MikeHolt_Section04_Motors, Transformers, and HVAC

Motor Calculation Steps:

  1.  Branch Circuit Conductor Size_Part II_430.22
  2. Motor Overloads_Part III_430.32
  3. Motor Branch Circuit Short-Circuit & Ground-Fault Protection_Part IV_430.52
  4. Motor Feeder Conductors_Part II_430.24
  5. Motor Feeder Short-Circuit & Ground-Fault Protection_Part V_430.62

MikeHolt_Section04_Motors, Transformers, & HVAC

Unit 04: Motors & Transformers

NEC Article 430

Motors

  • Motor windings are connected
    • parallel for low voltage operation
    • series for high voltage operation
  • At a motors shaft, 1 HP of mechanical energy = 746W of electrical energy
    • HP is based on output watts only, input isn’t considered
    • 1 HP = 746 W
    • HP = Output W / 746
  • Full-Load Ampere Rating (FLA)
    • Equals Nameplate Amps
    • Starting FLA is minimum 6-8 times FLA rating
    • Locked Rotor Current (LRC) is 6 times FLA rating
    • FLA formulas:
      • Single Ø
        • FLA = 746W x HP / E x Eff x PF
      • Three Ø
        • FLA = 746W x HP / E x Eff x PF X 1.732
      • Motor Running Current
        • I = E / Z
        • Z = √R2 + XL
      • W = watts
      • HP = horsepower
      • E = voltage
      • Eff = efficiency factor
      • PF = power factor
      • Z =
  • Overload Device Trip Sizing
    • 125% FLA
      • SF 1.15 & up
      • Temp rise of 40°C and below
    • 115% FLA
      • All other motors
  • Motor Types_Direct Current
    • Reverse rotation by switching lead polarity on either the armature or field, and leaving the other (armature or field) unchanged
    • Shunt-Wound
      • Constant speed under load
      • Armature and field winding are in parallel
      • Design has a built-in system for regulating its own speed
      • Disk drives, recording equipment
    • Series-Wound
      • Good torque characteristics
      • Armature and field winding are in series
      • Poor speed regulation
        • slows down when load applied
        • unloaded run at high RPM, possibly to point of motor ‘running-away’
      • Starter motor
  • Motor Types_Alternating Current
    • Reverse rotation
      • 3 Ø
        • Swapping 2 of the 3 power leads
      • 1 Ø
        • Change the start winding polarity in relation to the run winding
        • Check the Nameplate for details
    • Squirrel-Cage Induction
      • Most common type
      • Stator produces rotating magnetic field
      • Rotor is a closed loop series of coils (windings)
      • Stator magnetic field has faster RPM then Rotor RPM
      • No physical connection between rotor and stator
      • rotor is bars connected at ends by shorting rings
      • all major industrial applications
    • Synchronous
      • Rotor locked in step and synchronous with stator rotating magnetic field
      • Maintain speed with high accuracy
      • Able to operate unloaded
        • acts like capacitor
        • used for power factor correction
      • clock motors, large industry driving loads, compressors, crushers, large pumps
    • Wound-Rotor
      • Used in special applications due to complexity
      • only operate on 3 Ø AC power
      • Resistors used to limit starting inrush current
      • Applications requiring speed control
      • Mostly replaced by VFDs and induction motors
    • Universal
      • Fractional HP motors
      • Operate well on AC or DC
      • has disadvantage to DC motors, communications
        • parts wear out
      • vacuum cleaners, drills, mixers, light household appliances
  • Motor Efficiency

    • η = 0.7457 x hp x Load / Pi
    • Load = Pi x η / hp x 0.7457
      • η = Efficiency as operated in %
      • Por = Nameplate rated horsepower
      • Load = Output power as a % of rated power
      • P= 3Ø power in kW
      • hp = Nameplate rated horsepower
  • Troubleshooting
    • Current increases
      • running above HP rating
      • supply voltage is below nameplate rating

Transformers

    • Transformer is a machine used to transfer electrical energy from one system to another by induction with no physical connection between the 2 systems (except for auto-transformers)
    • Used for isolation and to raise or lower voltage
    • Efficiency typically is 95-97%
    • Transformer Losses
      • conductor resistance
        • Directly proportional to conductor length
        • Inversely proportional to conductor cross-sectional area
        • P = I2 * R used often for problems
      • flux leakage
        • Electromagnetic flux line leakage not absorbed by secondary winding
      • eddy currents
        • Expanding/collapsing AC-induced electromagnetic field causes circulating eddy currents and heat in iron core
        • Separating iron cores with (lacquer) insulation reduces eddy current losses
      • hysteresis losses
        • energy required for iron core molecules to realign with changing polarity due to iron magnetism created by AC current expanding/collapsing electromagnetic field
        • Directly proportional to AC frequncy
          • higher the Hz, the more times per second the molecules must realign, the greater the hysteresis losses
    • Transformers are rated in kVA (kilovolt-amperes)
    • Primary current increases in direct proportion to the secondary current (good txfr current explanation pg 160)
    • Auto-transformer
      • use a single winding for the primary and secondary windings
      • inexpensive
      • lack of electrical isolation
      • used to move voltage up/down, i.e. between 240v and 208v
    • Transformer Formulas
      • Efficiency
        • Eff = Output W / Input W
        • Input W = Output W / Eff
        • Output W = Eff * Input W
      • Turns Ratio = Primary : Secondary
      • Current
        • 1 Ø
          • I = VA/E
        • 3 Ø
          • I = VA/(E * 1.732)
    • Note: See pg 157-Fig 4-21 for an interesting note on secondary voltages to neutral (480/240 Txfr has 240V across 2 hots and 208V from 1 hot to neutral)Unit 06: Conductor Sizing and Protection Calculations

NEC Article 240, 310, 400, 402

  • Conductor heat is directly proportional to wire resistance and the square of current flow
  • Conductors 8 AWG & larger must be stranded when installed in a raceway
    • 310.106(C)
  • Conductor sizing determining factors:

    • current flow & resulting heat (ampacity adjustment)
    • number of conductors in same raceway (bundle amp adjustment)
    • ambient temperature
    • terminal temperature ratings
    • continuous load factor
    • overcurrent protection
    • conductor insulation temperature rating
  • Table 310.104(A)

    • Conductor insulation properties
      • letter type
      • operational temperature
      • application
      • insulation
      • outer cover properties
    • In general, only conductors in this table can be used unless permitted elsewhere in the NEC
  • Conductor Insulation Letter Ratings

    • Letter Designation Description
      No H 60°
      H 75°
      HH 90°, Dry
      -2 90°, Wet
      N Nylon Outer Cover
      T Thermoplastic
      U Underground
      W Wet or Damp
      X Cross-linked Polyethylene
      R (rubber – replaced by:) Thermoset
    • ?? Why is H & W identified in THWN-2 cable?  Isn’t this redundant??
  • Article 400

    • Tables 400.4 / 400.5(A) / 400.5(B)
    • Flexible cords and cables
  • Article 402
    • Tables 402.3 / 402.5
    • Fixture wires
  • Conductor sizes

    • 110.14(C) (70-45
      • Temperature Limitations
    •  AWG
      • 18 to 4/0 (4-ought)
      • larger than 4/0 is expressed in kcmil
        • 250 kcmil & up
    • kcmil
      • kcmil = 1000’s (K) of (C)ircular (M)ils
      • Mil means 1/1000 inch
      • Circular Mil means the area of a circle 1/1000 inch in diameter
      • 20 AWG = 1 kcmil
    • Table 310.15(B)(16)(A & B)
      • **Conductor Insulation Temperature Ratings
      • Equipment terminations
      • Conductor sizing
    • Equipment Ratings
      • ≤ 100 amps
        • 60°C
          • 110.14(C)(1)(A)(1)
          • Must be sized to table 310.15(B)(16)
        • 75°C
          • 110.14(C)(1)(A)(3)
          • Must be sized to table 310.15(B)(16)
          • Motor terminals
            • must be design letters B, C, D (on nameplate)
            • 110.14(C)(1)(A)(4)
            • Can be used within 75° column of table 310.15(B)(16)
      • ≥ 100 amps
        • 75°C
          • 110.14(C)(1)(B)(1)
          • Larger than 1 AWG
            • Must be sized to table 310.15(B)(16)
  • Branch Circuits Conductor sizing

    • Minimum 14 AWG
    • Smaller than 14 AWG permitted for:
      • class 1 remote controls
        • 725.43
      • Fixture wire
        • 402.6
      • Motor Control Circuits
        • Table 430.72(B)
  • Over-current

    • Article 240
    • Transformers secondary circuit can use the primary circuit for over-current protection
    • Conductors must be protected at the point receiving the supply
      • 310.15(B)(16)
      • Except for 240.4(A) to (G)
      • 310.15
        • Conductor amperage correction and adjustments
    • Must be on-the-line side of terminals
      • 110.9
    • Must have short circuit protection
      • 110.10 note
    • Causes by
      • Overload
      • short circuit
      • ground fault
    • Over-current ≤ 800 amps

      • 240.4(B)
      • Next higher rating permitted providing:
      • 240.6(A)
        • not supplying more than 1 receptacle cord-and-plug
        • conductor sizing requires
          • ambient temperature correction
            • 310.15(B)(2)(A)
          • conductor bundling adjustment
            • 310.15(B)(3)(A)
          • last two points don’t correspond with fuse nor circuit breaker ratings
        • not over 800 amps
    • Over-current≥ 800 amps

      • 240.4(C)
      • must have a rating not less than the over-current device
    • Over-current Small Conductors

      • 240.4(D)
      • Exceptions
        • 240.4(E)
        • 240.4(G)
      • Must not exceed:
        • Wire Size, AWG Amperage
          18-Cu 7
          16-Cu 10
          14-Cu 15
          12-Al 15
          12-Cu 20
          10-Al 25
          10-Cu 30
      • Exception 240.4(G)
        • Must comply with table 240.4(G)
        • Motors, Article 430
          • Over-current protection, Article 430
        • A/C equipment, Article 440
          • Over-current protection, Article 440.22
  • Conductor Ampacity

    • Conductor Ampacity Calculation

      • Table 310.15(B)(16)
      • Table 310.15(B)(2)(a)_ambient temp above 86°F/30°C
      • Table 310.15(B)(3)(a)_4+ hot conductors
    • Table 310.15(B)(16)

      • allowable ampacity of insulated conductors
      • Provided:
        • No more than 3 hot/ungrounded/current-carrying conductors
          • if 4 or more, correct using Table 310.15(B)(3)(a)
        • ambient temperature of 86°F/30°C
          • if not correct using Table 310.15(B)(2)(a)
      • **When using this table, if the ambient temperature where installed is outside 78°-86°C, the ampacity must be adjusted using table 310.15(B)(2)(a)
      • **When using this table, if there are more than 3 bundled current-carrying conductors, the ampacity must be adjusted using table 310.15(B)(3)(a)
    • Table 310.15(B)(2)(a)

      • Ampacity Correction
      • Ambient temperature correction formula
        • Corrected Amps = Table 310.15(B)(16) amps * Ambient Temp. Correction Factor table 310.15(B)(2)(a)
    • Table 310.15(B)(3)(a)

      • Conductor Ampacity Adjustment after table 310.15(B)(16)
        • Used when more than 3 bundled current-carrying conductors installed in any cross-sectional wireway
      • Conductor Bundling Ampacity adjustment formula
        • Adjusted Amps = Table 310.15(B)(16) amps * Bundled amp Adjustment Factor table 310.15(B)(3)(a)
      • Reduce conductor ampacity  when:
        • 4 or more hot conductors
        • raceway or cable is longer than 24″
        • adjust according to table 310.15(B)(3)(a)
    • Wet locations

      • 300.5(B)
      • 300.9
      • 310.10(C)
      • 300.6(D)
    • Rooftops

      • 310.15(B)(3)(6), pg 70-148
      • When exposed to sunlight and less than 7/8″ above a roof, add 60°F/33°C to table 310.15(B)(2)(a)
        • Exception: Cable XHHW-2 not subject to this rule
    • Cable Types AC and MC

      • Special amperage, adjustment rules do not apply
      • No outer jacket
      • No more than 3 current-carrying conductors
      • Conductors are 12 AWG copper
      • No more than 20 conductors installed without spacing, with length ≥ 24″
    • Conductor Ampacity Notes:

      • Neutral conductor
        • Only considered a current-carrying conductor according to 310.15(B)(5)
      • Equipment conductors
        • Never considered current-carrying conductors according to 310.15(B)(6)
      • Corrections based on conductors insulation temperature rating
        • determined by Table 310.15(B)(16)
        • not by terminal rating, 110.14(C)
      • Correct for multiple conditions when:

        • more than 3 hot conductors, and
        • ambient temperature is not between 78°-86°F
        • Combine adjustments of ambient temperature and conductor buldling
        • Adjusted & Corrected Ampacity = Table 310.15(B)(16) amps * Temperature factor * Bundled adjustment factor
      • Lower Ampacity Rule

        • When more then 1 ampacity applies, use the lower amperage rating
      • Higher ampacity Exception

        • 310.15(A)(2)(Ex)
        • If different amperage’s apply to different areas of one circuit, the higher amperage rating can be used if the lower amperage cable area :
          • length is not over 10′ or
          • ≥ 10% of total circuit length
      • Neutral, Bonding, and Grounding Conductors

        • refer to 310.15(B)(5) and (6)
        • Does not apply to conductors in cable trays
        • refer to 392.80
      • Neutral Conductor Current-Carrying Determination

        • Circuit Type Neutral Carrying Current Notes
          2-wire Yes 310.15()()()
          3-wire, 1 Ø, 120/240V, Wye-connect No 310.15(B)(5)(a)
          4-wire, 3 Ø, 120/208V or 277/480V, Wye-connect No 310.15(B)(5)(a)
          3-wire-from-4-wire, 3 Ø, Wye-connect Yes 310.15(B)(5)(b)

          4-wire, 3 Ø, 120/208V or 277/480V, Wye-connect

          (if more than 50% of neutral is non-linear load)

          Yes 310.15(B)(5)(c)
        • Non-Linear load is when the current wave form does not follow the voltage wave form
        • Unbalanced 3-wire Wye Secondary Neutral Current Formula
          • (INeutral = √(ILine12 + ILine22) – (ILine1 * ILine2)
  • Miscellaneous Over-current Protection and Conductor Sizing

    • Branch Circuits

      • Over-current protection
        • 210.20(a)
        • Must have a rating of not less than 125% of continuous loads, plus 100% of non-continuous loads
      • Conductor sizing
        • Must have an ampacity of not less than the maximum load served
        • Must be the larger of these 2 options:
          1. conductors must be sized with a rating of not less than 125% of continuous loads, plus 100% of non-continuous loads, based on terminals
          2. Temperature rating ampacity of table 310.15(B)(16)
            • Minimum size allowable amperage not less than maximum load to be served
    • Appliance Over-Current Protection

      • 422.11(E)
      • Not to exceed marked rating
      • If rating is unmarked
        • Rated ≤ 13.30 amps
          • not to exceed 20 amps
        • Rated ≥ 13.30 amps
          • 422.11(E)(3)
          • Not to exceed 150% of rated current
            • Note: Next higher rating permitted when amperage falls inbetween (2406(A)-pg70-95)
    • Water Heater Branch Circuit Over-Current Protection

      • 422.13
      • ≤ 120 gallon is a continuous load
        • not less than 125% continuous loads, refer to 210.19(A)(1)
      • Branch circuit conductor
        • 422.10
        • 125% of amperage of continuous load
      • Over-current protection device
        • sized to 422.11(E)(3)
    • Electric Space Heating Branch Circuit
      • 424.3(B)
      • considered a continuous load
      • Branch circuit and over-current protection
        • 210.19(A)(1)
        • 210.20(A)
        • Must be sized not smaller that 125% of the total load (heater and motor)
    • REVIEW MH-PG 269-QUESTIONS-FIG. 6-64-3 STEPS
  • Feeders

    • Feeder Over-Current Protection

      • 215.3
      • Must have a rating of not less than 125% of continuous loads, plus 100% of non-continuous loads
    • Feeder Conductor Sizing

      • 215.2(A)(1)
      • Must be sized to larger of:
        • 215.2(A)(1)(A) (has exceptions)
          • minimum feeder conductor ampacity is not less than 125% of continuous loads, plus 100% of non-continuous loads
          • 215.2(A)(1)(A)(Ex2)
            • Feeder conductors with a junction box at both ends into 90°C terminals can have an ampacity of not less than 100% of continuous loads and 100% of non-continuous loads based on the 90°C column of table 310.15(B)(16)
            • 110.14(C)(2), pg 70-45
            • ADD PHONE PICTURE
        • or
        •  215.2(A)(1)(B)
          • determined after ampacity adjustment & correction & not less than the load to be served
    • Feeder Circuits

      • 75°C
        • 125% of continuous loads for circuits ≥ 100 amps
          • 215.2(A)(1)(A)
        • Conductors sized to 75°C on table 315(B)(16) / 110.14(C)(1)(b)
        • Rated ≤ 800 amps
          • over-current protection to 240.4(B)
        • Rated ≥ 800 amps
          • over-current protection to 240.4(C)
        • Continue from pg 12
        • ADDED FROM PHONE
        • Neutral sized to 100% of continuous load to 75°C column of table 310.15(B)(16), 110.14(C)(1)(B), based on maximum unbalanced load according to 220.61 and not smaller then required for equipment grounding conductors by 220.122
        • 215.2(A)(1)(Ex3)
      • 90°C
        • Sized to 100% of continuous load according to 90C column on table 310.15(B)(16), 110.14(C)(2)
          • 215.2(A)(1)(a)(Ex1)
        • Rated ≤ 800 amps
          • over-current protection to 240.4(B)
        • Rated ≥ 800 amps
          • over-current protection to 240.4(C)
        • Neutral conductor
          • Sized to 100% of continuous load to 75C column on table 310.15(B)(16) based on maximum unbalanced load according to 220.61 and not smaller than 250.122 for equipment grounding conductors
            • 215.2(A)(1)(Ex3)
            • 110.14(C)(1)(b)
        • Exception 3
          • Neutral conductors must have an ampacity of not less than 100% of continuous and non-continuous loads
        • Feeder Over-current Protection
          • 215.3
            • Device sizing requirements for continuous and non-continuous loads
        • Feeder Taps
          • Tap is a conductor (not a service conductor) that has over-current protection rated higher than normally allowed in 240.2
          • Over-current protection must be placed where branch circuits or feeder conductors receive power
            • Except as permitted by (a)-to-(h)
          • 10′ feeder tap conductors
            • No over-current protection needed provided:
              • Ampacity is greater than the:
                • Calculated load according to article 220
                • rating of over-current protection device equipment and termination containing over-current protection supplied by tap conductors
              • must not extend beyond the equipment they supply
              • are installed within a raceway leaving an enclosure
              • must have an ampacity of not less than a 10% rating of the over-current protection device protecting the feeder
          • NOTE:  408.36 = over-current protection for panelboards
          • 25′ feeder tap conductors
            • No over-current protection needed provided:
              • Ampacity is not less than 1/3rd the rating of the over-current protection device protecting the feeder
              • terminate in an over-current protection device rated not more than the tap conductor ampacity from 310.5, table 310.15(B)(16)
          • Feeder Tap Conductors with unlimited length outside
            • No over-current protection needed for unlimited length provided:
              • protected from physical damage within a raceway
              • Terminates at a single over-current protection device limiting load to the ampacity of the outside feeder tap conductors
              • over-current protection device for outside feeder tap conductors is part of building feeder disconnect
              • Disconnecting means is readily accessible
  • Unit 6 Conclusion

    • NEC tables are based on 86°F/30°C
      • Conductor amperages must be corrected for other temperatures
    • NEC requires ampacity adjustments when bundling more than 3 current-carrying conductors
    • Section 110.14(C) is a confusing part of code
      • Do not size conductors to a higher rating then the terminals
    • With requirement of a rating of not less that 125% of continuous loads, plus 100% of non-continuous loads
      • Non-continuous load is not added when not mentioned

Unit 07: Motor and Air Conditioning Calculations

NEC Article 430, 440, Tables 310.15(B)(16), 430.247 to 430.250, 430.22(E)

  • A motor generally draws 6 times more current at startup then when running
  • Consider motors continuous duty unless noted non-continuous duty
    • Use table 430.22(E) for non-continuous duty motors
  • FLC is to Full Load Code as FLA is to Full Load Actual
    • FLC from NEC tables 430.247-250
    • FLA from motors nameplate

Motor Protection_2 parts

  1. Short Circuits and Ground Faults

    • Protection is Fuses and Circuit Breakers
    • Full Load Current (FLC)
      • Conductor amperage, branch circuit short & ground faults over-current protection
      • 430.6(A)(1)
      • Tables:
        • 430.247
          • DCV
        • 430.248
          • 1 Ø
        • 430.249
          • 2 Ø
        • 430.250
          • 3 Ø
      • 430.22
        • Conductor Ampacity
        • Single motor, cintinuous duty
          • Ampacity no less than 125% of the motors FLC listed in table 430.247-430.250
      • 430.52 & 430.62
        • Short Circuits and Ground Faults Over-current Protection Device sizing
      • 430.110
        • Disconnect switches Ampacity rating
  2. Overload Protection

    • Close-to-motor-running-current but with sufficient time delay to start
    • Usually ‘heaters’, overload sensing devices in magnetic starters
    • Full Load Amps (FLA)
      • 430.6(A)(2)
      • Use motor nameplate data to size overload protection
      • Motor FLA = 746 x HP / E x Eff x PF
      • Motor FLA = 746 x HP / E x 1.732 x Eff x PF
        • ?? When to use 1 formula over the other??
        • 746 = watts per hour standard
        • HP / E / Eff / PF all read from nameplate
        • 1.732 = square root of 3
      • Load Voltage Current
        ↑ &
        ↓ &

Motor Conductor Sizing Procedures

Motor Conductor Sizing Procedures

Motor Type Motor Conductor Sizing Rule NEC Tables Final Conductor Size
1 Ø, Continuous Duty not less than 125% of the motors FLC 430.247 to 430.250 310.15(B)(16)
3 Ø, Continuous Duty not less than 125% of the motors FLC 430.247 to 430.250 310.15(B)(16)
Non-Continuous Duty-Cycle not less than 85% of the motors FLA 430.22(E) 310.15(B)(16)
Motor Feeder Conductors Supplying Multiple Motors not less than 125% of the largest motors FLC plus the sum of the additional motor FLCs fed from the same feeder 430.24(1) 310.15(B)(16)

Motor Feeder Conductors Supplying Multiple Motors

  • ?? DISCREPANCY:  code says “sum of FLC ratings of all other motors in the group”  but the MH examples only add in the 2nd highest motor??

Motor Overload Protection

Motor Overload Protection Sizing

 Overload Rating 

 Motor Characteristic  Notes
125% SF 1.15 & ↑ Normal overload protection sizing
40°C Rise & ↓
140% SF 1.15 & ↑ Used when insufficient for motor starting or to carry the load
40°C Rise & ↓
115% OL rating when motor is not rated to SF 1.15 & ↑ nor a Temperature Rise of 40° & ↓
130% OL rating when motor is not rated to SF 1.15 & ↑ nor a Temperature Rise of 40° & ↓ and when insufficient for motor starting or to carry the load
Branch short-circuit & ╧ fault protection sufficient Non-Continuous Duty Cycle short-time, intermittent, periodic, or varying duty motors
Note: OL values can not be exceeded, round down. 430.32(C)

Motor Short-Circuit & Ground-Fault Protection

  • 430.52(B) & (C) compliance
  • Short-circuit & ╧-fault protection requires:
    • fast current rise
    • short duration
    • fast response time
  • Motor Branch-Circuit Short-circuit & ╧-fault Protection Table 430.52

     Motor Type 

     Non-Time Delay 

    Fast-Acting

     Dual-Element Fuse

    Time-Delay 

     Inverse Time Breaker 

    Instantaneous Trip

    Direct Current 150% 150% 150%
    Wound Rotor 150% 150% 150%
    All Other Motors 300% 175% 250%

 

  • Short-circuit & ╧-fault protection-Next Size Up Rule
    • When protecting device values derived from table 430.52 don’t correspond with the ratings listed in 240.6(A), the next higher OC device rating can be used
    • 430.52(C)(1)(Ex1)
    • Does not apply to feeder short-circuit & ╧-fault protection
  • DO THESE EXAMPLES, MH-pg 317-319

Motor Feeder Short-circuit & ╧-fault Protection

  • 430.62
  • Sized not more than the largest rating of the branch-circuit, plus the sum of the FLC of the other motors in the group
  • Branch-Circuit Next Size Up Rule does not apply, so round down
  • DO THESE EXAMPLES, MH-pg 321-322

Motor VA Calculations

  • Motor output
    • 1 HP = 746 watts
  • 1 Ø Motor Input VA Calculation
    • Input VA = motor volts * motor FLC amps
      • 1 Ø VA = E*FLC
        • P=IE
  • 3 Ø Motor Input VA Calculations
    • 3 Ø Input VA = Motor Volt Rating * Motor ampere Rating * 1.732
      • 1.732 = √3
      • 3 Ø VA = E*FLC*1.732

Variable Speed Drive Calculations

Variable Speed Drive Conductor Sizing

  • 430.122(A)
  • not less than 125% of the rated input current

Variable Speed Drive Branch-Circuit Protection

  • 430.130(A)(2)
  • must be in accordance with the manufacturers instructions

Variable Speed Drive Over-Current Protection

  • must be in accordance with the manufacturers instructions

Fire Pump Calculations

Fire Pump Conductor Size

  • 695.6(B)(2)
  • not less than 125% of the motor FLC as listed in tables 430.248 or 430.250
  • must comply with voltage-drop requirements of 695.7

Fire Pump Short-Circuit and ╧ fault Protection

  • 695.4(B)(2)(a)
  • must be sized to carry the motor locked-rotor current indefinitely

Fire Pump Over-Current Protection

  • 695.4(B)(2)(a)(1)
  • must be sized to carry the motor locked-rotor current indefinitely
  • Next-size Up Rule in use if the locked-rotor current does not correspond to a standard over-current device, round up
    • 240.6(A)

Air Conditioning Calculations

Mulitmotor Equipment Short-Circuit and ╧ fault Protection

  • 440.4(B)
  • Must have a nameplate identifying  branch-circuit short-circuit and ╧-fault protective device
  • RLA here, not FLA ??

Mulitmotor Equipment Conductor Size

  • 440.4(B)
  • Must have a nameplate identifying minimum conductor ampacity
  • RLA here, not FLA ??

Motor-Compressor & Other Motors Short-Circuit and ╧ fault Protection

  • 440.22(B)(1)
  • Must not be greater than 175% of the largest motor-compressor nameplate load current rating, plus the current of other motors
  • If unable to start at 175%, 225% is the maximum

Motor-Compressor & Other Motors Conductor Size

  • 440.33
  • sized to 125% of the largest motor-compressor nameplate load current rating, plus the sum of the other rated-load current of other motors