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SM and SML Power Fuses are especially suited for protecting cables and medium-to-large power transformers on utility, as well as industrial, commercial, and institutional power systems through 34.5 kV. They incorporate precision-engineered nondamageable silver or nickel-chrome fusible elements with time-current characteristics that are precise and permanently accurate — assuring not only dependable performance, but also continued reliability of system coordination plans.

S&C’s SM and SML Power Fuses are manufactured in accordance with a quality system certified to ISO9001:2000.

With SM and SML Power Fuses, source-side devices may be set for faster operation than practical with other power fuses or circuit breakers, thereby providing better system protection without compromising coordination.

SM and SML Power Fuses are offered with maximum continuous current ratings of 200, 300, 400, and 720 amperes, in a variety of fault-interrupting ratings. They’re available in a wide variety of ampere ratings, in five different speeds: S&C “K”, Standard, Slow, Very Slow, and Coordinating. This broad selection of ampere ratings and speeds permits close fusing to achieve maximum protection and optimum coordination.

SML Power Fuses, further, include Uni-Rupter®, which provides 200-ampere single-pole live switching of single-phase and three-phase circuits on distribution systems through 25 kV. Uni-Rupter offers the ultimate in live-switching simplicity: a firm, steady opening pull on the fuse with a hookstick is all that is required for circuit interruption. Since circuit interruption is internal to Uni-Rupter, there’s no external arc or flame.

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SM Power Fuses are available in the following ratings:
Fuse TypekVAmperes, RMS, Symmetrical
NominalMaximumBILMaximumInterrupting
60 Hz50 Hz
SM-20 13.8
25
34.5
17.0
27
38
95
125
150
200E or 200K
200E or 200K
200E or 200K
14 000
12 500
8 450
11 200
10 000
6 760
SM-40 4.8
13.8
25
5.5
17.0
29
60
95
150
400E
400E
400E
25 000
25 000
20 000
20 000
20 000
16 000
SM-4Z 4.8
13.8
25
34.5
5.5
17.0
27
38
60
95
150
200
200E
200E
200E
200E
17 200
12 500
9 400
6 250
13 760
10 000
7 520
5 000
SM-5S 4.8
13.8
25
34.5
5.5
17.0
27
38
60
95
150
200
400E or 720E
400E or 720E
300E
300E
27 000
25 000
20 000
17 500
27 000
25 000
20 000
17 500
SM-5SS 13.8 15.5 95 400E 34 000 25 000

 

SML Power Fuses are available in the following ratings:
Fuse TypekVAmperes, RMS, Symmetrical
NominalMaximumBILMaximumLive-SwitchingInterruptingFault-Closing, Asym.
60 Hz50 HzOne-TimeTwo-Time
SML-20 13.8
25
17.0
27
95
125
200E or 200K
200E or 200K
200
200
14 000
12 500
11 200
10 000
22 400
20 000
13 000
13 000
SML-40 13.8
25
17.0
27
95
125
200E
200E
200
200
12 500
9 400
10 000
7 520
20 000
15 000
13 000
13 000

Fault Interruption

Fast, positive fault interruption of SM Refill Units and SMU Fuse Units is achieved through high-speed elongation of the arc in the solid-material-lined bore, and by the efficient deionizing action of gases generated through thermal reaction of the solid material due to the heat of the confined arc. Here’s how it works.

Fault Interruption of SM-4Z, SML-4Z, SM-5S, and SM-5SS Power Fuses:

  • Overcurrent melts the silver fusible element. The strain wire severs, initiating arcing.
  • Both main and auxiliary arcing rods are drawn upward by spring-and-cable assembly in the holder. After approximately 1/8-inch travel, lower section of auxiliary arcing rod engages the auxiliary contact momentarily shorting out the arc.
  • For low-magnitude faults, arcing is reinitiated in small-diameter auxiliary bore when the tip of the auxiliary arcing rod travels about one inch (and clears auxiliary contact).
  • For moderate-to-high-faults, auxiliary arcing rod — momentarily providing the only path for the fault current — quickly melts at reduced section and separates from the one-inch long arcing tip. Any arcing in the auxiliary bore can’t persist, and quickly transfers to main arcing rod in the main bore.
  • For low-magnitude faults, large-diameter section of auxiliary bore delays arc extinction until a sufficient gap is attained to preclude reignition in the main bore
  • For moderate-to-high faults, arc is lengthened as main rod is drawn upward into the main bore. The large circumference of main bore provides greater surface exposure of the arc-extinguishing medium to the heating effects of the arc, thereby enhancing generation of arc-quenching deionizing gases.
  • For low-magnitude faults, after auxiliary arcing rod has traveled about one-half stroke, sufficient deionization has occurred to extinguish the arc.
  • For moderate-to-high faults, after main arcing rod has traveled about one-half stroke, sufficient deionization has occurred to extinguish the arc. The fluorescent fire-orange target is visible in the “blown-fuse” indicator window of the holder.


Fault Interruption of SM-20, SML-20, and SM-40 Power Fuses:

  • Overcurrent melts the silver fusible element. The strain wire severs, initiating arcing.
  • Released force of drive spring accelerates arcing rod upward, causing rapid elongation of the arc in the solids-material-lined bore.
    • Under maximum fault conditions, heat from confined arc causes solid material in the large-diameter lower section of the arc-extinguishing chamber to undergo thermal reaction, generating turbulent gases and effectively enlarging the bore diameter so that the arc energy is released with a mild exhaust.
    • Under low-to-moderate fault conditions, arc is extinguished in small-diameter upper section of the arc-extinguishing chamber, where deionizing gases are effectively concentrated for efficient arc extinction.
  • Continued upper travel of the arcing rod after arc extinction causes actuating pin to penetrate the upper seal, resulting in projection of the brilliant-red blown-fuse target from the upper end fitting.

Disconnect 45° Opening Style
SM-20, SM-40, SM-4Z, SM-5S, SML-20, and SML-4Z Power Fuses are available in the Disconnect 45 Opening Style

SML-20


Non-Disconnect Style
SM-4Z, SM-5S, and SM-5SS Power Fuses are available in the Non-Disconnect Style

SM-4Z

S&C Standard Speed
Curve TypekV Nom. RatingsFuse TypeTCC NumberPDFExcel
Minimum Melting All SMU-20 and SMU-40 TCC Number 153-2 PDF EXCEL
Total Clearing 4.8 SMU-40 TCC Number 153-2-1-4 PDF EXCEL
Total Clearing 14.4 SMU-20 TCC Number 153-2-2 PDF EXCEL
Total Clearing 14.4 and 25 SMU-40 TCC Number 153-2-3-4 PDF EXCEL
Total Clearing 25 and 34.5 SMU-20 TCC Number 153-2-4 PDF EXCEL
S&C Standard Speed for VTs
Curve TypekV Nom. RatingsFuse TypeTCC NumberPDFExcel
Minimum Melting All SMU-20 and SMU-40 TCC Number 115-2 PDF EXCEL
Total Clearing 4.8 through 25 SMU-40 TCC Number 115-2-3-4 PDF EXCEL
Total Clearing 14.4 through 34.5 SMU-20 TCC Number 115-2-4 PDF EXCEL
S&C Slow Speed
Curve TypekV Nom. RatingsFuse TypeTCC NumberPDFExcel
Minimum Melting All SMU-20 and SMU-40 TCC Number 119-2 PDF EXCEL
Total Clearing 4.8 SMU-40 TCC Number 119-2-1-4 PDF EXCEL
Total Clearing 14.4 SMU-20 TCC Number 119-2-2 PDF EXCEL
Total Clearing 14.4 and 25 SMU-40 TCC Number 119-2-3-4 PDF EXCEL
Total Clearing 25 and 34.5 SMU-20 TCC Number 119-2-4 PDF EXCEL
S&C Very Slow Speed
Curve TypekV Nom. RatingsFuse TypeTCC NumberPDFExcel
Minimum Melting All SMU-20 TCC Number 176-2 PDF EXCEL
Total Clearing 14.4 SMU-20 TCC Number 176-2-2 PDF EXCEL
Total Clearing 25 and 34.5 SMU-20 TCC Number 176-2-4 PDF EXCEL
S&C “K” Speed
Curve TypekV Nom. RatingsFuse TypeTCC NumberPDFExcel
Minimum Melting All SMU-20 TCC Number 165-2 PDF EXCEL
Total Clearing 14.4 SMU-20 TCC Number 165-2-2 PDF EXCEL
Total Clearing 25 and 34.5 SMU-20 TCC Number 165-2-4 PDF EXCEL
S&C “DR” Speed
Curve TypekV Nom. RatingsFuse TypeTCC NumberPDFExcel
Minimum Melting All SMU-20 TCC Number 175-2 PDF EXCEL
Total Clearing 14.4 SMU-20 TCC Number 175-2-2 PDF EXCEL
Total Clearing 25 and 34.5 SMU-20 TCC Number 175-2-4 PDF EXCEL

S&C Standard Speed
Curve Type kV Nom. Ratings Fuse Type TCC Number PDF Excel
Minimum Melting All SM-4 and SM-5 TCC Number 153-4 PDF EXCEL
Total Clearing 4.6 through 14.4 SM-4 and SM-5 TCC Number 153-4-2 PDF EXCEL
Total Clearing 25 and 34.5 SM-4 and SM-5 TCC Number 153-4-4 PDF EXCEL
S&C Standard Speed for VTs
Curve Type kV Nom. Ratings Fuse Type TCC Number PDF Excel
Minimum Melting All SM-4 and SM-5 TCC Number 115-4 PDF EXCEL
Total Clearing 4.6 through 34.5 SM-4 and SM-5 TCC Number 115-4-4 PDF EXCEL
S&C Slow Speed
Curve Type kV Nom. Ratings Fuse Type TCC Number PDF Excel
Minimum Melting All SM-4 and SM-5 TCC Number 119-4 PDF EXCEL
Total Clearing 4.6 through 14.4 SM-4 and SM-5 TCC Number 119-4-2 PDF EXCEL
Total Clearing 25 and 34.5 SM-4 and SM-5 TCC Number 119-4-4 PDF EXCEL
S&C Coordinating Speed
Curve Type kV Nom. Ratings Fuse Type TCC Number PDF Excel
Minimum Melting All SM-4 TCC Number 179-4 PDF EXCEL
Total Clearing 14.4 SM-4 TCC Number 179-4-2 PDF EXCEL
S&C Coordinating Speed
Curve Type kV Nom. Ratings Fuse Type TCC Number PDF Excel
Minimum Melting All SM-5 TCC Number 173-4 PDF EXCEL
Total Clearing 7.2 and 14.4 SM-5 TCC Number 173-4-2 PDF EXCEL
S&C Capacitor Speed
Curve Type kV Nom. Ratings Fuse Type TCC Number PDF Excel
Minimum Melting All SM-5 TCC Number 174-4 PDF EXCEL
Total Clearing 14.4 SM-5 TCC Number 174-4-2 PDF EXCEL

A new version of the Coordinaide protection and coordination assistant software is now available for use. Key new features include:

  • Download a device’s curve data-points in a .CSV file format.
  • A new notification for “Transformer (Damage Curve)” device indicates how other device TCC curves are affected.
  • Curve selections were updated for the S&C TripSaver® II Cutout-Mounted Recloser:
    • Added NE and NK Speed under “Definite Time and Fuse Link” selection
    • Added a 140-A trip-coil rating for McGraw Type L, V4L, and 4E devices
    • Added “S&C A*” fast curves for McGraw Type 4E, 4H, L and V4L devices
  • A new Provide Feedback feature was added to submit feedback right from the application.
  • An updated User Guide now includes revision history.
Click the link below to access the new version of the Coordinaide protection and coordination assistant software today!


The Coordinaide protection and coordination assistant software lets you quickly and easily select the optimal protective device (e.g., fuses, TripSaver II Cutout-Mounted Reclosers, Vista® Underground Distribution Switchgear, or IntelliRupter® PulseCloser® Fault Interrupters) to:

  • Protect transformers against damaging overcurrents and coordinate with primary- and secondary-side protective devices.  See how S&C's novel Transformer Protection Index (TPI) can be used to determine if the primary fuse will protect against certain types of secondary-side faults, including arcing phase-to-ground secondary-side faults.
  • Protect capacitor units against case rupture.
  • Protect underground cables from insulation damage due to excessive temperatures.
  • Protect overhead conductors from damage due to annealing.
  • Confirm the proper operation of protective devices against incident-arc energy curves for various Personal Protective Equipment (PPE) levels.
  • Selectively coordinate two or more devices in series to minimize service interruptions.

Launch Coordinaide

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