{"id":147,"date":"2026-07-08T08:45:37","date_gmt":"2026-07-08T08:45:37","guid":{"rendered":"https:\/\/industrialelectricmotor.net\/?p=147"},"modified":"2026-07-08T08:45:37","modified_gmt":"2026-07-08T08:45:37","slug":"how-to-select-the-right-electric-motor","status":"publish","type":"post","link":"https:\/\/industrialelectricmotor.net\/hi\/how-to-select-the-right-electric-motor\/","title":{"rendered":"How to Select the Right Electric Motor"},"content":{"rendered":"
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Korea Ever-Power \u00b7 Motor Selection Guide<\/span><\/p>\n

<\/div>\n<\/div>\n

How to Select the Right Electric Motor
\nfor Your Application<\/span><\/h1>\n

Choosing the wrong motor is one of the most common and costly mistakes in industrial machine design. This motor selection guide walks through every criterion that matters \u2014 load type, duty cycle, efficiency class, protection rating, mounting, and speed control \u2014 so you arrive at the right specification the first time.<\/p>\n

Load Torque Analysis<\/span>
\nDuty Cycle S1\u2013S9<\/span>
\nIE2 \/ IE3 \/ IE4<\/span>
\nIP44 \u2013 IP69K<\/span>
\nVFD Compatibility<\/span><\/div>\n<\/div>\n<\/div>\n

<\/p>\n

\n
\n
Step 1<\/div>\n
Define the Load<\/div>\n<\/div>\n
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Step 2<\/div>\n
Calculate Power<\/div>\n<\/div>\n
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Step 3<\/div>\n
Choose Speed<\/div>\n<\/div>\n
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Step 4<\/div>\n
Pick Protection<\/div>\n<\/div>\n
\n
Step 5<\/div>\n
Verify Efficiency<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

\"Electric<\/p>\n
Korea Ever-Power Y2 series motors \u2014 correct motor selection determines energy cost, reliability, and maintenance frequency over a 20 to 30-year service life.<\/div>\n<\/div>\n

<\/p>\n

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Contents<\/div>\n
1. Understanding Load Type<\/a>
\n2. Motor Power Calculation<\/a>
\n3. Speed, Poles and Gearing<\/a>
\n4. Duty Cycle and Service Factor<\/a>
\n5. Operating Environment and IP Class<\/a>
\n6. Motor Type Selection Matrix<\/a>
\n7. Efficiency Class and Lifecycle Cost<\/a>
\n8. Frequently Asked Questions<\/a><\/div>\n<\/div>\n

<\/p>\n

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1. Understanding Load Type<\/h2>\n

The first step in any motor selection process is characterising the driven load. This defines the torque and speed requirements across the full operating range, which in turn determines the required motor type, power rating, pole count, and whether a VFD or gearbox is needed. There are three fundamental load categories.<\/p>\n

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Constant Torque Loads<\/div>\n

Torque remains approximately constant regardless of speed. The required motor power therefore increases proportionally with speed. Examples: conveyors, positive-displacement pumps, compressors, mixers, and hoists. The motor must be sized to provide sufficient torque at the lowest operating speed, including during starting under full load.<\/p>\n

P = T \u00d7 n \u00f7 9550 (where T is constant, P varies with speed n)<\/div>\n<\/div>\n
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Variable Torque Loads (Centrifugal)<\/div>\n

Torque increases with the square of speed; power increases with the cube of speed. Examples: centrifugal pumps, fans, and blowers. At 50 percent of rated speed, the load only requires 25 percent of rated torque and 12.5 percent of rated power. This characteristic makes variable torque loads ideal for VFD speed control, where large energy savings are achievable at reduced flow demands.<\/p>\n

P \u221d n\u00b3 \u2014 reducing speed by 20% cuts power demand by nearly 50%<\/div>\n<\/div>\n
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Constant Power Loads<\/div>\n

Power remains constant while torque decreases as speed increases. Examples: metal cutting machine tools (spindle drives), winding machines, and some rolling mill drives. Motor selection for constant power loads must ensure the motor can provide full rated power at the highest required speed and sufficient torque for cutting or winding force at the lowest speed in the operating range.<\/p>\n

T = 9550 \u00d7 P \u00f7 n \u2014 torque falls as speed rises at constant power<\/div>\n<\/div>\n<\/div>\n

Identifying the load type first prevents the most common motor oversizing error: selecting a motor sized for starting torque on a centrifugal load that only requires 12.5 percent of rated torque at half speed. An oversized motor runs at low power factor and reduced efficiency across most of its operating range, increasing both energy costs and reactive power charges.<\/p>\n<\/div>\n

<\/p>\n

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2. Motor Power Calculation<\/h2>\n

Once the load torque-speed characteristic is known, the required motor shaft power can be calculated. The required power must be sufficient for the worst-case operating condition \u2014 typically maximum load at maximum speed \u2014 with a service factor applied for starting conditions and load variations.<\/p>\n

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Power Calculation Reference<\/div>\n
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From torque and speed:<\/div>\n
P (kW) = T (N\u00b7m) \u00d7 n (rpm) \u00f7 9550<\/div>\n<\/div>\n
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From flow and pressure (pumps):<\/div>\n
P (kW) = Q (m\u00b3\/s) \u00d7 \u0394p (Pa) \u00f7 (1000 \u00d7 \u03b7)<\/div>\n<\/div>\n
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Recommended motor power:<\/div>\n
P\u2011motor = P\u2011load \u00d7 Service Factor \u00f7 \u03b7\u2011drivetrain<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n\n\n\n\n\n\n\n\n\n
Application<\/th>\nStarting Service Factor<\/th>\nRunning Service Factor<\/th>\nNotes<\/th>\n<\/tr>\n<\/thead>\n
Centrifugal pump \/ fan<\/td>\n1.0<\/td>\n1.0\u20131.15<\/td>\nLow starting torque; size for max operating point<\/td>\n<\/tr>\n
Belt conveyor (loaded start)<\/td>\n1.5<\/td>\n1.15\u20131.25<\/td>\nHigh inertia or loaded start requires starting torque margin<\/td>\n<\/tr>\n
Screw compressor<\/td>\n1.5\u20132.0<\/td>\n1.25<\/td>\nUnloaded start possible; use soft starter or star-delta<\/td>\n<\/tr>\n
Agitator \/ mixer<\/td>\n2.0\u20132.5<\/td>\n1.25\u20131.5<\/td>\nHigh viscosity batch start is the worst-case condition<\/td>\n<\/tr>\n
Hoist \/ crane<\/td>\n2.0\u20133.0<\/td>\n1.5<\/td>\nStarting under full suspended load; use brake motor<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

After calculating the required motor power, round up to the next standard IEC power rating in the series (0.18, 0.25, 0.37, 0.55, 0.75, 1.1, 1.5, 2.2, 3.0, 4.0, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200 kW). Avoid selecting a motor more than one standard size above the calculated requirement, as this increases capital cost and reduces part-load efficiency and power factor.<\/p>\n<\/div>\n

<\/p>\n

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3. Speed, Poles and Gearing<\/h2>\n

Motor speed in revolutions per minute is determined by the number of magnetic poles and the supply frequency. At 50 Hz, the four standard pole configurations produce these synchronous speeds and approximate full-load speeds:<\/p>\n

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2,900<\/div>\n
rpm (2-pole)<\/div>\n
High-speed fans, centrifugal pumps, turboblowers. Highest specific output per frame size.<\/div>\n<\/div>\n
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1,450<\/div>\n
rpm (4-pole)<\/div>\n
Most common. Pumps, compressors, conveyors, machine tools. Best efficiency-to-torque ratio.<\/div>\n<\/div>\n
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960<\/div>\n
rpm (6-pole)<\/div>\n
Agitators, large fans, slow conveyors. Higher torque reduces gearbox ratio requirement.<\/div>\n<\/div>\n
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720<\/div>\n
rpm (8-pole)<\/div>\n
Very slow loads, large agitators, kiln drives. Maximum torque per kW; lowest noise.<\/div>\n<\/div>\n<\/div>\n

When the required output speed does not match any standard motor speed, a gearbox is used to step down (or occasionally step up) between motor and load. The gear ratio required is simply the motor speed divided by the required output speed. For example, a conveyor requiring 28 rpm from a 4-pole motor at 1,450 rpm needs a gear ratio of approximately 52:1. This would typically be achieved with a worm gearbox for modest torques or a helical gearbox for continuous heavy duty at high power.<\/p>\n

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Selection tip: When the required output speed is between 50 and 300 rpm, compare the total cost of a 4-pole motor with a two-stage gearbox against a 6-pole or 8-pole motor with a single-stage gearbox. The latter option often reduces drivetrain complexity, maintenance points, and total installed cost for agitator and conveyor applications. Korea Ever-Power\u2019s gearmotor combinations<\/a> cover all four pole configurations matched with worm, helical, and bevel-helical reducers.<\/p>\n<\/div>\n<\/div>\n

<\/p>\n

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4. Duty Cycle and Service Factor<\/h2>\n

IEC 60034-1 defines nine standard duty types (S1 through S9) that describe how a motor\u2019s load and rest periods alternate over time. The duty cycle determines the thermal loading on the motor and directly affects the required power rating.<\/p>\n

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S1<\/div>\n
Continuous Running Duty<\/div>\n<\/div>\n

Motor runs continuously at constant load for long enough to reach thermal equilibrium. The most common duty type \u2014 pumps, fans, compressors, conveyors. Motor is rated for continuous operation at the nameplate power.<\/p>\n<\/div>\n

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S2<\/div>\n
Short-Time Duty<\/div>\n<\/div>\n

Motor runs at constant load for a short defined period (10, 30, 60, or 90 minutes), then stops long enough for full cooling to ambient. Valve and sluice gate actuators, intermittent machine tools. Short-time duty motors can be rated above S1 continuous power for their defined run period.<\/p>\n<\/div>\n

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S3<\/div>\n
Intermittent Periodic Duty<\/div>\n<\/div>\n

Motor alternates between on-load and rest periods in a fixed cycle, and never reaches thermal equilibrium in either phase. Cyclic duty factor (CDF) is the ratio of on time to total cycle time. Packaging machines, presses, and elevator drives often operate on S3 duty with CDF of 25 to 60 percent.<\/p>\n<\/div>\n

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S4\u2013S8<\/div>\n
Starting, Braking and Speed-Varying Duties<\/div>\n<\/div>\n

S4 includes thermal effect of starting. S5 includes braking cycles. S6 covers continuous operation with intermittent overloads. S7 and S8 cover motor braking and speed-changing duties. These duty types are relevant for crane, hoist, and rolling mill applications where frequent acceleration-deceleration cycles impose additional thermal stress on the motor winding.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

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5. Operating Environment and IP Class<\/h2>\n
\n
\n

The installation environment determines the required IP ingress protection rating, insulation class, and in some cases the motor construction material. A motor installed in a clean, dry indoor environment can use IP44. The same motor in a chemical plant outdoor area subject to rain and dust requires IP55 or IP65. Food processing lines subject to daily high-pressure caustic washdown require IP69K with stainless steel construction.<\/p>\n

For classified hazardous areas containing flammable gases or combustible dust, standard motors are not permitted regardless of IP rating. Certified explosion-proof motors (Ex d IIB T4 for Zone 1 gas areas, or Ex t IIIB for Zone 21 dust areas) are mandatory. Korea Ever-Power\u2019s YB2 series explosion-proof motors<\/a> cover Zone 1 and Zone 2 gas areas from 0.55 to 200 kW in all four pole configurations.<\/p>\n<\/div>\n

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Environment to IP Class Guide<\/div>\n\n\n\n\n\n\n\n\n\n
Environment<\/th>\nMin. IP<\/th>\n<\/tr>\n
Clean indoor, dry<\/td>\nIP44<\/td>\n<\/tr>\n
General industrial, dusty<\/td>\nIP54<\/td>\n<\/tr>\n
Outdoor or water jets<\/td>\nIP55<\/td>\n<\/tr>\n
Washdown areas<\/td>\nIP65<\/td>\n<\/tr>\n
Food \/ pharma washdown<\/td>\nIP69K<\/td>\n<\/tr>\n
Hazardous gas area (Zone 1)<\/td>\nEx d IIB<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

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6. Motor Type Selection Matrix<\/h2>\n

Once load type, power, speed, duty cycle, and environment are defined, the motor type can be selected. This matrix matches the most common application requirements to the appropriate motor series from Korea Ever-Power.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Requirement<\/th>\nKorea Ever-Power Series<\/th>\nKey Feature<\/th>\n<\/tr>\n<\/thead>\n
Standard S1 continuous duty, clean indoor<\/td>\nY2 Series<\/td>\nIE3, IP54, 0.18\u2013200 kW, all 4 pole configurations<\/td>\n<\/tr>\n
Variable speed with VFD<\/td>\nYVF2 Series<\/td>\nIC416 external blower, Class H, PTC thermistors, 0.75\u2013200 kW<\/td>\n<\/tr>\n
Two fixed speeds needed (no VFD)<\/td>\nYD Series<\/td>\nDahlander \/ separate winding, 4\/2P through 12\/6P pole combos<\/td>\n<\/tr>\n
Load-holding \/ positioning duty<\/td>\nY2EJ Series<\/td>\nIntegral spring-applied DC brake, stop time < 0.1\u20130.4 s<\/td>\n<\/tr>\n
Hazardous area Zone 1 \/ Zone 2<\/td>\nYB2 Series<\/td>\nEx d IIB T4, IP55, 0.55\u2013200 kW, IECEx \/ ATEX certified<\/td>\n<\/tr>\n
IP69K daily washdown (food \/ pharma)<\/td>\nBXG Series<\/td>\n316L stainless, IP69K, FDA seals, Ra 0.8 um, Class H<\/td>\n<\/tr>\n
Small power (< 1 kW), aluminium frame<\/td>\nYS Series<\/td>\n25 W\u2013750 W, aluminium frame, IP44, capacitor-start option<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Full product specifications, model tables, and application guides for each series are in the three-phase motor product section<\/a>.<\/p>\n<\/div>\n

<\/p>\n

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7. Efficiency Class and Lifecycle Cost<\/h2>\n

For most industrial motors, the energy cost over a 10-year operational life far exceeds the initial purchase price. A 22 kW motor purchased for 600 USD will consume approximately 480,000 kWh over 10 years at full load (4,800 hours per year). At 0.12 USD\/kWh, this is 57,600 USD in electricity costs \u2014 96 times the motor purchase price. An efficiency improvement from IE2 (90.9%) to IE3 (91.6%) at 22 kW saves approximately 410 kWh per year per motor, or 4,100 kWh and 492 USD over 10 years at 0.12 USD\/kWh.<\/p>\n

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10-Year Total Cost of Ownership \u2014 22 kW Motor, 4,800 h\/year, 0.12 USD\/kWh<\/div>\n
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IE2 Motor (90.9% eff.)<\/div>\n
~57,890 USD<\/div>\n
Energy cost only; motor cost ~500 USD<\/div>\n<\/div>\n
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IE3 Motor (91.6% eff.)<\/div>\n
~57,398 USD<\/div>\n
Motor cost ~700 USD; saves 492 USD in energy<\/div>\n<\/div>\n
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Net saving (IE3 vs IE2)<\/div>\n
+290 USD<\/div>\n
After recouping higher IE3 purchase price in 4 years<\/div>\n<\/div>\n<\/div>\n<\/div>\n

For facilities with large motor populations, the accumulated energy saving from upgrading from IE2 to IE3 across 50 to 100 motors can represent significant annual operating cost reduction. The EU Regulation 2019\/1781 mandates IE3 as the minimum efficiency class for motors from 0.75 to 200 kW in the European market, and many other markets are adopting equivalent regulations. Specifying IE3 as a minimum for all new motor purchases is both regulatory compliance and sound operational economics.<\/p>\n<\/div>\n

<\/p>\n

\n
\"Electric<\/p>\n
Pump and HVAC Drives<\/div>\n<\/div>\n
\"Electric<\/p>\n
Textile Machine Drives<\/div>\n<\/div>\n
\"Korea<\/p>\n
Factory QC Testing<\/div>\n<\/div>\n
\"Korea<\/p>\n
Global Export Network<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

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8. Frequently Asked Questions<\/h2>\n
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Is it always better to select a motor one size larger for safety margin?<\/div>\n<\/div>\n
\n

No. Oversizing a motor reduces part-load efficiency and power factor simultaneously. A motor running at 50 percent of rated load typically operates at 2 to 5 percentage points below its peak efficiency and at a significantly reduced power factor. This increases energy consumption and reactive power charges. The correct approach is to size the motor for the actual maximum operating load with an appropriate service factor \u2014 not to add arbitrary size margins beyond the service factor already built into the calculation.<\/p>\n<\/div>\n<\/div>\n

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When should I use a VFD instead of selecting a different pole count for speed control?<\/div>\n<\/div>\n
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Use a VFD when: the load speed must vary continuously within a range (not just between two fixed speeds), the load is centrifugal (fan or pump) where VFD speed reduction provides large energy savings through the cube law, or where soft starting is needed to reduce supply disturbance or mechanical stress at startup. Pole changing (YD series multi-speed motors) is the right solution when only two fixed speeds are needed, VFD capital cost is not justified by the energy saving, or the installation environment makes electronic drive equipment impractical.<\/p>\n<\/div>\n<\/div>\n

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How does altitude affect motor selection?<\/div>\n<\/div>\n
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Above 1,000 metres altitude, air density decreases, reducing the cooling airflow heat-carrying capacity of the external fan. IEC 60034-1 requires motor derating above 1,000 m: approximately 1 percent reduction in rated power per 100 metres above 1,000 m (or a reduction in permitted ambient temperature of 1 K per 100 m). At 2,000 m altitude, a motor must be derated to 90 percent of its sea-level nameplate rating, meaning a 15 kW motor should be loaded to no more than 13.5 kW. For high-altitude installations, specify the installation altitude when ordering and Korea Ever-Power will confirm whether derating applies.<\/p>\n<\/div>\n<\/div>\n

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What is the difference between a motor\u2019s service factor and the application service factor used in sizing?<\/div>\n<\/div>\n
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A motor\u2019s nameplate service factor (SF) is a multiplier that indicates how much above nameplate power the motor can operate continuously without damage \u2014 typically 1.0 or 1.15 for standard IEC motors. The application service factor used in motor sizing calculations is a separate multiplier applied to the calculated load power to account for starting torque, load variations, and safety margin before selecting the next standard motor size. These are two independent concepts: a motor with SF 1.0 nameplate rating selected with an application service factor of 1.25 means you selected a motor 25 percent larger than the calculated continuous load requirement.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

<\/p>\n

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<\/div>\n

 <\/p>\n

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Korea Ever-Power \u00b7 Motor Selection Support<\/div>\n

Need Help Selecting the Right Motor?<\/h2>\n

Korea Ever-Power\u2019s engineering team reviews motor selection requirements for pumps, fans, conveyors, agitators, compressors, and specialist drives across the full Y2, YD, YVF2, Y2EJ, YB2, and BXG product range.<\/p>\n

Browse Motor Range<\/a><\/p>\n<\/div>\n<\/div>\n

Edited by Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 Motor Selection Guide How to Select the Right Electric Motor for Your Application Choosing the wrong motor is one of the most common and costly mistakes in industrial machine design. This motor selection guide walks through every criterion that matters \u2014 load type, duty cycle, efficiency class, protection rating, mounting, and speed […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-147","post","type-post","status-publish","format-standard","hentry","category-industrial-electric-motor"],"_links":{"self":[{"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/posts\/147","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/comments?post=147"}],"version-history":[{"count":2,"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/posts\/147\/revisions"}],"predecessor-version":[{"id":150,"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/posts\/147\/revisions\/150"}],"wp:attachment":[{"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/media?parent=147"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/categories?post=147"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/hi\/wp-json\/wp\/v2\/tags?post=147"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}