Why Short Circuit Current Ratings are Important

By Sarah Larson, commercial program manager, Rockwell Automation

For global machine builders looking to sell into North America, it can be tricky to navigate cultural and geographic barriers. But that’s nothing compared to complying with local standards and codes.

Different regions use different methodologies for determining a system’s short circuit current rating. This can create a huge headache for OEMs and system integrators trying to sell into North America.

Varying electrical standards affect every stage of a machine’s life cycle, from design and development to installation and operation. If these standards aren’t taken into consideration during the planning phase, it becomes much more challenging to determine the short circuit current ratings of a complete industrial control panel.

So what do machine builders need to know to confirm they’re building complaint machinery and control panels?

Know Your Codes

While some North American electrical standards have been evolving to harmonize with global standards for more than a decade, there still are a number of differences to take into account. Every machine builder should be familiar with these three standards:

• UL 508A, Standard for Industrial Control Panels.
• NFPA 70, National Electrical Code (NEC^®).
• NFPA 79, Electrical Standard for Industrial Machinery.

As machine and panel builders become more familiar with these standards, they can begin to identify the differences that exist between them and international standards in the pursuit of developing global offerings.

Get Specific

Any machine or panel design project should begin with well-defined requirements and specifications.

Types of information that should be requested and confirmed with the end-user customer include the following:

• Power supply, including voltage, phase, frequency, system grounding and required short circuit current rating.
• Operating conditions, such as temperature, vibration and environmental factors.
• Loads for devices, such as motors, drives, heaters and transformers.
• Functional descriptions, including sequence of operation and operator interfaces.
• Applicable standards and certifications, including local requirements.

Write It Down

One of the most basic but important things a machine or panel builder can do is document key project elements as part of the proposal process. These notes should include the customer’s specifications and requirements, applicable national and local standards, and proposed machine solution and project estimate. Putting everything into writing helps clarify all aspects of the machine design.

Thorough documentation also plays a critical role beyond the proposal process. Machine and panel builders should consider including special assembly and wiring instructions in their bill of material, as well as review and test documentation. This can include creating design-review and test checklists, and taking digital photos of completed control panels.

Be Resourceful

Machine and panel builders can take advantage of a bounty of tools, training, support and literature that can help them serve the North American market.

One example is the Global Short Circuit Current Ratings (SCCR) Selection Tool from Rockwell Automation. This online tool provides coordinated, high-fault SCCR ratings for all power devices used in a circuit, helping save time and effort when finding and determining these ratings. The tool’s data can be based on either UL or IEC standards.

While standards and codes can be daunting, they shouldn’t be a barrier to success in a new market. Understanding key standards can help OEMs and panel builders meet compliance requirements and improve their competitive edge in North America.

Learn about Rockwell Automation Safety and Connectivity Solutions.