Hazardous Areas: NEC vs IEC
How the North American Class/Division system lines up with the IEC Zone system, topic by topic.
NEC
Article 500: Class I (gases, vapors), Class II (combustible dust), Class III (fibers, flyings), each split into Division 1 and 2. Articles 505 and 506 allow the Zone system instead.
IEC
IEC 60079-10-1 (gas) and 60079-10-2 (dust) classify areas into Zones 0, 1, 2 for gas and 20, 21, 22 for dust.
NEC
Division 1 — ignitable concentrations can exist under normal operation, during repair or maintenance, or through leaks.
IEC
Zone 0 / 20 — present continuously or for long periods. Zone 1 / 21 — likely in normal operation.
Division 1 covers both Zone 0 and Zone 1.
NEC
Division 2 — present only under abnormal conditions (failure of a container or ventilation) or next to a Division 1 area.
IEC
Zone 2 / 22 — not likely in normal operation and, if it occurs, only for a short time.
Division 2 and Zone 2 are broadly equivalent.
NEC
Group A acetylene; Group B hydrogen and similar; Group C ethylene and similar; Group D propane and similar.
IEC
Group IIC acetylene and hydrogen; IIB ethylene; IIA propane. Equipment marked IIC suits IIB and IIA as well.
A and B together map to IIC, C to IIB, D to IIA.
NEC
Group E metal dust; Group F carbonaceous dust; Group G other combustible dust (flour, grain, plastics). Class III covers fibers and flyings.
IEC
Group IIIC conductive dust; IIIB non-conductive dust; IIIA combustible flyings.
E roughly maps to IIIC, F and G to IIIB, Class III to IIIA.
NEC
T1 to T6 with subdivisions (for example T2A to T2D, T3A to T3C, T4A) for Division-listed equipment.
IEC
T1 450 °C, T2 300 °C, T3 200 °C, T4 135 °C, T5 100 °C, T6 85 °C maximum surface temperature.
The T class must be below the autoignition temperature of the gas present.
NEC
Division listing states the Class, Division and Group; Zone equipment under Article 505 carries AEx marking with EPL.
IEC
Equipment protection level (EPL): Ga, Gb, Gc for gas and Da, Db, Dc for dust.
Zone 0 needs Ga; Zone 1 needs Ga or Gb; Zone 2 accepts Ga, Gb or Gc.
NEC
Class I, Division 1, Groups C and D, T4 — or, under Article 505, Class I, Zone 1, AEx db IIB T4 Gb.
IEC
Ex db IIB T4 Gb (IECEx or ATEX certificate).
In the US, IEC-certified equipment still needs a US listing (NRTL) to be accepted.
Sources: NEC 2023 Articles 500–506, IEC 60079-0, 60079-10-1 and 60079-10-2 — described in our own words. © RokBench.