Overview of U.S. Standards and Regulations

U.S. National Standards

The national standards governing electrical installations in the U.S.:

NOTE: UL 508A is both an application and a product standard.


  • National Electrical Code® (NEC), NFPA 70: Electrical Installation

  • NFPA 79: Electrical Standard for Industrial Machinery

  • UL 98: Enclosed and Dead-Front Switches

  • UL 248: Low Voltage Fuses

  • UL 489: Molded-Case Circuit Breaker, Molded-Case Switches

  • UL 508A: Industrial Control Panels

  • UL 512: Fuse Holders

  • UL 60947-4-1: Low Voltage Contactors and Starters (formerly UL 508)

  • UL 60947-5-1: Control Circuit Devices and Switching Elements

  • UL 61800-5-1: Adjustable Speed Electrical Drive Systems (formerly UL 508C)

UL 508 to UL 60947-4-1

The standard for Industrial Control Equipment, UL 508, has been harmonized with the relevant product standards of the IEC standard for low-voltage control and automation, IEC 60947-4-1.

This harmonization work was undertaken with the intent of creating standards that, while being based upon and adopting IEC requirements, would incorporate sufficient national differences to ease the transition from UL 508 to UL 60947-4-1. This goal has largely been accomplished in most cases. While the UL 508 and UL 60947-4-1 standards do not look the same, when taking into account the national differences included in the harmonized standards, they are essentially technically identical.

Products originally listed to UL 508 will maintain their listing with no expiration. UL 508 and UL 60947-4-1 products can be used interchangeably.

The following industrial control categories are affected by this harmonization effort.

Industrial Control Categories


Product Description

Category Control Number

UL 60947-4-1

Magnetic Motor Controllers


Manual Motor Controllers


Combination Motor Controllers


Auxiliary Devices (Overload Relays only, Thermal & Electronic)


Industrial Control Switches


UL 60947-5-1

Auxiliary Devices (Relays, Pilot Devices, Limit Switches)


For more information on this transition, please refer to UL’s website for Industrial Control Equipment Transition to IEC Standards.

Product Standards: UL 489 Circuit Breakers vs. UL 1077 Supplementary Protectors

UL 489 circuit breakers are used to protect feeder and branch circuits. UL 1077 supplementary protectors are intended for use as overcurrent protection within a piece of equipment where branch circuit overcurrent protection is already provided. UL 489 circuit breakers are required for compliance with NFPA 70 and NFPA 79.

UL 1077 supplementary protectors are redundant, or additional, protection on branch circuits for equipment. They complement other branch circuit protection, provided by either UL 489 circuit breakers or UL 248 fuses. UL 489 circuit breakers can be used in place of UL 1077 supplementary protectors, but UL 1077 supplementary protectors can never be used in place of UL 489 circuit breakers.

UL 1077 supplementary protectors are often called circuit breakers, but this is incorrect. Circuit breakers are listed to the UL 489 standard, while supplementary protectors are listed to the UL 1077 standard.

Certification Process

A nationally recognized testing laboratory (NRTL) can list or certify the equipment according to applications or product standards including the following: UL, CSA, ETL, and TUV. Other approved agencies are listed at the following website: http://www.osha.gov/dts/otpca/nrtl/index.html#nrtls.

Acceptance of Electrical Equipment in US

The process for acceptance is as follows:

  1. The equipment is listed or the manufacturer is certified:

    1. For mass production equipment, the industrial control panel itself is listed by an NRTL.

    2. For custom or low-volume equipment, the manufacturer or supplier of the industrial control panel is certified.

  2. A local inspector under the authority having jurisdiction (AHJ) inspects and approves the electrical equipment and the installation prior to commissioning. The product listing or labeling may be used to assist in the inspection.

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