Every wiring system should incorporate sufficient flexibility in branch circuitry, feeders, and panels to accommodate all reasonably probable patters, arrangements, and locations of electric loads.

Degree of Flexibility dependent on the type of faciility.

Determined by two factors: the incoming utility service and the building's electrical system.

Reliability of power is entirely dependent upon the wiring and distribution system.

Only as good as it's weakest element.

Electrical service and building distribution system act together.

Critical loads w/i facility should be defined to determine how best to serve them reliably.

NEC and other applicable NFPA codes ensure an initially safe electrical installation.

Designer must be alert to the potential for electric hazards caused by misuse or abuse of equipment or by equipment failure.

initial cost and life cycle cost

1st cost depends largely upon whther an owner is interested in the minimum first cost or the minimum overall ownership cost.

Inverse relationship to one another.

Low first cost generally results in higher maintance costs and shorter life -- with a resulting higher life cycle cost. and VICE VERSA.

Involves consideration of energy codes and budges, energy efficiency techniques and energy control.

ANSI/ASHRAE/IESNA Standard/codes

Electrical equipment is small and easily concealed only for wire and conduit.

Panels, motor control centers, budsduct, distribution centers, switchboards, transformers, and so on can be large, bulky, noisy, and highly sensitivie to tampering and vandalism.

Space allocation must be concerened w/ ease of maintenance, ventilation potential, expandability, centrality, limiting access to authorized personenel, and noise control.

Necessary to estimate the total building load in order to plan for such spaces as transformer rooms, conduit chases, and electrical closets.

Loads Categories

1. Lighting

2. Miscellaneous power, which includes data processing equipment, convenience outlets, and small motors.

3. Heating, ventilating, and air-conditioning HVAC equipment.

4. Plumbing and other piping-based systems.

5. Mechanized trasnportation equipment and fixed material-handling equipment

6. Kitchen Equipment

7. Special equipment.

System Voltage

120 V - Single-Phase, 2-Wire

Used for the smallest facilities, such as outbuildings, and isolated small loads of up to 6kVA.

Load is calculated by multiplying current and voltage.

For a 60A service which is the normal limit for this type of service, no more than 50A are usually drawn... thus

VA = 120 x 50 = 6000VA = 6kVA

Nominal system voltage is 120V, although it is also referred to as 110V and 115V.

System Voltage

120/240V - SinglePhased - 3-Wire

For somewhat heavier loads.

All one-family residences with six or more 2=wire crcuits or a net computed load of 10kVA or more have a minimum of 100-A, 3 wire service.

Usually for residences, small stores, and other occupancies where the load does not exceed 80A or 19.2 kVA

Load Calculated... 

kVA = ( V x I ) / 1000 = (240x 80) / 1000 = 19.2kVA

System Voltage 

120/208 V, Single Phase, 3-Wire

Most often found w/i a building that takes 3-phase service rather than constituting a service voltage arrangement.

Used to serve a load higher than 120 V.

Voltage System

120/208 V, 3-Phase, 4-Wire

Widely used 3-phase arrangement applkicable to all facilities except very large ones.

120V loads such as lighting, computers, and accessories, receptacles, and so on are fed at 120 V by connecting between a phase leg and a neutral.

Voltage System

277/480 V, 3-Phase, 4-Wire

Applicable to large buildings, where lighting is principally fluorescent and/or high intesity discharge (HID) and the 120 V load does not exceed one third of the total load.

Suitiable to multistory office buildings and large single-level or multilevel industrial buildings.

Cost savings are generated by the smaller feeder and conduit sizes and smaller switchgear, which more than offset the additional cost of step-down transformers for the 120V loads.

Vast majority of secondary wiring systems are solidly grounded.

1. To prevent sustained contact between a low voltage secondary system and a high voltage primary system in the even t of an insulation failure.

2. To prevent single grounds from going unnoticed until a second ground occurs, which would extensively disable the secondary system.

3. To permit locating ground faults w/ ease.

4. To protect against voltage surges.

5. To establish a neutral at zero potential for safety and for reference.

All insulated ground conductors must have their covering colored green for identification as a grounding conductor

Energy Conservation Considerations

(way tooooooooo long)

Before proceeding w/ a detailed description of design procedures, the many energy conservation ideas and techniques applicable to electrical distribution systems should be surveyed.

(Page 1294)

Vary greatly, depending upon the design and the nature of the building.

1. Residences - service equipment and the building panelboard are generally incorporated into a single unit.

2. Commercial Spaces - location of panelboards depends upon their type and number and upon availability of space.

Lighting panels are recessed into the corridor wall b/c the building is only two stories high and the panels can be vertically stacked and fed by a single conduit.

A buildings electric system, particularly for multistory construction, shape of this space can be varied to fit the architectural requirements, and it should provide...

1. one or more locking doors.

2. vertical stacking, above and below other electric closets. Location - don't block other shit and don't choose locations outside walls and adjoining shafts, columns, and stairs.

3. Space free of other utilities such as piping passing through closet.

4. Sufficient wall space.

5. Floor slots or sleeves of sufficient size for all present and future conduit or bus risers.

6. Sufficient floorspace so that electrician dude can fit comfortably and safely on initial installation and repair.

7. adequate illumination and ventilation.

Branch Circuits - Design/Expansion

Refers only to the circuit conductors

Multioutlet appliance or single-outlet type intended for specific piece of equipment.

multioutlet types are limited to 50 A in capacity

single outlet type is governed in size only by the requirements of the item being served and may be a 200A or a 300A in size.

Some rules of Practice must be followed.

Harmonic Currents

( a bit long )

Conventional electrical loads such as lighting, resistive devices (heaters), motors, and the like are linear. 

Most electronic equipment such as computers, modems, printers, electronic lighting ballasts, variable speed motor drives and solid state equipment of all types are essentially non linear loads, they produce harmonic currents.

Most troublesome of these are the third harmonics and it's odd mutiples. (9th, 15th, 21st, ...)

Cons

Deterioation of electronic equipment performance: continous or sporadic computer malfunctions.

Overheating of the neutral-possible causing neutral burnout and resulting in equipment being subjected to severe voltage variations

Overheating and premature failure of transformers - even when the transformer rating seems adequate.

Overheating of motors b/c of operation w/ a distorted voltage waveform.

Nuisance tripping of circuit breakers and adjustable speed drives.

Telephone interference

Capacitor fuse blowing.

Today at least half of the electric load in a modern office type facility is composed of nonlinear, harmonic producing equipment.

Emergency Systems

(general info)

Choice of equipment and arrangement and the size of equipment depend largely  upon the requirements of local codes, which determine the loads that must be supplied from the emergency system.

Three classes of electrical power supply systems that are included under the general category of emergency electric supply.

1. Emergency Systems :

2. Legally Required Standby systems

3. Optional Standby systems

Emergency Systems

(Emergency Systems)

Those essential to human safety.

Depend upon the type of facility involved, they may supply power for fire detection, lighting, alarm and communication systems, elevators, fire pumps, and such loads as ventilation, refrigeration, and industrial processes where power interruption would imperil human safety.

Must pick up the load w/i 10 secs of power interruption.

Emergency Systems

(Legally Required Standby Systems)

Required to provide power for essentially the same types of loads as emergency systems, except that their absence does not involve immediate danger to human life.

Systems for firefighting, control of health hazards, long term rescue operations, and industrial hazard prevention.

Loads must be picked up automatically w/i 60 secs of power interruption.

Emergency Systems

(Optional standby power systems)

Intended essentially to minimize economic loss, and therefore can supply any load identified by the building owner.

Manual or automatic, and duration of service is entirely up the the owner.

No restrictions are placed on the wiring system beyond those applied to the normal electrical wiring system.

Emergency Systems

(NFPA codes)

Emergency Systems

(technical considerations)

Left to the designer and owner to decide in the context of a given building situation.

Emergency system includes all devices, wiring, raceways, and other electrical equipment, including the emergency source that is intended to supply electric power to the selected loads.

An important aspect of code requirements permits the use of a single power source for 1. emergency, 2. legally required standby, 3. optional standby systems, provided that it is equipped w/ automatic selective load pickup and load shedding equipment that will ensure adequate power to the three types of systems in the order of priority stated. 1,2,3