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Short-circuit current ratings (SCCR)

Short-circuit current ratings

Short-circuit current ratings (SCCR) are tested values for motor control and protection devices to ensure safe reaction during short circuits and ground faults. Since even low-level faults are capable of producing incredible amounts of energy, unprotected equipment can easily cause damage to the installation and endanger personnel within close proximity. Short-circuit current ratings have been mandatory for Industrial Control Panels since 2006.

Components requiring short-circuit current ratings

All power circuit components for Industrial Control Panels are required to have marked short-circuit current ratings expressed in kiloamperes (kA) and voltage. This includes devices such as:

— Disconnect switches
— Branch circuit protective devices
— Branch circuit fuseholders
— Load controllers
— Motor overload relays
— Terminal blocks
— Busbar 

ABB manual motor starters are tested for short-circuit current ratings in a wide variety of applications. SCCR values for manual motor starters may differ depending on how they are applied. See page 34 for more guidance regarding selection.

Standard (low) fault ratings - Mandatory

In order for electrical products to be certified as suitable for use in motor applications, they must be tested to a minimum standard value based on the size and type of the device. These are referred to as standard fault or low fault ratings. The table below shows the standard values for motor controllers according to UL 60947-4-1 and CSA C22.2 60947-4-1.

The standard fault value is also the assumed rating for unmarked components.

IEC refers to standard fault current as prospective current “r”.

High fault ratings - Optional

The standard fault values shown on the previous page are the minimum requirement for all motor control components. Since the available fault current for a given installation can vary drastically, standard fault ratings alone are often too low for many applications. For this reason, manufactures, including ABB, often choose to test their devices beyond the minimum requirements. Any short-circuit testing above the minimum standard fault
level and up to a maximum of 200 kA is referred to as a high fault rating. 

There are two methods for testing high fault SCCR. The first method, referred to as component-level testing, is performed in an enclosure, but with the upstream short-circuit protective device mounted separately in open air. This is common for devices intended to be supplied separately from the short-circuit protection. The second method, which applies to combination starters, involves testing with all components in a single enclosure. This is referred to as Combination Motor Controller (CMC) testing. CMC testing is common for devices supplied as a complete assembly (e.g. enclosed starters).

IEC refers to high fault current as rated conditional current Iq.

Defined acceptance criteria

Failure of components under fault conditions can create safety concerns for personnel working in close proximity to electrical equipment. To outline what constitutes a pass, the harmonized UL 60947-4-1 and CSA C22.2 No.60947-4-1 standards define acceptance criteria for these components. Several criteria exist for all devices:

— The short-circuit protective device successfully interrupts the fault
— The enclosure door has not blown open, and it remains possible to open it manually
— No damage to, or separation between, the conductors and the terminals
— No damage to the insulating bases of live parts, and no access to current carrying parts

For Combination Motor Controllers, the included circuit breaker, switch, or manual motor starter should be capable of being manually operated, and should not be damaged, exposing conductive parts.

In addition to the above criteria, a distinction is made between two types of coordination: Type 1 and Type 2.This pertains to the suitability of components for continued service following a fault.

Type 1 coordination

Type 1 coordination allows some components, such as the controller and overload protection device, to sustain damage such that they become inoperable following a short-circuit fault. This coordination type requires that these components be replaced before re-commissioning.

Type 2 coordination

Type 2 coordination requires that no damage to overload protection and other components occurs, with the exception that the contacts of the contactor or starter are allowed to weld. This welding must be easily separated by manual effort (e.g. with a screwdriver). Both the overload tripping performance and controller switching capabilities are verified following the short-circuit test.

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North American standards and certifications

North American standards and certifications

To assist in understanding how to properly apply manual motor starters within North America, the following section provides a review of electrical product certification within this region.

North American standards

Below is an overview of the North American standards referenced within this document.

Installation standards

— Govern the installation of electrical components and conductors in each country
— Scopes include all electrical installations beyond the point of the utility service drop
— Applicable for residential, commercial, and industrial structures
— Often adopted into law by local governments

NFPA® 70 National Electrical Code® (NEC)
United States

CSA C22.1 Canadian Electrical Code (CEC)
Canada

NOM-001-SEDE-2012 Instalaciones Eléctricas (utilización)
Mexico

Application-specific standards

— Govern specific applications (e.g. industrial control panels)
— Can allow for greater flexibility when designing and building electrical equipment

NFPA® 79 – Industrial Machinery
UL 508A – Industrial Control Panels
CSA C22.2 No.14 – Industrial Control Equipment

Product standards

— Govern the products themselves
— Quantify the necessary product construction, marking and tests required for certification

UL 60947-4-1 – Electromechanical Contactors and Motor-Starters

UL 508 – Industrial Control Equipment
UL 508A – Industrial Control Panels
UL 508C – Power Conversion Equipment
UL 489 – Molded-Case Circuit Breakers, Molded-Case Switches, and C.B. Enclosures
UL 98 – Enclosed and Dead-Front Switches
UL 1077 – Supplementary Protectors for Use in Electrical Equipment
UL 248-1 – Low-Voltage Fuses

CSA C22.2 No.60947-4-1 – Electromechanical Contactors and Motor-Starters

CSA C22.2 No.14 – Industrial Control Equipment
CSA C22.2 No.274 – Adjustable Speed Drives
CSA C22.2 No.5 – Overcurrent Protection
CSA C22.2 No.4 – Enclosed and Dead-Front Switches
CSA C22.2 No.235 – Supplementary Protectors
CSA C22.2 No.248 – Low-Voltage Fuses

Global harmonization efforts

As globalization continues to impact consumers more and more each year, it is becoming increasingly important for customers to understand the rules and regulations of multiple world regions. In an effort to limit the scope of knowledge required to achieve this without sacrificing safety, Standards Development Organizations, including Underwriters Laboratories (UL), the Canadian Standards Association (CSA), and the International
Electrotechnical Commission (IEC) are working together. Taking their like-standards, they are combining best practices, eliminating antiquated verbiage, and producing harmonized global standards.

Most notably for the purpose of this document, these organizations have adopted the IEC 60947-4-1 standard to harmonize the UL 60947-4-1 and CSA C22.2 No. 60947-4-1 standards for Electromechanical Contactors and Motor-Starters, which now govern the certification of manual motor starters, replacing UL 508 and CSA C22.2 No.14.

Certifications in North America

For electrical products to be legally installed in the United States, the Occupational Safety and Health Administration (OSHA) lawfully requires these devices to be certified through a Nationally Recognized Test Laboratory (NRTL). An NRTL holds the responsibility to properly certify manufactures’ products to the appropriate product safety standards. OSHA currently recognizes 15 organizations as NRTLs, most notably including:

— UL - Underwriters Laboratories, Inc.
— CSA - Canadian Standards Association
— Intertek Testing Services NA, Inc.

Each product certified through an NRTL is given a unique certification mark to indicate conformity, which becomes a clear sign to inspectors, those Authorities Having Jurisdiction (AHJ) over an installation, that the product can be legally and safely accepted. 

Accreditation within Canada is performed by the Standards Council of Canada (SCC).

Product certification marks

Each Nationally Recognized Test Laboratory’s product mark is unique, and also differs depending on whether the product has been certified for use in the United States, Canada, or both. This is typically indicated by the inclusion of the letters “C” or “US” in the mark. Below are several examples.

Products are marked to differentiate between whether they are “Listed” devices, indicating that they meet all of the requirements outlined in the respective product standards, or “Recognized” devices, which meet only some of the requirements of their standard. Recognized components are subject to additional “Conditions of Acceptability” and can be somewhat limiting in regards to their use in electrical installations.

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