YB2 Series 8-Pole Explosion-Proof Motor

Eight-pole flameproof squirrel-cage induction motor certified Ex d IIB T4 for Zone 1 and Zone 2 hazardous areas, running at approximately 720 rpm on 380 V 50 Hz. Maximum shaft torque per unit power in the YB2 range — the specification of choice for slow-speed direct-coupled agitators, classified area conveyors, and low-speed fan drives where minimising driven equipment complexity inside the hazardous zone is the primary design objective.

Ex d IIB T4 Certified
Zone 1 / Zone 2
Speed: ~720 rpm (8P)
Power: 1.5 – 90 kW
Protection: IP55
Insulation: Class F

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Ex d Flameproof

Group IIB T4

8-Pole 720 rpm

Maximum Torque

IEC 60079-1

ISO 9001 Certified

YB2 Series 8-Pole Explosion-Proof Motor Ex d IIB T4 Korea Ever-Power

YB2 Motor IEC Mounting Methods IMB3 IMB5 IMB35

Highest Torque Density in the YB2 Ex d Range for Direct-Coupled Hazardous Area Drives

The 8-pole YB2 runs at approximately 720 rpm, delivering four times the shaft torque of a 2-pole motor at the same power rating. This extreme torque density enables direct coupling to driven equipment at very low shaft speeds without any intermediate reduction gearing inside the classified zone. For large agitators on chemical storage tanks and crude oil desalters, this means the motor can couple directly to the impeller shaft, and the motor frame can be bolted to the vessel top nozzle flange — the entire drive consisting of a single certified component plus the coupling.

The flameproof enclosure is engineered to the same IEC 60079-1 flame path standards as the rest of the YB2 range. At 720 rpm, all heat-generating mechanical phenomena — bearing friction, windage, shaft seal slip — are at their lowest in the range, giving the 8-pole motor the greatest thermal margin below the T4 surface temperature ceiling of 135 °C. This additional margin is valuable in outdoor installations in hot climates where ambient temperatures approach 40 °C, and where solar radiation on the motor casing can add 5 to 10 K to the effective ambient.

Frame sizes cover 100L through 280M (1.5 kW to 90 kW). Cast-iron construction throughout ensures the wall thickness needed for flame path geometry is maintained across all frame sizes. IP55 protection, Class F insulation with Class B temperature-rise limits, and CE plus Ex marking are standard on all models.

View the complete hazardous area motor range on the Explosion-Proof Motors page, or see standard motors at Three-Phase Induction Motors.

YB2 8-Pole Model Specifications — Ex d IIB T4

All models: 8-pole, ~720 rpm, 380 V 50 Hz, IP55, Class F insulation, Ex d IIB T4, Zone 1 and Zone 2.

Model	Frame	kW	Full-Load A	rpm	η %	cosφ	Tst/Tn	Ist/In	kg
YB2-100L1-8	100L	1.5	5.50	680	62.0	0.62	2.0	5.0	55
YB2-100L2-8	100L	2.2	7.70	690	65.0	0.63	2.0	5.0	62
YB2-112M-8	112M	3.0	10.00	700	68.0	0.64	2.0	5.0	80
YB2-132S-8	132S	4.0	13.00	706	71.0	0.65	2.0	5.0	102
YB2-132M-8	132M	5.5	17.20	710	74.0	0.66	2.0	5.5	130
YB2-160M-8	160M	7.5	23.00	715	77.0	0.67	2.0	5.5	182
YB2-160L-8	160L	11	32.80	718	79.5	0.68	2.0	5.5	218
YB2-180L-8	180L	15	43.50	720	81.5	0.69	2.0	5.5	272
YB2-200L-8	200L	18.5	52.50	722	83.0	0.70	2.0	5.5	348
YB2-225S-8	225S	22	61.20	724	84.5	0.71	1.8	5.5	428
YB2-225M-8	225M	30	82.00	726	86.0	0.71	1.8	5.5	502
YB2-250M-8	250M	45	120.00	728	87.5	0.72	1.8	6.0	628
YB2-280S-8	280S	55	144.00	730	88.5	0.73	1.8	6.0	752
YB2-280M-8	280M	90	233.00	732	90.0	0.74	1.8	6.0	920

Operating Conditions

Ambient temperature	−20 °C to +40 °C
Altitude	≤ 1000 m ASL
Supply voltage	380 V ± 5%
Frequency	50 Hz ± 1%
Mounting	IMB3 / IMB5 / IMB35
Protection	IP55
Insulation class	Class F
Temperature rise	Class B limit
Max surface temp	135 °C (T4)

Hazardous Area Certification

Protection method	Ex d (flameproof)
Gas group	IIB
Temperature class	T4 (135 °C max)
Zone suitability	Zone 1, Zone 2
Ex standard	IEC 60079-1
Motor standard	IEC 60034
Quality management	ISO 9001
Marking	CE / Ex

Typical Applications for YB2 8-Pole Explosion-Proof Motors

YB2 8-Pole Motor Classified Zone Agitator Application

Crude Oil Desalter Agitators

Horizontal crude oil desalter vessels use large-diameter impeller agitators running at 60 to 120 rpm. The 8-pole YB2 at 720 rpm through a small-ratio gearbox or direct coupling achieves this speed with maximum torque, while keeping the entire drive assembly inside the Zone 1 classified crude unit area as simple as possible.

YB2 8-Pole Motor Classified Conveyor Application

Classified Area Conveyors

Screw conveyors moving powdered chemicals and grain inside Zone 1 classified storage areas use 8-pole Ex d IIB motors for their high torque at low speed, avoiding jamming on startup under settled material while keeping drive equipment inside the zone to the minimum number of certified components.

YB2 8-Pole Motor Classified Fan Application

Very Large Diameter Fans

Cooling tower fans and large-diameter axial flow fans in classified areas use the 8-pole motor at 720 rpm for direct drive of fan hubs at the low blade tip speed required for efficient large-diameter axial flow designs, while maintaining Ex d flameproof protection throughout.

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LNG Tank Agitators

LNG stratification prevention agitators in classified cryogenic storage areas require Ex d motors rated for low ambient temperatures as well as flammable atmosphere protection. The 8-pole YB2 with low-temperature rating provides direct-shaft agitation of LNG stratification without internal zone gearboxes.

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Reactor Vessel Drives

Stirred-tank reactors for polymer and specialty chemical synthesis operating in classified areas use 8-pole Ex d motors for their ability to start and sustain rotation of large-diameter high-viscosity batch loads without excessive starting current at moderate supply capacity.

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Thickener and Filter Drives

Rake drives on thickeners and vacuum filter drum drives in classified mineral processing areas use 8-pole Ex d motors for the high torque needed to move rake arms through settled slurry, combined with the flameproof protection required by the process chemicals present in the area.

Selecting Between 6-Pole and 8-Pole Ex d Motors for Classified Area Agitators

Required Impeller Speed

The primary factor in choosing between 6-pole (960 rpm) and 8-pole (720 rpm) for an agitator is the impeller tip speed required by the mixing duty. High-shear duties (emulsification, gas dispersion) typically require 200 to 500 m/min tip speed, which with a 600 mm diameter impeller requires 100 to 265 rpm — achievable with a single-stage gearbox from either pole count. Low-shear duties (bulk blending, solids suspension) require 30 to 100 rpm tip speed, which favours the 8-pole motor with lower ratio reduction because the starting torque requirement at these low impeller speeds is highest and benefits from the maximum torque of the 8-pole configuration.

T4 Compliance in Hot Climates

In outdoor classified area installations in the Middle East, Southeast Asia, and equatorial Africa where ambient temperatures regularly reach 40 °C and solar radiation can add 10 to 15 K to the effective surface temperature, the thermal margin provided by the 8-pole motor at 720 rpm versus the 6-pole motor at 960 rpm can be decisive. The lower windage losses and bearing friction of the 8-pole motor reduce the motor surface temperature by an estimated 3 to 5 K at the same rated load and ambient, providing measurable additional compliance margin below the T4 ceiling in the most demanding installation environments.

Gearbox Elimination Inside Zone

For agitator duties requiring 50 to 150 rpm output, the 8-pole motor at 720 rpm requires a gearbox ratio of only 5:1 to 15:1. Single-stage helical or worm gearboxes can cover this range, whereas the same duty from a 4-pole motor at 1460 rpm would require a 10:1 to 30:1 ratio, typically necessitating a two-stage gearbox. In Zone 1 areas where every additional component inside the boundary adds to the maintenance burden and the number of items requiring periodic inspection under IEC 60079-17, eliminating a gearbox stage has real safety management and cost value over the motor service life.

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Frequently Asked Questions — YB2 Series 8-Pole Explosion-Proof Motor

Why does the 8-pole YB2 power range stop at 90 kW when the 4-pole range reaches 200 kW?

Above 90 kW at 720 rpm, the shaft torque becomes very large (approximately 1,200 N·m for a 90 kW 8-pole motor), requiring a shaft diameter and bearing arrangement that pushes the motor into a larger frame series than is covered by the standard IEC 72-1 table for frame 280M. Very large slow-speed motors above 90 kW in classified areas are typically specified as custom designs with separate engineering and Ex certification assessment. Korea Ever-Power can discuss custom Ex d slow-speed motor requirements above 90 kW on a project-specific basis. For most standard agitator and conveyor applications, the 90 kW ceiling of the YB2-8 range covers the large majority of process equipment in the relevant duty range.

Is the power factor penalty of the 8-pole motor significant in hazardous area installations?

Yes. The 8-pole motor has a typical full-load power factor of 0.62 to 0.74, which is significantly lower than the 0.84 to 0.89 of a 4-pole motor at the same frame size. In classified area installations where hazardous area regulations restrict the installation of capacitor banks inside the zone (capacitors can generate sparks on connection and disconnection), power factor correction must be applied outside the zone boundary. This means the supply cable to the classified area must be sized for the higher apparent current of the uncorrected 8-pole motor, which increases cable cost on long runs. For supply cable runs above 50 metres, the cable sizing cost difference between an 8-pole and a 4-pole motor at the same output power should be included in the total system cost comparison.

What shaft extension options are available for direct impeller mounting?

The standard IEC 72-1 shaft extension dimensions are supplied as default. For direct impeller mounting applications (where the impeller is mounted directly on the motor shaft extension without a separate agitator shaft), Korea Ever-Power can supply extended and reinforced shaft variants with larger diameter and longer extension to accommodate impeller hub mounting, key and keyway, and end-plate retention. The shaft extension must be specified to carry the combined bending moment from the impeller weight and the hydraulic forces at the impeller face. Korea Ever-Power application engineers can assist with shaft sizing calculations when the impeller geometry and process conditions are provided.

What starting method is recommended for the 8-pole YB2 starting under full load?

For frame sizes up to 160L, direct-on-line starting is the standard method. The lower starting current multiplier (Ist/In of 5.0 to 6.0) of the 8-pole motor relative to 2-pole and 4-pole motors of the same power means that direct starting current is manageable from most industrial supply systems. For frame sizes 180L and above, star-delta starting or a thyristor soft starter located outside the Zone 1 boundary reduces supply disturbance and mechanical shock on impeller and gearbox at start. The soft starter must be bypassed after run-up to avoid continuous thyristor losses, and the bypass contactor must be outside the zone boundary or Ex certified if located inside.

Can the YB2 8-pole be fitted with an encoder for speed monitoring?

Yes. An incremental encoder can be factory-fitted on the non-drive end shaft extension of the YB2 8-pole as an option. The encoder itself must be Ex certified for the applicable zone and gas group (typically Ex d or Ex ec for Zone 1). The encoder signal cable exits the motor through a certified flame-path gland in a dedicated entry point on the terminal box or through a separate junction box mounted on the motor. The encoder output provides actual shaft speed feedback to the DCS or motor protection system, enabling shaft stall detection and speed monitoring independent of motor current. Specify the encoder type, signal format, and required Ex certification at the time of enquiry.

What documentation is supplied with each YB2 8-pole motor?

Each YB2 8-pole motor is supplied with: the Ex certification certificate (IECEx or ATEX as specified), the installation and maintenance instruction manual covering Ex-specific requirements, a dimensional drawing, a wiring diagram for the supply and any sensor connections, and the factory test record including dielectric withstand test, insulation resistance measurement, no-load test at rated voltage and frequency, and frame surface temperature measurement at the most thermally loaded point. For large-frame motors (frame 225 and above), a vibration test record at no-load is also included. All documents are in English as standard; other languages are available on request.

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