1. wiring and raceways

2. power-handling equipment

3. utilization equipment

System Components

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Block Diagram (b/c major components are shown as rectangles)

Illustrates that power distribution equipment proceeds from the service point to the utilization po9ints in a progression of decreasing circuit capacity.

Reverse is true in collection systems such as drainage and venting, and piping is smallest at the initial collection points, growing larger as the quantities of fluid increase.

Define the fundanmental safety measures that must be followed in the selection, construction, and installations of electrical equipment and systems.

Incorporated into the OSHA (Occupational Safety and Health Administration) act of 1970.

Underwriters Laboratories (UL) Ensure a minimum standard of intrinsic electrical safety for electrical equipment. Publishes extensive lists of inspected and approved electrical equipment.

Selection of electrical materials involves choosing a material or assembly that is functionally adequate and, where necessary, visually acceptable, and costs.

Deciding factor during a selection is most often "first cost" rather than "life-cycle cost"

First cost is usually the deciding factor for a developer because others will bear the operating costs.

All electrical equipment must be rated for the normal service it is intended to perform.

Ratings may refer to volate, current, duty, horsepower, kW, kVA, temperatures, enclosure, and so on.

Ratings that are specifically and characteristically electrical are those of voltage (V) and current (I).

Voltage rating of an item of electrical equipment is the maximum voltage that the item can safely handle continuously.

Rating is determined by the type and quantitiy of insulation used and the physicial spacing between electrically energized parts.

Current rating of a device is determined by the maximum operating temperature at which its components can operate at full load.

Depends on upon the type of insulation used.

Motor is rated in horsepower (or KW), a transformer is rated in kVA, and a cable is in amperes.

Actual criterion on which all these ratings are based is the maximum permissible operating temperature of the device's insulation (and other components).

Electrical Power System - Primary purpose of a is to distribute electrical energy.

Electrical Signal or Communication System - Primary purpose is to transmit information.

Principal types of interior wiring systems in use today are exposed insulated calbes, insulated cables in open raceways, and insulated conductors in closed raceways.

Most general type and applicable to all types of facilities. Raceway installed first and the wiring is pulled in or laid in later. Raceways themselves may be:

1. Buried in structure, e.g. conduit in the floor slab or underfloor duct.

2. Attached to the structure, e.g.  all types of surface raceways, including conduit and wireways suspended above hung ceilings.

3. Part of the structure, e.g. cellular concrete and cellular metal floors.

Intended to cover all types of factory-prepared and factory-constructed integral assemblies of conductor and enclosre.

All types of busway, busduct, and cablebus: flat-cable assemblies and lighting track: flat cable intended for undercarpet installation and manufactured wiring systems.

"Wires"

Means by which current is conducted through the electrical system, corresponding to the piping of a hydraulic system.

AWG -- Standard of the U.S. wire and cable industry for round cross-section conductors.

No. 6 AWG or larger, or several conductors of any size assembled into a single unit, are feferred to as cable.

Single No. 8 AWG and smaller are called wire.

All wire sizes up to No. 0000 aka No. 4/0 are expressed in AWG.

AWG numbers run in reverse order to the size of the wire: the smaller the AWG number, the larger the size.

No. 10 is a heavier wire than No. 12 wire and is thinner than No. 8.

No. 4/0 size is the largest AWG designation, beyond which a different designation called kcmil (thousand circular mill) is used.

In kcmil designation, wire diameter increases with number: 500kcmil is a heavier wire (double the area) than 250 kcmil. Former designation was MCM

Ampacity increases with increasing conductor size and with maximum permissible insulatin temperature.

Heat generated as a result of current flow is dissipated into the environment, if more than three conductors are placed in a conduit, the resultant increase in temperature requires that the conductors be derated by a certain amount, shown in table 27.3 (if provided by Hertz)

Aluminum - Inherent weight advantage over copper, which brings with it lower installation costs. Economic in larger cable sizes, generally proves less expensive particularly in many urban areas with high labor costs.

Copper - Economic in small-and medium-sized cable, because weight is not a problem, and the smaller conduit required for the smaller copper conductor generally maekes the combined installation cheaper.

Difficulties in splicing and terminating aluminum, which can be overcome with the use of proper equipment, techniques, and workmanship.

Aluminums cold-flow characteristic when under pressure causes joints to loosen and aluminums oxide.

Oxide is and adhesive, a poorly conductive film that must be removed and prevented from reforming. The oxide causes a high-resistance joint with excessive heat generation and possible incendiary effects; could be overcome with copper-clad aluminum wire, but cold-flow problem remains.

Among the most common types of exposed wiring is NEC type AC armored cable, aka BX.

Assembly of insulated wires, bound together and enclosed in a protective armor made of spirl wound interlocking strip of steel tape.

Installed with simple U-clamps or staples holding it against beams, walls, and so on.

Frequently usedin residences and in the rewiring of existing buildings.

AC calbe is generally restricted to dry locations. 

Metalclad (MC Cable) holds a similar construction with much broader application.

May be used exposed or concealed and in cable trays, and when covered with a moisture-impervious jacket, in wet and outdoor locations.

Nonmetallic Sheathed Cable

ROMEX

NEC types NM and NMC aka Romex, are restricted to small building applications -- residential and other structures not exceeding three floors above grade.

Plastic outer jackets, easy to handle, but more vulnerable to physical damage.

High-voltage cables, armored cables, corrosion-resistant jacketed cables, underground cables, and so on.

A busway (busduct) is an assembly of copper or aluminum bars in a rigid metallic housing.

Use is preferable, from an economic viewpoint, in two instances.

1. when it's necessary to tap onto an electrical power conductor at freqent intervals along its length.

2.when it is necessary to carry large amounts of power.

Specified by type, material, number of buses, current capacity, and voltage. e.g. Aluminum feeder busduct, 4-wire, 1000 A, 600 V, or copper plug-in busway, 100 A, 3-wire, 600 V.

Feeder busduct (no plug-in capability) is available in ratings from 400 to 4000 A.

Devices are available for indoor and outdoor applications.

Similar to ventilated busduct, except that it uses insulated cables instead of busbars.

Ridigidly mounted in an open space-frame.

Advantage to this construction is that it carries ampacity rating of its cables in free air, which is much higher than for the same cables in conduit.

Disadvantages are bulkiness and difficulty in making taps.

Lower first cost usually means higher operating cost.

the smaller copper sizes in busduct and cablebus, permitetd by high-temperature insulation and good ventilation, cause increased power loss b/c of their higher resistivity.

If the heat loss can be used to advantage, the related energy cost can be credited instead of being considered a total loss.

Widely used b/c of their simplicity of installation and more importantly b/c of their plug-in mode of connection.

Special prefabricated assemblies that act as light-duty (branc-circuit) plug-in electrical feeders.

May be used either for feeder or branch circuit apps.

Rated from 20 to 60 A at 300 V, in 2 and 3 wire construction.

App is principally for direct connection of light machinery and industrial lighting.

Specially designed cable consisting of two, three, or four No. 10 AWG conductors, field installed in a rigidly mounted standard square structural channel.

Factory assembled channel, w/ conductros for one to four circuits permanently installed in the track.

Generally rated at 20 A, and unlike FC cable assemblies, may feed only lighting fixtures.

This system is simply a continuous open support for approved cables.

Cables must be self protected.

Pros -  free-air-rated cable ampacities, easy installation and maintenance, and relatively low cost.

Cons - Bulkiness and accessibility requirements

Primarily used in industrial apps.

Exceed expected space requirements, and as a result it is best considern them early in the design process.

Purpose of conduit:

1. Protect the enclosed wiring from mechanical injury and damage from the surrounding atmosphere.

2. Provide a grounded metal enclosure for the wiring in order to avoid a shock hazard.

3. Provide system ground path.

4. Protect surroundings against fire hazard as a result of overheating or arcing of the enclosed conductors.

5. Support the conductors.

Manufactured in several types

hot-dip galvanzied, sherardized (coated with zinc dust), enameled, and plastic covered.

3 types of steel conduit that differ only in wall thickness. (order of decreasing weight)

1. Heavy wall steel conduit aka rigid steel coduit

2. Intermediate metal conduit aka IMC (THREADED)

3. Electric metallic tubing, aka EMT or thin-wall conduit (not threaded, instead uses a set-screw and pressure fittings)

1. Outside diamater (OD) no greater than 1/3 the slab thickness as measured at its thinnest point.

2. Conduits running parallel to each other shall be spaced not less than 3 times the OD of the largest conduit center to center.

3. Crossings shall be as close to a right angle as possible.

4. Minimum cover over conduits shall be 3/4 inches.

Weight advantage over steel, being even lighter than EMT/ 

Better corrosion resistant, savings in labor costs usually more than offest the addicitonal cost of the material itself, non magnetic : giving it lower voltage drop, non sparking and generally does not require painting.

Cons - deleterious effect on many types of concrete, cuasing spalling and cracking when embedded.

Best not be buried in earth.

May be used in all locations where steel conduit is used.

Empty, spirally wound, interlocked armor steel or aluminum raceway.

AKA greenfield, used principally for motor connections and other locations where vibration is present, where movement is encoutered, or where physical obstructions make its use necessary.

When covered w/ a liquid-tight plastic jacket it is known as a sealtite.

Formed from materials such as, fiber, asbestos-cement, soapstone, rigid polyvinyl chloride (PVC) and high density polyethylene.

For use above ground, flame retardant, tough, and resistant to heat distortion, sunlight, and low temp effects.

For use underground, last two above ground req's are waived.

PVC conduit is the material of choice for indoor exposed use, rest for underground and outside use.

Surface Metal Raceways 

(Metallic and NonMetallic)

Surface metal raceways may be only used in dry, nonhazardous, noncorrosive locations and may contain only wiring operating below 300 V.

Such raceways are normally installed exposed, in places subject to physical injury.

Principal Apps of Surface and Metal raceways are:

1. Economy weighs heavily in favor of surface raceways and where expansion is anticipated.

2. Where outlets are required frequent intervals, and where rewiring is required/anticipated.

3. Access to raceways is required

4. Where extensive and expensive cutting and patching required to "bury" a raceway during rewiring is to bea voided.

Galvanized stamped sheet metal.

Common sizes are 4-in square and 4-in octagonal boxes used for fixtures, junctions, and devices

For commercial spaces w/ large open floor areas.

Not recommended, but most often used in large institutions and high-grade commercial spaces.

Underfloor raceways, Cellular metal floor raceways, Cellular concrete floor raceways.

Underfloor raceways are added on to the structure, whereas cellular floor raceways are part of the structure itself and therefor have architectural effect.

Installed underneath or flush w/ the floor.

Most used in office spaces b/c their use permits placement of power, data, and signal outlets close to tdesks and other furniture, regardless of spatial layout.

Arrangement of parallel rectangular metal or heavy plastic raceways laid on the strucutural slab and covered with concrete fill.

Pros. 

1. Ducts can be run in any direction, w/o conflict w/ structural elements.

2. Finishing is simplified.

3. Coordination is simplified.

4. Formwork and construction sequence are simplified.

Cons.

1. Additional concrete increases costs directly by increasing the weight of the structure. Expensive in seismic designs.

2. Building height may be increased.

EXPENSIVE, can easily add 50% to the building's electric system cost w/o consideration of the other construction costs involved.

If the floor is to be used for electrification.

Part of the structural system.

Three types of wiring systems generally run in separate floor cells and header ducts --- electric power, data-transmission wiring, and telephone and signal systems.

Last two may be combined in a single cell only if the signal system voltage and power level are low and the local telephone company approves.

Same advatanges as cellular metal floor and is similar in application.

Advantages include - large capacity, versatility in that each cell is a potential raceway, and flexibility in outlet placement and movement. 

First cost is higher, than that of standard underfloor duct installation, life cycle cost is lower, depending upon space use and reconfigurations.

Can be used for air distribution and even for piping, although these elements are generally installed in a hung ceiling.

Construction is applicable to spaces with very heavy cabling requirements, particularly if frequent recabling and reconnection are required.

Provides rapid and complete access to an underfloor plenum.

Usually fireproof.

Use of multiservice distribution modules and modular wiring avoids cable tangles and reduces labor costs significantly.

Inexpensive alternative to an underfloor or cellular floor system and a means for providing a flexible floor-level branch circuit wiring system.

Approved for installation only under carpet squares.

Low cost, combined with the inherent advantages of a flexible floor-level wiring system, particularly in open office areas, has made them a widely used first choice in new construction as well.

More flexible than their underfloor counterparts b/c they energize lighting, provide power and telephone facilities, and even supply outlets for the floor above, in addition to permitting very rapid layout changes at low cost.

Not as elegant as the underfloor raceways.