Article 90 - Part One

Article 90 
Note: This article is a guide for how to use NEC, it is very important that you read and review this article.

What you need to know: 
  • The purpose of the NEC is the protection of persons and property by minimizing the risks caused by the use of electricity. 
  • When installations comply with the NEC, this does not mean that the electrical system will be efficient, convenient, and adequate for good service or that it will work properly. Because The NEC is a safety standard not a design guide. 
  • The NEC does not contain any rule that requires consideration for future expansion of electrical use but the electrical designer must be concerned with future expansion. 
  • NEC code is not intended as a design specification or an instruction manual for untrained and unqualified persons. 
  • The National Electrical Code is not intended to apply to all electrical installations as follows: 

(a) Covered installations by NEC 
The Code covers most electrical installations, including:

  • most buildings 
  • mobile homes 
  • recreational vehicles 
  • floating buildings 
  • yards 
  • carnivals 
  • parking and other lots 
  • private industrial substations 
  • Also covered are conductors and equipment that connect to the supply of electricity, conductors and equipment outside on the premises, and the installation of fiber optic cable. 

Note (see fig.1 ) Installation within buildings used by the electric utility, such as office buildings, warehouses, garages, machine shops, and recreational buildings that are not an integral part of a generating plant, substation, or control center must be installed in accordance with the NEC.
-in case (1), the warehouse is not an integral part of the generating power, so NEC code will be applied to the electrical installations in the warehouse building.
-in case (2), the warehouse is an integral part of the generating power, so NEC code will be not be applied to the electrical installations in the warehouse building.

(b) Not covered installations by NEC 
  • Installations in cars, trucks, boats, ships, planes, electric trains, or underground mines. 
  • Self-propelled mobile surface mining machinery and their attendant electrical trailing cable. 
  •  Railway power, signaling and communications wiring. 
  • Communications equipment under the exclusive control of a communication utility, such as telephone and cable TV companies, are covered by their own wiring and equipment rules and are not required to comply with the NEC. However, the interior and exterior wiring of phone, communications, and CATV not under the exclusive control of communication utilities must comply with NEC Chapter 8. 
  • Installations, including associated lighting, under the exclusive control of electric utilities for the purpose of power generation, distribution, control, transformation, and transmission are not required to comply with the NEC. This includes installations located in buildings used exclusively by utilities for such purposes, outdoors on property owned or leased by the utility, or on public highways, streets, roads, etc., or outdoors on private property by established rights such as easements. 

Note.(see fig. 2) Any wiring installation such as lighting fixtures on private property without established rights and not intended for the purpose of communications, metering, generation, control, transformation, transmission, and distribution of electric energy, must be installed according to the NEC requirements, even if installed by the electric utility.
fig. 2
-poles#(1&2) are on private property (warehouse in this case) and used only for lighting purpose, so NEC code will be applied to the electrical installations for these poles.
-poles#(3) are on private property and used for distribution of electrical energy , so NEC code will not be applied to the electrical installations for these poles.
  • The Code is divided into the Introduction and nine chapters. These chapters are divided as follow: (see fig.3)

  • General rules: Introduction and Chapters 1 through 4 apply in general to all installations; this represents the scope of this book. 
  • Special rules: Chapters 5 through 7 apply to special occupancies, equipment, or conditions and may modify the general rules of Chapters 1 through 4. Examples include; aircraft hangers, health care facilities, x-ray equipment, etc. 
  • Communications Systems: Chapter 8 covers communications systems (phone, CATV, satellite dishes, etc.). This chapter of the NEC is independent of the other chapters. This means that the rules of Chapters 1 through 4 do not apply to Chapter 8, unless there is a specific reference in Chapter 8 to a rule in Chapters 1 through 4. 
  • Tables: Chapter 9 consists of tables that are used for raceway sizing and conductor fill and voltage drop.

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