UL 248-1-2017 pdf download – Low-Voltage Fuses – Part 1: General Requirements.
2.2.13 Non-interchangeability A condition which prevents the inadvertent interchange of fuses because of physical characteristics (slot, groove, pin, overall dimensions, and the like). 2.3 Characteristic quantities 2.3.2 Prospective current The current that would flow in a circuit if a fuse therein were replaced by a shorting bar of negligible impedance. The prospective current is also referred to as the available current and is the quantity to which the interrupting rating, I 2 t, and peak let-through current are normally referred. 2.3.4 Interrupting rating The highest prospective rms symmetrical alternating current or direct current which a fuse will interrupt under specified conditions verified by operation at rated voltage tests. 2.3.4.1 Maximum energy A specified test condition which causes a fuse to experience maximum arc energy during interruption within the first 1/2 cycle. 2.3.5 Current-limiting range The range of prospective currents from the threshold current to the interrupting current rating of a fuse. 2.3.5.1 Threshold current The lowest prospective rms symmetrical current above which a fuse is current limiting. 2.3.5.2 Threshold ratio The threshold current divided by the fuse current rating.
5.2 Voltage rating For AC, the preferred values of voltage are 125, 250, 300, 480, or 600 V ac as specified for the particular fuse class. For DC, the preferred values of voltage are 60, 1 25, 160, 250, 300, 400, 500, or 600 V dc. 5.3 Current rating Typical current ratings are: 1/10, 15/100, 2/10, 3/10, 4/1 0, 1/2, 6/10, 8/10, 1, 1-1/8, 1-1 /4, 1-4/10, 1-6/10, 1-8/10, 2, 2-1/4, 2-1/2, 2-8/10, 3, 3-2/10, 3-1/2, 4, 4-1/2, 5, 5-6/10, 6, 6-1/4, 7, 8, 9, 10, 12, 15, 17-1/2, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000 A. 5.4 Frequency rating The AC frequency rating shall be 48 – 62 Hz. 5.5 Interrupting rating The AC interrupting rating of a fuse under specified conditions correlates to and is in accordance with the fuse classification. The preferred DC interrupting ratings are 10,000, 20,000, 50,000, 100,000, 150,000, 200,000 or 300,000 A at the manufacturer’s option. 5.6 Peak let-through current and clearing I 2 t characteristics The peak let-through current and clearing I 2 t characteristics of a fuse correlate to and are in accordance with the fuse classification.
7.5 Contact alignment Contacts shall be held in substantial alignment by means other than friction between surfaces, unless the press-fitted assembly is not subject to shrinkage or warping due to heat or moisture. 7.6 Body The body of a fuse shall be glass, ceramic, melamine, impregnated glass fiber, or vulcanized fiber. Other materials may be used that are shown by investigation to be acceptable for the purpose. 7.7 Corrosion protection Iron and steel parts shall be protected against corrosion. 8 Tests 8.1 General 8.1.1 Types of tests The highest current rating of each homogeneous series of fuses shall be subjected to the following tests: a) verification of temperature rise and current-carrying capacity; b) verification of overload operation; c) verification of operation at rated voltage; and d) verification of peak let-through current and clearing I 2 t. The number of fuses to be tested is shown in Table 1. Note: If the body material is other than indicated in Clause 7.6, two sets of samples are used for rated voltage tests; one set is conditioned in accordance with footnote (e) and the other set in accordance with footnote (f), of Table 5.