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Terminology
FLA Vs FLC:

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LRC:

Locked Rotor Current

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Motor Inrush
Current

6-10x FLA

When an AC induction motor is started, the supplied voltage creates a magnetic field in the stator, which induces a magnetic field in the rotor. The interaction of these two magnetic fields produces torque and causes the motor to turn.

Motor Nameplate Data
Transformer nameplate
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Full Load Amp Rating:

The FLA rating is the rate at which a motor will consume power at 100% of rated load and at rated and balanced voltage. This number is extremely important, especially when dealing with electrical components. The wiring, starter, circuit breaker, and thermal overloads are all sized based upon the full load amp rating. When it comes to sizing a VFD the FLA rating is a very important piece of information. Learn more about sizing VFDs at our VFD Buying Guide.

Work

distance in feet x force in pounds, both applied in the same direction.

Power

time rate of doing work (work/time). Some units of measuring power are watts, kilowatts, HP, etc.

Horse Power

is defined as doing work at the rate of 33,000 ft x lbs/minute. A horse can do work at this rate continuously without being overloaded. A human cannot sustain doing work at the rate of 1 HP for very long. There is an interesting video of an Olympic cyclist on a stationary bike generating enough power to operate a toaster at ~700+ watts (746 watts = 1 HP).

Standard KVA Ratings:
  1. Work

    2. distance in feet x force in pounds, both applied in the same direction.

  2. Power

    3. time rate of doing work (work/time). Some units of measuring power are watts, kilowatts, HP, etc.

Service Factor

Motors are often designed to handle a temporary increase in demand. Service factor represents the motor’s ability to handle these temporary demand increases. Think of service factor as an insurance policy. It is designed for ambient temperatures, altitude, high and low line voltages, and imbalanced voltages. It should not be used as a method of increasing motor horsepower. The service factor is expressed as a decimal. If you do not see a service factor rating on the motor nameplate the service factor is typically 1.00. Additionally, all motors running on a VFD (even at 60 HZ) will lose service factor and be rated at 1.00. Please consult your manual for more information. You can dramatically reduce the life of your motor by consistently running into the service factor rating.

Efficiency
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A motor’s efficiency rating measures how well the motor converts electrical energy (input) into mechanical energy (output). This is usually displayed as a decimal. A motor’s energy consumption is by far its largest operating expense. As a general rule, a motor that runs 24/7/365 for one year could cost three times more than the purchase price in power consumption. In many applications a VFD can provide considerable savings with regards to operational costs. Centrifugal pumps often have great potential for energy savings. Under some circumstances using a VFD to reduce speed by 20% can result in energy savings of 50%. However, energy savings will vary based upon several factors, such as motor conditions, application, and energy costs in your area.

Frame Size:

Frame size data on the nameplate is an important piece of information. It determines mounting dimensions such as the and the. The frame size is often a part of the type designation which can be difficult to interpret because special shaft or mounting configurations are used NEMA frame size outlines motor footprint and shaft dimensions. The first two numbers represent the shaft height from the mounting base. This number divided by four represents the shaft height in inches. The third number is the bolt mounting hole dimensions, some motors may have multiple holes for different mounting options.

The enclosure of the must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit. NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings.

https://electrical-engineering-portal.com/7-most-common-motor-enclosure-types-defined-by-nema-standards
  1. Opwn Drip Proof

    2. Allows air to circulate through the , but prevent drops of liquid from falling into motor within a 15 degree angle from vertical. Typically used for .

  2. Totally enclosed Fan Cooled (TEFC)

    3. The enclosure of the must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit. NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings. Allows air to circulate through the , but prevent drops of liquid from falling into motor within a 15 degree angle from vertical. Typically used for . Prevents the free exchange of air between the inside and outside of the frame, but does not make the frame completely air tight. A fan is attached to the shaft and pushes air over the frame during its operation to help in the cooling process.

    The Ribbed frame is the designed to increase areafor cooling purposes.

    TEFC style enclosure is the most versatiled of all. It is the pumps, fans, compressors, general industrial belt drive and directed connected equipment.

  3. Totally enclosed Non- Ventilated (TENV)

    4. The enclosure of the must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit. NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings. Allows air to circulate through the , but prevent drops of liquid from falling into motor within a 15 degree angle from vertical. Typically used for . Prevents the free exchange of air between the inside and outside of the frame, but does not make the frame completely air tight. A fan is attached to the shaft and pushes air over the frame during its operation to help in the cooling process. It is used on pumps, fans, compressors, and direct connected equipment. Similar to a TEFC, and relies on convention for cooling. No vent openings, tightly enclosed to prevent the free exchange of air, but not airtight

    These are suitable for uses which are exposed to dirt or dampness, nbut not very moist hazurdous (explosive) locations

The letter is the type of frame, each type is provided below: Fractional type motors (frame size 48 and 56) C Face mounting (can be round body or footed) G Gasoline pump motor H Indicates a frame with a larger “F” dimension J Jet pump motor Y Special mounting dimensions Z All mounting dimensions are standard except shaft extension and or design Integral type motors (frame size 143 to 449)

A DC motor or generator C Face mounting (can be round body or footed) D Flange mounting (can be round body or footed) P Vertical hollow and solid shaft with P-base flange HP Vertical solid shaft with P-base flange, normal thrust JM Closed coupled pump motor with C-face mounting and special shaft extensions JP Closed coupled pump motor with C-face mounting and special long shaft extensions LP Vertical sold shaft with P- base flange, medium thrust S Standard short shaft T Standardized shaft (1964 and newer) U Standardized shaft (1964 and older) V Vertical mounting Y Special mounting dimensions Z All mounting dimension are standard except shaft extension

Nema Motor Insulation Classes:

NEMA motor insulation classes describes the ability of motor insulation in the windings to handle heat. There are four insulation classes in use namely: A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most common in many applications.

Temperature rises in the motor windings as soon as the AC motor is started. As shown in the table below, the combination of ambient temperature and allowed temperature rise equals the maximum rated winding temperature. Allowable temperature rise is made up of the maximum temperature rise for each insulation class plus a hot-spot over-temperature allowance. If the motor is operated at a higher winding temperature, service life will be reduced. As a rule, a 10° C increase in the operating temperature above the allowed maximum can cut the motor’s insulation life expectancy in half. The table below shows the different insulation classes as defined by NEMA:

Nema Motor Insulation Classe Table
Classes Maximum Ambient
Temperature (°C) 		Maximum Temperature
Rise (°C) 		Hot-spot
Over Temperature (°C) 		Maximum Winding
Temperature (Tmax)(°C)
A 40 60 5 105
B 40 80 10 130
F 40 105 10 155
H 40 125 15 180
Bearings:

Bearings are the component in an AC motor . The information is usually given for both the and the bearing opposite the drive-end, .

Bearings:

Bearings are the component in an AC motor . The information is usually given for both the and the bearing opposite the drive-end, .

NETA Test Procedure

NETA ATS

7.16.1.1 Motor Control, Motor Starters, Low-Voltage

A. Visual and Mechanical Inspection:
  1. Compare equipment nameplate data with drawings and specifications.
  2. Inspect physical and mechanical condition.
  3. Inspect anchorage, alignment, and grounding.
  4. Verify the unit is clean.
  5. Inspect contactors.
    1. Verify mechanical operation.
    2. Verify contact gap, wipe, alignment, and pressure are in accordance with manufacturer’s published data.
  6. *Motor-Running Protection
    1. Verify overload element rating/motor protection settings are correct for application.
    2. If motor-running protection is provided by fuses, verify correct fuse rating.
  7. Inspect bolted electrical connections for high resistance using one or more of the following methods:
    1. Use of low-resistance ohmmeter in accordance with Section 7.16.1.1.B.1.
    2. Verify tightness of accessible bolted electrical connections by calibrated torquewrench method in accordance with manufacturer’s published data or Table 100.12.
    3. Perform thermographic survey in accordance with Section 9.
  8. Verify appropriate lubrication on moving current-carrying parts and on moving and sliding surfaces.
B. Electrical Tests:
  1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter, if applicable, in accordance with Section 7.16.1.1.A.7.1.
  2. Perform insulation-resistance tests on each pole, phase-to-phase and phase-to-ground with starter closed, and across each open pole for one minute. Test voltage shall be in accordance with manufacturer’s published data or Table 100.1.
  3. *Perform insulation-resistance tests on all control wiring with respect to ground. Applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. Test duration shall be one minute. For units with solid-state components, follow manufacturer’s recommendation.
  4. Test motor protection devices in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Section 7.9.
  5. Test circuit breakers in accordance with Section 7.6.
  6. Perform operational tests by initiating control devices.
C. Test Values – Visual and Mechanical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.16.1.1.A.7.1)
  2. Bolt-torque levels shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.16.1.1.A.7.2)
  3. Results of the thermographic survey shall be in accordance with Section 9. (7.16.1.1.A.7.3)
D. Test Values – Electrical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
  2. Insulation-resistance values shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.1. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated.
  3. Insulation-resistance values of control wiring shall not be less than two megohms.
  4. Motor protection parameters shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Section 7.9.
  5. Circuit breaker test results shall be in accordance with Section 7.6.1.1.
  6. Control devices shall perform in accordance with system design requirements.

NETA MTS

7.16.1.1 Motor Control, Motor Starters, Low-Voltage

A. Visual and Mechanical Inspection:
  1. Inspect physical and mechanical condition.
  2. Inspect anchorage, alignment, and grounding.
  3. Prior to cleaning the unit, perform as-found tests, if required.
  4. Verify the unit is clean.
  5. Inspect contactors.
    1. Verify mechanical operation.
    2. Inspect and adjust contact gap, wipe, alignment, and pressure in accordance with manufacturer’s published data.
  6. *Motor-Running Protection
    1. Verify overload element rating/motor protection settings are correct for application.
    2. If motor-running protection is provided by fuses, verify correct fuse rating.
  7. Inspect bolted electrical connections for high resistance using one or more of the following methods:
    1. Use of low-resistance ohmmeter in accordance with Section 7.16.1.1.B.1.
    2. Verify tightness of accessible bolted electrical connections by calibrated torquewrench method in accordance with manufacturer’s published data or Table 100.12.
    3. Perform thermographic survey in accordance with Section 9.
    1. Verify appropriate lubrication on moving current-carrying parts and on moving and sliding surfaces.
  8. Use of a low-resistance ohmmeter in accordance with Section 7.16.1.1.B.1.
    1. Verify tightness of accessible bolted electrical connections by calibrated torquewrench method in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12.
    2. Perform a thermographic survey in accordance with Section 9.
  9. Use appropriate lubrication on moving current-carrying parts and on moving and sliding surfaces.
  10. Perform as-left tests.
B. Electrical Tests:
  1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter in accordance with Section 7.16.1.1.A.7.1.
  2. Perform insulation-resistance tests for one minute on each pole, phase-to-phase and phaseto- ground with starter closed, and across each open pole. Test voltage shall be in accordance with manufacturer’s published data or Table 100.1.
  3. *Perform insulation-resistance tests on all control wiring with respect to ground. The applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. Test duration shall be one minute. For units with solid-state components, follow manufacturer’s recommendation.
  4. Test motor protection devices in accordance with manufacturer’s published data. In the absence of manufacturer’s data, use Section 7.9.
  5. Test circuit breakers in accordance with Section 7.6.1.1.
  6. Perform operational tests by initiating control devices.
C. Test Values – Visual and Mechanical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.16.1.1.A.7.1)
  2. Bolt-torque levels should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.16.1.1.A.7.2)
  3. Results of the thermographic survey shall be in accordance with Section 9. (7.16.1.1.A.7.3)
D. Test Values – Electrical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
  2. Insulation-resistance values should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.1. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated.
  3. Insulation-resistance values of control wiring should be comparable to previously obtained results but not less than two megohms.
  4. Motor protection parameters shall be in accordance with manufacturer’s published data or Section 7.9.
  5. Circuit breaker test results shall be in accordance with Section 7.6.1.1.
  6. Control devices should perform in accordance with system design and/or requirements.

NETA ATS

7.16.2.1 Motor Control, Motor Control Centers, Low-Voltage

  1. Refer to Section 7.1 for appropriate inspections and tests of the motor control center bus.
  2. Refer to Section 7.5.1.1 for appropriate inspections and tests of the motor control center switches.
  3. Refer to Section 7.6.1.1 and 7.6.1.2 for appropriate inspections and tests of the motor control center circuit breakers.
  4. Refer to Section 7.16.1.1 for appropriate inspections and tests of the motor control center starters.

NETA MTS

7.16.2.1 Motor Control, Motor Control Centers, Low-Voltage

  1. Refer to Section 7.1 for appropriate inspections and tests of the motor control center bus.
  2. Refer to Section 7.5.1.1 for appropriate inspections and tests of the motor control center switches.
  3. Refer to Section 7.6 for appropriate inspections and tests of the motor control center circuit breakers.
  4. Refer to Section 7.16.1.1 for appropriate inspections and tests of the motor control center starters.
Motor Protection

The NEC or CEC requires that motor branch circuits be protected against overloads and short circuits. Overload protection may be provided by fuses, overload relays or motor thermal protectors. Short circuit pro

The NEC or CEC allows fuses to be used as the sole means of overload protection for motor branch circuits. This approach is often practical with small single phase motors. If the fuse is the sole means of protection, the fuse ampere rating must not exceed the values shown in Table 1. Most integral horsepower 3 phase motors are controlled by a motor starter which includes an overload relay. Since the overload relay provides overload protection for the motor branch circuit, the fuses may be sized for short circuit protection.

The motor branch circuit fuses may be sized as large as shown in Table 2 when an overload relay or motor thermal protector is included in the branch circuit. Time delay fuse ratings may be increased to 225% and non-time delay fuse ratings to 400% (300% if over 600 amperes) if the ratings shown in Table 2 will not carry motor starting current. Some manufacturers’ motor starters may not be adequately protected by the maximum fuse sizing shown in Table 2. If this is the case, the starter manufacturer is required by UL 508 to label the starter with a maximum permissible fuse size. If so labeled, this maximum value is not to be exceeded. Where the percentages shown in Table 2 do not correspond to standard fuse ratings the next larger fuse rating may be used. Standard fuse ratings in amperes: 15 20 25 30 35 40 45 50 60 70 80 90 100 110 125 150 175 200 225 250 300 350 400 450 500 600 700 800 1000 1200 1600 2000 2500 3000 4000 5000 6000

Fuse Protection & Sizing

  1. The overload protection shall be sized according to the motor nameplate current rating [430.6(A), 430.32(A)(1), and 430.55].
  2. You also have to consider another factor: nameplate temperature rise. For motors with a nameplate temperature rise rating not over 40°C, size the overload protection device no more than 125% of the motor nameplate current rating. Thus, 28A×1.25=35A [240.6(A)]

The overload protection is sized per the motor nameplate current rating, not the motor full load current (FLC) rating. Thus, 60A×1.25=75A. Overload protection shall not exceed 75A, so you need to use a 70A dual-element fuse [240.6(A) and 430.32(A)(1)]. Motors that don't have a service factor rating of 1.15 or higher or a temperature rise rating of 40°C and less must have an overload protection device sized at not more than 115% of the motor nameplate ampere rating (430.37).

Table 1- Maximum Fuse Rating For Overload Protection
Motor Service Factor or Marked Temperature Rise Fuse Rating as %*
Service factor of 1.15 or greater 125
Marked temperature rise not Exceeding 40°C 125
All Others 115
Rated Voltage of windings Windings Bushings
Insulation Class Bil Insulation Class Bil
480V 1.2KV 10KV 1.2KV 10KV
4160V 5KV 30KV 5KV 30KV
13.8KV 15KV 95KV 15KV 95KV
34.5KV 34,500V 150KV 34,500V 150KV

Estimate of Normalized Incident Energy

\(\large D_{B}=\) \(\text{Distance of the Boundary from the Arcing Point (mm)} \)

\( D_{B} = 610 \cdot \begin{bmatrix} 4.184 \cdot \color{blue} {C_{f}} \cdot \color{green} {E_{n}}\cdot \left(\begin{array}{c}\frac{t}{0.2} \end{array}\right) \left(\begin{array}{c}\frac{1}{E_{b}} \end{array}\right) \end{bmatrix}^{\frac{1}{x}} \)

  1. Where:
  2. \(\color{blue} {C_{f}}= \) \(\text{Calculation Factor = 1.0 ; Voltage > 1kV } \)
  3. \(\color{blue} {C_{f}}= \) \(\text{Calculation Factor = 1.5 ; Voltage < 1kV } \)
  4. \(E_{n}=\) \( \text{incident energy normalized } ( J/cm^{2}) \)
  5. \( t : \) \(\text{Arcing Time (seconds)}\)
  6. \( x : \) \(\text{ Distance Exponent }\)
  7. \(E_{B}=\) \( \text{incident energy at the boundary distance } ( J/cm^{2}) \);
  8. \(E_{B}\) \(\text{ can be set at 5.0 } J/cm^{2} (1.2 Cal/cm^{2}) \) \( \text{for bare skin } \)

Can Transformers be Operated at Voltages other than Nameplate Voltages

NEMA motor insulation classes describes the ability of motor insulation in the windings to handle heat. There are four insulation classes in use namely: A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most common in many applications.

430.22 Single Motor

The distance at which a person without personal Conductors that supply a sing le motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating, as determined by 430.6(A)(1), or not less than specified in 430.22(A) through (G).

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Ampere Rating

The selection of fuse ampere rating is a matter of experience and personal preference. Some prefer to size time delay fuses at 125% of motor full load amperes. This sizing will provide a degree of overload protection for motors with a service factor of 1.15. Sizing fuses at 125% of motor nameplate amperes in some applications may result in nuisance fuse openings. Time delay fuses sized at 125% may open at motor locked rotor current before some NEMA Class 20 overload relays operate. Nuisance fuse openings may result if Class RK1 or Class J fuses are sized at 125% of motor full load current. These fuses are more current limiting than the RK5 and have less short time current carrying capability

Ampere Rating

The selection of fuse ampere rating is a matter of experience and personal preference. Some prefer to size time delay fuses at 125% of motor full load amperes. This sizing will provide a degree of overload protection for motors with a service factor of 1.15. Sizing fuses at 125% of motor nameplate amperes in some applications may result in nuisance fuse openings. Time delay fuses sized at 125% may open at motor locked rotor current before some NEMA Class 20 overload relays operate. Nuisance fuse openings may result if Class RK1 or Class J fuses are sized at 125% of motor full load current. These fuses are more current limiting than the RK5 and have less short time current carrying capability

Time VS. Non-Time Delay Fuses

Time delay fuses are the most useful fuses for motor branch circuit application. A time delay fuse can be sized closer to motor full load current, providing a degree of overload protection, better short circuit protection, and possible use of a smaller disconnect switch.

Motor Inrush Current

When an AC induction motor is started, the supplied voltage creates a magnetic field in the stator, which induces a magnetic field in the rotor. The interaction of these two magnetic fields produces torque and causes the motor to turn.

Motor Contribution, short circuit condition

Motor's contribution is the current generated by a motor or motors during a short circuit condition. It represents a small but important value that is needed to determine the maximum short circuit current available and thereby establishing the short circuit rating of electrical equipment. Regardless of the size or voltage rating of a motor, it can be demonstrated that motor contribution is present during a fault.

During normal operation a motor converts electrical energy into mechanical energy. Current flowing in the stator produces a rotating magnetic field with the poles facing toward the rotor. This rotating magnetic field induces a current into the rotor. A magnetic field with the poles facing out is produced in the rotor due to the stator induced current. This causes the rotor (motor shaft) to rotate. As long as the stator is supplied to a stable voltage supply, the motor shaft will continue to rotate.

Motor Terminology
PROTECTION COORDINATION:

An electric arc or an arcing fault is the flow of electric current through the air from one conductor to another or to ground. Arcs are generally initiated by a flashover caused by some type of conductor that subsequently vaporizes or falls away, leaving an arc. Arcing faults create many hazards, but the greatest risk is burn injuries due to exposure to the heat generated by the arc. This heat can cause serious, even fatal burns, as well as ignite clothing and other nearby material and objects. In addition, electric arcs can produce molten metal droplets, UV radiation, and explosive air pressure waves.

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