Blog IronAxis Technical Team 23 Oct 2026 views ( )

Explosion-proof Electric Hoist for Zone 1 / Zone 2: Selection Guide for Ex db IIC T4 Gb (IIC T4 / CT4)

In petroleum, chemical, gas and pharma plants, flammable gases may be present continuously or intermittently. Standard hoists create ignition sources through fault arcs, contactor switching, brake friction or impact. A reinforced standard hoist is unacceptable; the design must be explosion-proof from the outset, electrically and mechanically.
 
"CT4" is Chinese industry shorthand, not a complete marking; it generally means "IIC T4". A full marking includes protection type, gas group, temperature class and EPL: Ex db IIC T4 Gb (IEC) or II 2G Ex db IIC T4 Gb (ATEX). Check the valid Ex certificate and nameplate.
 
Ex: explosion-proof compliant.
db: flameproof enclosure, IEC 60079-1; older "d".
IIC: most stringent subgroup (hydrogen, acetylene); covers IIA and IIB per certificate.
T4: max surface 135°C (T1–T6: 450/300/200/135/100/85°C).
Gb: EPL, Ga for Zone 0, Gb for Zone 1/2, Gc for Zone 2 only.
ATEX: Zone 1 is normally 2G, Zone 2 may be 3G; North America uses Class I Division 1/2. IECEx, ATEX, Chinese Ex and UL/CSA are not mutually recognized; export projects must meet target-market regulations.
 
Safety rests on three features. Flameproof joints: controlled gap, length and finish quench internal flame and hot gases. Surface temperature: motor design, load limit, duty cycle and cooling hold the class; T4 is stricter than T3/T2. Non-sparking parts: hooks and trolley wheels in non-sparking material; control boxes flameproof or intrinsically safe.
 
Selection: confirm area classification (Ex db suits Zone 1/2, not Zone 0), gas type (IIB or IIC), ignition temperature (T3/T4 with margin), capacity, height, duty class and frequency. Export projects generally need an IECEx CoC or ATEX EU-type certificate; China needs GB/T 3836.
 
Maintenance red lines: never open a flameproof enclosure while energized; never strike, scratch, paint or re-gasket joints; replacement parts must match the protection level.
 
Zhejiang Vertex International Trade Co., Ltd supplies lifting equipment and customizes gas group, temperature class, capacity, height, voltage, control and mounting, plus OEM/ODM within certificate scope. Send gas type, ignition temperature, area class and lifting needs for advice.
 
Zhejiang Vertex International Trade Co., Ltd. Parent Companies:
1. Zhejiang Boneng Lifting Technology Co., Ltd. (Former Name: Taizhou Boneng Lifting Machinery Equipment Co., Ltd.)
2. Sanmen Youbang Machinery Co., Ltd.