US / Canadian Standards

Motors and generators intended for the US and Canadian markets must fulfil certain NEMA or CSA standards.

When the main design meets North American standards, the Ex-protection and area classification can now be made according to two different systems: the Division system, which has been in use for several years, or the new Zone system, which refers to IEC standards. According to new NEC Article 506 zone classification system (Zone 20, 21, 22), as an alternative to the division classification system, can be also used locations where fire and explosion hazards may exist due to combustible dusts, or ignitable fibers or flyings. Combustible metallic dusts are not covered.

Both systems have similar main classification arrangements, which are based on the explosive substance.

Main classifications according to NEC or CE Code
Class IGases and vapors (e.g. chemical plant, oil refinery)
Class IICombustible dusts (e.g. sugar, aluminum, grain elevator)
Class IIIFlying and ignitable fibers, such as cotton lint (e.g. textile mill)

Temperature classes according to NEC and CE Code
Temperature classT1T2T2AT2BT2CT2DT3
Max temperature / °C450300280260230215200
Temperature classT3AT3BT3CT4T4AT5T6
Max temperature / °C18016516013512010085


Zone system

NEC and CE Code have introduced a new system to classify and mark motors and generators. The zone system refers directly to IEC standards, which define zones.

IEC has classified hazardous areas into three zones. The classification is based on the incidence of explosive gas or material.

Incidence of explosive gas
Zone 0Flammable gases or vapors are present continuously or for long period
Zone 1Flammable gases or vapors are likely to exist under normal operation
Zone 2Flammable gases or vapors are not likely to occur in normal operation and if they do occur, they will exist for short periods

All electrical devices have been divided into two groups, which indicate the suitable operational area for apparatus. Group I is for mines and group II is for surface industry. The type of the surrounding gas also influences the design. As a result IEC has also classified three gas groups, which are A, B and C. The gas groups are used only for group II apparatus.

The following table shows the existing apparatus and gas groups. There is also an example gas given for each gas group.

Apparatus and Gas groups
Apparatus groupGas groupExample gas
I - Mines susceptible to firedampMethane
II - Other placesIIAPropane
IIBEthylene
IIB + H2IIB gases + Hydrogen
IICAcetylene, Hydrogen
Marking


Graphics for CSA zones in US, used in web pages for hazardous area motors

Division system

The division system has been used in North America for a long time and will remain important for many years in the future. At the same time, however, the number of industrial plants classified according to the zone system is continuously increasing.

The division system describes two divisions, which are based on the incidence of the flammable material.

Incidence of flammable material according to the division system
Division 1Flammable gases or vapors are present continuously, for long period or occasionally in normal operation
Division 2Flammable gases or vapors are present in abnormal conditions only for short periods

Gas and dust groups
NEC and CE Code have four groups for gases and three groups for dusts. The gas group has the same meaning as in IEC standards (IIA, IIB, IIC). Note that in IEC standards IIC is the most and IIA the least demanding gas group, while in NEC and CE code IIA is the most and IID the least demanding group.


Example gas for each gas group (Class I)
Gas GroupExample gas
Group AAcetylene
Group BHydrogen
Group CEthylene
Group DMethane, Propane

The dust groups and temperature limits for each operation condition are presented below with example dusts. The limits only concern the external parts of the motor or generator, such as the frame and bearings.

Example dust for each dust group (Class II)
Dust GroupExample dust
Temperature limit
Normal operationsAbnormal operations
Group EMetal dust (e.g. Magnesium, Aluminum)200°C200°C
Group FCoal dust150°C200°C
Group GGrain dust (e.g. Flour)120°C165°C

Marking


CSA divisions for US, used in web pages for hazardous area motors


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ABB contact for

United States of America
Judy Johnson
 

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