MIL-PRF-23419/9D
VERIFICATION:
Inspection routine: The number of group II samples for qualification and subgroup 2 samples for group C
inspection shall be as shown in table II.
TABLE II. Group II and subgroup 2 samples. 1/
Inspection
Number of sample fuses
Group II and subgroup 2
20
Terminal strength
20
Overload interrupt
135% at room ambient
4
200% at -55°C
4
200% at +85°C
4
300% at -55°C
4
300% at +85°C
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1/ For characteristic B fuses only, four additional fuses shall be tested
at 200 percent of rating at room ambient temperature.
The number of group III samples for qualification and subgroup 1 for group C inspection, shall consist of four fuses
of each of the styles shown in table III. Short circuit interrupt tests shall be conducted at the alternating current
voltage indicated, and the fuses shall be capable of withstanding a minimum short circuit current as shown in table
III.
TABLE III. Short circuit tests.
Fuse style
Current rating
Short circuit current
AC type voltage
FM09A
4A
35 A
250
FM09A
10 A
100 A
250
FM09A
15 A
200 A
250
FM09A
30 A
10,000 A
125
FM09B
3 2/10 A
35 A
250
FM09B
30 A
10,000 A
125
Fuse selection: The following steps should apply in the selection of a fuse for any application:
Step 1:
Select a fuse with a voltage rating equal to or in excess of the circuit voltage.
Step 2:
The short circuit interrupting rating of the fuse should be checked to determine that it is adequate to
protect against the short circuit currents that the particular equipment or circuit can be exposed to.
Step 3:
The ambient temperature in which the fuse is to be used should be compared to the curves shown on
figure 1 or figure 2 to determine the effect the ambient will have on the current rating. For example, if a
characteristic A fuse is to be used in a 60°C ambient, it will only carry 95 percent of its nominal rating.
A fuse which is used in a -20°C ambient will carry 107 percent of its nominal rating.
Step 4:
A fuse rating should be selected on the basis of equipment ampere load with compensation made for
ambient temperature (see figure 2 and figure 3). Characteristic A and characteristic B fuses should not
be loaded to more than 80 percent of the fuse rating (or 80 percent of the adjusted rating based on
ambient temperature consideration) to avoid nuisance openings caused by inrush currents and other
harmless overloads. Time lag (characteristic B) fuses can be loaded to a higher level because of the
ability to override harmless overloads, transients, and inrush currents of short duration.
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