Important Electrical Terms - Part One

This article will contain some important electrical terms which are essential to the proper application and understanding of Beginners' Electrical design course EE-1.

1- NEMA and IEC Enclosure Ratings:see fig.1

 

fig (1): IP ratings

IEC publication 529 ‘Classification of Degrees of Protection Provided by Enclosures’ provides a system for specifying the enclosures of electrical equipment on the basis of the degree of protection provided by the enclosure. IEC529 does not specify degrees of protection against mechanical damage of equipment, risk of explosions, or conditions such as moisture, corrosive vapours, fungus or vermin.


NEMA Standards Publication 250 does test for environmental conditions such as corrosion, rust, icing, oil and coolants. For this reason, and because the tests and evaluations for other characteristics are not identical, the IEC

Enclosure Classification Designations cannot be exactly equated with NEMA Enclosure Type Numbers.


For downloading documents which are explaining the full IEC IP numbering scheme and the NEMA numbering system and its nearest IP equivalent, please click the following links:

• NEMA and IEC Enclosure Ratings#1 

• NEMA and IEC Enclosure Ratings#2 

2- FORMS OF SEPARATION: see fig.2

fig (2): Forms of Separation

It is the classification for the internal separation of enclosures/assemblies by barriers or partitions.

BS EN 60439:1999 Incorporating Amendments No. 1 and Corrigenda Nos. 1 and 2 is the applicable standard for Type-tested and partially type tested assemblies. This defines the Forms of Separation.

For downloading documents which are explaining the forms of separation, please click the following links:

• FORMS OF SEPARATION#1 

• FORMS OF SEPARATION#2 

3- TYPES OF COORDINATION: see fig.3

 

fig (3): Motor starting/protection Devices coordination

The International Electrotechnical Commission (IEC) developed short circuit performance criteria for contactors and starters called Type 1 coordination and Type 2 coordination.

This defines motor controller protection levels following a short circuit fault. In order to achieve this performance, the combination of a motor controller (contactor or starter) and short circuit protective device (manual motor protector, circuit breaker or fuse) must meet the following criteria as specified by IEC 60947-4-1 — Low voltage switchgear and control gear — Part 4-1: Contactors and motor-starters —Electromechanical contactors and motor-starters.



For downloading documents which are explaining the TYPES OF COORDINATION, please click the following links:

• TYPES OF COORDINATION#1 

4- NEMA MOTOR INSULATION TEMPERATURE RATINGS: see fig.4

 

fig (4): NEMA MOTOR INSULATION TEMPERATURE RATINGS

NEMA specifies letter designations for motor insulation temperature ratings. Also, NEMA specifies allowable temperature rises for motors at full load (and at service factor, if applicable). These allowable temperature rises are based upon a reference ambient temperature of 40°C, and are determined by the "resistance method", in which the resistance of the windings is measured with a bridge after the motor has achieved thermal equilibrium under load.


For downloading documents which are explaining the NEMA MOTOR INSULATION TEMPERATURE RATINGS, please click the following links:

• NEMA MOTOR INSULATION TEMPERATURE RATINGS#1 

5- NEMA EQUIPMENT CLASSIFICATIONS FOR USE IN HAZARDOUS LOCATIONS

fig (5): Class/Division Hazardous Location

The National Electrical Manufacturers Association (NEMA) has developed a rating system to identify the ability of a device or system to afford protection from the outside environment. NEMA Standard Publication 250, Enclosures for Electrical Equipment, establishes requirements that must be met for an enclosure to gain a specific Type designation.

These rating systems provide information that assists users in making informed product choices in selecting the proper enclosures for hazardous locations.



For downloading documents which are explaining the NEMA EQUIPMENT CLASSIFICATIONS FOR USE IN HAZARDOUS LOCATIONS, please click the following links:

• NEMA EQUIPMENT CLASSIFICATIONS FOR USE IN HAZARDOUS LOCATIONS #1 

• NEMA EQUIPMENT CLASSIFICATIONS FOR USE IN HAZARDOUS LOCATIONS #2 

in the next topic, another important electrical terms - Part Two will be explained, please keep following.