W-F-1814D
4.7.6.4 Low interrupting ability. Fuses shall be subjected to an rms symmetrical current of not less than 10,000 amperes nor more than 11,000 amperes at a power factor of 50 percent or less. The voltage shall be not less than rated voltage (see 3.1), and at rated frequency (see 3.1). The instant of closure shall be at random with reference to the phase of the voltage wave. Oscillographic records are not required.
4.7.7 Threshold ratio (see 3.11). Fuses shall be subjected to an available rms symmetrical current of not more than the product of the fuse current rating and the threshold ratio (see 3.1), for the fuse being tested. The voltage shall be not less than rated voltage (see 3.1), and the frequency shall be as specified (see 3.1). Oscillographic records shall be used to determine that the circuit was cleared as specified (see 3.11).
4.7.8 Peak let-thru current (see 3.12). Fuses shall be subjected to rms symmetrical currents of 25,000 amperes (if not below threshold), 100,000 amperes, and 200,000 amperes (if not above the interrupting capacity rating). Tolerance on currents is +20, -0 percent. The power factor shall be 20 percent or less. The closing angle shall be essentially at zero of the voltage wave (maximum offset) or later, so as to produce start of arcing within 30 electrical degrees prior to system peak voltage. The peak let-thru current shall not exceed the value specified (see 3.1) when tested on circuits between threshold current and the interrupting capacity rating of the fuse. The test voltage shall be not less than rated voltage (see 3.1). The maximum peak voltage occurring during the interruption shall be not more than 3000 volts. This voltage shall be measured with an instrument having a frequency response that is linear from
50 to 3000 hertz.
4.7.9 Maximum clearing I2T (see 3.13). The maximum clearing I2T shall be determined from an oscillogramshowing the current trace obtained in 4.7.8 . The determination shall be made by application of Simpson's rule or the use of an integrating planimeter as shown in UL 248-1, UL 248-5, or UL 248-8, UL 248-9, UL 248-10, and UL 248-12.
5. PACKAGING
5.1 Packaging. For acquisition purposes, the packaging requirements shall be as specified in the contract or order (see 6.2). When packaging of materiel is to be performed by DoD or in-house contractor personnel, these personnel need to contact the responsible packaging activity to ascertain packaging requirements. Packaging requirements are maintained by the Inventory Control Point's packaging activities within the Military Service or Defense Agency, or within the Military service's system commands. Packaging data retrieval is available from the managing Military Department's or Defense Agency's automated packaging files, CD-ROM products, or by contacting the responsible packaging activity.
6. NOTES
INFORMATION FOR GUIDANCE ONLY. (This section contains information of a general or explanatory nature that is helpful, but is not mandatory).
6.1 Intended use. Fuses furnished to this specification and listed by Underwriters Laboratories Inc. are intended for use in accordance with the National Electrical Code (NFPA 70). These fuses are designed for use on circuits which may be subjected to high short circuit currents, and these fuses are capable of limiting the peak let-thru current
and maximum clearing I2T (see 3.1 and 3.3).
6.1.1 Class G fuses. These fuses provide safe protection for circuits in homes, commercial buildings, and industrial plants of 120/208, 120/240, and 277/480 volts (not to exceed 300 volts line to ground).
6.1.2 Class J fuses. These fuses provide safe protection on circuits of 600 volts or less that have available short circuit currents up to 200,000 amperes. These fuses are fast (no time delay) and are current limiting.
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