NFPA (Fire) 496

NFPA (Fire) 496 - Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2003 Edition

September, 2003

National Fire Protection Association

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NFPA 496 contains requirements for design and operation of purged and pressurized electrical equipment enclosures. This protection technique is used in Class I and Class II hazardous (classified) locations to reduce or prevent the presence of combustible materials within electrical equipment enclosures. This Standard also includes chapters covering protection of analyzers and rooms housing analyzers and a chapter on pressurized control rooms. The 2003 edition has chapter arrangement and editorial revisions in accordance with the NFPA Manual of Style. Definitions of hazardous (classified) locations have been revised to parallel with those contained in the National Electrical Code.


Contents
Chapter 1 Administration ............................... 496– 4
1.1 Scope ............................................... 496– 4
1.2 Purpose ............................................ 496– 4
1.3 Application ....................................... 496– 4
1.4 Equivalency ....................................... 496– 4
1.5 Units of Measurement ......................... 496– 4
1.6 Mandatory Rules, Permissive Rules, and
Explanatory Material ........................... 496– 4
Chapter 2 Referenced Publications ................... 496– 4
2.1 General ............................................ 496– 4
2.2 NFPA Publication ................................ 496– 5
2.3 Other Publications .............................. 496– 5
Chapter 3 Definitions .................................... 496– 5
3.1 General ............................................ 496– 5
3.2 NFPA Official Definitions ...................... 496– 5
3.3 General Definitions ............................. 496– 5
3.4 NEC
®
Extracted Definitions ................... 496– 5
Chapter 4 General Requirements for
Pressurized Enclosures ..................... 496– 6
4.1 Applicability ...................................... 496– 6
4.2 Enclosure ......................................... 496– 6
4.3 Pressurizing System ............................. 496– 6
4.4 Protective Gas System .......................... 496– 6
4.5 Determination of Temperature Marking .... 496– 7
4.6 Ventilated Equipment .......................... 496– 7
4.7 Power Equipment ............................... 496– 7
4.8 Type Z Pressurizing ............................. 496– 7
4.9 Type Y Pressurizing .............................. 496– 8
4.10 Type X Pressurizing ............................. 496– 8
4.11 Markings .......................................... 496– 8
Chapter 5 Pressurized Enclosures for Class I ...... 496– 9
5.1 Applicability ...................................... 496– 9
5.2 General Requirements ......................... 496– 9
5.3 Markings .......................................... 496– 9
5.4 Additional Requirements for Type Y or
Type Z Pressurizing ............................. 496– 9
5.5 Additional Requirements for Type X
Pressurizing ....................................... 496– 9
Chapter 6 Pressurized Enclosures for Class II ..... 496– 9
6.1 Applicability ...................................... 496– 9
6.2 General Requirements ......................... 496– 9
6.3 Markings .......................................... 496–10
6.4 Marking Information ........................... 496–10
6.5 Additional Requirements for Type X
Pressurizing ....................................... 496–10
6.6 Additional Requirements for Ventilated
Equipment ........................................ 496–10
Chapter 7 Pressurized Control Rooms ............... 496–10
7.1 Applicability ...................................... 496–10
7.2 Protective Gas .................................... 496–10
7.3 Considerations Relating to Positive
Pressure Ventilation ............................. 496–10
7.4 Requirements for Positive Pressure Air
Systems ............................................ 496–10
Chapter 8 Pressurized Enclosures Having an
Internal Source of Flammable
Gas or Vapor .................................. 496–11
8.1 Applicability ...................................... 496–11
8.2 General Requirements ......................... 496–11
8.3 Specific Requirements ......................... 496–11
Chapter 9 Pressurized Analyzer Rooms
Containing a Source of
Flammable Gas, Vapor, or Liquid ........ 496–12
9.1 Applicability ...................................... 496–12
9.2 General ............................................ 496–12
9.3 Specific Requirements ......................... 496–13
Annex A Explanatory Material ......................... 496–13
Annex B Informational References ................... 496–17
Index ........................................................... 496–19
496–3CONTENTS
2003 Edition

Product Replaces

NFPA (Fire) 496 - Purged and Pressurized Enclosures for Electrical Equipment, 1998 Edition