HAZARDOUS LOCATIONS ACCORDING TO THE NATIONAL ELECTRIC CODE

In North America the standard reference documents for electrical installations are the National Electric Code (NEC) for the USA and the Canadian Electrical Code (CEC) for Canada.

Electrical Equipment used in Ordinary, Wet and Hazardous (or Classified) Locations must be 'listed' by an accredited approval agency for use in the intended location. The hazardous locations include areas in which flammable, combustible or ignitable substances may occur in hazardous amounts. The NEC and CEC codes allow two methods of categorising Hazardous Locations, which are Class and Division, and Class and Zone.

Electrical Apparatus approved for use in Hazardous Locations must be categorised with an Equipment Class and suitable for a specified Division and Gas Group. Their classification is made in line with the amount of combustible materials as :-

Class I - Flammable gases, vapours or mists
Class II - Combustible Dusts
Class III - Ignitable Fibres and Flyings

A similar arrangement of categorising Gas Groups is used in the North American / Canadian standards as in IEC standards although the identification of Gas Groups is different. eg. :-

Division Definitions : Division 1 or Division 2
Equipment Classified : Class I, Division 1, A B C D

SURFACE TEMPERATURE CLASSIFICATION
UL844 MAXIMUM TEMEPRATURE (ºC) IEC 60079
T1 450 T1
T2 300 T2
T2A 280 T2
T2B 260 T2
T2C 230 T2
T2D 215 T2
T3 200 T3
T3A 180 T3
T3B 165 T3
T3C 160 T3
T4 135 T4
T4A 120 T4
T5 100 T5
T6 85 T6
GAS GROUPS
GAS/COMPOUND NATIONAL ELECTRIC CODE ATMOSPHERE IEC 60079 GAS GROUP
ACETYLENE A IIC
CARBON DISULPHIDE B IIC
HYDROGEN B IIC
ETHYLENE OXIDE B IIB
HYDROGEN SULPHIDE C IIB
ETHYLENE C IIB
ACRYLONITRILE D IIA
INDUSTRIAL METHANE D IIA
PROPANE D IIA
ETHYL ACETATE D IIA

The major Approvals bodies authorised for investigation or assessment of electrical equipment include Underwriters Laboratory (UL), Factory Mutual Inc (FM) & Canadian Standards Association (CSA). In some cases, Electrical equipment may also need to meet certain Marine Standards and comply with the requirements of the US Coast Guard 14 CFR. It should be noted that the information provided here reflects the current position but since the NEC and CEC codes are being continuously reviewed and developed, there may be other changes in process which will affect some of the rules and regulations referenced herein which are understood to be correct at the time of going to print.