Why is short-circuit current rating important?

It is important to verify and improve short-circuit rating to remain in compliance.

12/19/2016


It is important to verify and improve short-circuit rating to remain in compliance. Courtesy: L&S ElectricThere are several problems with electrically powered equipment. One of them is a short circuit. However, prior to 2008 there was no definition of a short-circuit current rating in the NEC. Since this rating is now part of the NEC guidelines, it is important to verify and improve the short-circuit rating in order to remain in compliance.

Article 100 of the NEC defines a short-circuit rating as:

"The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria."

In essence, a short-circuit current rating gives a baseline for the fault current that a piece of equipment or individual component within the equipment can withstand for a specific amount of time, or until it clears the circuit with a fuse or the opening of a circuit breaker. In newer equipment with higher short-circuit current ratings, this baseline is not much of an issue. However, it can be a problem in older equipment when the equipment is moved from one location to another.

If a short circuit exists and is an ongoing problem, there are a number of different approaches that may help reduce the issue.

One potential solutions is to replace the existing circuit breakers with circuit breakers that have a higher interrupting capability. It may also help to reduce the current to the breakers by installing fault current limiters or series reactors. Isolating any issue that is leading to the short circuit may help but sometimes it may be necessary to rebuild the system.

How to improve the short-circuit current rating

There are a number of ways in which the current rating can be improved. The first step in the process is to have the equipment or component tested to ensure that it is in compliance. Determine the available short-circuit current at the part or point of installation to test compliance. The available fault current must be lower than the current rating associated with the equipment or component.

Not meeting those factors means the equipment or component is in violation of NEC 110.10. Do not use or install the equipment unless the current rating is improved or the fault current is reduced through an acceptable method.

One way to improve the short-circuit current rating is through the installation of current limiting fuses. When considering the equipment options, there may be additional solutions.

Test NEC compliance whenever installing or moving new equipment from one area to another. Also, it is recommended to perform testing on an ongoing basis as part of a preventive maintenance program. 

-David Manney is a marketing administrator at L&S Electric. This article originally appeared on L&S Electric Watts New Blog. L&S Electric Inc. is a CFE Media content partner.



Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2017 Top Plant.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
February 2018
2017 Product of the Year winners, retrofitting a press, IMTS and Hannover Messe preview, natural refrigerants, testing steam traps
March 2018
SCCR, 2018 Maintenance study, and VFDs in a washdown environment.
Jan/Feb 2018
Welding ergonomics, 2017 Salary Survey, and surge protection
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
February 2018
Focus on power systems, process safety, electrical and power systems, edge computing in the oil & gas industry
December 2017
Product of the Year winners, Pattern recognition, Engineering analytics, Revitalize older pump installations
April 2018
Implementing a DCS, stepper motors, intelligent motion control, remote monitoring of irrigation systems
February 2018
Setting internal automation standards
December 2017
PID controllers, Solar-powered SCADA, Using 80 GHz radar sensors

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Maintenance & Safety
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Industrial Analytics
This digital report explains how plant engineers and subject matter experts (SME) need support for time series data and its many challenges.
IIoT: Operations & IT
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me