A motor nameplate identifies the motor’s rated mechanical output and the electrical and operating conditions associated with that rating. Read voltage, current, frequency, phase, speed, efficiency, and power factor as a matched set—not as independent numbers that can be combined across different rating rows. Nameplate ratings describe specified operating conditions; they are not measurements of the motor’s present load or energy consumption. ABB’s nameplate reference explains these fields and distinguishes primary ratings from alternate operating data.
Start by recording the complete plate, including connection symbols and supplementary markings. A cropped photograph of horsepower and amps can omit the frequency, connection, duty, or inverter restrictions needed to interpret those values.
An Annotated Motor Nameplate Reference
The following reference transcribes selected fields from the published nameplate for the Baldor-Reliance EM3711T. It is a reading aid, not a terminal connection diagram. The manufacturer’s customer information packet reproduces the nameplate on page 4.
| Nameplate field | Published marking | How to read it |
|---|---|---|
| CAT. NO. | EM3711T | Catalog identifier used to locate the correct product documentation. |
| HP | 10 | Rated mechanical shaft output—not electrical input power. |
| VOLTS | 230/460 | Two rated voltages; retain the corresponding current pairing. |
| AMPS | 24.1/12 | 24.1 A at 230 V; 12 A at 460 V, for the stated rating conditions. |
| HZ / PH | 60 / 3 | The main rating is for 60 Hz, three-phase operation. |
| RPM | 3490 | Rated full-load shaft speed, not synchronous speed. |
| NEMA NOM. EFF | 90.2 | Nominal efficiency of 90.2%; use 0.902 in formulas requiring a decimal. |
| PF | 85 | Power factor expressed as a percentage: 85%, or 0.85. |
| SF | 1.15 | Service factor associated with the main rating. |
| SFA | 27.6/13.8 | Published service-factor amps paired with 230/460 V. |
| CODE / DES | G / B | Locked-rotor kVA code and NEMA design letter—different classifications. |
| CLASS | F | Winding insulation class. |
| FRAME / ENCL | 215T / TEFC | Mechanical frame designation and totally enclosed fan-cooled enclosure. |
| RATING | 40C AMB-CONT | A 40°C ambient, continuous-duty rating. |
| Alternate rating | 50HZ 10HP 190/380V 28.2/14.1A SF1.0 | A separate 50 Hz rating with different voltage, current, and service factor. |
All values in this reference belong to the published EM3711T nameplate. They should not be transferred to another motor merely because it has the same horsepower or frame size.
The alternate rating shows why complete transcription matters: this motor’s 1.15 service factor at its main 60 Hz rating does not carry over to the separately marked 50 Hz rating, which states SF 1.0.
What the Main Electrical Fields Mean
Rated Power: HP or kW
For the AC induction motors discussed here, nameplate horsepower or output kW describes mechanical power available at the shaft under rated conditions. Electrical input is higher because the motor has losses. Efficiency relates the two:
[
\eta=\frac{P_{\text{out}}}{P_{\text{in}}}
]
Therefore:
[
P_{\text{in}}=\frac{P_{\text{out}}}{\eta}
]
Here, (P_{\text{out}}) and (P_{\text{in}}) must use the same power unit, and efficiency (\eta) is a decimal. ABB’s nameplate reference defines horsepower as mechanical output and efficiency as the ratio of output to input.
For mechanical horsepower, the rounded conversion is:
[
P_{\text{out,kW}}\approx0.746\times HP
]
A 10 hp rating therefore represents approximately 7.46 kW of shaft output, not a 7.46 kW electrical load.
Voltage, Phase, and Frequency
VOLTS identifies the rated motor voltage. For a three-phase motor, use the line-to-line voltage when applying the three-phase power relationships below. PH identifies the supply phase count; HZ identifies the frequency associated with the rating.
When the plate lists both 50 Hz and 60 Hz data, preserve each complete rating separately. Do not assume that output, voltage, current, speed, or service factor remains unchanged between frequencies. ABB specifically identifies alternate frequency ratings as additional application data.
Rated Current: A, AMPS, FLA, or F.L. AMPS
Nameplate full-load current is the current associated with rated load and rated electrical conditions. It is not:
- A measurement of the installed motor’s current.
- The starting or locked-rotor current.
- A universal current value for every motor of that horsepower.
- Automatically the current basis required by every conductor or protection calculation.
ABB defines nameplate full-load amps by rated load and rated voltage. Its published EM3711T data separately identifies full-load current, no-load current, starting current, and service-factor current.
Keep four data types distinct in a calculation record: manufacturer-rated current, any applicable code-table current, estimated operating current, and measured operating current. If a calculation requires a code-table value, obtain it from the applicable adopted code and edition rather than relabeling nameplate amps as a table value.
Efficiency: EFF, η, or NEMA NOM. EFF
Efficiency describes conversion of electrical input into mechanical output. A marking of 90.2 means 90.2%, not 0.902%.
Use the efficiency associated with the relevant rating and load point. A full-load efficiency value is not automatically valid at quarter load, service-factor load, or variable-speed operation. The EM3711T packet provides separate load-dependent efficiency values in a table explicitly labeled “Typical performance—not guaranteed values.” Those values are not interchangeable with the nameplate nominal efficiency.
An IE efficiency-class designation is also not a numerical efficiency input. Record the actual efficiency percentage for the relevant operating point when a calculation requires it. ABB discusses efficiency classes and declared efficiency values separately in its IEC motor guide.
Power Factor: PF or cos φ
Power factor relates electrical real power to apparent power. For a sinusoidally supplied motor, a cos φ marking describes the displacement between voltage and current. ABB’s motor guide explains this relationship in its power-factor discussion.
Check the printed format:
- PF 85 means 0.85 when the manufacturer expresses PF as a percentage.
- PF 0.85 already uses decimal form.
- Power factor and efficiency are different quantities; one cannot replace the other.
The EM3711T nameplate uses PF 85 alongside efficiency 90.2. Its performance table also shows power factor changing with load.
Do not apply a motor’s rated power factor to the supply input of a variable-frequency drive. That is a different measurement boundary. Where distorted waveforms matter, use true power factor and a suitable power measurement method rather than assuming cos φ alone represents total power factor.
Reading Multiple Voltages and Connection Symbols
Paired Voltage and Current Values
For a plate marked:
- VOLTS: 230/460
- AMPS: 24.1/12
the ordered pairs are 230 V with 24.1 A and 460 V with 12 A. Do not average the voltages or combine the higher voltage with the higher current. This pairing is explicitly confirmed in the EM3711T specifications.
A slash does not mean the motor can run at every voltage between the two numbers. Obtain the motor’s connection diagram and any additional voltage-rating information before treating an intermediate supply voltage as suitable.
Nor does a 230/460 V marking, by itself, specify a star-delta starting arrangement. The actual winding and lead configuration must come from the manufacturer’s diagram.
Delta and Star: Δ and Y
Δ means delta; Y means star, also called wye. These symbols identify winding connections, not phase counts.
For a hypothetical plate explicitly marked 230 V Δ / 400 V Y:
- The 230 V rating applies to delta connection.
- The 400 V rating applies to star connection.
- Each voltage must remain paired with its marked connection and current.
For balanced three-phase conditions, winding voltage is approximately:
[
V_{\text{winding}}=V_{LL}\quad\text{in delta}
]
[
V_{\text{winding}}=\frac{V_{LL}}{\sqrt{3}}\quad\text{in star}
]
Thus, 400 V in star places approximately 231 V across each winding. ABB’s motor guide presents corresponding delta/star voltage ranges and connection diagrams in Sections 3.6 and 4.12.
Star-delta starting requires a motor suitable for delta running at the supply voltage, with the necessary winding terminals accessible. A 230 V Δ / 400 V Y motor is not suitable for the final 400 V delta-running connection of a conventional star-delta starter. ABB explains the delta-running requirement in Section 4.5.2 of its motor guide.
These relationships explain the markings; they do not replace the specific motor’s terminal diagram.
Speed, Service Factor, and Starting Markings
RPM: Rated Speed Versus Synchronous Speed
On an induction-motor nameplate, RPM normally identifies rated full-load shaft speed. Synchronous speed depends on frequency and pole count:
[
n_s=\frac{120f}{p}
]
where:
- (n_s) is synchronous speed in rpm.
- (f) is frequency in Hz.
- (p) is the number of poles.
An induction motor’s rotor runs below synchronous speed while producing motoring torque; the difference is slip. ABB explains this distinction in its induction-motor and nameplate references.
The EM3711T specifications list two poles and a 3600 rpm synchronous speed at 60 Hz, while its nameplate lists 3490 rpm at full load. Neither number proves the installed motor’s current operating speed.
SF and SFA: Related, but Not Interchangeable
Service factor is an output-rating multiplier applicable under the manufacturer’s stated conditions:
[
P_{\text{SF}}=P_{\text{rated}}\times SF
]
For the example motor, (10\times1.15=11.5) hp. This arithmetic describes the service-factor output level; it does not establish a preferred continuous design load. ABB notes that operation above rated horsepower can increase temperature, reduce life expectancy, and change efficiency, power factor, and speed.
Do not calculate service-factor amps by assuming current increases exactly in proportion to service factor. The example nameplate states 12 A full-load current and 13.8 A SFA at 460 V; use the published SFA where it is relevant rather than substituting a generic rule.
SF is not a blanket multiplier for generator capacity, cable ampacity, breaker size, or overload settings.
CODE, DES, and LRA
These fields describe different characteristics:
| Marking | Meaning | What it does not establish alone |
|---|---|---|
| CODE | NEMA locked-rotor apparent-power range in kVA per horsepower. | Exact starting current, acceleration time, or acceptable supply voltage dip. |
| DES | NEMA design classification associated with torque, slip, and starting characteristics. | Locked-rotor code or insulation class. |
| LRA | Locked-rotor current for the stated conditions. | The complete current-versus-time profile during acceleration. |
| (I_s/I_N) or a similar manufacturer-defined ratio | Starting current relative to rated current. | Suitability of a particular starter or generator. |
ABB distinguishes design letters from locked-rotor code letters in its nameplate reference. Its EM3711T performance data separately publishes starting current and torque characteristics.
For starting studies, obtain the motor’s performance data, load inertia and torque requirements, starting method, and supply characteristics. Running kVA alone does not describe the starting event.
Operating and Mechanical Fields That Affect Interpretation
| Field | Meaning and required follow-through |
|---|---|
| Duty: CONT, S1, or another duty designation | Identifies the operating duty associated with the rating. Timed or intermittent duties cannot be treated as continuous output without checking the specified cycle. |
| Ambient and altitude | Identify environmental conditions affecting thermal capability. Use the marked limits and model-specific manufacturer guidance. |
| Insulation CLASS | Identifies winding insulation thermal classification. It is not the allowable external surface temperature or an overload setting. |
| Temperature rise | Where stated, identifies a rise above ambient under specified conditions. Do not confuse it with insulation class. |
| FRAME and mounting | Identify mechanical interfaces. Confirm shaft, mounting, flange, and dimensional drawings before replacement. |
| ENCL, IP, and cooling code | Describe enclosure, ingress protection, or cooling arrangements. They address different characteristics and are not automatically interchangeable. |
| DE / NDE / ODE | Identify drive-end and non-drive-end/opposite-drive-end bearing information. Preserve the complete bearing identifiers. |
| Inverter markings; CT / VT | Identify manufacturer-stated variable-speed capability, including constant-torque or variable-torque ranges. Check cooling and drive-related restrictions. |
| Hazardous-location markings | Identify specific protection and certification information. TEFC or an IP rating alone does not establish suitability for a classified location. |
ABB’s NEMA nameplate reference explains these common markings. Its IEC motor guide provides separate discussions of cooling, IP protection, mounting arrangements, duty types, ambient conditions, and variable-speed loadability. These are manufacturer explanations, not a substitute for the project’s applicable installation requirements.
Using Nameplate Data in Calculations
Match the data to the quantity a calculation actually requests. A field labeled “motor power” is ambiguous until it specifies mechanical output or electrical input.
| Calculation input | Appropriate nameplate starting point | Additional information needed |
|---|---|---|
| Shaft output in kW | Rated hp or output kW | Confirm whether the calculation concerns rated output or actual operating load. |
| Electrical input kW | Output rating and efficiency at the same load point | Operating load and relevant efficiency data, or measured input power. |
| Running current estimate | Output, efficiency, PF, voltage, and phase | Matching rating conditions and the model’s supply assumptions. |
| Running kVA | Rated line voltage and current | Actual loading if estimating operating rather than rated demand. |
| Torque | Output power and corresponding shaft speed | Actual speed and load point where different from the rating. |
| Starting-load comparison | LRA, locked-rotor code, or manufacturer starting data | Starting method, acceleration duty, load characteristics, and source response. |
| Conductor or protection calculation | The current basis explicitly required by that method | Applicable adopted code, installation details, and equipment instructions. |
These are data-matching rules, not a claim that a particular online calculator implements every field or method.
Three-Phase Power Relationships
For balanced three-phase operation with a sinusoidal supply:
[
S_{\text{kVA}}=\frac{\sqrt{3}V_{LL}I_L}{1000}
]
[
P_{\text{in,kW}}=\frac{\sqrt{3}V_{LL}I_LPF}{1000}
]
Combining electrical input with shaft output and efficiency gives:
[
I_L\approx
\frac{1000P_{\text{out,kW}}}
{\sqrt{3}V_{LL}\eta PF}
]
Here, (V_{LL}) is line-to-line voltage in volts, (I_L) is line current in amperes, and (\eta) and (PF) are decimals. ABB’s motor guide discusses the three-phase power and power-factor relationships underlying these expressions.
The current estimate assumes efficiency and PF apply at the selected output load. It is not a starting-current model. Do not divide the result by three: the three-phase relationship already accounts for the complete balanced system.
For single-phase operation, the input-power relationship is (P_{\text{in,kW}}=VIPF/1000), without (\sqrt{3}). For materially unbalanced or distorted supplies, use an appropriate multiphase power measurement or analysis rather than treating one current reading as a balanced-system value.
Worked Check Using the Published Nameplate
Use the EM3711T’s main 460 V, 60 Hz rating:
- Output: 10 hp.
- Efficiency: 90.2%, entered as 0.902.
- PF: 85%, entered as 0.85.
- Supply: three-phase.
- Published full-load current: 12 A.
The output conversion is:
[
P_{\text{out}}\approx10\times0.746=7.46\text{ kW}
]
Estimated electrical input using nominal efficiency is:
[
P_{\text{in}}\approx\frac{7.46}{0.902}=8.27\text{ kW}
]
Estimated apparent power and current are:
[
S\approx\frac{8.27}{0.85}=9.73\text{ kVA}
]
[
I_L\approx\frac{9730}{\sqrt{3}\times460}=12.2\text{ A}
]
Using the published 12 A directly instead gives:
[
S_{\text{nameplate}}\approx
\frac{\sqrt{3}\times460\times12}{1000}
=9.56\text{ kVA}
]
The 12.2 A estimate is close to, but not identical to, the published 12 A. Nominal efficiency, rounded PF, and rated current should not be forced into exact numerical agreement. The same manufacturer packet also contains a separate typical-performance table with different full-load values, explicitly identified as not guaranteed. Keep the nameplate dataset and typical-performance dataset distinct.
These results support a rated-running-load comparison. They do not determine actual operating demand, starting capacity, or final generator or UPS size.
Recording an Installed Motor Without Losing Context
- Record the manufacturer, catalog/model number, specification number, and serial number. Keep a full-plate photograph and a reference to the corresponding manufacturer document.
- Transcribe each voltage/frequency rating as a separate row, retaining its output, connection, current, speed, and any efficiency, PF, or SF explicitly associated with it.
- Copy additional markings exactly. Do not normalize an unfamiliar code into a more familiar one.
- Record the selected operating rating and connection-diagram reference separately from the raw transcription.
- Keep measurements in a separate section. Include the measurement point, operating load, supply frequency, time, and instrument information.
- Mark unreadable fields as unreadable. Do not fill them from another motor’s plate or infer them solely from horsepower.
When operating measurements are available, retain all three line currents and line-to-line voltages rather than only an average. A low current reading does not directly establish a proportional shaft load: the example motor’s published data shows current, efficiency, and PF changing differently with load.
For a drive-fed motor, identify whether each measurement was taken at the drive input or motor output and record the output frequency. Those locations represent different electrical conditions. ABB discusses converter supply and variable-speed motor limitations separately from fixed-frequency operation.
Printable Motor Nameplate Data Collection Sheet
The accompanying printable PDF separates transcribed nameplate ratings from measurements and project assumptions. Use one record per motor and retain additional rating rows when the plate contains more than two operating combinations.
| Identification | Recorded value |
|---|---|
| Asset tag / site / driven equipment | |
| Manufacturer / model / catalog number | |
| Serial / specification number | |
| Plate photo / manufacturer document reference | |
| Recorder / date |
| Nameplate data | Recorded value |
|---|---|
| Rated output, with hp or kW explicitly stated | |
| Phase / frequency | |
| Rating row 1: voltage / connection / current / rpm | |
| Rating row 2: voltage / connection / current / rpm | |
| Efficiency / load basis / PF as printed | |
| Service factor / SFA with corresponding voltage | |
| Duty / ambient / altitude limits | |
| Frame / mounting / enclosure / IP / cooling | |
| Insulation class / temperature rise, if marked | |
| Design letter / locked-rotor code / starting data | |
| Inverter rating / CT and VT ranges | |
| Hazardous-location markings / certificate reference | |
| DE and NDE/ODE bearings / other markings |
| Operating context—kept separate from nameplate ratings | Recorded value |
|---|---|
| Selected rating row / confirmed connection diagram | |
| Starter or drive model / operating frequency | |
| Measured voltage: L1–L2 / L2–L3 / L3–L1 | |
| Measured current: L1 / L2 / L3 | |
| Measured input kW / true PF / measurement point | |
| Operating load / date / instrument reference | |
| Assumptions / sources / unreadable fields |
For each downstream calculation, identify the selected rating row and label every additional input as measured, manufacturer-supplied, code-derived, or assumed. If a required value is missing, obtain the matching manufacturer documentation or retain a clearly identified conditional estimate; do not turn an unverified field into a rated value.