TIA-4950 Historical [ Revised ]

This standard applies to:

a) Apparatus or parts of apparatus in Class I, II, or III, Division 1 locations.

Note: Section 500-8(B)(2) of National Electrical Code, ANSI/NFPA 70, states that equipment that has been approved for a Division 1 location shall be permitted in a Division 2 location of the same class and group.

b) Those parts of apparatus located outside of the Class I, II, or III, Division 1 location having a design and construction that may influence the intrinsic safety of an electrical circuit within the Class I, II, or III, Division 1 location;

c) Apparatus or parts of apparatus in Class I, Zone 0 or 1, Groups IIA, IIB, and IIC locations;

d) Those parts of apparatus located outside of the Class I, Zone 0 and 1, Groups IIA, IIB, or IIC location having a design and construction that may influence the intrinsic safety of an electrical circuit within the Class I, Zone 0 and 1, Group IIA, IIB, or IIC location.

These requirements are based on consideration of ignition in locations made hazardous by the presence of flammable or combustible material under normal atmospheric conditions.

For the purposes of this standard, normal atmospheric conditions are considered to be:

• An ambient temperature of 40°C (104°F);
• An oxygen concentration not greater than 21 percent; and
• A pressure of one atmosphere.

This standard does not cover mechanisms of ignition from external sources, such as static electricity or lightning, which are not related to the electrical characteristics of the apparatus. This standard does not cover apparatus based on high voltage electrostatic principles, such as electrostatic paint spraying apparatus.

Purpose

The purpose of this standard is to provide requirements for the construction and testing of electrical apparatus, or parts of such apparatus, having circuits that are not capable of causing ignition in Division 1 hazardous locations as defined in Article 500.5 of the National Electrical Code, ANSI/NFPA 70 - 1987.

This standard is not to be considered an instruction manual for untrained persons. It is intended to promote uniformity of practice among those skilled in the field of intrinsic safety.