Level 1, Unit 4, Section 2 – 2.1 Motor Nameplate

2.1.1 — The Motor Nameplate

The motor nameplate is a permanent metal plate affixed to the motor housing that contains critical information about the motor’s electrical characteristics, mechanical specifications, and operating parameters. Learning to accurately interpret nameplate data is essential for proper motor selection, installation, troubleshooting, and replacement. Every piece of information on the nameplate serves a specific purpose and must be considered when working with motors.

MOTOR-CO

MODEL: MC-56-1HP | SER: 2024-08-0142

HP 1

Voltage 115/230V

Phase 1PH

FLA 13.8/6.9A

Speed 1725RPM

Hz 60

Frame 56

Ins. Class B

S.F. 1.15

Enclosure TEFC

Amb. Temp 40°C

Duty CONT

Design / Code B / L

Efficiency 85.5%

Manufacturer Information

The nameplate includes the manufacturer’s name, model number, and serial number. This information is crucial for:

Obtaining exact replacement parts
Accessing technical documentation and wiring diagrams
Contacting technical support
Verifying warranty coverage

The model number often encodes information about motor specifications, while the serial number identifies the specific production date and manufacturing batch — important for tracking quality issues or recalls.

2.1.2 — Electrical Ratings

The electrical section of a nameplate defines the power supply requirements. Using a motor on the wrong voltage, frequency, or phase supply causes overheating, poor performance, or immediate failure.

Voltage

Single-Voltage Motor

Lists one operating voltage — e.g. 230 V
Must be connected at the rated voltage
Typically higher-voltage winding for efficient operation

Dual-Voltage Motor

Lists two voltages — e.g. 115/230 V
Windings reconnected in parallel (low) or series (high)
Nameplate wiring diagram shows lead connections for each voltage

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Voltage Tolerance: ±10%

A 230 V motor operates satisfactorily from 207 V to 253 V. Low voltage causes excessive current draw and overheating. High voltage damages insulation and creates unsafe conditions. Always measure supply voltage under full load before energizing a motor.

Current — FLA and LRA

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FLA — Full Load Amps

Current drawn at rated load, voltage, and frequency. For dual-voltage motors both values are listed (e.g. 13.8/6.9 A). Circuit conductors must be sized for 125% of FLA per electrical codes.

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LRA — Locked Rotor Amps

Starting inrush current with the rotor stationary — typically 6–8× FLA for compressors. Some nameplates list a code letter (A–V) representing locked rotor kVA per HP instead of the actual LRA value.

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Why LRA matters for circuit sizing

Short-circuit and ground-fault protection devices (fuses, breakers) must be large enough to ride through starting inrush without nuisance trips, but small enough to protect the wiring. The LRA or code letter is the key input for this calculation under the Canadian Electrical Code.

Frequency

Specifies the AC supply frequency for which the motor is designed. Canadian utility power is 60 Hz. Some motors are rated 50/60 Hz for international use. Running a 60 Hz motor on 50 Hz power reduces its speed to approximately 5/6 of rated RPM and changes torque characteristics, potentially causing overheating.

Phase

Single-Phase — 1 PH or 1Ø

Two current-carrying conductors plus equipment ground
Common in residential and light-commercial HVAC/R
Requires starting components (capacitors, relays)
Typical voltages: 115 V, 208 V, 230 V

Three-Phase — 3 PH or 3Ø

Three conductors, 120° apart in phase
Standard for commercial and industrial equipment
Self-starting; no run capacitors required
Typical voltages: 208 V, 460 V, 575 V

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Single-phase and three-phase motors are NOT interchangeable

Attempting to operate a three-phase motor on single-phase power, or vice versa, results in failure to start, improper operation, or immediate motor damage.

2.1.3 — Mechanical Performance Specifications

These ratings describe what the motor delivers at its shaft under rated operating conditions. They are the starting point for equipment selection and load matching.

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Horsepower / Kilowatts

Continuous shaft output at rated voltage, frequency, and ambient temperature. North American nameplates use HP; international standards use kW.

1 HP = 0.746 kW | 1 kW = 1.34 HP

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Speed (RPM)

The full-load speed — the actual shaft speed under rated load, accounting for slip. Slightly lower than synchronous speed. A 4-pole 60 Hz motor has a synchronous speed of 1 800 RPM and a typical nameplate speed of 1 725 RPM (4.2% slip).

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Service Factor (SF)

Allowable continuous overload expressed as a multiplier. A 1 HP motor with SF = 1.15 can deliver 1.15 HP continuously. Common values: 1.0, 1.15, 1.25. Running at SF load reduces motor life — use it as a buffer, not a routine operating point.

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Understanding Motor Slip

Synchronous speed is determined by the supply frequency and number of motor poles:

Synchronous Speed

N_s = (120 × f) ÷ P

N_s = synchronous speed (RPM) | f = frequency (Hz) | P = number of poles

A 4-pole, 60 Hz motor has N_s = (120 × 60) ÷ 4 = 1 800 RPM. Because an induction motor must have rotor speed slightly below the rotating magnetic field to generate torque (slip), the actual nameplate speed is 1 725 RPM. Under lighter loads, actual speed rises slightly but never reaches synchronous speed.

2.1.4 — Construction & Environmental Specifications

NEMA Frame Size

The NEMA frame designation standardises mounting dimensions — bolt pattern, shaft diameter, and shaft height — so that motors with the same frame number are mechanically interchangeable regardless of manufacturer.

Frame Category	Common Frames	Typical HP Range	Notes
Fractional HP	42, 48, 56	Under 1 HP	Most common in residential HVAC fan and pump motors
Integral HP “T” Frame	143T, 145T, 182T, 184T, 213T, 215T	1 HP and above	“T” suffix = standardised shaft dimensions; introduced 1964

Enclosure Type

The enclosure protects the motor windings from the environment and defines how the motor dissipates heat. Choosing the wrong enclosure for the environment leads to premature failure or safety hazards.

ODP Open Drip Proof Ventilation openings allow airflow for cooling; protected against dripping liquids from above. Used in clean, dry indoor locations.

TEFC Totally Enclosed Fan Cooled No ventilation openings; an external shaft-mounted fan forces air over the frame. Most common general-purpose choice for HVAC/R.

TENV Totally Enclosed Non-Ventilated No openings and no external fan; heat dissipates through the frame. Used for small motors in dirty or wet environments.

TEAO Totally Enclosed Air Over Totally enclosed but depends on the airstream from a connected fan blade for cooling. Common in direct-drive evaporator fan motors.

EXP Explosion Proof Designed to contain any internal ignition and prevent it from igniting surrounding hazardous atmospheres (e.g. refrigerant-rich areas).

Ambient Temperature

Standard motors are rated for a 40°C (104°F) maximum ambient temperature. Operating above rated ambient causes excessive winding temperatures and accelerated insulation degradation.

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The 10°C Rule — Insulation Life

Each 10°C (18°F) rise above rated ambient temperature reduces insulation life by approximately 50%. A motor rated for 40°C installed in a 50°C equipment room will have roughly half the expected service life. Always verify ambient conditions before specifying a motor.

Insulation Class

Insulation class defines the maximum winding temperature the insulation can withstand continuously. Higher classes support higher temperature rises, allowing smaller physical size for equivalent HP or longer life in demanding applications.

Class	Max. Winding Temperature	Typical Application
A	105°C (221°F)	Older motors; limited new use
B	130°C (266°F)	Standard general-purpose motors — most common in HVAC/R
F	155°C (311°F)	Premium efficiency motors; higher service factor applications
H	180°C (356°F)	Severe duty; high ambient temperature; washdown environments

Duty Cycle

The duty rating specifies the intended operating pattern for which the motor is thermally designed. Running an intermittent-duty motor continuously overheats the windings even if the current is within FLA limits.

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Continuous Designed for 24/7 operation at rated load without rest periods. Standard for compressor motors, condenser fans, and pump motors.

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Intermittent Operates for specific on-periods followed by off-periods for cooling. Common for actuators, damper motors, and economiser controls.

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Short-Time Rated for limited run periods (5, 15, 30, or 60 min) with sufficient rest to return to ambient. Used for valve operators and positioning motors.

2.1.5 — Specialized Nameplate Information

NEMA Design Letter

NEMA design letters (A, B, C, D) classify a motor’s torque-speed curve and starting current characteristics. Matching the design to the load type ensures reliable starting and efficient running.

A Normal Torque, Normal Slip Higher starting current than B. Less common in HVAC/R; used for loads requiring high starting torque with low slip.

B Normal Torque, Low Starting Current Most common general-purpose design. Moderate starting torque with lower locked-rotor current. Standard for fans, pumps, and compressors.

C High Starting Torque Higher starting torque for hard-to-start loads. Used for loaded conveyors, reciprocating compressors, and positive-displacement pumps.

D Very High Starting Torque, High Slip Maximum starting torque with high slip under load. Used for high-inertia loads and applications with shock loading; less efficient at full speed.

Code Letter — Locked Rotor kVA

The code letter (A through V, skipping I and O) represents the locked rotor kVA per horsepower. It is used to calculate starting current and to size the branch-circuit short-circuit and ground-fault protection per the Canadian Electrical Code. Higher letters indicate higher starting current.

Code Letter	Locked Rotor kVA/HP	Relative Starting Current
A – D	3.15 – 5.59	Low
E – G	4.5 – 6.29	Moderate
H – K	6.3 – 8.99	High — most single-phase motors
L – V	9.0 – 22.39	Very high — hard-start compressors

Wiring Diagrams on the Nameplate

Dual-voltage motors include wiring diagrams showing lead connections for high and low voltage operation. Additional diagrams may show connections for:

Reversing rotation on dual-rotation motors
Each speed setting on multi-speed motors
Thermoprotector and capacitor wiring

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Always follow the nameplate wiring diagram

Connecting a dual-voltage motor incorrectly — for example, wiring high-voltage leads in parallel on a 230 V supply — applies twice the rated voltage per winding, causing immediate insulation damage and creating a shock and fire hazard.

Bearing Information

Some nameplates list bearing type, part numbers, and lubrication requirements. This information is essential for planned maintenance:

Sleeve Bearings

Require SAE 20 or SAE 30 non-detergent oil
Service interval: annually or semi-annually
Oil wicks or reservoirs must not run dry
Mounting orientation must match manufacturer spec

Ball Bearings

Permanently sealed types require no field lubrication
Re-greasable types use NLGI Grade 2 grease
Service interval based on operating hours and speed
Over-greasing causes as much damage as under-greasing

Efficiency & Power Factor

Modern motors often list nominal efficiency as a percentage. Premium efficiency motors meeting NEMA Premium or IE3/IE4 standards provide significant energy savings over standard efficiency motors, particularly in continuous-duty applications such as condenser fan motors and pump motors running thousands of hours per year.

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Efficiency Matters for Replacement

When replacing a failed motor, selecting a higher-efficiency model reduces operating costs over the motor’s lifetime. A 1 HP motor running continuously at 85% vs. 92% efficiency draws an extra ~80 W at all times. Over 8 760 hours of annual operation, that equals roughly 700 kWh per year of wasted energy.

Higher-efficiency motors also run cooler, extending bearing and insulation life. The incremental cost of a premium-efficiency motor is typically recovered within one to three years through energy savings.