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Short circuit current ratings of industrial control panels incorporating combination motor controller components

General
Article 409 of the 2005 National Electric Code (NFPA 70) requires industrial control panels to be marked with a short circuit current rating. As specified in the National Electric Code, UL508A-2001 Supplement SB, the Standard of Safety for Industrial Control Equipment, provides an accepted method for determining the short-circuit current rating of the control panel. The linked spreadsheets provide guidance for industrial control panel manufacturers who purchase the discreet components and assemble combination motor controllers within their panels to achieve a combination short-circuit rating that is higher than the lowest-rated individual component.

Linked spreadsheets

 

Use
The combinations listed in the linked spreadsheets may be applied in a manufacturer’s Listed industrial control panel without further evaluation or specific documentation in the manufacturer’s UL procedure pages.

The spreadsheets cover the application of individual components, including a disconnecting means, an overcurrent protective device, motor controller and motor overload protection, as a combination motor controller having specified ratings, including a short-circuit current rating (SCCR). Each of the individual components is Listed or Recognized to the requirements in the applicable component Standard.

The specified ratings for the combination motor controller may be applied to the end-product equipment only when all of the specific components listed are provided in the end-product equipment and installed according to any applicable conditions of acceptability.

Components other than those identified in the combination motor controller and connected in the power circuit of the combination motor controller will require additional evaluation.

The following statements explain tabular information:

I. Combination Type / ID number
The letter designating the construction type of the combination motor controller as defined in UL508, the Standard of Safety for Industrial Control Equipment comprising specific components are described below:

A — Type A combination motor controller consisting of a disconnect switch, fuses, motor controller and overload relay

C — Type C combination motor controller consisting of Inverse time circuit breaker, motor controller and overload relay

D — Type D combination motor controller consisting of instantaneous trip circuit breaker, motor controller and overload relay

E — Type E (self-protected) combination motor controller consisting of manual self-protected combination motor controller and motor controller

F — Type F combination motor controller consisting of manual self-protected combination motor controller and motor controller

ID number — The identification number is assigned as a reference by the submitter for each combination motor controller construction or rating.
II. Individual component information
Identification of all components of a combination motor controller

Component Type — Identifies each type of component provided in combination motor controller:

Database
Abbreviation

Signifies

DS

Listed or Recognized Unfused Disconnect Switch (UL98, WHTY, WHTY2) or Listed Unfused Molded Case Switch (UL489, WJAZ)

FDS

Listed or Recognized Fused Disconnect Switch (UL98, WHTY, WHTY2) or Listed Fused Molded Case Switch (UL489, WJAZ)

F

Listed Branch Circuit Cartridge Fuse (UL248 Series, JDDZ)

FH

Listed Discrete (separate) Fuseholder (UL512, IZLT)

CB

Listed Inverse-Time Circuit Breaker (UL489, DIVQ)

ICB

Recognized Instantaneous Trip Circuit Breaker (UL489, DKPU2)

MSP

Listed Self-Protected Combination Motor Controller or Listed Manual Self-Protected Combination Motor Controller (UL508, NKJH)

ACC (*)

Listed Accessory for Self-Protected Combination Motor Controller (UL508, NKJH) where * is replaced with accessory description, such as adaptor, control unit, or current limiter

STR

Listed Electromechanical Motor Starter (UL508, NLDX) or Listed Solid State Motor Starter (UL508, NMFT), includes Motor overload Relay or solid state motor overload relay function

(2SPD) STR

Listed Two- Speed Motor Starter (UL508, NLDX).

(AUTO) STR

Listed Autotransformer Motor Starter (UL508, NLDX)

(REV) STR

Listed Reversing Starter (UL508, NLDX)

REVCON

Listed Reversing Contactor (UL508, NLDX)

MC

Listed Electromechanical Motor Controller (UL508, NLDX) or Listed Solid State Motor Controller (UL508, NMFT), without motor overload protection

(FAST) MC,

(SLOW) MC

Same as MC above, except designates two individual contactors, fast speed and slow speed, for two-speed motor controller.

(MAIN) MC (START) MC, (RUN) MC

Same as MC above, except designates two or three individual contactors for autotransformer starting motor controller (main, start, and run may be replaced by corresponding designation on wiring diagram required in B10.

(FOR) MC (REV) MC

Same as MC above, except designates two individual contactors, forward and reverse, for reversing motor controller.

(ISO) MC,

(SHORT)MC

Same as MC above, except designates two individual contactors, isolation and shorting, for use with solid state (soft-starter) MC.

AUTOXFR

Recognized Motor-starting Autotransformer (UL508, NMTR2) – Only used when individual parts of Listed autotransformer starter are described.

INTERLOCK

Recognized Mechanical Interlock (UL508, NKCR2, NLDX2) – Only used when individual parts of Listed reversing contactor are described.

OLR

Listed or Recognized Mechanical (bimetal or eutechtic) or Solid State / Electronic Overload Relay (UL508, NKCR, NKCR2)

(FAST) OLR,

(SLOW) OLR

Same as OLR above, except designates two individual overload relays, fast speed and slow speed, for two-speed motor controller.

Company name and model number — Identification of the specific component in the combination motor controller.

Individual component ratings:
HP — Horsepower rating for component, if provided

kA — Marked short circuit current rating (SCCR) on individual component

Max Amps — Maximum ampere rating of individual component

V — Voltage rating of individual component

II. Combination motor controller information
Identifies information required to install combination motor controller in end-product:

Combination ratings — ratings for combination motor controller:

kA — Maximum short circuit current rating for combination motor controller

V, Ph — Maximum voltage rating and number of phases for combination motor controller

HP or Maximum Amperes — Maximum horsepower or current at the corresponding voltage rating for combination motor controller

CA — Conditions of acceptability specific for combination motor controller — See descriptions of specific conditions of use clauses under “Conditions of Acceptability” below.

 

Conditions of acceptability
Unless specified otherwise in the individual Recognitions, consider the following conditions of acceptability when these components are employed as a combination motor controller in the end-use equipment:

Specific conditions of use — Number refers to specific condition number as defined below and number in parenthesis identifies specific information applicable to the combination motor controller.

  • All of the specified individual components of the combination motor controller have been installed in an enclosure having a specified internal volume in cubic feet. Additional testing in the combination motor controller is not required when installed in an enclosure having the same or larger volume.
  • When specified, the motor controller and overload relay shall be installed to maintain the specified distance, in inches, from the overcurrent protective devices and other components shall not be installed in this area.
  • When specified, the overload relay heater table number shall be provided with the equipment.
  • Unless otherwise specified, all connections between components are made with insulated wire having an ampacity of 125 percent of the rated motor current and connected to the terminals supplied with the individual components.
  • The need for cautionary markings applicable to high fault short circuit current ratings, Type D and Type E combination motor controllers shall be considered in the end-product application.
  • Additional conditions of acceptability may be specified in the individual tables.