Short Circuit Events and the Havoc They Wreak on Infrastructure Projects

Why NEC 392.20(C) leaves you unprotected

There are many ways for a short circuit fault to develop, and they can happen anywhere along the electrical distribution system. Short circuit faults occur when an abnormal connection between two nodes of an electric circuit is made.

During a short circuit fault, maximum electromechanical stress between conductors occurs at or before 0.005 second. Current levels in these events can range upwards of 200 kA. In the worst case of a 3-phase short, magnetic field induced repulsive forces between the cables can range upwards of 10,000 pounds.

When a short circuit fault occurs, tremendous magnetic forces repel the power cables from each other resulting in violent forces that damage everything in their path. Typical circuit breakers and other protection devices trip and interrupt a fault between 0.06 to 0.1 second, leaving just enough time for substantial damage to occur.

Cable cleats reduce damage and rework by performing their function within those first 0.005 second (i.e. at peak kA) before a circuit breaker trips and interrupts a fault, making them the best option for short circuit mitigation.

Without the use of a cable cleat system, there is no protection for the employees or equipment in a facility when the short circuit forces are at their peak prior to a circuit interrupter engaging. To avoid potentially severe damage to the facility and infrastructure, as well as personal injury, cable cleats are used to restraint cables during short circuit events.

Cable tray systems provide more design flexibility and can be easier to install than traditional pipe and wire but must be properly engineered for protection against short circuit faults. Cable tray applications are only a safe and viable solution when paired with the right cable cleat.

Specifying and installing the right cable cleats when electrical infrastructure is first established is paramount to setting projects up for success. While metal conduit is often used in several areas of a project to distribute power, it is also often distributed by cables in a cable tray system.

In the U.S., NEC 392.20(C) is the National Electrical Code that governs the safety of the cable installations in cable tray. NEC Article 392.20(C) states: “Parallel connected single conductor cables shall be securely bound in circuit groups to prevent excessive movement due to fault current magnetic forces.”

While NEC 392.20(C) includes language for securing cables during a short circuit fault, it does not specify how to design the proper containment system to meet those forces. Often the lack of clear guidelines on short circuit protection in the NEC results in inadequate or no cable containment
to protect against short circuit events in tray cable installations. Europe has been utilizing cable tray systems for several decades and leads the industry in design standards and best practices.

As such, the IEC 61914:2015 standard provides the testing methodology and process to ensure reliability of cable cleats and ultimate protection in the event of a short circuit event. Cable in cable trays are only a safe and viable solution when paired with the right cable cleat solution to protect against short circuit events.

Unfortunately, NEC 392.20(C) does not currently provide specific guidance on how to securely contain cables in the event of a short circuit when routing cables in a cable tray. To protect the electrical infrastructure when using power cables in a tray, installing an IEC 61914:2015 compliant
cable cleat is the best option when protecting against a peak short circuit fault.


To learn more about Panduit Cable Cleats, visit www.panduit.com/cablecleat

Set your project up to avoid disaster and remain compliant with short circuit protection

When the decision is made to launch infrastructure projects, the engineers responsible for their design undoubtedly look forward to seeing their vision come to fruition. They want to create a lasting impact, and they want to help those needing their work, but there are several ways for projects to go wrong before they can benefit those they’re being worked on for.

It is imperative that engineers know how to protect their designs, and at the forefront of avoiding significant setbacks is the prevention of short circuit events. By preventing these occurrences downtime can be reduced, damage to equipment can be avoided, and the workforce can be protected from significant injuries or death. However, when it comes to short circuit event protection, the U.S. is far behind Europe and Asia.

When it comes to U.S. electrical code, like NEC, cable cleats are not mandatory like they are elsewhere in the world. While they are designed and tested to ensure the retention and support of cables, the U.S. has lagged in the benefits. The approach to cable cleats in North America historically has involved just throwing cables into a tray with no coding, meaning if a short circuit event occurs, the cables and cable trays will fly out and immediately cause catastrophic damage. This is especially common when it comes to thermal expansion, which Panduit has created solutions to be properly ready for.

However, internationally the IEC 61914 standard has been adequately used, especially in Europe and Asia, to calculate the forces between two conductors in the event of a significant fault in order to specify the correct type of cable cleats being used in those regional projects. This European standard, not officially used on U.S. soil, especially helps with cable routing in harsh industrial environments.

Fortunately for the U.S. this disparity won’t always be the case. As American projects continue to experience setbacks because of their struggle to anticipate thermal changes and expansion, the future holds the likelihood of standards migration and harmonization. By anticipating this change, EPCs can future proof their projects to remain compliant while avoiding the disasters that come from short circuit events.

Panduit recommends the use of its cable cleat offerings – stainless steel locking tie cleats, stainless steel strap cleats, and clamp-style cable cleats – for many reasons, but one particular way Panduit benefits EPCs, is through their ability to allow for future proofing.

Stainless steel locking tie cleats feature a polyurethane cushion to prevent damage to cables and mounting brackets to secure the tie to various styles of ladder rack. These cleats are suited for lower to medium peak short circuit current requirements and can be installed using a manual or battery-operated installation tool, which helps reduce installation time.

Stainless steel strap cleats also feature a polyurethane cushion sleeve to prevent damage to cable and mounting brackets to secure the strap to various styles of ladder rack. These cleats are suited for a broad range of peak short circuit current requirements, including some of the higher peak kA requirements. A manually-operated installation tool provides quick installation.

Clamp-style cable cleats are a widely used cleat solution also suited for a broad range of peak short circuit current requirements and are the most durable for high peak kA requirements.

Not only do these offerings allow the EPCs who use them to rest assured that their projects will be successfully completed without short circuit events, but they will also be given the peace of mind that comes from knowing their project will be compliant and need no re-work when international standards are harmonized and migrated here to the U.S.

This means that, not only will the engineers creating infrastructure project designs be assured their vision won’t be altered by the potential for a short circuit event, but they’ll also know and be assured that their vision will stay intact for the duration of its lifecycle because of its adherence to any impending standards harmonization and migration.

Short Circuit Faults – Are You Protected?

When running power cable through a facility using a ladder rack, the design considerations on how to affix the cables to the ladder arise. Options such as nylon cable ties, stainless strapping, cable cleats, tie wire and, believe it or not, even doing nothing at all, are all practices that have been witnessed in the field. In addition to cable management, engineering firms must also consider the implications of a short circuit fault as part of the design process. When a short circuit fault occurs, tremendous magnetic forces repel the power cables from each other resulting in violent forces that damage everything in their path.

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