Bussmann Division
114 Old State Road
Ellisville, MO 63021
tel: 636-394-2877
fax: 800-544-2570
www.eaton.com/bussmannseries
July 28, 2015
To: Bussmann® series Fuse Customers
Subject: Fuse Time-Current Curves
This document covers our general policy regarding time-current curves and the basic testing
conditions upon which these curves are developed. This applies to all Bussmann series Class L,
Class R, Class H, Class K, Class J, Class T, Class CC, Supplemental (miscellaneous, miniature, micro
and surface mount) and plug fuses.
The opening time tolerances are not listed on the curves as they differ between fuse designs
and the percentage of the overload relative to the amp rating. The following table shows the
tolerances per design and the corresponding overload percentage.
Fuse Type
Fast/Normal Acting
Dual Element/Time Delay
Percent of Rated Current
200%
±20%
±25%
500%
±10%
±20%
1000%
±10%
±10%
All time-current curves must meet the same basic testing requirements when attempting to
duplicate a curve as well as adhering to specific testing conditions relative to each type of curve.
Listed below are the basic conditions required to be followed for accurate verification:
1.
2.
3.
4.
5.
6.
7.
8.
Fuses shall be tested in a single pole fuse block mounted in the horizontal plane.
Fuses shall be tested one at a time.
The ambient temperature shall be +25°C, ±2°C.
The fuse and fuse mounting shall be at +25°C, ±2°C prior to the test.
The conductor size shall be in accordance with the table below.
The fuse block shall be selected based on the appropriate fuse class and current rating.
The test current shall be calibrated using a dummy fuse.
For longer opening times, greater than 3 seconds, the current applied to the test fuse
shall be increased, if necessary, to the correct value within 3 seconds of its inception.
9. The test time shall be from when the current is turned on until the fuse melts open.
Page 2 of 2
Temperature Test Conditions per UL 248
a
Fuse Current Ratings In , A
0 - 30
31 - 60
61 - 100
Minimum Length a, m (ft)
0.6 (2)
0.6 (2)
0.6 (2)
Wire Size, AWG or kcmil (mm2)
8 (8.4)
4 (21.2)
1 (42.4)
101 - 200
201 - 400
0.6 (2)
1.2 (4)
4/0 (107.2)
500 (253)
401 - 600
1.2 (4)
1000 (507)
Any connection to the source of supply shall not be less than 1.2 m (4 ft) long.
The current ratings covered in the testing procedure will include the maximum ampere rating
for each physical size and any construction breaks within a specific size.
If you have any questions, please contact our Application Engineering team at
1-855-BUSSMANN or e-mail fusetech@eaton.com.
Sincerely,
Eaton’s Bussmann Division Application Engineering