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Selecting an explosion-proof motor for a hazardous area comes down to three questions: which zone, which gas group, and which temperature class. This guide walks through each step so you can specify the correct flameproof (Ex d) motor for Zone 1 and Zone 2 applications — and avoid the costly mistake of installing an under-rated motor in a classified area.
1. Step 1: Identify the Zone
Hazardous areas are classified by how often an explosive atmosphere is present. In the IEC/ATEX system, gas zones are Zone 0 (continuous), Zone 1 (likely in normal operation) and Zone 2 (unlikely, brief if it occurs). Dust zones are Zone 20, 21 and 22. The zone determines the minimum protection concept:
| Zone | Atmosphere Presence | Typical Motor Protection |
| Zone 1 | Occasional in normal operation | Flameproof (Ex d) or increased safety (Ex e) |
| Zone 2 | Rare and brief | Ex e, Ex nA or Ex d |
| Zone 21/22 | Combustible dust | Dust-ignition protected (Ex tb) enclosure |
2. Step 2: Match the Gas Group
Gas groups rank the difficulty of igniting the gas: Group IIA (propane), IIB (ethylene) and IIC (hydrogen/acetylene) — the most demanding. A motor certified for IIC can be used for IIB and IIA; the reverse is not true. For hydrogen service, specify IIC-certified motors. See our IIB vs IIC selection guide for a detailed breakdown of gas groups and typical applications.
3. Step 3: Select the Temperature Class
The temperature class (T-code) is the maximum surface temperature of the motor under the most severe conditions, and it must stay below the auto-ignition temperature (AIT) of the surrounding gas. The table shows the standard classes:
| T-Code | Max Surface Temp | Typical Gas AIT |
| T1 | 450°C | Methane 595°C, Hydrogen 560°C, Propane 470°C |
| T2 | 300°C | Acetylene 305°C |
| T3 | 200°C | Gasoline 280°C, naphtha |
| T4 | 135°C | Diethyl ether 160°C |
| T5 | 100°C | Carbon disulfide 102°C |
| T6 | 85°C | — |
Most petrochemical and gas applications require T3 or T4; the flameproof enclosure itself limits the surface temperature so the motor stays within its T-class even under fault conditions. For a deeper look at how the Ex d enclosure achieves this, read what makes an explosion-proof motor different.
4. Step 4: Verify Certification and Ratings
Check that the motor carries a valid ATEX and/or IECEx certificate covering your zone, gas group and T-class — for example Ex db IIB T4 Gb for Zone 1. For export to North America, confirm the equivalent Class/Division rating. Our IEC Zone vs North American Division comparison explains how the two systems map to each other. Also verify IP rating (IP55 or higher for outdoor/chemical environments), cooling method and ambient temperature range.
5. A Practical Selection Checklist
- Zone of installation (gas: Zone 1/2; dust: Zone 21/22)
- Gas group of the process medium (IIA/IIB/IIC)
- Auto-ignition temperature → required T-class
- ATEX/IECEx certificate scope and validity
- Power, voltage, frequency, duty and installation form
- Efficiency class (IE4/IE5) for energy compliance
Need Help Specifying Your Explosion-Proof Motor?
Send us your zone classification, gas group, temperature requirements and duty data — our engineers will recommend the right flameproof motor model. Browse the Wolong explosion-proof motor product range, or check our CSA-certified motor guide for North American projects.
