1 Scope

NOTE This Standard covers low-voltage (600 V and below) pulse-width-modulated variable frequency drives furnished as individually mounted, enclosed units for adjustable-speed control of three-phase AC induction and permanent-magnet motors. (1.1)

NOTE Covered applications include process pumps, process fans, compressors, conveyors, mixers, water and wastewater treatment equipment, and general industrial, institutional, and municipal motor loads specified under the electrical division rather than embedded in a mechanical or process equipment specification. (1.2)

NOTE The scope spans drives from fractional horsepower through at least 500 HP, in wall-mount and floor-mount configurations, NEMA 1 through NEMA 4X enclosures, indoor and outdoor installations, and both variable-torque and constant-torque duty ratings. (1.3)

1.4Each drive provided under this Standard shall be a complete adjustable-speed power drive system listed to UL 61800-5-1, including its converter, DC link, inverter, control, enclosure, and integral accessories.

1.5The work of this Standard includes input protection, harmonic mitigation, optional bypass arrangements, fieldbus and network communication, output filtering for motor cable compatibility, and field acceptance testing.

NOTE HVAC fan and pump drives specified under the mechanical division are excluded and are governed by Hvac Variable Frequency Drives. (1.6)

NOTE VFD units furnished as plug-in bucket contents within a motor control center assembly are excluded; the MCC assembly, bus structure, and compartment construction are governed by Motor Control Centers, which defers drive performance back to this Standard. (1.7)

NOTE Medium-voltage drives operating above 600 V are excluded; they fall outside the UL 61800-5-1 low-voltage listing and require a separate medium-voltage drive specification. (1.8)

NOTE Drives integral to factory-packaged process equipment — packaged pump skids, chillers, and compressor packages — are excluded and are governed by the respective equipment specification. (1.9)

NOTE Conductors and cables between the drive output and the motor terminals are excluded; their sizing, insulation class, and shielding are governed by Conductors And Cables. (1.10)

NOTE Feeder and branch-circuit panelboard distribution upstream of the drive is excluded and is governed by Low Voltage Panelboards. (1.11)

2 Referenced Standards

2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.

2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

Standard	Title
UL 61800-5-1	Adjustable Speed Electrical Power Drive Systems — Electrical, Thermal and Energy Safety Requirements
NEMA ICS 7-2020	Adjustable-Speed Drives
NEMA 250-2020	Enclosures for Electrical Equipment (1000 Volts Maximum)
IEEE 519-2022	Standard for Harmonic Control in Electric Power Systems
NFPA 70 (NEC) 2023	National Electrical Code (Articles 409 and 430)
NEMA MG 1-2021	Motors and Generators (Part 31)
IEC 61800-3	Adjustable Speed Electrical Power Drive Systems — EMC Requirements and Test Methods
IEC 61800-9-2	Adjustable Speed Electrical Power Drive Systems — Energy Efficiency Indicators for Power Drive Systems
IEC 61800-5-2	Adjustable Speed Electrical Power Drive Systems — Functional Safety Requirements
NETA ATS-2021	Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems
ASHRAE 90.1-2022	Energy Standard for Buildings Except Low-Rise Residential Buildings
ASCE 7-22	Minimum Design Loads and Associated Criteria for Buildings and Other Structures

NOTE UL 508C, the historical listing standard for power conversion equipment, was withdrawn and superseded by UL 61800-5-1 effective February 28, 2020; specifications and submittals shall reference UL 61800-5-1 and shall not cite UL 508C. (2.3)

3 Submittals

3.1 Action Submittals

3.1.1The Contractor shall submit the following action submittals for review before fabrication or release of the drives:

Product data sheets for each drive, including catalog rating, listing, efficiency class, and accessory complement.
Shop drawings showing enclosure dimensions, weight, conduit entry locations, internal device layout, and nameplate schedule.
Wiring and interconnection diagrams showing power, control, and network terminations.
Drive schedule correlating each tag to motor nameplate data, duty type, enclosure type, and mitigation and bypass options.
IEEE 519-2022 harmonic analysis demonstrating compliance at the designated point of common coupling.
Short-circuit current rating (SCCR) documentation for each enclosed drive assembly.
Seismic anchorage calculations and certification for floor-mounted enclosures where required by the seismic design category.

Action submittals required before fabricationcheckbox

☑ Product data sheets (rating, listing, efficiency)

☑ Shop drawings (enclosure, layout, nameplates)

☑ Wiring and interconnection diagrams

☑ Drive schedule (motor data, duty, enclosure)

☑ IEEE 519-2022 harmonic analysis

☑ SCCR documentation

☐ Seismic anchorage calculations and certification

NOTE Action submittals shall be coordinated with the building automation or process control submittal so that the network protocol matches the controlling system before the drives are released. (3.1.2)

3.2 Informational Submittals

3.2.1The Contractor shall submit the following informational submittals for the record:

Manufacturer certification of UL 61800-5-1 listing for each drive.
Manufacturer certification of NEMA MG 1 Part 31 output compatibility analysis, including motor cable length limits and any required output filtering.
Ambient temperature and altitude derating documentation for the installed site conditions.
Functional safety certification for drives furnished with Safe Torque Off, where specified.

Informational submittals required for the recordcheckbox

☑ UL 61800-5-1 listing certification

☑ NEMA MG 1 Part 31 output compatibility analysis

☑ Derating documentation (ambient and altitude)

☐ Functional safety (STO) certification

3.3 Closeout Submittals

3.3.1The Contractor shall submit the following closeout submittals before final acceptance:

Field acceptance test reports per NETA ATS-2021, including insulation resistance and functional verification.
As-left parameter records for each drive, listing every adjusted setting.
Operation and maintenance manuals, including troubleshooting and fault-code references.
Manufacturer warranty documentation.

Closeout submittals required before final acceptancecheckbox

☑ NETA acceptance test reports

☑ As-left parameter records

☑ Operation and maintenance manuals

☑ Warranty documentation

4 Quality Assurance

NOTE Each drive shall be listed by a Nationally Recognized Testing Laboratory to UL 61800-5-1 and shall bear the listing mark. (4.1)

4.2The manufacturer shall regularly produce adjustable-speed drives of the type and rating specified, with a documented production history of not less than five years.

4.3The complete enclosed drive assembly, including integral disconnect, fusing, reactors, and bypass where furnished, shall carry a marked short-circuit current rating equal to or greater than the available fault current at the point of installation.

4.4The drive shall be designed and rated in accordance with NEMA ICS 7 for adjustable-speed drives.

NOTE Where the drive is furnished as an enclosed industrial control panel, the assembly shall comply with the applicable construction and marking requirements of NEC Article 409. (4.5)

4.6Field test personnel shall be qualified to perform acceptance testing in accordance with NETA ATS-2021.

5 Ratings and Performance

5.1 Voltage and Horsepower

NOTE The drive system voltage and horsepower or kW rating shall match the connected motor nameplate, accounting for service factor where the motor is operated continuously above nameplate. (5.1.1)

5.1.2Each drive shall be rated for continuous operation at the connected motor full-load current at the installed ambient and altitude.

System voltageradio

○ 208

○ 240

● 480

○ 600

Drive continuous output ratingrange

HP

0.5500

Default: 25 HP

Rated output frequency rangerange

Hz

0120

60120

Default: 60 Hz

5.2 Duty Type and Overload

NOTE The drive overload rating shall match the load torque characteristic. Variable-torque loads (centrifugal pumps and fans) require only modest overload; constant-torque and high-starting-torque loads (conveyors, positive-displacement pumps, compressors, mixers) demand sustained and instantaneous overload margin. (5.2.1)

NOTE Applying a variable-torque-rated drive to a constant-torque load causes nuisance overload trips or drive damage under high starting torque; the duty type shall be confirmed against the actual load before the drive is sized. (5.2.2)

5.2.3A drive serving a variable-torque load shall provide not less than 110% of rated output current for 60 seconds.

5.2.4A drive serving a constant-torque load shall provide not less than 150% of rated output current for 60 seconds.

5.2.5A drive serving a high-starting-torque load shall provide not less than 150% of rated output current for 60 seconds and 175% instantaneous current.

Duty typeradio

○ Variable torque (110% for 60 s)

● Constant torque (150% for 60 s)

○ Heavy duty / high starting torque (150% for 60 s, 175% instantaneous)

5.3 Efficiency

NOTE The complete power drive system (motor plus drive) shall meet the efficiency provisions applicable to the project under ASHRAE 90.1, and variable-speed control thresholds for pumps and fans shall be documented in the submittal. (5.3.1)

5.3.2The drive shall meet not less than the IE2 efficiency class for power drive systems defined in IEC 61800-9-2.

Minimum power drive system efficiency class (IEC 61800-9-2)radio

○ IE1

● IE2

6 Environmental and Service Conditions

6.1 Enclosure Type

NOTE The enclosure type shall be selected for the actual installed environment per NEMA 250; enclosure cost, size, and cooling capacity differ substantially between types, so over- and under-specification both carry consequences. (6.1.1)

NOTE Specifying a NEMA 1 drive where the environment exposes it to water spray, washdown, dust, or condensation causes premature failure and warranty dispute; the enclosure rating shall reflect the worst-case service condition at the device location. (6.1.2)

6.1.3The drive enclosure shall be of the type listed below and shall maintain its rating with all field-installed conduit entries and accessories in place.

Enclosure type (NEMA 250)radio

● NEMA 1 (indoor, clean)

○ NEMA 12 (indoor, dust and dripping liquid)

○ NEMA 3R (outdoor, rain)

○ NEMA 4 (washdown, hose-directed water)

○ NEMA 4X (corrosive, stainless or nonmetallic)

Mounting configurationradio

● Wall mount

○ Floor mount (freestanding)

6.2 Ambient and Altitude

NOTE Standard drives are rated for a maximum ambient of 40°C at altitudes up to 3300 ft; output current capacity falls at higher ambient and elevation. (6.2.1)

NOTE Above 3300 ft a typical drive loses approximately 1% of rated current per 330 ft of additional elevation; high-altitude sites are frequently overlooked and require derating or cooling accessories. (6.2.2)

6.2.3The drive shall be rated for the maximum ambient temperature at its installed location without exceeding its current rating; where the ambient exceeds the standard rating, the drive shall be upsized or provided with supplemental cooling.

6.2.4The drive shall be derated or otherwise compensated for installations above 3300 ft so that it delivers full motor full-load current at the site elevation.

Maximum design ambient temperaturerange

°C

055

404550

Default: 40 °C

Installation altituderange

ft

012000

3300660010000

Default: 3300 ft

7 Input Power and Protection

7.1 Input Disconnect and Branch-Circuit Protection

NOTE Adjustable-speed drives are governed by NEC Article 430 Part X; the supply conductors are sized at not less than 125% of the rated drive input current, which differs from a standard motor branch circuit sized on motor full-load current. (7.1.1)

NOTE Drive input overcurrent protection sized on the drive input current rather than the motor full-load current per NEC 430.52 is a common error that leaves the drive either over-fused or under-fused; the protective device shall be coordinated to the rule that applies to the installation. (7.1.2)

7.1.3Branch-circuit short-circuit and ground-fault protection ahead of the drive shall be selected and sized in accordance with NEC Article 430.

7.1.4A disconnecting means shall be provided for the drive in accordance with NEC Article 430, located within sight of the drive or provided with a lockable disconnect.

7.1.5The marked short-circuit current rating of the enclosed drive assembly shall equal or exceed the available fault current at the point of installation.

Integral input disconnectradio

○ None (external disconnect by others)

○ Non-fusible disconnect switch

● Fusible disconnect switch

○ Molded-case circuit breaker

Minimum assembly short-circuit current rating (SCCR)radio

○ 5

○ 10

○ 14

○ 18

○ 22

○ 42

● 65

○ 100

7.2 Input Power Quality Accessories

NOTE Input accessories protect the drive from supply transients and reduce conducted disturbances back onto the source; the complement is selected from the supply impedance and the sensitivity of co-located equipment. (7.2.1)

7.2.2Each drive shall be provided with the input power-quality accessories listed below, coordinated with the harmonic mitigation strategy so that protective devices are not duplicated.

Input power quality accessoriescheckbox

☑ AC line reactor

☐ DC link choke

☐ Input EMC / RFI filter

☐ Transient voltage surge suppressor (TVSS)

8 Harmonic Mitigation

NOTE The drive rectifier draws nonsinusoidal current that injects harmonic distortion onto the supply; without a study and a specified mitigation method, the contractor quotes the cheapest (no mitigation) option, risking utility non-compliance and interference with neighboring loads. (8.1)

NOTE Harmonic mitigation shall be engineer-specified based on an IEEE 519-2022 analysis at the point of common coupling; it shall not be left to the contractor to determine in the field. (8.2)

8.3An IEEE 519-2022 harmonic analysis shall be performed for the installation and shall demonstrate that current and voltage distortion at the designated point of common coupling are within the limits of the standard.

8.4The harmonic mitigation method selected shall achieve the IEEE 519-2022 distortion limits at the point of common coupling under the project's worst-case operating condition.

8.5The point of common coupling for the analysis shall be the location designated on the drawings: PCC location on one-line.

Harmonic mitigation methodradio

○ None

○ 3% AC line reactor

● 5% AC line reactor

○ DC link choke

○ Passive harmonic filter

○ Active harmonic filter

○ 12-pulse drive topology

○ 18-pulse drive topology

○ Active front end (regenerative)

Maximum total demand distortion (current) at PCCrange

%

520

58121520

Default: 8 %

Maximum total harmonic voltage distortion at PCCrange

%

38

358

Default: 5 %

9 Output and Motor Compatibility

9.1 Motor Cable Length and Output Filtering

NOTE A PWM drive produces fast-rising voltage pulses; on long motor cables these pulses reflect at the motor terminals and can double, producing peak voltages that stress the motor insulation. (9.1.1)

NOTE NEMA MG 1 Part 31 inverter-duty motors withstand up to 1600 V peak, but non-inverter-duty motors may not; the threshold cable length depends on the drive switching frequency, so the maximum cable length and required output filter shall be established from the actual installation rather than omitted. (9.1.2)

NOTE Failing to specify a motor cable length limit or output filter is a frequent omission; the resulting reflected-wave overvoltage can exceed the motor insulation rating and cause early winding failure. (9.1.3)

9.1.4The maximum motor cable length and the corresponding output filter shall be established from a NEMA MG 1 Part 31 compatibility analysis for each drive and motor pair.

9.1.5Where the connected motor is not rated for inverter duty, output filtering shall be provided to limit the terminal peak voltage and rate of voltage rise to within the motor insulation withstand.

9.1.6The output filter type shall be selected to suit the cable length and motor rating per the table below.

Output filterradio

● None (bare cable, short run)

○ dV/dt filter

○ Output line reactor

○ Sine-wave filter

Maximum motor cable length (unfiltered)range

ft

251000

50100200400

Default: 100 ft

Drive carrier (switching) frequencyrange

kHz

116

248

Default: 4 kHz

9.2 Motor Protection

9.2.1The drive shall provide electronic motor overload protection in accordance with NEC Article 430 for the connected motor.

9.2.2The drive shall provide motor thermal protection and shall accept a motor thermistor or thermal switch input where the motor is so equipped.

10 Bypass

NOTE A bypass connects the motor directly across the line when the drive is unavailable, preserving operation of life-safety and process-critical loads; it is selected from the criticality of the load. (10.1)

NOTE In bypass mode the motor runs across the line at full speed, so motor running overload protection must be provided in the bypass path separately from the drive's electronic overload; many specifications omit this and the omission surfaces at startup. (10.2)

10.3Where bypass is specified, the bypass arrangement shall be provided as listed below.

10.4Where bypass is provided, a motor running overload relay shall be furnished in the bypass path to protect the motor when it is operated across the line.

10.5Where automatic bypass is provided, an output contactor and transfer logic shall be furnished to transfer the motor between drive and line operation.

Bypass configurationradio

● None

○ Manual bypass (selector switch, across-the-line)

○ Automatic bypass (output contactor and transfer logic)

11 Control and Communication

11.1 Control Interface

11.1.1The drive shall provide a control terminal strip for speed reference, start and stop, and fault signaling.

11.1.2The drive shall accept an analog speed reference signal of the type listed below.

11.1.3The drive shall provide an operator keypad with local and remote control selection and fault display.

Analog speed reference inputradio

○ 0-10 VDC

● 4-20 mA

Discrete (digital) input countrange

inputs

212

Default: 6 inputs

Form C relay (digital) output countrange

outputs

16

Default: 2 outputs

11.2 Network Communication

NOTE The fieldbus protocol shall match the building automation system or SCADA system; specifying a protocol the control system does not speak forces field rewiring or protocol converters after installation. (11.2.1)

NOTE The network protocol shall be coordinated with the building automation or process control contractor before the drives are released for fabrication. (11.2.2)

11.2.3The drive shall be furnished with the network communication interface listed below, with all addressing and configuration coordinated with the controlling system.

Network communication protocolradio

○ None

○ Modbus RTU

○ Modbus TCP

○ BACnet MS/TP

● BACnet/IP

○ PROFIBUS

○ EtherNet/IP

○ PROFINET

11.3 Functional Safety

NOTE Machinery applications increasingly require a SIL-rated Safe Torque Off function under machinery safety standards and lockout/tagout practice; retrofitting STO after equipment selection is costly, so the requirement shall be established at specification. (11.3.1)

11.3.2Where Safe Torque Off is specified, the drive shall provide a Safe Torque Off function listed to IEC 61800-5-2 at the safety integrity level required for the application.

Safe Torque Off (STO) per IEC 61800-5-2radio

● Not required

○ STO, SIL 2 / PLd

○ STO, SIL 3 / PLe

11.4 Electromagnetic Compatibility

11.4.1The drive installation shall meet the EMC immunity and emission requirements of IEC 61800-3 for the category appropriate to the installation environment.

11.4.2The drive shall meet not less than IEC 61800-3 Category C2 emission limits, which is the minimum acceptable for most commercial and industrial installations.

Minimum IEC 61800-3 EMC categoryradio

○ C1 (first environment, residential)

● C2 (first environment, restricted)

○ C3 (second environment, industrial)

12 Source Quality Control

12.1Each drive shall be factory tested before shipment, including a functional power-on test of the control, protection, and communication features.

NOTE Drives furnished as factory-assembled combination packages — input reactor, output filter, and bypass in one enclosure — shall be assembled and wired at the factory and shipped as a tested unit. (12.2)

13 Installation

13.1The drive shall be installed in accordance with the manufacturer's published instructions and NEC Articles 409 and 430.

13.2The drive shall be mounted to maintain the manufacturer's required clearances for cooling airflow and service access.

13.3Floor-mounted drive enclosures in applicable seismic design categories shall be anchored and braced in accordance with ASCE 7 and the project structural requirements.

13.4Anchorage layout and conduit entry locations shall follow the arrangement shown on the drawings: VFD plan location and conduit entry.

13.5Input, output, and control conductors shall be terminated to the manufacturer's torque values, and shielded motor cable shall be terminated to maintain shield continuity.

NOTE On generator-backed projects, simultaneous starting of multiple drives shall be coordinated with the generator kVA rating so that drive inrush does not exceed the generator capacity; this is a frequent commissioning-discovered issue and shall be addressed in the sequence of operation. (13.6)

13.7The drive starting sequence on standby generator power shall be coordinated with the transfer and generator system so that connected drives start within the generator's capability.

14 Testing

14.1Field acceptance testing shall be performed in accordance with NETA ATS-2021 for adjustable-speed drives.

14.2Insulation resistance of the motor and motor circuit shall be measured and recorded before energizing the drive.

14.3Each drive shall be functionally verified for speed reference response, start and stop, fault and bypass operation, and network communication.

14.4Where an IEEE 519-2022 compliance threshold is specified, harmonic current and voltage distortion shall be measured at the point of common coupling and recorded.

14.5All adjusted parameters shall be recorded as as-left settings and submitted with the test report.

Field acceptance tests requiredcheckbox

☑ Insulation resistance (motor and circuit)

☑ Functional verification (speed, start/stop, fault)

☐ Bypass transfer verification

☑ Network communication verification

☐ Harmonic measurement at PCC

☑ As-left parameter record

15 Identification

15.1Each drive enclosure shall be provided with an engraved nameplate identifying the drive tag, the served motor, voltage, and horsepower.

15.2Each drive shall bear a permanent warning label identifying the stored-energy hazard and the discharge time before the enclosure may be opened.

Nameplate engraving contentcheckbox

☑ Drive tag / designation

☑ Served equipment designation

☑ Voltage and horsepower

☐ Source feeder designation

16 Delivery, Storage, and Handling

16.1Drives shall be delivered in the manufacturer's original packaging, protected from moisture, dust, and physical damage.

16.2Drives shall be stored indoors in a clean, dry, temperature-controlled space within the manufacturer's storage temperature range until installed.

NOTE Drives containing electrolytic DC-link capacitors that have been stored longer than the manufacturer's shelf limit shall be reformed in accordance with the manufacturer's instructions before energizing. (16.3)

17 Warranty

17.1The manufacturer shall warrant each drive against defects in materials and workmanship for not less than the period specified below from the date of substantial completion.

Manufacturer warranty periodradio

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