SECTION 26 2419 – MOTOR CONTROL CENTERS

SUPPLEMENTAL INFORMATION

Motor Controller Overview

Motor controllers are defined in NFPA 70 (NEC) as “any switch or device that is normally used to start and stop a motor by making and breaking the motor circuit current”. The controller might utilize manual or automatic means to start and stop the motor and might also perform other supplementary functions including:

  • Providing motor overload protection and/or motor branch-circuit short-circuit and ground-fault protection.
  • Allowing for selection of forward or reverse motor rotation.
  • Allowing for selection of multiple motor speeds.
  • Allowing for motor jogging or inching, which provide for momentary motor operation for the purposes of performing small movements.
  • Allowing for motor plugging, which provides for momentary reversal of motor rotation for the purposes of braking.

Motor starters are a form of motor controller that include the switching means necessary for starting and stopping the motor in combination with overload protection. Manual motor starters utilize contacts that are directly operated by mechanical means when a toggle switch or pushbutton is actuated by hand. Magnetic motor starters utilize a contactor with an electromagnetic coil, which may be electrically operated by control devices actuated by hand (either locally or remotely) or by automatic means. Combination motor starters combine a magnetic motor starter with an externally operable disconnecting means in a common enclosure. A contactor alone (without additional integral overload protection) might be utilized for motor control where overload protection is provided separately or where the motor contains integral thermal protectors.

Magnetic motor starters are classified by their starting methods, which are described in NEMA ICS 2 - Industrial Control and Systems Controllers, Contactors and Overload Relays Rated 600 Volts. Full-voltage starters are often called "across-the-line" starters because they apply full line voltage to start the motor. This results in a high starting current (typically 600 percent of full load current for standard motors, and higher for high-efficiency motors) and high starting torque. Reduced-voltage starters use various methods to limit starting current and/or torque. Reduced-voltage starting is commonly applied to larger motors, often to comply with utility company requirements for limiting line voltage dip. Multi-speed starters reconnect motor windings to achieve selected speeds. Reversing starters reconnect motor windings for rotation in either direction. Keep in mind that certain starting methods can only be applied to compatible motors with special winding arrangements. Common available starter configurations include:

  • Full-voltage non-reversing.
  • Full-voltage reversing.
  • Two-speed, one-winding (constant horsepower or constant/variable torque).
  • Two-speed, two-winding (constant horsepower or constant/variable torque).
  • Reduced-voltage autotransformer.
  • Reduced-voltage part-winding.
  • Reduced-voltage wye delta (open or closed transition).

Motor Protective Devices

Overcurrent protection for motors consists of protection against faults, such as short circuits and ground-faults, and protection against overloads. This protection is usually provided by a combination of fuses or circuit breakers for fault protection and overload relays for overload protection, though in some cases protection requirements may be satisfied by a single device. Overloads are defined in NFPA 70 (NEC) as “the operation of equipment in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating.” Causes of motor overloads include:

  • Locked rotor condition.
  • Load exceeds motor torque rating.
  • Bad bearings.
  • Low line voltage.
  • Loss of phase on polyphase motor.

Overload relays are reusable and resettable and are of either the thermal or solid-state electronic type. Thermal overload relays utilize interchangeable current elements called “heaters”. Current elements/heaters use either a melting eutectic alloy (solder) or a bimetallic strip to open contacts and remove power from the motor upon sensing excessive heat from an overload condition. Solid-state electronic overload relays do not sense heat but rather use a specific measured current to determine overload conditions. Considerations for selection of overload relays include:

  • Melting alloy thermal overload relays must be manually reset, while bimetallic thermal and solid-state electronic overload relays often allow for selection of manual or automatic reset, or allow for remote reset.
  • Bimetallic thermal overload relays are available with ambient temperature compensation to ensure consistent operation where the motor is at a constant ambient temperature and the controller/overload relay is located elsewhere with varying ambient temperature conditions. Ambient temperature compensation is not required where the controller/overload relay is at a constant ambient temperature and the motor is located in a varying ambient temperature, nor if the controller/overload relay and motor are both located together in the same varying ambient temperature. Melting alloy thermal overload relays are not available with ambient temperature compensation. Solid-state electronic overload relays are not affected by ambient temperature.
  • Inverse-time overload relay trip class ratings (e.g. Class 10, 20, and 30) identify the maximum time in seconds for an overload relay to trip at 600 percent of its current rating (i.e. Class 20 relays will trip in 20 seconds or less at 600 percent of rated current). Melting alloy thermal overload relays have fixed trip class and current ratings according to selected heater elements. Bimetallic thermal overload relays have a fixed trip class rating but often allow for slight adjustment of current rating. Solid-state electronic overload relays have an adjustable current rating and often also allow for selection of trip class rating.
    • 1) Class 20 (standard trip) is usually suitable for most general motor applications.
    • 2) Class 30 (slow trip) may be suitable for motors driving high inertia loads requiring extended starting periods.
    • 3) Class 10 (quick trip) may be suitable for hermetically sealed, submersible pump, and other motors which can only endure locked rotor current for a very short time, or motors which have a low ratio of locked rotor to full load current.
  • Solid-state electronic overload relays often include additional features such as phase loss protection, phase unbalance protection, and ground fault detection. Bimetallic thermal overload relays may be designed for a quicker trip response under a phase loss condition to provide limited protection.

Disconnects for combination motor starters are of either the fusible switch or circuit breaker type. Circuit breaker disconnects use either motor circuit protectors or thermal magnetic circuit breakers. Motor circuit protectors are instantaneous-trip (magnetic-only) circuit breakers furnished with magnetic instantaneous tripping elements for short circuit protection, but not thermal inverse time tripping elements for overload protection (thermal magnetic circuit breakers are furnished with both types of tripping elements). Motor circuit protectors are only permitted for use as part of a listed combination motor controller with overload protection.

NEMA vs IEC Motor Controllers

Motor controllers are designed to meet standards published by either NEMA (National Electrical Manufacturers Association) or IEC (International Electrotechnical Commission).

NEMA/IEC motor controller comparison:

  • NEMA controllers are available in a relatively small number of standard controller sizes, designed conservatively for use in a broad range of applications. For example, one NEMA table lists 11 sizes (from size 00 through size 9) to cover motors from 2 Hp through 1600 Hp at 460V. IEC controllers do not come in standard sizes, but rather are selected based on assigned ratings and utilization categories for a specific and narrowly defined range of applications.
  • NEMA controllers are generally more robust devices than IEC controllers. NEMA contactor coils are commonly encapsulated for protection from contaminates and IEC contactor coils are commonly tape-wound.
  • NEMA controllers often have replaceable parts for improved maintainability over IEC controllers, which typically offer replaceable contacts only on larger horsepower-rated controllers.
  • NEMA controllers typically include factory assembly of contactors and overload relays, along with control and power circuit wiring. IEC controllers often involve field assembly of these components.
  • NEMA controllers are generally significantly more expensive than IEC controllers.
  • NEMA controllers are generally significantly larger than IEC controllers.

For a more in-depth evaluation of NEMA and IEC controllers, refer to NEMA ICS 2.4 – NEMA and IEC Devices for Motor Service-A Guide for Understanding the Differences.

NEMA motor controllers are most commonly specified in North America and IEC motor controllers are predominant in Europe, Asia, and most other global markets. IEC controller use in North America is primarily for installation in manufactured products and/or control panel assemblies by original equipment manufacturers (OEMs). Consequently the section text and this supporting document describe only NEMA controllers.

NEMA Motor Control Centers

Motor control centers are defined in NFPA 70 (NEC) as “an assembly of one or more enclosed sections having a common power bus and principally containing motor control units.” They provide an alternative to grouping individual enclosed motor controllers in a common location. Motor control centers may contain a combination of equipment including:

  • Main overcurrent protective device
  • Feeder units
  • Combination magnetic motor starter units
  • Solid-state reduced voltage motor starter units
  • Variable-frequency AC drive units
  • Programmable logic control (PLC) units
  • Power factor correction capacitor units
  • Distribution transformers and/or panelboards
  • Metering
  • Surge protective devices

Wiring classes and types for NEMA motor control centers (MCCs) are defined in NEMA ICS 18 – Motor Control Centers.

NEMA Wiring Classes:

  • Class I - Independent Units:  The manufacturer does not provide interlocking and wiring between units. The manufacturer furnishes standard drawings and standard wiring diagrams for individual units and master terminal blocks (where applicable, see Type C wiring below).
  • Class II - Interconnected Units:  The manufacturer provides interlocking and wiring between units according to specified control requirements. In addition to the standard drawings and wiring diagrams furnished for Class I MCCs, the manufacturer also furnishes drawings indicating factory interconnections within the MCC.
  • Class I-S and II-S - Motor Control Centers with Custom Drawing Requirements:  These are the same as for Class I and Class II described above except the manufacturer provides custom drawings per user-specified requirements in lieu of standard drawings.

NEMA Wiring Types:

  • Type A:  User field wiring (both power and control) connects directly to device terminals; no terminal blocks are provided; applicable only to Class I MCCs.
  • Type B:  User field control wiring connects to terminal blocks in or adjacent to unit (manufacturer wires from device terminals to unit terminal blocks). User field power wiring for combination motor control units larger than size 3, and for feeder tap units, connects directly to device terminals. User field power wiring for combination motor control units size 3 or smaller connects according to two subcategories:
    • 1. Type B-D:  User field power wiring connects directly to device terminals.
    • 2. Type B-T:  User field power wiring connects to terminal blocks in or adjacent to unit (manufacturer wires from device terminals to unit terminal blocks).
  • Type C:  User field control wiring connects to master terminal blocks at the top or bottom of a vertical section (manufacturer wires from device terminals to master terminal blocks). User field power wiring for combination motor control units larger than size 3, and for feeder tap units, connects directly to device terminals. User field power wiring for combination motor control units size 3 or smaller connects to master terminal blocks at the top or bottom of a vertical section (manufacturer wires from device terminals to master terminal blocks).

Arc-resistant motor control centers are available to reduce arc flash risk for personnel by containing and redirecting incident energy. IEEE C37.20.7 provides methods for testing switchgear for arc-resistant functionality. Although this standard does not specifically address motor control centers, it is commonly applied for that purpose. A revision to the standard incorporating an annex covering motor control centers has been proposed. IEEE C37.20.7 defines accessibility types, which may include suffix designations:

  • Type 1:  Arc-resistant functionality at the front of equipment only.
  • Type 2:  Arc-resistant functionality at the front, rear, and sides of the equipment only.
  • Suffix B:  Arc-resistant functionality is maintained in designated low-voltage compartments.
  • Suffix C:  Arc-resistant functionality in compartments adjacent to the compartment in which the arc occurs.

Motor Control Circuits

Most motor control circuits utilize either two-wire control or three-wire control. Two-wire control employs maintained contact control devices and three-wire control employs momentary contact devices. Two-wire control circuits provide low-voltage release, which is the automatic restarting of the motor after a power interruption and subsequent power restoration. Three-wire control circuits provide low-voltage protection, which requires the motor to be manually restarted after a power interruption and subsequent power restoration. Two-wire control is applied where automatic restarting of the motor after power interruption is desirable, and three-wire control is applied where automatic restarting of the motor after power interruption could create a hazardous condition for the operator.

Auxiliary contacts are often provided as a standard feature on magnetic motor starters or are available as an optional accessory. The auxiliary contacts operate in unison with the main power contacts and are used to perform various control and/or status indication functions, such as providing a holding circuit to keep the starter contactor coil energized after a momentary contact start pushbutton operator has been released.

Pilot devices provide local control and/or status indication for motor controllers and may include pushbuttons, selector switches, and indicating (pilot) lights. Pushbuttons and selector switches use manually controlled operators to open and close contacts. Pushbuttons are typically momentary-contact type (i.e. contacts change state upon button press and return to their normal state upon button release) and selector switches are typically maintained-contact type (i.e. contacts remain in their current state until a manual change in switch position). Pushbuttons may be furnished with or without illumination and are available with a variety of button operator styles (e.g. flush, extended). Selector switches may be furnished with knob, lever, or key operators and are available in multiple configurations (e.g. 2-position, 3-position, etc.). Indicating lights may be furnished with LED, incandescent, or neon lamp sources and are available with lenses in a variety of colors or clear. Devices may be standard or heavy duty (as defined in NEMA ICS 5) and are generally available in two nominal sizes, 22 mm and 30 mm.

Control and timing relays are used in motor control circuits to perform various functions. Timing relays may be pneumatic or solid-state, with timed contacts applied for either on or off delay. Pneumatic timing relay timing period is controlled by the rate at which air moves through an adjustable or fixed orifice.

Control power transformers are used to deliver control power to the motor controller at the appropriate voltage. They are sized to accommodate the burden of all connected contactor coil(s) and auxiliary devices, and often include designated spare capacity. Control power may also be derived at line voltage or from a separate control power source.

Sequencing control involves the interconnection of magnetic starter control circuits to start and stop a number of separate motors in a definite sequence. Sequencing control is often applied to prevent large inrush currents resulting from multiple motors starting at the same time.

NFPA 70 (NEC) Requirements

Article 430 contains requirements for motors, motor circuits, and motor controllers, including parts specifically covering the following subjects:

  • Motor Circuit Conductors (Part II)
  • Motor and Branch-Circuit Overload Protection (Part III)
  • Motor Branch-Circuit Short-Circuit and Ground-Fault Protection (Part IV)
  • Motor Feeder Short-Circuit and Ground-Fault Protection (Part V)
  • Motor Control Circuits (Part VI)
  • Motor Controllers (Part VII)
  • Motor Control Centers (Part VIII)
  • Disconnecting Means (Part IX)
  • Adjustable-Speed Drive Systems (Part X)

Article 440 contains requirements for air-conditioning and refrigeration equipment and associated branch circuits and controllers, including special considerations necessary for hermetic refrigerant motor-compressors.

Key Requirements:

  • NEC 430.6 requires conductor ampacity and branch-circuit short-circuit and ground-fault overcurrent devices for general motor applications to be selected from specific tables (not from motor nameplate values). It also requires motor overload protection to be selected based on motor nameplate current rating (not from specific tables).
  • NEC 430.75 requires a disconnecting means for motor control circuits that, where separate from the motor controller disconnecting means, must be located adjacent to the motor controller disconnect.
  • NEC 430.87 requires each motor to have its own individual controller (with certain exceptions).
  • NEC 430.102 requires a disconnecting means for each motor controller located within sight of the controller (with certain exceptions). It also requires a disconnecting means for each motor located within sight of the motor and the driven machinery (with certain exceptions). It permits the controller disconnect to also serve as the motor disconnect, if it is also located within sight of the motor.
  • NEC 430.107 requires at least one of either the controller disconnecting means or the motor disconnecting means to be readily accessible.

Other Applicable Standards

IEEE C37.20.7 – IEEE Guide for Testing Metal-Enclosed Switchgear Rated up to 38 kV for Internal Arcing Faults; provides basis for testing and rating of arc-resistant motor control centers.

NECA 402 - Standard for Installing and Maintaining Motor Control Centers.

NEMA 250 - Enclosures for Electrical Equipment (1000 Volts Maximum); classifies enclosure types according to degree of protection provided; common NEMA types available for motor control center enclosures include:

  • Type 1:  Indoor use; provides a degree of protection against ingress of falling dirt.
  • Type 2:  Indoor use; provides a degree of protection against ingress of falling dirt and dripping and light splashing of water.
  • Type 3R:  Indoor or outdoor use; provides a degree of protection against ingress of falling dirt, rain, sleet, and snow; undamaged by external formation of ice on the enclosure.
  • Type 12:  Indoor use (without knockouts); provides degree of protection against ingress of falling dirt, circulating dust, lint, fibers, and flyings, dripping and light splashing of water, and light splashing and seepage of oil and non-corrosive coolants.

NEMA ICS 1 - Industrial Control and Systems General Requirements; describes usual service conditions for industrial control and systems equipment, including altitude and ambient temperature limits.

NEMA ICS 2 - Industrial Control and Systems Controllers, Contactors and Overload Relays Rated 600 Volts; includes parts specifically covering the following subjects:

  • General Standards for Manual and Magnetic Controllers (Part 1).
  • AC Noncombination Magnetic Motor Controllers Rated 600 Volts (Part 2).
  • Nonmagnetic Motor Controllers (Part 3).
  • Overload Relays (Part 4).
  • AC Combination Motor Controllers (Part 6).
  • Disconnect Devices for Use in Industrial Control Equipment (Part 8).

NEMA ICS 2.3 - Instructions for the Handling, Installation, Operation, and Maintenance of Motor Control Centers.

NEMA ICS 5 - Industrial Control and Systems:  Control Circuit and Pilot Devices; includes parts specifically covering the following motor control components:

  • Industrial Control Relays (Part 2).
  • Pushbuttons, Selector Switches, Indicating Lights, and Pushbutton Stations (Part 5).

NEMA ICS 6 - Industrial Control and Systems:  Enclosures (references NEMA 250 for enclosure types, described above).

NEMA ICS 18 – Motor Control Centers; includes definitions of wiring classes and types (see NEMA Motor Control Centers above for detailed descriptions).

NEMA KS 1 - Heavy Duty Enclosed and Dead-Front Switches (600 Volts Maximum).

NETA ATS – Acceptance Testing Specifications for Electrical Power Equipment and Systems; includes the following applicable sections:

  • Section 7.5.1.1 – Switches, Air, Low-Voltage.
  • Section 7.6.1.1 – Circuit Breakers, Insulated-Case/Molded-Case.
  • Section 7.10 – Instrument Transformers.
  • Section 7.11.2 – Metering Devices, Microprocessor-Based.
  • Section 7.14 – Ground-Fault Protection Systems, Low-Voltage.
  • Section 7.16.1.1 – Motor Control, Motor Starters, Low-Voltage.
  • Section 7.16.2.1 – Motor Control, Motor Control Centers, Low-Voltage.

UL 98 - Enclosed and Dead-Front Switches.

UL 489 - Molded-Case Circuit Breakers, Molded-Case Switches and Circuit Breaker Enclosures.

UL 845 - Motor Control Centers.

UL 869A - Reference Standard for Service Equipment.

UL 1053 - Ground-Fault Sensing and Relaying Equipment.

How to Specify

Start under PART 2, progress to PART 3, and finish up with PART 1.

PART 2:
MANUFACTURERS Article:  Specify acceptable manufacturers. A basis of design manufacturer or product may be specified if applicable.

MOTOR CONTROL CENTERS Article:

“Description” Paragraph:  Indicate whether or not motor control centers are arc-resistant type. Before specifying arc-resistant motor control centers, consider the additional cost of equipment and design issues related to discharge of arc flash gases which often involves a plenum and associated ductwork to a designated area, usually outdoors.

“Configuration” Paragraph:
•    Indicate arrangement. Use option “front-mounted units, front- and rear-mounted units, or back-to-back configuration as indicated” if arrangement is indicated on drawings.
•    Select NEMA classification and wiring type. See NEMA Motor Control Centers above for detailed descriptions. Class I, Type B wiring is generally the most common. Class II wiring may be appropriate where more complex interconnection and remote control is involved, keeping in mind that the additional manufacturer engineering and factory wiring generally adds to both cost and lead time.

“Arc-Resistance Rating” Paragraph:

  • Paragraph is turned on automatically via linking based on type selected in “Description” paragraph.
  • Indicate required IEEE C37.20.7 accessibility type. See NEMA Motor Control Centers above for descriptions.
  • Indicate whether or not arc exhaust gases must be discharged through a plenum to a designated area.

Include “Service Entrance Motor Control Centers” paragraph where applicable.

Include “Motor Control Centers with Busway Transitions” paragraph where applicable.

“Service Conditions” Paragraph:  NEMA ICS 1 (referenced by NEMA ICS 18) describes usual service conditions for industrial control and systems equipment, including altitude and ambient temperature limits. Consult manufacturer for unusual service conditions and edit paragraphs accordingly.

“Short Circuit Current Rating” Paragraph:  Motor control center sections and units are each assigned short circuit current ratings independently. Combination motor control units may be assigned a short circuit current rating that is higher than the interrupting capacity of the overcurrent protective device in the unit. Series ratings are permitted (as described in NEMA ICS 18), but are not commonly applied. NFPA 70 (NEC) 240.86 includes requirements for application of series ratings, including limitations on motor contribution.

  • Indicate whether the available fault current or short circuit current rating are indicated on the drawings or are to be determined by a short circuit study performed in accordance with Section 26 0573 – Power System Studies.
  • An optional minimum rating may be specified.
  • Indicate whether or not series ratings are permitted.

Include “Selectivity” paragraph where applicable. Among other applications, selective coordination may be required to comply with NFPA 70 (NEC) requirements for emergency systems (see Article 700), legally required standby systems (see Article 701), or critical operations power systems (see Article 708). NEMA ABP 1 – Selective Coordination contains useful information on selective coordination.

Include “Main Devices” paragraph where applicable.

“Bussing” Paragraph:

  • “Horizontal Main Bus” Paragraph:  NEMA ICS 18 includes temperature rise requirements for motor control centers. Horizontal bus requires a temperature rise not exceeding 65 degrees C (117 degrees F), which is the default choice option. The second choice option of 50 degrees C (90 degrees F) may be available as an option from certain manufacturers. Verify availability with listed manufacturers.
  • “Vertical Bus” Paragraph:  NEMA ICS 18 requires a minimum vertical bus rating of 300 A, which is the default choice option. The second choice option of 600 A and other bus ratings higher than the minimum may be available as an option from certain manufacturers. Verify availability with listed manufacturers.
  • Select option for neutral conductor terminations where applicable.
  • An optional vertical ground bus may be specified for each motor control center section in addition to standard horizontal ground bus.
  • Select option for phase, neutral, and ground bus material. Copper is typically standard, but aluminum may be offered by certain manufacturers for cost savings.

“Conductor Terminations” Paragraph:  Specify main and neutral lug material and type. Aluminum lugs are typically standard with copper lugs offered as an optional feature for an additional cost. Since copper lugs are not suitable for use with aluminum conductors, do not specify them unless only copper conductors will be used. Mechanical lugs are typically standard with compression lugs offered as an optional feature for an additional cost.

“Enclosures” Paragraph:

  • Specify default enclosure environment types per NEMA 250 (see description under Other Applicable Standards above), where not indicated on drawings.
  • Include enclosure space heaters where applicable. These may be appropriate outdoors or in unconditioned indoor spaces to prevent condensation.

Include “Surge Protective Devices” paragraph if motor control center may contain factory-installed, internally mounted surge protective devices. Coordinate with Section 26 4300 - Surge Protective Devices.

Include “Ground Fault Protection” paragraph where applicable. Among other applications, ground fault protection may be required to comply with NFPA 70 (NEC) 215.10, 230.95, and 240.13. NEMA PB 2.2 - Application Guide for Ground Fault Protective Devices for Equipment includes useful information on ground fault protection.

  • Include zone selective interlocking where applicable. NEMA ABP 1 contains useful information on selective coordination including application of zone selective interlocking. Zone selective interlocking might be one solution for complying with arc energy reduction requirements of NFPA 70 (NEC) 240.87, revised for 2014 edition to apply to any circuit breaker 1200A or higher (previously applied only to circuit breakers with non-instantaneous trip).

Include “Arc Flash Energy-Reducing Maintenance Switching” paragraph where applicable. Energy-reducing maintenance switching might be one solution for complying with arc energy reduction requirements of NFPA 70 (NEC) 240.87, revised for 2014 edition to apply to any circuit breaker 1200A or higher (previously applied only to circuit breakers with non-instantaneous trip). This requires a circuit breaker with an electronic trip unit.

Include appropriate “Owner Metering” paragraph if motor control center contains metering for Owner’s use.

  • If Owner metering is specified in Section 26 2713 – Electricity Metering, coordinate with that section.
  • If Owner metering is specified in this section, .edit measured parameters, meter accuracy, and features according to project requirements. A basis of design product may be specified if applicable.

MOTOR CONTROL CENTER UNITS Article:

Include “Feeder Units” paragraph where applicable. Select feeder unit type. Use option “circuit breaker or fusible switch type as indicated” if feeder unit types are indicated on drawings.

Include “Combination Magnetic Motor Starter Units” paragraph where applicable.

  • “Configuration” Paragraph:  Select the first choice option to specify full-voltage non-reversing as the default unit type. Select the second choice option if unit types are indicated on drawings.
  • Indicate whether or not substitution of suitable non-standard starter sizes for specified NEMA sizes is permitted. Some manufacturers offer non-standard “half-sizes” that fall between standard NEMA sizes.
  • “Disconnects” Paragraph:  Select disconnect type. Use option “circuit breaker or fusible switch type as indicated” if disconnect types are indicated on drawings. Indicate circuit breaker type where applicable. See Motor Protective Devices above for a description of differences between motor circuit protectors and thermal magnetic circuit breakers.
  • “Overload Relays” Paragraph:  Select overload relay type. See Motor Protective Devices above for descriptions of bimetallic thermal, melting alloy thermal, and solid-state overload relays.
  • “Pilot Devices Required” Paragraph:  Include this optional paragraph to specify pilot devices required for motor starters, if requirements are not clearly indicated on drawings.

Include cross references to other sections specifying motor control center unit components. Coordinate with applicable sections.

OVERCURRENT PROTECTIVE DEVICES Article:

“Overload Relays”, “Fusible Devices” and “Circuit Breakers” paragraphs are turned on automatically via linking.

“Overload Relays” Paragraph:

  • “Inverse-Time Trip Class Rating” Paragraph:  Select the first choice option to specify Class 20 as the default trip class rating. Select the second choice option if trip class ratings are indicated on drawings. See Motor Protective Devices above for description of overload relay inverse-time trip class ratings.
  • Indicate if/when automatic and/or remote reset is to be employed. Automatic or remote overload relay reset may be desirable where access to controller/overload relay is not convenient. Automatic reset should normally be limited to three-wire control arranged to prevent automatic restarting of motors, which can result in hazardous conditions for the operator or damage to motor from cycling of overload relay.
  • Edit features for applicable overload relay types (bimetallic thermal, melting alloy thermal, solid-state) according to project requirements. A basis of design product may be specified for solid-state overload relays if applicable.

“Fusible Devices” Paragraph:

  • Include “Fusible Switches” and “Fused Power-Circuit Devices” paragraphs as applicable. Fused power-circuit devices include bolted-pressure contact switches and high-pressure butt contact switches.
  • “Fused Power-Circuit Devices” Paragraph:  Edit optional features and accessories according to project requirements.

“Circuit Breakers” Paragraph:

  • “Motor Circuit Protectors” paragraph is turned on automatically via linking if specified for combination magnetic motor starter units. Edit optional features and accessories according to project requirements.
  • Include “Molded Case Circuit Breakers” and “Insulated Case Circuit Breakers” paragraphs as applicable. Insulated case circuit breakers are a type of molded case circuit breaker designed to provide features typically available in low-voltage power circuit breakers used in low-voltage switchgear. They are equipped with a two-step stored energy closing mechanism, electronic trip unit, and may be available in drawout construction.
  • “Molded Case Circuit Breakers” Paragraph:
    • 1)  Indicate application of thermal magnetic and electronic trip circuit breakers, which may be specified according to frame sizes.
    • 2)  Minimum interrupting capacity may be specified.
  • “Thermal Magnetic Circuit Breakers” Paragraph:
    • 1)  Include field-adjustable magnetic instantaneous trip setting, specified according to frame size, as applicable. Adjustable trip response settings can provide increased flexibility by allowing the time-current curve to be shaped to improve system selectivity.
    • 2)  Include interchangeable trip units as applicable.
  • “Electronic Trip Circuit Breakers” Paragraph:
    • 1)  Edit available field-adjustable trip response settings according to project requirements. Circuit breaker trip functions are often described by a combination of the abbreviations L, S, I, and G (L=Long time, S=Short time, I=Instantaneous, G=Ground fault).
    • 2)  Include zone selective interlocking capability where applicable. Zone selective interlocking might be one solution for complying with arc energy reduction requirements of NFPA 70 (NEC).
    • 3)  Include 100 percent rated or current limiting circuit breakers as applicable.
    • 4)  Edit optional features and accessories according to project requirements.
  • “Insulated Case Circuit Breakers” Paragraph:
    • 1)  Indicate application of manually and electrically operated circuit breakers.
    • 2)  Indicate application of fixed-mount and drawout circuit breakers.
    • 3)  Minimum interrupting capacity may be specified.
    • 4)  Edit available field-adjustable trip response settings according to project requirements.
    • 5)  Include zone selective interlocking capability where applicable.
    • 6)  Include 100 percent rated or current limiting circuit breakers as applicable.
    • 7)  Edit optional features and accessories according to project requirements.

MOTOR CONTROL ACCESSORIES Article:  Edit features for accessories according to project requirements. See Motor Control Circuits above for description of auxiliary contacts, pilot devices, control and timing relays, and control power transformers.

PART 3:
EXAMINATION article is optional.

INSTALLATION is turned on automatically via linking. Applicable installation requirements for components are turned on automatically via linking according to selections made under PART 2.

FIELD QUALITY CONTROL article is optional.

  • 1)  Include optional services of a manufacturer's authorized representative according to project requirements. Edit choice to indicate extent of responsibilities.
  • 2)  Applicable NETA ATS testing requirements for components are turned on automatically via linking according to selections made under PART 2.
  • 3)  Motor Starters:  Indicate if NETA ATS tests listed as optional are required.
  • 4)  Circuit Breakers:  Indicate which circuit breakers require testing and if NETA ATS tests listed as optional are required.
  • 5)  Ground Fault Protection Systems:  Indicate if NETA ATS tests listed as optional are required.

ADJUSTING, CLEANING, CLOSEOUT ACTIVITIES and PROTECTION articles are optional. Under CLOSEOUT ACTIVITIES indicate requirements for demonstration and training where applicable.

PART 1:
SECTION INCLUDES:  Corresponding components will be activated via linking according to selections made under PART 2.

RELATED REQUIREMENTS: Article will automatically include other sections cited within the specification text (except for standard Division 1 cross references). Other sections may be listed because they include items that might be expected to be found within this Section or include items important for the completion of the work that are not specified in an obvious location (e.g. isn’t obvious from the section title).

REFERENCE STANDARDS: Article will automatically include standards cited within the specification text. If the Consolidated List of Citations option is active, cross sectional links (not visible in the links window) will activate the reference standard in Section 01 4219 – Reference Standards as well.

ADMINISTRATIVE REQUIREMENTS article is optional.

SUBMITTALS: Edit according to project requirements.

QUALITY ASSURANCE: Qualifications for manufacturer and product listing organization may be included.

DELIVERY, STORAGE, AND HANDLING and FIELD CONDITIONS