National Electricity code,NFPA 70 for Examination, Identification, Installation, and Use of electrical Equipment

NFPA – National Fire protection association 70 is also known as National Electrical Code

Examination, Identification, Installation, and Use of Equipment as per NFPA 70:-

(i)                 Examination:-

In judging equipment, considerations such as the following shall be evaluated:

(1)   Equipment usage can be identified by an equipment description either marked on the product or by description provided with a product to identify the suitability of the product for a

(a)    Specific purpose,

(b)   Environment, or

(c)    Application

Conditions required for its usage and limitations or other pertinent information may be marked on the equipment, included in the product instructions, or included in the appropriate listing and labeling information. Suitability of equipment may be evidenced by listing or labeling.

(2)   Mechanical strength and durability, including, for parts designed to enclose and protect other equipment, the adequacy of the protection thus provided

(3)   Wire-bending and connection space

(4)   Electrical insulation

(5)   Heating effects under normal conditions of use and also under abnormal conditions likely to arise in service

(6)   Arcing effects

(7)   Classification by type, size, voltage, current capacity, and specific use

(8)   Other factors that contribute to the practical safeguarding of persons using or likely to come in contact with the equipment

(B) Installation and Use:-

Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

Voltages:-

Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

Conductors:-

Conductors normally used to carry current shall be of copper unless otherwise provided in this Code. Where the conductor material is not specified, the material and the sizes given in this Code shall apply to copper conductors. Where other materials are used, the size shall be changed accordingly.

Conductor Sizes:-

Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils.

Wiring Integrity:-

Completed wiring installations shall be free from short circuits, ground faults, or any connections to ground other than as required or permitted elsewhere in this Code.

Wiring Methods:-

Only wiring methods recognized as suitable are included in this Code. The recognized methods of wiring shall be permitted to be installed in any type of building or occupancy, except as otherwise provided in this Code.

Interrupting Rating:-

Equipment intended to interrupt current at fault levels shall have an interrupting rating not less than the nominal circuit voltage and the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage not less than the current that must be interrupted.

Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics:-

The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor.

Deteriorating Agents:-

Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other agents that have a deteriorating effect on the conductors or equipment; or where exposed to excessive temperatures.

Equipment not identified for outdoor use and equipment identified only for indoor use, such as “dry locations,” “indoor use only,” “damp locations,” or enclosure Types 1, 2, 5, 12, 12K, and/or 13, shall be protected against damage from the weather during construction.

Mechanical Execution of Work:-

Electrical equipment shall be installed in a neat and workmanlike manner.

 (A) Unused Openings. Unused openings, other than those intended for the operation of equipment, those intended for mounting purposes, or those permitted as part of the design for listed equipment, shall be closed to afford protection substantially equivalent to the wall of the equipment. Where metallic plugs or plates are used with nonmetallic enclosures, they shall be recessed at least 6 mm (1⁄4 in.) from the outer surface of the enclosure.

(B) Integrity of Electrical Equipment and Connections.

Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and other surfaces, shall not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues.

There shall be no damaged parts that may adversely affect safe operation or mechanical strength of the equipment such as parts that are broken; bent; cut; or deteriorated by corrosion, chemical action, or overheating.

(i)                 ELECTRICAL EQUIPMENTS MOUTING AND COOLING AS PER NFPA 70

(a) Mounting of electrical equipment’s:-

Electrical equipment shall be mounted firmly and secured on to the surface on which it is required to be mounted. There is an old practice of mounting electrical equipment’s using wooden plugs which were mounted in holes of masonry, Concrete, plaster or similar material this practice should not be used.

(b) Cooling of electrical equipment’s:-

The electrical equipment’s which required sufficient natural air circulation for not getting heated up should be installed in such a way that room airflow over such equipment’s could not get restricted either by wall or by adjacent equipment. The equipment’s which were designed for floor mounting i.e. that directly mounted on trenches should have clearance between top surface and adjacent surfaces so as to dissipate heat generated from equipment’s. 

There will be equipment’s which have ventilation openings shall be installed in such way that there will  not be any obstructions to free circulation of air through the equipment.

(ii)               Electrical Connections.

There are different characteristics of different metals and we should not mix conductors of dissimilar metals in a terminal or splicing connector where there is contact occurs between dissimilar conductors such as:-

(a)    Copper and aluminum

(b)   Copper and copper-clad aluminum

(c)    Aluminum and copper-clad aluminum

When there is requirement of using solder, Fluxes, Inhibitors and Compounds then it must be kept in mind that they may not cause adverse effect on conductors, Installations or equipment.

(A)   Terminals:-  

Connections of conductors to the terminal parts should ensure good connection. Connections should not cause damage to the conductors. Connections to the conductors should be done by means of :-

(i)                 Hydraulic punching machine

(ii)               Pressure connectors

(iii)             Solder lugs

(iv)             Splices to flexible leads.

(B)   Splices:-

Conductors shall be spliced or joined with splicing devices by means of

(i)                 Brazing,

(ii)               Welding, or

(iii)             Soldering with a fusible metal or alloy.

Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered.

All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an insulating device identified for the purpose.

(C)   Temperature Limitations:-

The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

Equipment Provisions:-

(i)     For Termination if there is circuit having rating 100 A or less , or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:

(a)    Conductors rated 60°C (140°F).

(b)   Conductors with higher temperature ratings provided the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used.

(c)    Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.

(d)   For motors marked with design letters B, C, or D, conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity.

(ii)   Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:

(a)    Conductors rated 75°C (167°F)

(b)   Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors

Separate Connector Provisions:-

Separately installed pressure connectors shall be used with conductors at the ampacities not exceeding the ampacity at the listed and identified temperature rating of the connector.

(ii)High-Leg Marking:-

On a 4-wire, delta-connected system where the midpoint of one phase winding is grounded, only the conductor or busbar having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that is orange in color or by other effective means. Such identification shall be placed at each point on the system where a connection is made if the grounded conductor is also present.

(iii) Arc-Flash Hazard Warning:-

For electrical equipment’s such as:-

(a)    Switchboard’s

(b)   Panel-boards

(c)    Industrial Control Panels

(d)   Motor control centers

(e)    Panels

There is need of routine examination, Maintenance while these remains energized so there should be marking to warn the qualified person against electrical flash hazard. The marking shall be located at such a place that it should be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

(iv)  Arcing Parts

Parts of electrical equipment that in ordinary operation produce arcs, sparks, flames, or molten metal shall be enclosed or separated and isolated from all combustible material.

(v)   Light and Power from Railway Conductors:-

Circuits for lighting and power shall not be connected to any system that contains trolley wires with a ground return.

(vi) Marking:-

The manufacturer’s name, trademark, or other descriptive marking by which the organization responsible for the product can be identified shall be placed on all electrical equipment. Other markings that indicate voltage, current, wattage, or other ratings shall be provided as specified elsewhere in this Code. The marking shall be of sufficient durability to withstand the environment involved.

(vii)                       Identification of Disconnecting Means:-

(A)  General.

Each disconnecting means shall be legibly marked to indicate its purpose unless located and arranged so the purpose is evident. The marking shall be of sufficient durability to withstand the environment involved.

(B)  Engineered Series Combination Systems.

Equipment enclosures for circuit breakers or fuses applied in compliance with series combination ratings selected under engineering supervision in accordance with 240.86(A) shall be legibly marked in the field as directed by the engineer to indicate the equipment has been applied with a series combination rating. The marking shall be readily visible and state the following:

CAUTION — ENGINEERED SERIES COMBINATION

SYSTEM RATED _______ AMPERES. IDENTIFIED

REPLACEMENT COMPONENTS REQUIRED.

(C)  Tested Series Combination Systems:-

Equipment enclosures for circuit breakers or fuses applied in compliance with the series combination ratings marked on the equipment by the manufacturer in accordance with 240.86(B) shall be legibly marked in the field to indicate the equipment has been applied with a series combination rating. The marking shall be readily visible and state the following:

CAUTION — SERIES COMBINATION SYSTEM

RATED ____ AMPERES. IDENTIFIED REPLACEMENT

COMPONENTS REQUIRED.

(viii)                     Current Transformers:-

 Unused current transformers associated with potentially energized circuits shall be short-circuited.

(ix) Available Fault Current:-

(A)  Field Marking:-

Service equipment in other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved.

(B)   Modifications:-

When modifications to the electrical installation occur that affect the maximum available fault current at the service, the maximum available fault current shall be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment. The required field marking shall be adjusted to reflect the new level of maximum available fault current.