SCADA_DA_IIEE_tech_rep_

Views:
 
Category: Entertainment
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

Slide 1: 

MOTOR CIRCUITS, AND CONTROLLERS based on Phil. Electrical Code part 1 with reference to product standards Prepared by : Gem Tan Fuji-Haya Audit Inspection & Maintenance Corp.

Slide 2: 

Why need Philippine Electrical Code ( PEC )? What is the purpose of PEC? The purpose of PEC is the practical safeguarding of persons and property from hazards arising from the use of electricity. The code contains provisions that are considered the minimum requirements necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessary efficient, convenient, or adequate for good service or future expansion of electrical use.

Approach to Electrical Safety : 

Approach to Electrical Safety Installation Code (PEC) Product Standards & Certification Safe Products & Safe Installation Inspection & Enforcement Understand the relationship between the product standards and installation codes. Design & test requirement assure that it can be relied on the function safely. Provide the best technical information, ensuring the practical safeguarding of persons & property from the hazards.

Motor Protection : 

Motor Protection Any device using electrical energy could malfunction due to :  an electrical problem: - overvoltage, undervoltage, phase imbalance or single-phasing ( phase loss ), - short-circuits which can surpass the breaking capacity of the contactor.  a mechanical problem: - stalled rotor, momentary or prolonged overload.

Basic Protection Schemes : 

Basic Protection Schemes Range 1.05 - 1.20 In Characteristic of thermal relay Cable thermal-withstand limit Limit of thermal-relay constraint In Is I” short-ckt current breaking capacity 20 to 30 ms 1 to 10 s t Circuit breaker contactor Thermal relay motor

What Current To Use ? Sec. 4.30.1.6 : 

What Current To Use ? Sec. 4.30.1.6 For general motor applications (excluding applications of torque motors and sealed hermetic-type refrigeration motor-compressors), current rating shall be based on the following: (1) Table Values. The values given in Table 4.30.14.1 to 4.30.14.4, including notes, shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short circuit & ground-fault protection, instead of actual current rating marked on the motor nameplate. (2) Nameplate Values. Separate motor overload protection shall be based on the motor nameplate current rating. Sec 4.30.1.6 (a) p572

What Current To Use ? Sec. 4.30.1.6(b) : 

What Current To Use ? Sec. 4.30.1.6(b) Sec 4.30.1.6(b) p573 Torque Motors. For torque motors, the rated current shall be locked-rotor current, & this nameplate current shall be used to determine the ampacity of the branch-circuit conductors covered in Sec. 4.30.2.2 (Single Motor) & 4.30.2.4 (Several Motors or a Motor & other Load. The ampere rating of motor overload protection, & the ampere rating of motor branch-circuit short-circuit & ground-fault protection in accordance with Sec. 4.30.4.2(b).

What Current To Use ? Sec. 4.40.1.6(a) : 

What Current To Use ? Sec. 4.40.1.6(a) Sec 4.40.1.6(a) p631 Hermetic Refrigerant Motor-Compressor. The rated-load current marked on the nameplate of the equipment in which the motor-compressor is employed shall be used in determining the rating or ampacity of the disconnecting means, the branch-circuit conductors, the controller, the branch circuit short circuit & ground fault protection & the separate motor overload protection. Where no rated-load current shown on the equipment nameplate, the rated-load current shown on the compressor nameplate shall be used.

Motor Circuit Conductors Sec. 4.30.2.2(a) : 

Motor Circuit Conductors Sec. 4.30.2.2(a) Branch-circuit conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125% of the motor’s full-load current rating . p582 Single Motor. - General Branch Circuit Short Circuit & Ground Fault Protection Motor Overload Protection Motor Controller Branch Circuit Conductors

Ampacity Table : 

Ampacity Table FPN: Tables 3.10.1.16 through 3.10.1.19 are application tables for use in determining conductor sizes on loads calculated in accordance with Article 2.20. Allowable ampacities result from consideration of one or more of the following: 1. Temperature compatibility with connected equipment, especially at the connection points. 2. Coordination with circuit and system overcurrent protection. 3. Compliance with the requirements of product listings or certifications. 4. Preservation of the safety benefits of established industry practices and standardized procedures. p295

Temperature Limitations Sec. 1.10.1.14 (c) : 

Temperature Limitations Sec. 1.10.1.14 (c) The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for termination’s shall be permitted to be used for ampacity adjustment, correction, or both. p39

Temperature Limitations Sec. 1.10.1.14 (c) : 

Temperature Limitations Sec. 1.10.1.14 (c) (1) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 2.0 mm2 (1.6 mm dia.) through 38 mm2 conductors, shall be used only for one of the following. p39 a. Conductors rated 60oC, or b. Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60oC ampacity of the conductor size used, or c. Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors, or d. For motors marked with design letters B, C, D, or E, conductors having an insulation rating of 75oC or higher shall be permitted to be used provided the ampacity of such conductors does not exceed the 75oC ampacity.

NEMA Motor Design-Letters Classification : 

NEMA Motor Design-Letters Classification NEMA Classes A NEMA Classes B NEMA Classes C NEMA Classes D NEMA Classes F

Temperature Limitations Sec. 1.10.1.14 (c) : 

Temperature Limitations Sec. 1.10.1.14 (c) (2) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 38 mm2, shall be used only for p39 a. Conductors rated 75oC, or b. Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75oC ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors.

Minimum Branch Circuit Conductor Size Sec. 2.10.2.1(a) : 

Minimum Branch Circuit Conductor Size Sec. 2.10.2.1(a) The minimum branch circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the non-continuous load plus 125% of the continuous load. Exception: Where the assembly, including the overcurrent devices protecting the branch circuit, is listed for operation at 100% of its rating, the ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load. p66

MCCB Temperature Test (Non 100% Rated) : 

MCCB Temperature Test (Non 100% Rated) The temperature rise on a wiring terminal at point to which the insulation of a wire is brought up as in actual service shall not exceed 50oC. The temperature rise on a circuit breaker, or an extension member, where a bus bar is to be connected shall not exceed 50oC. UL 489 p 29

MCCB Temperature Test(Non 100% Rated) : 

MCCB Temperature Test(Non 100% Rated) If the temperature rise at the points where the connection are made exceed 50oC but not more than 65oC with the circuit breaker carrying 100% of rated current, the temperature test may be repeated using an untested circuit breaker installed in an enclosure that is representative of the smallest enclosure with which the circuit breaker is likely to used. Under these conditions, with the circuit breaker carrying 80% of its maximum rated current, the temperature rise at the points where the connection to the external wires or bus bars are made shall not exceed 50oC. UL 489 p 29

MCCB Temperature Test(100% Rated) : 

MCCB Temperature Test(100% Rated) UL 489 p 30 The temperature rises (1) where connections are made to external bus bars, when bus bar are used; or (2) on a wiring terminal at a point to which the insulation of a wire is brought up as in actual service when tested with insulated wire shall not exceed 60oC. Exception: The marking required need not be provided if the temperature rise measured on the insulated cable does not exceed 50oC.

Marking : 

Marking A circuit breaker that is intended to be operated continuously at 100% of its rating and that has a temperature rise on a wiring terminal exceeding 50oC, shall be marked, A. For use with 90oC wire and the wire size. The wire size shall be based on the ampacity of 75oC rated conductor. UL 489 p80A

Over-current Protection For Conductors : 

Over-current Protection For Conductors Circuit Breaker should be tested and wired in accordance with the Table given in the Circuit Breaker Standard. Nema AB1, part2 p32 Caution:- The use of conductors smaller than those shown in Nema AB1 or ANSI/UL 489 Molded Case Circuit Breakers standard Table can result in unsafe conditions such as overheating and change in tripping characteristics; consult the manufacturer.

Temperature-rise Limits for Terminals : 

Temperature-rise Limits for Terminals Terminal material Temp.-rise limits1) (K) Bare copper 60 Bare brass 65 Tin plated copper or brass 65 Silver plated or nickel plated copper or brass 70 Other metals 2) IEC 60947-1 p183 1) The use in service of connected conductors significantly smaller than those listed in Table 9 & 10 could result in higher terminals & internal parts temperature & such conductors should not be used w/o the manufacturer’s consent since higher temp. could lead to equipment failure. 2) Temp-rise limits to be based on service experience or life tests but not to exceed 65K.

Motor Circuit Conductors Sec. 4.30.2.2(b) : 

Motor Circuit Conductors Sec. 4.30.2.2(b) Other than Continuous Duty. Conductors for a motor used in a short-time, intermittent, periodic, or varying duty application shall have an ampacity of not less than the percentage of the motor nameplate current shown in Table 4.30.2.2(b), unless the authority having jurisdiction grants special permission for the conductors of lower ampacity. Sec 4.30.2.2(b) p583

Duty-Cycle Service Table 4.30.2.2(b) : 

Duty-Cycle Service Table 4.30.2.2(b) Nameplate Current Rating Percentages Classification of Service 5-min. 15-min. 30&60 min. Cont.rated Short time duty operating 110 120 150 - valves, raising or lowering rolls, etc. Intermittent duty freight & 85 85 90 140 passenger elevators, pumps, etc. Periodic duty rolls, ore & coal 85 90 95 140 handling machines, etc. Varying duty 110 120 150 200 Note:Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use. Table 4.30.2.2(b) p 583 4.30.2.2(b) 4.30.3.3

Wound-Rotor Secondary Sec 4.30.2.3 : 

Wound-Rotor Secondary Sec 4.30.2.3 Primary conductors rated not less than 125% of motor primary current Motor Secondary conductor rated not less than 125% of full load secondary current or Table 4.30.2.2(b)other than Cont. Duty The ampacity of the conductors between controller and resistor shall not be less than that shown in Table 4.30.2.3(c). Line

Wound-Rotor Secondary Conductor Table 4.30.2.3(c) : 

Wound-Rotor Secondary Conductor Table 4.30.2.3(c) Resistor Duty Classification Amp. of Conductor in % of Full load Secondary Current Light starting duty 35 Heavy starting duty 45 Extra heavy starting duty 55 Light intermittent duty 65 Medium intermittent duty 75 Heavy intermittent duty 85 Continuous duty 110 PEC 1,2000 p 584

Thermal Devices : 

Thermal Devices Thermal relays and other devices not designed to open short circuits or ground faults shall not be used for the protection of conductors against overcurrent due to short circuits or ground faults, but the use of such shall be permitted to protect motor branch circuit conductors from overload if protected in accordance with Sec.4.30.3.10 NEC 2002, 240.9 Circuit breaker Motor Controller motor Overload Protection

Overload Relays Sec.4.30.3.10 : 

Overload Relays Sec.4.30.3.10 Overload relays and other devices for motor overload protection that are not capable of opening short circuits shall be protected by fuses or circuit breakers with rating or settings in accordance with Section 4.30.4.2. NEC 2002, 240.9

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 : 

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 GT Motor Ser.No. 123 Frame OPEN PF 75% EFF. 70% S.F. 1.15 PHASE 1 VOLTS 115/230 FLA 18.5/9.27 CYCLE 60 RPM 1725 oC RISE 40 DUTY CONT HP 1.5 CODE LETTER F PEC 1 Table FLA Motor Nameplate FLA Table is used to size: conductors & disconnects short circuit & ground fault protective devices Motor nameplate FLA is used to size overload protection

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 : 

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 Continuous-Duty Motors. Each continuous duty motor shall be protected against overload by a separate overload device that is responsive to motor current, This device shall be selected to trip or shall be rated at no more than the following percent of the motor nameplate full-load current rating: Motors with a marked service factor not less than 1.15 125% Motors with a marked temperature rise not over 40oC 125% All other motors 115% p 588 4.30.3.5

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 : 

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 Continuous-Duty Motors. Where a separate motor overload device is connected so that it does not carry the total current designed on the motor nameplate, such as for wye-delta starting, the proper percentage of the nameplate current applying the selection or setting of the overload device shall be clearly designated on the equipment, or manufacturer’s selection table shall take this into account. FPN: Where power factor correction capacitors are installed on the load side of the motor overload device, see Sec 4.60.1.9 Sec 4.30.3.2(a)1 p 588

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 : 

Branch Circuit Overload Protection Sec. 4.30.3.2(a)1 Case 1 Case 2 Overload Relay?

Rating or Setting of Motor Overload Device Sec. 4.60.1.9 : 

Rating or Setting of Motor Overload Device Sec. 4.60.1.9 Capacitors with Motors. Sec 4.60.1.9 p665 Rating or Setting of Motor Overload Device. Where a motor installation includes a capacitor connected on the lode side of the motor overload device, the rating or setting of the motor overload device shall be based on the improved power factor of the motor circuit. The effect of the capacitor shall be disregarded in determining the motor circuit conductor rating in accordance with Sec. 4.30.2.2.

Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 : 

Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 Capacitors with Motors. p3.27 Ex.: A motor with 70% pf has a full load current rating of 143 A. Normally, the OL relay would be set for say, 125% of 143 or 179 A. But , because a PF capacitor is installed at the motor, the OL relay no longer will have 143 A flowing through it at full load. If the capacitor corrects to 100% PF, the effect will be as follows:

Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 : 

Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 Capacitors with Motors. p3.27 Motor PF Capacitor C Total Motor Current *A B Working current from supply Reactive or magnetizing current from capacitor Controller Overload units should be set for 125% of current produce by improved power factor instead of motor full-load current. *A (total motor current) = Vector sum of B and C

Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 : 

Rating or Setting of Motor Overload Device. Sec. 4.60.1.9 Capacitors with Motors. p3.27 θ Iw E I = 143 A Ixc IxL Cos θ = 0.70 IxL = Magnetizing current Ixc = Capacitor current Iw = Working current Working current = Total motor current x PF = 143 x 0.70 = 100 Amps That is the current that will be flowing through the OL relay at full-load. Therefor, The OL relay must be set at 125% x 100 Amps = 125 Amps

Motor Capacitor Circuit Conductors Sec. 4.60.1.8(a) : 

Motor Capacitor Circuit Conductors Sec. 4.60.1.8(a) Capacitors with Motors. Sec 4.60.1.8(a) p664 The ampacity of the capacitor circuit conductors shall not be less than 135% of the rated current of the capacitor. The ampacity of conductors that connect a capacitor to the terminals of a motor or to motor circuit conductors shall not be less than one-third the ampacity of the motor circuit conductors & in no case less than 135% of the rated current of the capacitor.

Branch Circuit Overload Protection Sec. 4.30.3.3 : 

Branch Circuit Overload Protection Sec. 4.30.3.3 Intermittent and Similar Duty. A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 4.30.2.2(b), shall be permitted to be protected against overload by the branch circuit short circuit & ground fault protective device, provided the protective device rating or setting does not exceed that specified in Table 4.30.14.6. Any motor application shall be considered to be for continuous duty unless the nature of the apparatus it drive is such that the motor cannot operate continuously with load under any condition of use. p 590

Branch Circuit Overload Protection Sec. 4.30.3.4 : 

Branch Circuit Overload Protection Sec. 4.30.3.4 Selection of Overload Relay. Where the overload relay selected in accordance with Sec. 4.30.3.2(a)(1) and ( c )(1) is not sufficient to start the motor or to carry the load, the next higher size overload relay shall be permitted to be used, provided the trip current of the overload relay does not exceed the following percentage of motor nameplate full load current rating: Motors with a marked service factor not less than 1.15 140% Motors with a marked temperature rise not over 40oC 140% All other motors 130% Sec 4.30.3.4 p 591

Special Feature of Overload Relay : 

Special Feature of Overload Relay Selection of Overload Relay. An special feature of overload relay can ease the relay current setting which can be varied to match the requirements of the load. The changeover is effected by simply turning a dial to the new value required. The range of adjustment is approximately 100% - 125% - 150%. Fe 01/98

Branch Circuit Overload Protection Sec. 4.30.3.4 : 

Branch Circuit Overload Protection Sec. 4.30.3.4 Selection of Overload Relay. If not shunted during the starting period of the motor as provided in Section 4.30.3.5, the overload device shall have sufficient time delay to permit the motor to start & accelerate its load. Sec 4.30.3.4 p 591 FPN: A Class 20 or 30 overload relay will provide a longer motor acceleration time than a Class 10 or 20, respectively. Use of a higher class overload relay may preclude the need for selection of a higher trip current.

Thermal Overload Relays : 

Thermal Overload Relays Long time operating type - In the case of loads having large inertia moments such as blowers, winders or centrifuges the starting time will be extended. Quick operating type - The windings of submersible pump and compressor motors normally have a smaller overload capacity than those of standard motors, since they are generally cooled by water and other medium being pump. Therefore, it will be needing faster response time from protective relays.

Basic Protection Schemes : 

Basic Protection Schemes Range 1.05 - 1.20 In Characteristic of thermal relay (140% In) Cable thermal-withstand limit In 6In I” short-ckt current breaking capacity 20 to 30 ms 1 to 10 s t Circuit breaker contactor Thermal relay motor 30 s 20 s Class 30 Class 20 Class 10 Motor Damage characteristic

Trip Class of Thermal, Time-delay Magnetic or Solid State Overload Relays : 

Trip Class of Thermal, Time-delay Magnetic or Solid State Overload Relays Tripping time Tp in seconds under the conditions Trip class specified in Table II, Column D 10 A 2 < Tp  10 10 4 < Tp  10 20 6 < Tp  20 30 9 < Tp  30 IEC 60947-4-1 p59 Table I

Overload Relay Performance : 

Overload Relay Performance Test current as % Maximum Trip Times of Overload Relay Rating Class 10 Class 15 Class 20 Class 30 100 % ----------- Ultimately* ------------------- 200 % ----------- 8 Minutes ------------------- 600 % 10 seconds 15 seconds 20 seconds 30 seconds * Experience indicates that 2 to 4 hrs. is generally sufficient to verify this value. Systems which have large masses may require additional time. NEMA ICS 2-2000 p4-12

Limits of Operation of Time-delay Overload Relays When Energized on All Poles : 

Limits of Operation of Time-delay Overload Relays When Energized on All Poles Type of overload Multiple of current setting Ref. ambient relay A B C D air temperature Thermal type not compensated for ambient air temp. 1.0 1.2 1.5 7.2 +40oC variations and magnetic type Thermal type compensated for ambient air temp. 1.05 1.2 1.5 7.2 +20oC variations Table II IEC 60947-4-1 p 81

Limits of Operation of Time-delay Overload Relays When Energized on All Poles : 

Limits of Operation of Time-delay Overload Relays When Energized on All Poles IEC 60947-4-1 p 79 The relays shall comply with the requirements of Table II when tested as follows: a) with the overload relay or starter in its enclosure, if normally fitted, & at A times the current setting from the cold state, at the value of reference ambient air temperature stated in Table II. However, when the overload relay terminals have reached thermal equilibrium at the test current in less than 2 hr., the test duration can be the time needed to reach such thermal equilibrium; b) when the current is subsequently raised to B times the current setting, tripping shall occur in less than 2 Hr;

Limits of Operation of Time-delay Overload Relays When Energized on All Poles : 

Limits of Operation of Time-delay Overload Relays When Energized on All Poles IEC 60947-4-1 p 79 The relays shall comply with the requirements of Table II when tested as follows: c) for class 10A overload relays energized at C times the current setting, tripping shall occur in less than 2 min. starting from thermal equilibrium at the current setting; d) for class 10, 20, & 30 overload relays energized at C times the current setting, tripping shall occur in less than 4, 8, or 12 min. respectively, starting from thermal equilibrium at the current setting; e) at D times the current setting, tripping shall occur within the limits given in Table I for the appropriate trip class starting from the cold state.

Motor-Compressor & Branch Circuit Overload Protection Sec. 4.40.6.2 : 

Motor-Compressor & Branch Circuit Overload Protection Sec. 4.40.6.2 (a) (1) Each motor-compressor shall be protected against overload & failure to start by a separate overload relay that is responsive to motor compressor current. This device shall be selected to trip at not more than 140% of the motor-compressor rated-load current. (3) A fuse or inverse time circuit breaker responsive to motor current, which shall also be permitted to serve as the branch-circuit short circuit & ground fault protective device. This device shall be rated at not more than 125% of motor compressor rated load current. p 639 Air-Conditioning/Refrigerating Equipment

Motor Controllers Sec. 4.30.7.2 : 

Motor Controllers Sec. 4.30.7.2 Controller Design. (a) Starting and Stopping. Each controller shall be capable of starting and stopping the motor it controls and shall be capable of interrupting the locked-rotor current of the motor. p605 Circuit breaker Motor Overload Protection Motor Controller

Motor Controllers Sec. 4.30.7.3 : 

Motor Controllers Sec. 4.30.7.3 Ratings The controller shall have a rating as specified in (a) of this section, unless otherwise permitted in (b) or (c), or as specified in (d) of this section, under the conditions specified. p605

Motor Controllers Sec. 4.30.7.3 : 

Motor Controllers Sec. 4.30.7.3 Ratings (a) General. (1) Controllers, other than inverse time circuit breakers and molded case switches, shall have horsepower ratings at the application voltage not lower than the horsepower rating of the motor. A controller for use with a Design E motor rated more than 2 hp shall (1) be marked as rated for use with a Design E motor, or (2) have a horsepower rating not less than 1.4 times the rating of a motor rated 3 through 100 hp, or not less than 1.3 times the rating of a motor rated over 100 hp. p606

Motor Controllers Sec. 4.30.7.3 : 

Motor Controllers Sec. 4.30.7.3 Ratings (b) Small Motors. Device as specified in Section 4.30.7.1(b) & (c) shall be permitted as controller. p606 (c) Stationary Motors of 2 Horsepower or Less. For stationary motors rated at 2 hp or less & 300 volts or less, the controller shall be permitted to be either of the following: (1) A general-use switch having an ampere rating not less than twice the full-load current rating of the motor (2) On ac circuits, a general-use snap switch suitable only for use on ac (not general-use ac-dc snap switches) where the motor full-load current rating is not more than 80% of the ampere rating of the switch.

Motor Controllers Sec. 4.30.7.3 : 

Motor Controllers Sec. 4.30.7.3 Ratings (d) Torque Motors. For torque motors, the controller shall have a continuous-duty, full-load current rating not less than the nameplate current rating of the motor. For a motor controller rated in horsepower but not marked with the foregoing current rating, the equivalent current rating shall be determined from the horsepower rating by using Tables 4.30.14.1, 4.30.14.2, 4.30.14.3, or 4.30.14.4. p606

Magnetic Starter Specification : 

Magnetic Starter Specification Rating N5 N6 N7 N8 AC- 3 200-240V 22 30 37 45 kW 3-Phase 380-440V 45 55 75 90 AC-4 200-240V 18.5 22 30 37 3-Phase 380-440V 37 45 55 75 AC- 3 200-240V 93 125 152 180 A 3-Phase 380-440V 90 110 150 180 AC-4 200-240V 80 93 125 150 3-Phase 380-440V 80 90 110 150 AC-1 200-440V 150 150 200 260

Utilization Categories of A.C. Motor Starters : 

Utilization Categories of A.C. Motor Starters Utilization cat. Typical application AC-1 Non-inductive or slightly inductive loads, resistive furnaces. AC-2 Slip-ring motors: starting, switching off AC-3 Squirrel-cage motors: starting, switching off motors during running1) AC-4 Squirrel-cage motors: Starting, plugging, inching 1) AC-3 category may be used for occasional inching (jogging) or plugging for limited time periods such as machine set-up; during such limited periods the number of such operations should not exceed five per min. or more than ten in a 10-min. period IEC 60947-4-1 p55

Making & Breaking Capacities According to Utilization Category : 

Making & Breaking Capacities According to Utilization Category Utilization Make & break test conditions category Ic/Ie Ur/Ue Cos θ On-time(s) Off-time No. of oper. cycle AC-1 1.5 1.05 0.80 0.05 6) 50 AC-2 4.0 1.05 0.65 0.05 6) 50 AC-39) 8.0 1.05 1) 0.05 6) 50 AC-49) 10.0 1.05 1) 0.05 6) 50 IEC 60947-4-1 p91 1) Cos θ = 0.45 for Ie  100 A, 0.35 for Ie > 100 A. 6) These off-times shall be not greater than the values specified in TableVIIa. Making conditions 9) AC-39) 10 1.05 1) 0.05 10 50 AC-49) 12 1.05 1) 0.05 10 50

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 Rating or Setting for Individual Motor Circuit. (a) General.The motor branch circuit short circuit & ground fault protective device shall comply with (b) and either (c) or (d), as applicable. (b) All Motors. The motor branch circuit short circuit & ground fault protective device shall be capable of carrying the starting current of the motor. Sec. 4.30.4.2 p 595 Branch Circuit Short Circuit & Ground Fault Protection Motor Overload Protection Motor Controller

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 Rating or Setting for Individual Motor Circuit. (c)(1) Rating or Setting. A protective device that has a rating or setting not exceeding the value calculated according to the value given in Table 4.30.14.6 shall be used. % of Full-Load Current Type of Motor Nontime Dual Element Instantaneous Inverse Time Delay Fuse Time Delay Fuse Trip Breaker Breaker single phase motor 300 175 800 250 AC polyphase motor other than wound rotor Squirrel cage other than design E 300 175 800 250 Design E 300 175 1100 250 Synchronous 300 175 800 250 Wound rotor 150 150 800 150 DC (constant voltage) 150 150 250 150 4.30.4.2 4.30.3.3 4.30.4.2 4.30.3.10 4.30.4.3 4.30.5.3

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c) Rating or Setting. Exception No. 1: Where the values for branch circuit short circuit & ground fault protective devices determined by Table 4.30.14.6 do not correspond to the standard sizes or rating of fuses, nonadjustable circuit breakers, thermal protective devices, or possible settings of adjustable circuit breakers, the next higher standard size, rating, or possible setting shall be permitted. Sec. 4.30.4.2 p595 (1) A protective device that has a rating or setting not exceeding the value calculated to the values given in Table 4.30.14.6 shall be used.

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c)(1) Rating or Setting. Exception No. 2: Where the rating specified in Table 4.30.14.6, as modified by Exception No. 1, is not sufficient for the starting current of the motor: Sec. 4.30.4.2 p595 (a) The rating of a nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400% of the full-load current. (b) The rating of a time-delay (dual-element) fuse shall be permitted to be increased but shall in no case exceed 225% of the full-load current.

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c)(1) Rating or Setting. Exception No. 2: Where the rating specified in Table 4.30.14.6, as modified by Exception No. 1, is not sufficient for the starting current of the motor: Sec. 4.30.4.2 p595 (c) The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400% for full-load currents of 100 amperes or less or 300% for full-load currents greater than 100 amperes. (d) The rating of a fuse of 601-6000 ampere classification shall be permitted to be increased but shall in no case exceed 300% of the full-load current.

Nonreversing Combination Magnetic Starters : 

Nonreversing Combination Magnetic Starters NEMA size Volt Max. Hp Cont. Amp. Motor FL Amp. CB Rating % 0 3 18 9.6 20 208 1 7½ 27 22.0 50 227 2 15 45 42.0 100 238 3 230- 30 90 80.0 125 156 4 240 50 135 130 200 154 5 100 270 248 400 161 6 200 540 480 800 167 Ge p 1-27, 1999

Nonreversing Combination Mag-Break Magnetic Starters : 

Nonreversing Combination Mag-Break Magnetic Starters NEMA size Volt Max. Hp Cont. Amp. Motor FL Amp. CB Rating % 0 3 18 9.6 15 156 1 7½ 27 22.0 30 136 2 15 45 42.0 50 119 3 230- 30 90 80.0 100 125 4 240 50 135 130 150 115 5 100 270 248 400 161 Ge p 1-229, 1999

Protection for Motor Branch Circuits, NEMA AB1 : 

Protection for Motor Branch Circuits, NEMA AB1 The circuit breaker which is selected shall have a rated continuous current of at least 115% of the full load current of the motor and shall have a calibration setting sufficiently high to permit the motor or motors to start under normal operating conditions. Nema ab1,part2 p32

Wye-Delta Motors : 

Wye-Delta Motors Advantage is that no resistors or transformers are present to produce heat. Disadvantage is that starting torque is low and there are no torque/voltage adjustments.

Setting of Instantaneous Element : 

Setting of Instantaneous Element When motor data are not available, it is usually assumed that the locked-rotor current is equal to six times the motor full-load current, and that the motor acceleration time is 10 seconds. Normally, it is recommended that the setting of the motor feeder instantaneous element be at least twice the locked-rotor current. Example, if locked-rotor current is 450 A, the instantaneous elements of the 125 A MCCB should be set at 900 A, approximately 7.2 times the CB rating. IEEE Std 241 p457

Assumed Max. Short Circuit Current Rating of Unmarked Components : 

Assumed Max. Short Circuit Current Rating of Unmarked Components Component Short circuit current, kA Circuit breaker (including GFCI type) 5 Motor controller, rated in horsepower(kW) a. 0 - 50 (0 - 37.3) 5 b. 51 - 200 (38 - 149) 10 c. 201 - 400 (150 - 298) 18 d. 401 - 600 (299 - 447) 30 e. 601 - 900 (448 - 671) 42 f. 901 - 1500 (672 - 1193) 85 UL 508A, p SB3

Coordination with Short-Circuit Protective Devices : 

Coordination with Short-Circuit Protective Devices Table XI Value of the prospective test current according to the Ie Rated operational current Prospective current “ r “ Ie (AC-3) (A) (kA) 0 < Ie  16 1 16 < Ie  63 3 63 < Ie  125 5 125 < Ie  315 10 315 < Ie  630 18 630 < Ie  1000 30 1000 < Ie  1600 42 IEC 60947-4-1 p 137

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c) Rating or Setting. (2) Where maximum branch-circuit short-circuit and ground-fault protective device ratings are shown in the manufacturer’s overload relay table for use with a motor controller or are otherwise marked on the equipment, they shall not be exceeded even if higher values are allowed as shown above. Sec. 4.30.4.2 p595

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c) Rating or Setting. (3) An instantaneous trip circuit breaker shall be used only if adjustable and if part of a listed combination motor controller having coordinated motor overload and short-circuit and ground-fault protection in each conductor, and the setting is adjusted to no more than the value specified in Table 4.30.14.6 Sec. 4.30.4.2 p596

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 : 

Motor Branch Circuit Short Circuit & Ground Fault Protection, Sec. 4.30.4.2 (c)(3) Rating or Setting. Exception No. 1: Where the setting specified in Table 4.30.14.6 is not sufficient for the starting current of the motor, the setting of an instantaneous trip circuit breaker shall be permitted to be increased but shall in no case exceed 1300 % of the motor full-load current for other than Design E motors or Design B energy efficient motors and no more than 1700 % of full load motor current for Design E motors or Design B energy Efficient motors. Trip settings above 800 % for other than Design E motors or Design B energy efficient motors shall be permitted where the need has been demonstrated by engineering evaluation. In such cases, it shall not be necessary to first apply an instantaneous-trip circuit breaker at 800 % or 1100 %. Sec. 4.30.4.2 p596

Example for Motor Branch Circuit Short Circuit & Ground Fault Protection : 

Example for Motor Branch Circuit Short Circuit & Ground Fault Protection A 30 hp, 230-V, 3 phase squirrel-cage motor is marked with the code letter M, indicating that the motor has a locked-rotor current of 10 to 11.19 kVA/hp. A full-voltage controller is also provided, with running overload protection in the controller to protect the motor within its heating-damage curve on overload. Select a circuit breaker which will provide short-circuit protection & will qualify as the motor-circuit disconnect means. 1. The motor has a full-load current of 80 A. P 3.8 2. A CB suitable for use as the disconnect must have a current rating of at least 115% of 80 A.

Example for Motor Branch Circuit Short Circuit & Ground Fault Protection : 

Example for Motor Branch Circuit Short Circuit & Ground Fault Protection 3. Based on Table, it permits the use of an inverse-time CB rated not more than 250% of the motor full-load current. 2.5 x 80 A = 200 A, a 225 AF with 200 AT setting could be selected. P 3.8 4. The starting current of the motor will be [(30 hp x 11.19 kVA/hp) / (230 V x 1.732)]= 843 A. 5. The instantaneous characteristic of a 200 AT inverse-time CB will be about 200 A x 10 = 2000 A. Such a CB will provide protection for ground and short circuit without interfering with the motor running overload protection.

Branch-Circuit Short-circuit & Ground Fault Protection Sec. 4.40.3.2 : 

Branch-Circuit Short-circuit & Ground Fault Protection Sec. 4.40.3.2 Air-Conditioning/Refrigerating Equipment (a) Rating or Setting for Individual Motor-Compressor. A protective device having a rating or setting not exceeding 175% of the motor-compressor rated load current or branch circuit selection current, whichever is greater, shall be permitted, provided that, where the protection specified is not sufficient for starting current of the motor, the rating or setting shall be permitted to be increased, but shall not exceed 225% of the motor rated load current of branch circuit selection current, whichever is greater. p635

Air Condition & Refrigeration Equipment Short Circuit & Ground Fault Protection : 

Air Condition & Refrigeration Equipment Short Circuit & Ground Fault Protection 60 Hz 1 PH 197 Min.V Comp 24.0 FLA 88.0 LRA 1 PH 40 Max. Fuse Size 30 Min Circuit Ampacity 230 Volts 40A Fuse

Air Condition & Refrigeration Equipment Short Circuit & Ground Fault Protection : 

Air Condition & Refrigeration Equipment Short Circuit & Ground Fault Protection What size of conductor and protection is required for 24 A motor compressor connected to 240 V circuit? Step 1. Branch Circuit Conductor 24 x 1.25 = 30 A, rated 30A at 75oC Step 2. Branch Circuit Protection 24 x 1.75 = 42 A, what is the rating of protective device? Next size down = 40 A since Sec. 4.40.3.2(a) does not indicate that the next higher standard rating may be used. If the 40A protection device isn’t capable of carrying the starting current, then the protection device can be sized up to 225% of the equipment load current rating. 24 x 2.25 = 54 A.

Example Calculation for Sealed Hermetic Motor Compressor : 

Example Calculation for Sealed Hermetic Motor Compressor Size the protective devices & cable for the circuit components of a sealed hermetic motor compressor with a nameplate current rating of 10 A. 1. The full-load current used for all calculation for a sealed hermetic motor compressor is the current marked on the unit’s nameplate. 2. For continuous operation, the branch circuit conductors must have at least equal to 125% of 10 A or 13 A. 3. Conductors for branch circuit must, therefore, be not smaller than 2mm2 (Type TW or THW). P 3.5

Example Calculation for Sealed Hermetic Motor Compressor : 

Example Calculation for Sealed Hermetic Motor Compressor 4. Running overload protection from overload relays in the starter must have a rating or setting not over 140% of full-load (nameplate) current rating. This calls for an overload relay set to trip at 1.4 x 10 A, or 14 A. 5. The max. fuse rating for short circuit protection for a hermetic motor compressor is 175% of the motor nameplate full-load current rating, which is 1.75 x 10 A or 17.5 A. That would indicate the used of 20 A fuses. P 3.6 Where Sec.4.40.3.2(a) does not indicate that the next higher standard sizes or ratings of fuse may be used, but it does permit up to 225% of the motor current where needed for starting of the motor.

Disconnecting Means Section 4.30.10.2 : 

Disconnecting Means Section 4.30.10.2 P 3.20 Basic Rule Driven Machinery Motor Disconnecting means w/in sight from motor & driven machinery Disconnect means Disconnect means Controller Individual disconnecting means shall be located in sight from each controller location. This additional switch is not needed if disconnect ahead of starter is lock-open type. (a) (b)

Disconnecting Means Section 4.30.10.3 : 

Disconnecting Means Section 4.30.10.3 P 612 Operation. The disconnecting means shall open all ungrounded supply conductors & shall be designed so that no pole can be operated independently. The disconnecting means shall be permitted in the same enclosure with the controller. Branch Circuit Short Circuit & Ground Fault Protection Motor Overload Protection Motor Controller Disconnecting Means

Disconnecting Means Section 4.30.10.10 : 

Disconnecting Means Section 4.30.10.10 P 614 Ampere Rating & Interrupting Capacity. (a) General. The disconnecting means for motor circuits rated 600 volts, nominal, or less, shall have an ampere rating of at least 115% of the full-load current rating of the motor. (b) Torque Motors. Disconnecting means for torque motor shall have an ampere rating of at least 115% of the motor nameplate current. (c) For Combination Loads. Where two or more motors are used together or where one or more motors are used in combination with other loads, such as resistance heaters, & where the combined load may be simultaneous on a single disconnecting means, the ampere & horsepower ratings of the combined load shall be determined as follows:

Disconnecting Means Section 4.30.10.10 : 

Disconnecting Means Section 4.30.10.10 P 615 (c) For Combination Loads. (1) The rating of the disconnecting means shall be determined from the sum of all currents, including resistance loads, at the full load condition & also at the locked-rotor condition. The full load current equivalent to the hp rating of each motor shall be selected from Tables 4.30.14.1, 4.30.14.2, 4.30.14.3, or 4.30.14.4. The locked-rotor current equivalent to the hp rating of each motor shall be selected from Table 4.30.14.5(a) or 4.30.14.5(b). The locked-rotor currents shall be added to the rating in amperes of other loads to obtain an equivalent locked-rotor current for the combined loads.

Disconnecting Means Section 4.30.10.10 : 

Disconnecting Means Section 4.30.10.10 PEC 1 2000, p615 (c) For Combination Loads. (2) The ampere rating of the disconnecting means shall not be less than 115 % of the sum of all currents at the full load condition determined in accordance with Sec. 4.30.10.10(c)(1). Exception: A listed nonfused motor circuit switch having a horsepower rating equal to or greater than the equivalent horsepower of the combined loads, determined in accordance with Sec.4.30.10.10(c)(1), shall be permitted to have an ampere rating less than 115% of the sum of all currents at the full load condition.

Table 4.30.14.5(b) Conversion Table of Polyphase Design BCD & E Max. Locked-Rotor Currents for Sel. of Disconnecting Means & Controller as Det. fr. Hp : 

Table 4.30.14.5(b) Conversion Table of Polyphase Design BCD & E Max. Locked-Rotor Currents for Sel. of Disconnecting Means & Controller as Det. fr. Hp p627 Rated Max. Motor Locked-Rotor Current in Amp. 3-Phase, Design B,C,D & E Hp 115 Volts 208 Volts 230 Volts 460 Volts B,C,D E B,C,D E B,C,D E B,C,D E 1/2 40 40 22.1 22.1 20 20 10 10 3/4 50 50 27.6 27.6 25 25 12.5 12.5 1 60 60 33 33 30 30 15 15 1-1/2 80 80 44 44 40 40 20 20 2 100 100 55 55 50 50 25 25 3 -- -- 71 81 64 73 32 36.5 5 -- -- 102 135 92 122 46 61 7-1/2 -- -- 140 202 127 183 63.5 91.5

Example of Disconnect for Combination Load : 

Example of Disconnect for Combination Load Assume a load consists of one 5hp, one 3hp, and two 1/2hp motors, plus a 10 kw heater, all rated 240 V, 3 phase, 60 hz. All motors are design B motors. Determine the size of disconnect. Motor & other load Table Current (A) 5 hp 4.30.14.4 15.2 3 hp 4.30.14.4 9.6 1/2 hp 4.30.14.4 2.2 1/2 hp 4.30.14.4 2.2 10 kw (10 x 1000)/(240 x 1.732) 24.1 Total 53.3 Sol’n.: Calculation of equivalent Full Load Current Rating

Example of Disconnect for Combination Load : 

Example of Disconnect for Combination Load Motor & other load Table Current (A) 5 hp 4.30.14.5(b) 92 3 hp 4.30.14.5(b) 64 1/2 hp 4.30.14.5(b) 20 1/2 hp 4.30.14.5(b) 20 10 kw (10 x 1000)/(240 x 1.732) 24.1 Total 220.1 Calculation of equivalent Locked Rotor Current Rating:

Example of Disconnect for Combination Load : 

Example of Disconnect for Combination Load Minimum ampere rating of Disconnect = 1.15 x 53.3 = 61.3 A Using Table 4.30.14.5(b) to obtain equivalent hp = 15 hp ( locked rotor current 232 A which is more than 220.1 A, but Table 4.30.14.4 FLA = 42A is less than 53.3A.) General purpose switch satisfies the minimum hp requirement but fail to satisfy the minimum current requirement of 61.3 A (53.3). Therefor, the next larger size disconnect switch must be used which is 20hp. 54 A (over 53.3 A), locked rotor 290 A Based on Sec.4.30.10.10(c)(2) Exception: A listed non-fused motor circuit switch having a horsepower rating equal to or greater than the equivalent horsepower of the combined loads, determined in accordance with Section 4.30.10.10(C)(1), shall be permitted to have an ampere rating less than 115% of the sum of all currents at the full load condition. NEC2002,p548

Load Break Switch Disconnector Specification : 

Load Break Switch Disconnector Specification Thermal current Ith 100 A 125A 160A Rated operational current Ie A/B A/B A/B 400 V AC AC 21A / AC 21B 100 / 100 125 / 125 160 / 160 AC 22A / AC 22B 100 / 100 125 / 125 160 / 160 AC 23A / AC 23B 63 / 63 63 / 63 160 / 160 WITHSTAND (AC 23A) Mechanical (No. of operation) 20000 20000 10000 Electrical (No. of operation) 1500 / 300 1000 / 200 1000 / 200 Sirco vm, socomec

Utilization Categories : 

Utilization Categories Nature of Utilization categories current Category A Category B Typical applications AC-20A* AC-20B* -Connecting & disconnecting under no-load conditions Alternating AC-21A AC-21B -Switching of resistive loads including moderate overloads Current AC-22A AC-22B -Switching of mixed resistive & inductive loads, including moderate overloads AC-23A AC-23B -Switching of motor loads or other highly inductive loads IEC 60947-3 p27 * The use of these utilization categories is not permitted in the U.S.A.

Utilization Category : 

Utilization Category The designation of utilization categories is completed by suffix A or B according to whether the intended applications require frequent or infrequent operations. Utilization categories with suffix B are appropriate for devices which, due to design or application, are only intended for infrequent operation. This could apply, for example, to disconnectors normally only operated to provide isolation for maintenance work or switching devices where fuse-link blade forms the moving contact. IEC 60947-3 p25

Verification of rated making & breaking capacities : 

Verification of rated making & breaking capacities Utilization Rated oprn’l Making Breaking Number of category current I/Ie U/Ue cos q Ic/Ie Uf/Ue cos q oprt’g cycle AC-20A/B All Values AC-21A/B All Values 1.5 1.05 0.95 1.5 1.05 0.95 5 AC-22A/B All Values 3 1.05 0.65 3 1.05 0.65 5 AC-23A/B 0< Ie £100 A 10 1.05 0.45 8 1.05 0.45 5 100 A < Ie 10 1.05 0.35 8 1.05 0.35 3 Conditions for making & breaking corresponding to various utilization categories IEC 60947-3 p37

Feeder Tap Conductors Sec. 4.30.2.8 : 

Feeder Tap Conductors Sec. 4.30.2.8 Motor Controller Motor Branch Circuit Short Circuit & Ground Fault Protection Feeder Short Circuit & Ground Fault Protection Feeder Conductor Feeder Tap Conductor Branch Circuit Conductors Feeder tap conductors shall have an ampacity not less than that required by Part 4.30.2, shall terminate in a branch circuit and, in addition, shall meet one of the following requirements:

Feeder Tap Conductors Sec. 4.30.2.8 : 

Feeder Tap Conductors Sec. 4.30.2.8 (1) Be enclosed by either an enclosed controller or by a raceway, be not more than 3000 mm in length, and, for field installation, be protected by an overcurrent device on line side of the tap conductor, the rating or setting of which shall not exceed 1000% of tap conductor capacity (2) Have an ampacity of at least one-third that of the feeder conductors, be suitably protected from physical damage or enclosed in a raceway, and be not more than 7600 mm in length (3) Have the same ampacity as the feeders conductors p586

Motor Circuit Conductors Sec. 4.30.2.4 : 

Motor Circuit Conductors Sec. 4.30.2.4 Several Motors or a Motor(s) & Other Load(s) p584 Conductors supplying several motors, or a motor and other load, shall have an ampacity at least equal to the sum of the full-load current rating of all the motors, plus 25% of the highest rated motor in the group, plus the ampere rating of other loads . Motor Controller Motor Feeder Conductor Feeder Tap Conductor Branch Circuit Conductors Branch Circuit short Circuit & Ground Fault Protection Feeder Short Circuit & Ground Fault Protection

Motor Feeder Short-Circuit & Ground-Fault Protection, Sec. 4.30.5.2 : 

Motor Feeder Short-Circuit & Ground-Fault Protection, Sec. 4.30.5.2 Rating or Setting - Motor Load. (a) Specific Load. A feeder supplying a specific fixed motor load(s) & consisting of conductor sizes based on Sec. 4.30.2.4 shall be provided with protective device having a rating or setting not greater than the largest rating or setting of the branch-circuit short-circuit & ground-fault protective device for any motor supplied by the feeder [based on the maximum permitted value for the specific type of a protective device shown in Table 4.30.14.6, or Sec. 4.40.3.2(a) for hermitic refrigerant motor-compressors], plus the sum of the other motors of the group. p600 4.30.5.3

Example of Feeder Protection : 

Example of Feeder Protection p473 Motor Controller Motor Feeder Conductor Feeder Tap Conductor Branch Circuit Conductors Branch Circuit short Circuit & Ground Fault Protection Feeder Short Circuit & Ground Fault Protection 20 hp 10 hp What is the size of feeder protection (inverse time CB with 75oC terminals) & conductor are required for the following two motors? Motor 1 - 20hp, 460V, 27A Motor 2 - 10hp, 460V, 14A

Example of Feeder Protection : 

Example of Feeder Protection p473 Step 1. Feeder Conductor Size ( 27A x 1.25 ) + 14 A = 48 A Use 8 mm2 rated 50A at 75oC Step 2. Branch Circuit protective device 20hp Motor = 27A x 2.5 = 68A, use next size up = 70A 10hp Motor = 14A x 2.5 = 35A Step 3. Size of Feeder Protection 70A + 14A = 84A Next size down = 80A, The next size up protection rule for branch circuit Exception 1 does not apply to feeder protection device sizing.

Motor Feeder Short-Circuit & Ground-Fault Protection, Sec. 4.30.5.2 : 

Motor Feeder Short-Circuit & Ground-Fault Protection, Sec. 4.30.5.2 Rating or Setting - Motor Load. (b)Other Installations. Where feeder conductors have an ampacity greater than required by Section 4.30.2.4, the rating or setting of the feeder overcurrent protective device shall be permitted to be based on the ampacity of the feeder conductors. p600

Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection : 

Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection P 5.5 5 Hp 10 Hp 25 Hp 25 Hp 18 A 32 A 78 A 78 A Nontime delay fuse Time delay fuse 3 phase, 200 V, 60 Hz., squirrel cage induction motors Time delay fuse Time delay fuse

Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection : 

Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection P 5.5 1) The feeder conductors must have a carrying capacity that is computed as follows: (1.25 x 78) +78 + 32 +18 = 225.5 A , used 125 mm2 THW 2) Branch circuit protection 2-1) Nontime delay fuse= 300% x 78 = 234 A, used 250 A fuse 2-2) Time delay fuse = 175% x 78 = 136.5 A , used 150 A fuse 2-3) Time delay fuse = 175% x 32 = 56 A, used 60 A fuse 2-4) Time delay fuse = 175% x 18 = 31.5 A, used 35 A fuse

Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection : 

Ex. On Motor Feeder Short-Circuit & Ground-Fault Protection P 5.5 3) Feeder Protection The maximum rating or setting for the overcurrent device protection must not be greater than the largest rating or setting of branch circuit protective device plus the sum of the full-load currents of the other motors. 250 + 78 + 32 + 18 = 378 A Used 350 A Fuse or Circuit Breaker

Motor Control Centers Section 4.30.8.3 : 

Motor Control Centers Section 4.30.8.3 Motor control centers shall be provided with overcurrent protection in accordance with Article 2.40 based on the rating of the common power bus. This protection shall be provided by (1) an overcurrent protective device located ahead of the motor control center or (2) a main overcurrent protective device located within the motor control center. Overcurrent Protection. p608

Series Ratings Sec.2.40.7.7 : 

Series Ratings Sec.2.40.7.7 Series Ratings. Where a circuit breaker is used on a circuit having an available fault current higher than its marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having higher rating, the following shall apply. (b) Motor Contribution. Series ratings shall not be used where: (1) Motors are connected on the load side of higher rated overcurrent device and on the line side of the lower rated overcurrent device, and (2)The sum of the motor full load currents exceeds 1% of the interrupting rating of the lower rated circuit breaker. p153

Series Ratings Sec.2.40.7.7 : 

Series Ratings Sec.2.40.7.7 NEC 2002 p169 M Motor Contribution Fault Series combination: 22 kA interrupting rating 10kA

Slide 105: 

Thank You Very Much for Listening

authorStream Live Help