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CONTENTSPageForeword IIIPreface IVSec. A.Definitions of Special Terms1Sec. 10.Purpose, Scope and Application of the Rules100. Purpose of the Rules101. Scope of the Rules102. Application of the Rules and ExemptionsA. ApplicationB. Intent of the RulesC. Temporary Installations5556666Sec. 11.Protective Arrangements in Electrical Supply Stations110. General RequirementsA. Enclosure of EquipmentB. Rooms and Spaces1. Fireproof Construction2. Use3. Ventilation4. Moisture and WeatherC. Rotating Machinery111. IlluminationA. Under Normal ConditionsB. Emergency SourceC. FixturesD. Attachment Plugs and Receptacles for GeneralUse112. Floor, Floor Openings, Passageways, StairsA. FloorsB. PassagewaysC. RailingsD. Stair Guards113. ExitsA. Clear ExitsB. Double Exits114. Fire Extinguishing Equipment115. Oil Filled Apparatus6667777788888Sec. 12.Protective Arrangements of Equipment120. General Requirements121. InspectionsA. In-Service EquipmentB. Idle EquipmentC. Emergency EquipmentD. New Equipment122. Guarding Shaft Ends, Pulleys, Belts and SuddenlyMoving PartsA. Mechanical Transmission MachineryB. Suddenly Moving Parts123. Protective GroundingA. Protective Grounding or Isolation of Non-CurrentCarrying Metal PartsB. Grounding MethodIX8999999910101010101010111111111111111112

Electrical Supply StationsPageC.Provision for Grounding Equipment DuringRepairs124. Guarding Live PartsA. Where RequiredB. Strength of GuardsC. Types of Guards1. Location or Isolation2. Metal Cable Sheaths3. Shields or Enclosures4. Railings5. Fences6. Insulating Covering on Conductors or Parts7. Mats8. Live Parts Below Supporting Surfaces forPersons125. Working Space About Electrical Equipment126. Equipment for Work on Live PartsA. Voltages from 600 to 15,000 Volts Between PhasesB. Voltages Over 15,000 Volts Between Phases127. Hazardous LocationsA. Enclosure of Arcing and Heating PartsB. Grounding128. Identification »A. MethodB. NameplateSec. 13.Sec. otating Equipment130. Speed Control and Stopping DevicesA. Automatic Overspeed Tripping Devices for PrimeMoversB. Other Stopping DevicesC. Speed Limit for MotorsD. Low-Voltage or Under-Voltage ProtectionE. Adjustable-Speed MotorsF. Protection of Control Circuits131. Guards for Rotating EquipmentA. Moving PartsB. Live Parts132. Access to Equipment133. MotorsA. ControlB. Motors in Hazardous Locations134. Hydrogen Cooled EquipmentA. Control EquipmentB. Hydrogen StorageC. e Batteries140. General141. Location142. Ventilation143. Racks and TraysA. RacksB. Trays144. Guarding Live PartsA. Guarding222222222222222323

ContentsPageB.C.145.146.147.A.B.Bare ConductorsDetails of GuardsFloors in Battery RoomsWiring in Battery RoomsIllumination and Heating for Battery RoomsLighting FixturesHeating Appliances23232323232324Transformers and Regulators150. Current-Transformer Secondary Circuits151. Grounding Secondary Circuits of InstrumentTransformers152. Grounding of Cases153. Location and Arrangement of Power Transform ers and RegulatorsA. Outdoor InstallationsB. Indoor Installations2424242425Sec. 16.Conductors160. Electrical ProtectionA. Overcurrent Protection RequiredB. Grounded Conductors161. Mechanical Protection162. Isolation163. Conductor TerminationsA. InsulationB. Metal-Sheathed or Shielded Cable262626262626262626Sec. 17.Switches, Circuit Breakers, Fuses and Reclosers170. Arrangement171. Application172. Circuit Breakers, Switches, and Reclosers Con taining Oil173. Switches and Disconnecting DevicesA. CapacityB. Provisions for DisconnectingC. Visible Break Switch174. Disconnection of Fuses272727272828282829Sec. 18.Switchboards180. Location and AccessibilityA. General LocationB. Spaces About BoardsC. Arrangements181. Material182. Instrumentation and Control183. Arrangement and Identification184. Spacings and Barriers185. Instrument Cases29292929292929303030Sec. 19.Lightning Arresters190. General Requirements191. Indoor Locations192. Grounding Conductors193. Guarding Live Parts194. Installation303030303131Sec. 15.XI2424

SI CONVERSION UNITSIn view of present accepted practice in this country inthis technological area, common U.S. units of measurementhave been used throughout this paper. In recognition of theposition of the USA as a signatory to the General Confer ence on Weights and Measures, which gave official status tothe metric SI systems of units in 1960, conversion factorsapplicable to the U.S. units used in this paper are presentedbelow.Length1 in “ 0.0254* meter (m)1 ft 0.3048* meter (m)Electricity1 volt—SI Unit1 ampere—SI UnitPower1 watt—SI UnitLight1 foot-candle10.76391 lumens per square meter (lm/m2)* Exactly.XII

SECTION A. DEFINITIONS OF SPECIAL TERMSThe following definitions are for use with Part 1 of theNational Electrical Safety Code. For other use and fordefinitions not contained herein, see:(1)(2)NBS Handbook 81 (ANSI C2.2—1960)Definitions of Electrical Terms (ANSI C42)NOTE: Definitions of terms marked with an asterisk (*) aredefined differently in NBS Handbook 81, Safety Rules for theInstallation and Maintenance of Electric Supply and Communi cation Lines (Part 2 of the NESC). However, except in the caseof Definition A-6-CONDUCTOR, those differences are of an edi torial nature. Changing technology in the electrical field hasnecessitated a different definition for the term “CONDUCTOR.”A—1.Alive or Live means electrically connected to a source ofpotential difference, or electrically charged so as to have a potentialdifferent from that of the earth. The term “live” is sometimes usedin place of the term “current-carrying,” where the intent is clear, toavoid repetitions of the longer term.*A-2.Appliance means current-conducting,energy-consumingequipment, fixed or portable; for example, heating, cooking, and smallmotor-operated equipment.A—3.Automatic means self-acting, operating by its own mecha nism when actuated by some impersonal influence—as, for example,a change in current strength; not manual, without personal interven tion. Remote control that requires personal intervention is not auto matic, but manual.A—4.Circuit means a conductor or system of conductors throughwhich an electric current is intended to flow.*A—5,Circuit Breaker means a mechanical switching device,capable of making, carrying and breaking currents under normal cir cuit conditions and also making, carrying for a specified time andbreaking currents under specified abnormal conditions such as thoseof short circuits.*A—6.Conductor means a material usually in the form of awire, cable, or bus bar suitable for carrying an electric current.A-7.Current-Carrying Part means a conducting part intended tobe connected in an electric circuit to a source of voltage. Noncurrent carrying parts are those not intended to be so connected.*A-8.De-energized (Dead) means free from any electric con nection to a source of potential difference and from electric charge;not having a potential different from that of the earth.NOTE:The term is used only with reference to current-carrying partswhich are sometimes alive.*A—9.Disconnecting or Isolating Switch (Disconnector, Isolator)means a mechanical switching device used for changing the connec1

Electrical Supply Stations2tions in a circuit, or for isolating a circuit or equipment from a sourceof power.NOTE:It is required to carry normal load current continuously, and alsoabnormal or short-circuit currents for short intervals as specified.It is also required to open or close circuits either when negligiblecurrent is broken or made, or when no significant change in thevoltage across the terminals of each of the switch poles occurs.A—10.Effectively Grounded means permanently connected toearth through a ground connection or connections of sufficiently lowimpedence and having sufficient current-carrying capacity to preventthe building up of voltages which may result in undue hazard toconnected equipment or to persons.A—11.Electric-Supply Equipment means equipment which pro duces, modifies, regulates, controls, or safeguards a supply of electricenergy. Similar equipment, however, is not included where used inconnection with signaling systems under the following conditions:(a) Where the voltage does not exceed 150 volts.(b) Where the voltage is between 150 and 400 volts and the powertransmitted does not exceed 3 kilowatts.A—12.Electrical Supply Station means any building, room, orseparate space within which electric supply equipment is located andthe interior of which is accessible, as a rule, only to properly qualifiedpersons.NOTE:This includes generating stations and substations and generator,storage-battery, and transformer rooms.A-13.Enclosed means surrounded by a case, cage or fence, whichwill protect the contained equipment and prevent accidental contactof a person with live parts.A—14.Equipment means a general term including fittings, devices,appliances, fixtures, apparatus, and the like, used as a part of, orin connection with, an electric installation.A-15.Explosion Proof means capable of withstanding withoutinjury and without transmitting flame to the outside any explosion ofgas which may occur within.A-16.Grounded means connected to earth or to some extendedconducting body which serves instead of the earth whether the con nection is intentional or accidental.A—17.Grounded Conductor means a conductor which is inten tionally grounded, either solidly or through a current limiting device.A-18.Grounded System means a system of conductors in whichat least one conductor or point (usually the middle wire, or neutralpoint of transformer or generator windings) is intentionally grounded,either solidly or through a current-limiting device.A—19.Grounding Conductor means a conductor which is used toconnect the equipment or the wiring system with a grounding elec trode or electrodes.A-20.Guarded means covered, shielded, fenced, enclosed, orotherwise protected by means of suitable covers or casings, barrier

3Definitionsrails or screens, mats or platforms, to remove the liability of dan gerous contact or approach by persons or objects to a point of danger.NOTE:Wires which are insulated, but not otherwise protected, are notconsidered as guarded.A—21.Insulated means separated from other conducting surfacesby a dielectric substance or air space permanently offering a highresistance to the passage of current and to disruptive dischargethrough the substance or space.NOTE:When any object is said to be insulated, it isinsulated in a suitable manner for the conditionsjected. Otherwise, it is, within the purpose ofsulated. Insulating covering of conductors is onethe conductors insulated.understood to beto which it is sub these rules, unin means for makingA—22.Insulating (where applied to the covering of a conductor,or to clothing, guards, rods, and other safety devices) means thata 'device, when interposed between a person and current-carryingparts, protects the person making use of it against electric shockfrom the current-carrying parts with which the device is intendedto be used; the opposite of conducting.A—23.Isolated means that an object is not readily accessible topersons unless special means for access are used.A—24.Isolation by Elevation means elevated sufficiently so thatpersons may safely walk underneath.*A-25.Lightning Arrester means a protective device for limitingsurge voltage on equipment by discharging or by-passing surge cur rent ; it prevents continued flow of follow current to ground, and iscapable of repeating these functions as specified.NOTE:In general, arresters consist of series gaps and characteristic ele ments arranged within or upon suitable insulating members.A—26.Low Voltage Protection means the effect of a device oper ative on the reduction or failure of voltage so as to cause and main tain the interruption of power supply to the equipment protected.A-27.Manualmeans capable of being operated by personalintervention.A—28.Qualified means familiar with the construction and opera tion of the apparatus and the hazards involved.A—29.Raceway means any channel for loosely holding wires orcables in interior work, which is designed expressly and used solelyfor this purpose. Raceways may be of metal, wood, or insulatingmaterial, and the term includes wood and metal moldings consistingof a backing and capping, and also metal ducts into which wires areto be pulled.A—30.Reconstruction means replacement of any portion of anexisting installation by new equipment or construction. Does notinclude ordinary maintenance replacements.A—31.Substantial means so constructed and arranged as to beof adequate strength and durability for the service to be performedunder the prevailing conditions.A—32.Supply Station—See Electrical Supply Station.

4Electrical Supply StationsA—33.Switch means a device for opening and closing or forchanging the connection of a circuit. In these rules, a switch willalways be understood to be manually operated, unless otherwisestated.A-34.Switchboard means a type of switchgear assembly thatconsists of one or more panels with electric devices mounted thereon,and associated framework.A—35. Tags mean “men at work” tags of distinctive appear ance, indicating that the equipment or lines so marked are beingworked on.A—36, Transformer Vault means an isolated enclosure eitherabove or below ground with fire-resistant walls, ceiling, and floor,in which transformers and related equipment are installed, and whichis not continuously attended during operation.A—37. Utilization Equipment means equipment, devices, and con nected wiring which utilize electric energy for mechanical, chemical,heating, lighting, testing, or similar purposes and are not a part ofsupply equipment, supply lines, or communication lines.A—38. Voltage of an Effectively Grounded Circuit means thehighest effective voltage between any conductor and ground unlessotherwise indicated.A—39.Voltage of a Circuit Not Effectively Grounded means thehighest effective voltage between any two conductors unless otherwiseindicated.If one circuit is directly connected to another circuit of highervoltage (as in the case of an autotransformer), both are consideredas of the higher voltage, unless the circuit of lower voltage iseffectively grounded, in which case its voltage is not determinedby the circuit of higher voltage. Direct connection implies electricconnection as distinguished from connection merely through elec tromagnetic or electrostatic induction.A-40,Voltage to Ground of a Grounded Circuit means the high est effective voltage between any conductor of the circuit and thatpoint or conductor of the circuit which is grounded.A—41,Voltage to Ground of an Ungrounded Circuit means thehighest effective voltage between any two conductors of the circuitconcerned.A—42. Voltage to Ground of a Conductor of a Grounded Circuitmeans the highest effective voltage between such conductor and thatpoint or conductor of the circuit which is grounded.A—43.Voltage to Ground of a Conductor of an UngroundedCircuit means the highest effective voltage between such conductorand any other conductor of the circuit concerned.A-44.Wire Gages:—the American Wire Gage (AWG), otherwiseknown as Brown & Sharpe (B&S), is the standard gage for copper,aluminum, and other conductors, excepting steel, for which the SteelWire Gage (Stl. WG) is used throughout these rules.

5NATIONAL ELECTRICAL SAFETY CODEPart 1. Rules for the Installation and Maintenanceof Electrical Supply Stations and Equipment.SEC. 10. PURPOSE, SCOPE AND APPLICATION OFTHE RULES100:Purpose of the Rules.The purpose of Part 1 of this Code is the practical safe guarding of persons from hazards arising from the instal lation and maintenance of electrical supply stations andassociated equipment. It contains basic minimum pro visions considered necessary for safety. Compliance there with will result in an installation essentially free ofhazards. It is not intended as a design specification or asan instruction manual for untrained persons.101.Scope of the Rules.Covered:—Part 1 of this Code covers the electric conduc tors and equipment in electrical supply stations along withthe associated structural arrangements employed, for ex ample, by an electrical or railway utility in the exerciseof its function as a utility and accessible only to properlyqualified personnel. It also covers similar electric conduc tors and equipment in electrical supply stations whenowned by and installed in an industrial establishment,where the electrical supply stations are under the controlof and accessible only to properly qualified persons. Exam ples of such industrial establishments are the paper andsteel industries.Not Covered:—It does not cover installations in mines,ships, railway rolling equipment, aircraft, automotiveequipment or the conductors and equipment used primarilyfor the utilization of electric power, except those in elec trical supply stations. It does not cover installations inindustrial or commercial establishments not under thecontrol of and accessible only to properly qualified persons.Examples of such establishments are apartment houses andshopping centers.

Electrical Supply Stations6102.A.Application of the Rules and Exemptions.Application.The rules shall apply to all installations except thatthey may be modified or waived by the proper adminis trative authority when shown to be impracticable. Insuch cases, equivalent or safer construction shall besecured in other ways, including special working meth ods. Methods of construction and installation other thanthose specified in the rules may also be made as experi ments to obtain information, if done where proper super vision can be administered.B.Intent of Rules.The intent of these rules, which constitute a minimumstandard, will be realized by applying the rules in fullto all new installations, alterations, reconstructions, andextensions. Rules in this Code which are to be regardedas mandatory are characterized by the use of the Avord“shall.” Where a rule is of an advisory nature, it is indi cated by the use of the word “should.” Other practiceswhich are considered desirable but not intended to bemandatory are stated as recommendations. It is realizedthat conditions may exist which necessitate departuresfrom such recommendations. Notes contained herein arefor information

NATIONAL ELECTRICAL SAFETY CODE HANDBOOKS . NBS Handbook 110-1 (ANSI C2.1—1971), National Electrical Safety Code, Part 1, Rules for the Installation and Maintenance of Elec trical Supply Stations and Equipment, 1971. (Supersedes NBS Handbook H31 and pages 31-76 of NBS Handbook H30.