UL 248-1:2000 pdf download – Low-Voltage Fuses – Part 1:General Requirements.
8.2.3 Test method
The current carrying capacity test, which confirms the conventional non-fusing current. 1riV. IS conducted as part of the temperature rise test.
Measurement of temperatures shall be by thermocouples. The thermocouples stiau be secured by Fuller’s earth and watergiass. welding, soldering, or other method that provides thermal contact.
The thermocouples shall consist of iron and constantan or chromel and alumel wires not larger than No. 24 AWG (0.21 mm2).
An alternative method of temperature measurement may be used if upon investigation it is shown that the alternative method provides equivalent results.
8.2.3.1 Fuses rated 600 A or less
Fuses rated 600 A or less shall carry 1.0 I, until temperature stabilization occurs.
Stabilization shall be considered to have occurred when no individual temperature rise reading of 4 consecutive readings taken at 5 mm intervals exceeds the average reading of these 4 readings by more than 2°C and no indication of increasing temperature rise is observed. This average temperature nse reading shall be deemed to be the temperature rise of the fuse.
Thermocouples shall be placed against the center of the top or upper surface of the fuse — midway between the caps or ferrules on the bedy and on each ferrule or blade at the top center of the fuse clip.
8.2.3.2 Fuses rated 601 — 6000 A
Fuses rated more than 600 A shall carry 1.1 l, until temperature stabilization occurs.
Stabilization shall be considered to have occurred when no indiwdual temperature rise reading of 4 consecutive readings taken at 10 mm intervals exceeds the average reading of these 4 readings by more than 2°C and no indication of increasing temperature rise is observed. This average temperature rise reading shall be deemed to be the temperature rise of the fuse.
The test equipment shall be calibrated, with a shorting bar substituted for the fuse to be tested. to produce a temperature rise on the shorting bar within the limits specified in Table 3.
The shorting bar shall be the same length as the fuse for which it is substituted. The cross-sectional dimensions of the shorting bar shall be the same as those of the bus bar. The shorting bar shall be of copper, shall be silver-plated at the terminal connections, shall have holes to permit mounting to the bus bar, and shall be one-piece or laminated without space between the laminations.
During calibration, a thermocouple shall be located at the top center of the shorting bar.
Dunng the temperature test, a thermocouple shall be secured at the lop center of each fuse contact, approximately 6.4 mm (114 in) from the end of the fuse body.
84.3.2 Tests 5a. 5b, 5c
The fuse may be pre-heated by means of a reduced voltage circuit. This current shall be within ± 20 percent of the required test current. The switchover to the test circuit shall be before the arc is initiated. (The switching time should not exceed 1.0 s).
At least one full cycle (or at least 17 ms) of current at rated voltage shall flow before arcing starts.
The time required for the fuse to clear and the duration of arcing are not specified.
8.4.4 Acceptability of test results
The fuse sham operate arid permanently clear the circuit without damage to the components of the complete fuse within the following parameters:
a) there shall be no re-establishment of current. If evidence of a tendency to restrike is noted. application of the recovery voltage shall be continued for 60 s past the time of restrike:
b) the fuse shall not emit molten metal;
c) no external soldered connections shall melt
d) the fuse shail not exhibit movement nor deformation of either or both end caps that would result in more than 3.2 mm (0.125 in) increase in overall length;
e) there shall be no holes in the fuse as a result of this test:
f) the fuse body may discolor but shall be readily identifiable for replacement purposes;
g) for fuses with glass or ceramic bodies, cracking of the body is permissible provided that the fuse remains in one piece, without loss of filler, prior to removal from the holder or test rig; and
h) for the threshold test. fuses shall clear in the first half cycle after closing.