Underwriters Laboratories Inc.

About UL | Careers | Contact Us

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, the Standard for Industrial Control Equipment, UL508A-2001, Supplement SB, 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, Standard for Industrial Control Equipment comprised of 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:

CB - Listed Inverse - time circuit breaker

DS - Listed or Recognized Disconnect switch or Listed Molded-case Switch

F - Listed Fuses

FH - Discrete Fuseholder

ICB - Recognized Instantaneous trip circuit breaker

MC - Listed or Recognized Motor Controller

MSP - Listed Manual Self-Protected combination motor controller

OLR - Listed or Recognized Overload Relay

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

III. 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, consideration is to be given to 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.

  1. 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.
  2. 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.
  3. When specified, the overload relay heater table number shall be provided with the equipment.
  4. 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.
  5. 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.
  6. Additional Conditions of Acceptability may be specified in the individual tables.

Top of Page