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Home > Trends & Technology > The New Short Circuit Current Rating: What You Need to Know
Wednesday, September 20, 2017
POSTED BY TURTLE & HUGHES INDUSTRIAL CONTROL & AUTOMATION DEPARTMENT BLOG IN
INDUSTRY NEWS & EVENTS, PRODUCTS & TECHNOLOGY
Short circuits in equipment panels can cause fires, shock employees and even hit workers with explosive shrapnel. That’s why the National Electrical Code now requires marking of the short circuit current rating (SCCR) for more equipment within the system, often with attached documentation and dating.
When the available fault current of the system is greater than the equipment’s SCCR, it can cause serious safety hazards. The enclosure can become energized from conductors pulling out of their terminations or other breakages in the equipment. Internal device failure could lead to explosions that cause fire and molten metal to spew from the closed and latched door. The enclosure door may even blow open or off and shrapnel can fly out. In laboratory tests, SCCR failures have resulted in enclosure doors flying up to 100 feet after an electrical explosion.
Every component in the system needs to be in line with the SCCR — there can be no weak links in the panel circuit that adversely alter the entire panel’s rating. The new 2017 regulation will affect every part of the supply chain:
Manufacturers and end users face particular challenges with the new rating system.
OEMs will need to meet each and every end-user’s SCCR requirements. An OEMs’ standard design might meet an SCCR of 5,000 amps, but what if the end-user needs 50,000 amps or 85,000 amps?
Power management company Eaton’s Bussmann, which is a supplier on many Turtle & Hughes projects, found in a survey of OEMs that nearly half have difficulty applying or interpreting the standard that determines panel SCCR. More than half of the manufacturers also said they had some difficulties when they were trying to locate SCCRs for components needed to design an SCCR solution.
Once equipment is installed, it’s very difficult to increase its SCCR – it either has to be modified and recertified or the available fault current at the control panel needs to be reduced. To mitigate for either of these costly measures, OEMs should be considering SCCR during the design phase of the manufacturing process.
For end-users, the challenge lies in first understanding the available fault current at the location where they want the equipment to be installed. They then need to communicate those requirements to their manufacturer for new equipment and verify that already installed equipment meets the requirement.
A range of electrical equipment is subject to the new rule. Marking requirements include:
In addition, there are new documentation requirements for:
End-users and manufacturers need a variety of solutions to meet the new requirements. They need to be able to quickly determine the available fault current, find component SCCR solutions and easily determine the SCCR of a control panel.
Eaton Bussmann series offers a mobile app, FC², which can quickly deliver fault current calculations by considering transformer size, conductors and conduit. The app:
Eaton Bussmann series also offers software that can quickly find components with the SCCR that manufacturers need to satisfy end-user requirements and software that can calculate the SCCR for an entire assembly using a one-line diagram of a control panel circuit.
Solutions like these take the guesswork out of identifying and creating the right short circuit current rating. Manufacturers and end-users can ensure they meet SCCR regulations and, more importantly, protect staff and other equipment from the catastrophic effects of a short circuit explosion.
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