Explosion-proof motor selection matches the motor's surface temperature class to the gas group present, so it cannot ignite the surrounding atmosphere.
The Classification Logic
A gas group identifies the explosive atmosphere: IIA, IIB, and IIC in the typical industrial scheme, with IIC being the most easily ignited, such as hydrogen or acetylene, demanding the strictest equipment and the most careful installation practice.
The point of an explosion-proof motor is containment, not prevention of the spark inside; the certified enclosure is built so that if an ignition occurs within, the flame path cools the gas before it can leave and ignite the surrounding atmosphere. The whole path, joints, terminal box, and shaft seal, is part of the rating.
Gas group and temperature class are read from the site's hazard study, which lists the actual gas, its auto-ignition temperature, and the zone. The motor's group must cover that gas and its T class must sit below the ignition temperature with margin, because a motor that is fine for one gas can be unsafe for another that ignites more easily.
Zone 1, where the gas is expected in normal operation, demands a higher equipment protection level than Zone 2, where it appears only in fault. The enclosure certificate states the zone it is valid for, and mixing them is a compliance failure that an authority review will catch and reject at the specification stage.
Maintenance keeps the protection real: a damaged flame path, a missing bolt, or a scored shaft seal can void the containment, so inspection and correct reassembly are written into the safe-operating procedure and the records show the equipment remains in its certified condition. The motor is only as safe as its last correct rebuild.
The company's 80,000 m² production site builds fans under ISO 9001:2015 with CCC certification, and its engineers respond to selection enquiries within 24 hours to match motor gas group, T class, and zone to the site hazard data so the certified enclosure meets the duty without over-specifying cost.
The certified path continues at the cable entry: glands and conduit seals must match the zone or the enclosure is breached at the very point the wiring passes through, so the termination is specified for the same gas group and zone as the motor. A correct flameproof gland and a sealed conduit keep the containment intact, and the installation is verified against the certificate so the motor that passed the test is not defeated by a standard fitting at the junction box.
The temperature class, T1 through T6, states the maximum surface temperature the motor can reach; T6 means below 85°C while T1 allows up to 450°C, so the class must sit below the gas auto-ignition temperature with an adequate safety margin.
Zones describe likelihood: Zone 1 is an area where explosive gas is expected during normal operation, while Zone 2 is where it appears only in fault, and the equipment protection level follows the zone with stricter requirements for the more hazardous case.
The selection rule is simple to state: the motor's gas group must cover the site's gas, and its T class must be lower than the gas ignition temperature, with the zone setting the required protection level that the certified enclosure must demonstrably meet.
Applying It
A fan in a solvent area with a low auto-ignition gas needs a T4 or better motor and a group rating that includes that gas, or the unit is unsafe regardless of its mechanical performance, and an authority review will reject the specification.
Overspecifying the T class is safe but can cost more and run the motor with tighter thermal margins, so the correct class is chosen from the actual gas data, not a blanket T6 everywhere, balancing safety, cost, and the motor's operating headroom.
The enclosure must be certified as a whole, not just the motor, because the terminal box, seals, and joints are part of the explosion-proof path that contains an internal spark and stops it reaching the surrounding flammable atmosphere.
Maintenance discipline matters: a damaged flame path or a missing bolt can void the protection, so inspection and correct reassembly are part of safe operation, and records should show the equipment remains in its certified condition.
| Item | Specification | Note |
|---|---|---|
| Gas group | IIA / IIB / IIC | IIC strictest |
| T class | T1-T6 | Max surface T |
| T6 limit | <85°C | T1 up to 450°C |
| Zone 1 | normal ops | Higher protection |
| Zone 2 | fault only | Lower level |
| Enclosure | certified | Whole path |
Selection Checklist
- Identify the gas group and auto-ignition temperature on site.
- Choose a T class below that ignition temperature.
- Match the motor gas group to the atmosphere present.
- Select protection level for Zone 1 or Zone 2.
- Use a certified explosion-proof enclosure, not just motor.
- Keep the flame path intact through inspection and rebuild.
About the Manufacturer
Keruite Air Conditioning Group, headquartered in Dezhou, Shandong, has more than 30 years of HVAC manufacturing experience and operates an 80,000 m² production site with its own performance testing laboratory. Products are built under ISO 9001:2015 quality management and carry CCC certification, and are supplied to customers in over 50 countries.
Our engineers respond to selection enquiries within 24 hours and can provide project-specific sizing, performance curves, and documentation to support specification and procurement.