Motor Nameplate Decoded

Horsepower, Voltage, Phase, and Frequency

Horsepower (HP) is the rated mechanical output at the shaft, not the electrical input. A 10 HP motor produces 10 HP (7.46 kW) of mechanical power at full load. The electrical input will be higher than this due to motor losses (typically 8 to 15 percent). Some motors show power in kW instead of HP, particularly IEC-rated motors. 1 HP = 0.746 kW.

Voltage is the supply voltage for which the motor is designed. Common US industrial voltages are 208V, 230V, 460V, and 575V for three-phase, and 115V and 230V for single-phase. Dual-voltage motors show both ratings: "230/460V" means the motor can be connected in low-voltage (delta or parallel) or high-voltage (wye or series) configuration. The slash notation is important - "230/460V" means both voltages are acceptable, while "460V" means only 460V is acceptable.

Phase (PH) indicates single-phase (1PH) or three-phase (3PH). Three-phase motors produce smoother torque, are more efficient, and cost less per horsepower than single-phase motors. Single-phase motors above 5 HP are uncommon in industrial applications.

Frequency (Hz) is the supply frequency - 60 Hz in North America and most of the western hemisphere, 50 Hz in Europe, Asia, and much of the rest of the world. Running a 60 Hz motor on 50 Hz without derating reduces the speed by 17 percent and requires a voltage reduction to maintain the volts-per-hertz ratio and prevent core saturation.

Full-Load Amps and Service Factor

Full-Load Amps (FLA), also labeled as Full-Load Current (FLC), is a selected-motor nameplate field at rated load and rated conditions. It is important for overload, controller, VFD, and diagnostic review, but it is not the only current basis used in motor-circuit work.

Adopted NEC text, local amendments, selected motor type, controller, overload device, terminal ratings, conductor conditions, manufacturer instructions, and AHJ requirements determine which current basis applies to each decision. Do not use a local lookup row or nameplate entry as final conductor, breaker, fuse, overload, or controller selection without that source review.

Service Factor (SF) is also source-sensitive. It must be read with ambient, voltage, duty, altitude, enclosure, cooling, manufacturer limits, and operating history. Treat it as a review field, not free continuous capacity or proof that an undersized motor is acceptable.

Speed, Frame Size, and Enclosure Type

The nameplate RPM is the full-load speed at rated conditions. It can suggest pole count and slip context, but actual running speed also depends on load, voltage, frequency, drive settings, motor condition, and measurement method.

Frame size is a physical-dimension cue, not drop-in replacement approval. Verify the manufacturer drawing, shaft diameter, keyway, shaft extension, foot bolt pattern, flange or face, enclosure, bearings, coupling, base, driven equipment, and fit tolerances before ordering or installing a replacement.

Enclosure type describes how the motor is protected from the environment, but final suitability depends on product data and site conditions. ODP, TEFC, TENV, TEBC, and explosion-proof markings all need review against contamination, moisture, washdown, cooling, hazardous-location classification, ambient, duty, and AHJ requirements.

Insulation Class and Efficiency Rating

Insulation class is a thermal-context field that must be interpreted with temperature rise, ambient, altitude, enclosure, duty, cooling, service factor, VFD waveform, manufacturer limits, and motor condition. Local class-temperature rows are only prompts to check the selected source data.

Do not infer remaining insulation life from the class letter alone. A meaningful thermal review needs measured temperatures, load profile, cooling condition, winding history, test records, and qualified motor or reliability review.

Efficiency is expressed as a percentage at full load. NEMA, DOE, and manufacturer records provide important source context, but exact covered-product status, table values, label data, and certification depend on the selected motor and current authorized source material. Treat local sample rows as planning context only.

The nameplate may show nominal and minimum efficiency values. Use the selected motor label, manufacturer data, DOE/eCFR context, and project requirements before calculating energy costs, comparing motors, or making repair/replacement decisions.

NEC, Conductor, And Protection Source Boundaries

Motor-circuit work requires adopted NEC source text, local amendments, selected motor data, equipment instructions, terminal ratings, conductor conditions, voltage drop, available fault current, SCCR/AIC, time-current curves, standard device sizes, controller data, disconnect requirements, labels, and AHJ interpretation.

A decoder can help keep current bases visible, but it cannot choose the conductor, raceway, overload relay, fuse, breaker, starter, VFD, disconnect, grounding conductor, or label. It also cannot approve a permit drawing, inspection result, repair, replacement, or energization.

Use local rows as review prompts only. Final decisions need qualified electrical review and the controlling source material.

Special Markings and Code Letters

The NEMA code letter is a locked-rotor kVA per horsepower cue, while the design letter is torque-speed context. Both fields are useful screening inputs, but neither one chooses the starter, protection setting, voltage-dip result, VFD, soft starter, utility approval, or safe operating condition by itself.

Other nameplate markings can include duty cycle, ambient, altitude, bearings, lubrication, thermal protection, catalog number, serial number, and inverter-duty context. Use those markings to locate the selected motor record and manufacturer instructions.

VFD and inverter-duty decisions need product manuals, cable length, grounding, bearing-current mitigation, PWM voltage stress, cooling at low speed, harmonics, protection coordination, and qualified review.