Fuse Holders Leverage Protection

SCCR Requirements Increase Need for Fuse-Based Branch-Circuit Protection in Control Panels

The defined short Circuit Current Rating (SCCR) requirements in NEC Article 409 and UL 508A increased the need for fuse-based branch-circuit protection in control panels.

To achieve desired or maximum SCCR ratings, fuses are better suited than circuit breakers. They facilitate higher SCCR ratings. For example, many terminal blocks tested with fuses achieve a rating of 100 kA, while the same terminal block tested with a circuit breaker is rated 65 kA. Additionally, fuses are brand-independent because of defined over-current characteristics. Unlike circuit breakers (which also require a specific brand, frame and ampacity for testing), fuses are simply definable by class (e.g. Class CC, J, T, etc.), not brand.

"A trend further facilitating new fuse holder development is the adoption of Class CC fuses over Class J fuses," says Michelle Goeman, Wago's product manager for terminal blocks and electronic interface. "Due to their increased use, OEMs that previously used Class J fuses to support a broad range of over-current requirements now replace these with Class CC fuses for requirements up to 30 A. This is in response to needs for reducing panel space and fuse/fuse holder costs."

Wago says its new 811 Series of lever-actuated Class CC and midget-style fuse holders represents a new approach to branch and supplemental circuit protection. The company says its DIN-rail-mount 811 Series advances usability and reliability by replacing screw-based terminations with lever-operated Cage Clamp spring-pressure terminations.

The Class CC fuse holder supports branch-circuit applications with up to 200 kA SCCR (30 A, 600 V). Its midget-style sibling achieves a 100 kA SCCR (30 A, 750 Vac/1,000 Vdc) for supplemental protection. Both accommodate conductor sizes 16–6 AWG. "Unique in the 811 Series is the one-pole, 811-316 midget-style holder and its ability to provide 1,000 Vdc fusing in PV combiner boxes," Goeman says. "Beyond protecting PV strings, the 811-316 minimizes in-the-field install time and operating costs via maintenance-free connections."

Wago says these Class CC and midget-style fuse holders are touch-safe and feature a DIN-rail-mount clip for easy install or removal. Each fuse holder also is equipped with a test point at each conductor entry for general troubleshooting/testing. An available coupling kit adapts the 811 Series to more applications by creating multi-pole configurations. Flexible circuit identification/marking options are provided by Wago's WMB multi-marking strip and continuous marking strip adapters.

"Vibration, temperature change, or current-induced thermal cycling necessitate checking and retightening screw-based connections," Goeman says. "So, instead of screws, torque specs and torque screwdrivers, the 811 Series' intuitive lift-and-lock terminations cut wiring times by up to 50%."

By surrounding conductors on all four sides, Cage Clamp administers preprogrammed, proportional contact force, so larger conductors receive greater contact force, Goeman explains. "The resulting dynamic connection constantly adjusts to environmental changes such as settling of conductor strands, metal expansion, vibrations and contraction due to current- or temperature-induced thermal cycling," she adds. "Terminations are independent of operator skill and eliminate torque requirements by simply lifting the lever, inserting a prepared conductor, and lowering the lever."

Beyond expediting assembly and install, "they enable panel and machine builders to avoid connection-related startup issues, since connections won't loosen during shipment, and future warranty claims," Goeman says.

The fuse holders carry UL, CSA and IEC listings, recognitions and certifications.

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