S&C SM-4, SM-5 Outdoor Power Distribution Protection


S&C SM-4, SM-5 Power Fuses for Outdoor Distribution Equipment Protection

Power fuses are like overdraft protection on checking accounts, and in this case, outdoor power equipment is the bank. Power overloads are like bouncing a check, and fuses respond to overdraws accordingly, protecting the system and keeping it balanced.

In this article we’ll discuss how S&C Type SM power fuses offer superior “overdraft” protection for outdoor power equipment. We’ll also compare S&C SM fuses to Current-Limiting fuse construction and explain why SM fuses are a superior choice for protecting outdoor power transformers, cables and of course, (capacitor) banks.

S&C Type SM Fuses Protect Outdoor Power Distribution Equipment

S&C SM fuses performance characteristics and reliability protect the system upstream, the downstream equipment, and everything in between. Like other S&C Fuses, SM-4 and SM-5 fuses have precision, rugged silver or nickel-chrome fusible elements that protect

SM Fuse Mounting

SM Fuse Mounting

the circuit with reliable and predictable performance when surges of current occur. This precision is important as it allows upstream devices to be set for faster operation. Fast operation provides superior system protection without compromising coordination with other protective devices like circuit breakers when current moves through a system’s power circuit.

S&C Type SM Fuses
Vs. Current-Limiting Fuses

S&C SM fuses are superior to current limiting fuses because of the helically coiled silver fusible element’s solderless construction which is surrounded by air, eliminating mechanical and thermal stress. In contrast, current-limiting fuses consist of a number of fine diameter wires or one or more perforated or notched ribbons that are in contact with materials (e.g. silica sand), making them susceptible to element damage. Current-limiting fuses in this case may interrupt otherwise harmless current surges in the equipment downstream.


A broad range of amp ratings and time-current performance allows for “close fusing”. S&Csm-fuse-styles
Type SM are available with maximum continuous current ratings of 200, 300, 400 and 720 amps. They are available with fault-interrupting ratings from 28,000 amperes RMS asymmetrical at 34.5kV to 60,000 amperes RMS asymmetrical at 4.16kV for delivering maximum protection in a wide range of systems and applications.


Transformer Protection with S&C SM Power Fuses

SM Power Fuses with their unique solid-material construction provide full-fault spectrum protection capable of detecting and interrupting all faults. Whether the fault is on the primary or secondary side, with line to line or line to ground voltage across the fuse; whether the transformer is adjacent to the fuse or cable connected to it remotely and regardless of the transformer winding connections. In addition, the construction prevents the fuse elements from damage caused by transient surges and can withstand transformer magnetizing-inrush currents as well as hot- and cold-load pickup currents assuring maximum protection for your transformer.


Underground Cable Protection with S&C SM Power Fuses

Insulated cables in underground distribution systems need protection to prevent conductor temperature rise under short circuit conditions. Type SM Power Fuses provide excellent protection for insulated cables because they are extremely fast operating with a wide selection of ampere ratings and permanently accurate and precise time-current performance.


Capacitor Bank Protection with Type SM Power Fuses

Along with transformer and cable protection, SM Power Fuses are ideal for group fusing of in-station capacitors that have high fault currents. SM power fuses can endure significant continuous peak-loads, allowing for smaller ampere ratings without risking nuisance fuse operations. This gives them greater durability and performance than current limiting fuses during capacitor bank inrush and outrush current.

Key Features

• Full-fault-spectrum protection interrupts large, medium, and small faults
• High dielectric strength avoids system damage when exposed to full system voltage
• Silver or nickel-chrome fusible elements are not damaged by surges that heat element
• Variety of speeds and ampere ratings, permitting close fusing for maximum protection and optimum coordination.
• Conductor temperature rise following fault is minimized by fast operation of the fuse
• Permanent accuracy and reliability
• 3 mounting configurations for fitting station layouts

Summarizing Protection of Your Outdoor Equipment Investment

SM fuses are especially suited for protecting equipment such as transformers, capacitor banks, and cables in outdoor distribution substations or systems. They are superior to current limiting fuses in applications requiring a wide range of time-current performance.

[pullquote align=”full” cite=”” link=”” color=”” class=”” size=””]Power fuses are like overdraft protection on checking accounts, and in this case, outdoor power equipment is the bank.[/pullquote]

SM4 and SM5 Power fuses will protect your outdoor power equipment investment and keep your system balanced and coordinated.

Power distribution systems come in all sizes and configurations and handle a wide range of currents. You can avoid fuse sizing mistakes when selecting and correctly sizing replacement fuses for power distribution systems. Proper fuse selection depends on many factors, so consult a professional engineer for your application.

Monster Electrical is a “knowledge-based” independent distributor of fuses, fuse hardware and control equipment. We don’t just ship boxes. Our product and application knowledge goes into every transaction.

Monster Fuses provides immediate shipment of power fuses and power fuse mountings from our extensive inventory. Clients can access more than 14,000 power fuse solutions provided from a stock of 100,000+ fuses, eliminate long factory power fuse lead times, and supply real time solutions for urgent fuse challenges in utility, industrial, institutional and commercial applications.

Call us for help calculating fuse current ratings for transformers or selecting fuse hardware, power equipment and electrical replacement parts.
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