Why does the 372 Series datasheet include 400% and 1000% current data while the 373 Series does not?

If you are looking for the data at 400% and 1000% current levels for the Littelfuse 37306300430 fuse, please note that we have checked this with the manufacturer, and the details are provided below.

The 373 Series is a fuse designed in accordance with UL 248-14.

Since UL 248-14 does not specify opening (blow) characteristics at 400% and 1000% of the rated current, we do not perform data collection under these conditions. Since the 372 Series is an IEC-compliant fuse, its datasheet includes opening characteristic data under these conditions.

On the other hand, opening characteristics at 400% and 1000% of rated current are primarily requirements based on IEC standards.

Regarding time tolerance (maximum operating time) until fuse opening

We would like to adjust our design based on the time tolerance (maximum operating time) until the fuse opens. It would be helpful if there is any documentation showing the time variation.

The variation in opening time for a given current on the Time-Current (TC) curve is generally as follows:

  • At 200% of rated current: approximately ±15%
  • At currents above 200% of rated current: approximately ±6%

Examples are shown below.

Example: 1A rated fuse

Based on the TC curve:

  • 200% of rated current (2A): 10 seconds ±1.5 seconds
  • 400% of rated current (4A): 1 second ±0.06 seconds

The above variations are general guidelines based on the typical values shown on the TC curve.

They do not represent maximum operating times guaranteed by any standard and should not be considered guaranteed values.

Applicable Part Numbers
DigiKey Part Number Manufacturer Part Number
WK3063BK-ND 37315000410
WK3071BK-ND 37321000410
WK3062BK-ND 37314000410
WK3057BK-ND 37312000410
WK3048BK-ND 37311000410
WK3041BK-ND 37305000410
WK6240-ND 37318000410
WK3022BK-ND 37300500410
WK3066BK-ND 37316300410
WK3046BK-ND 37308000410
WK3035BK-ND 37302500410
WK3050BK-ND 37311250410
WK3053BK-ND 37311600410
WK3024BK-ND 37313150410
WK3034BK-ND 37302000410
F4500-ND 37321000430
F4496-ND 37314000430
F4490-ND 37311000430
18-37316300000CT-ND,18-37316300000TB-ND 37316300000
18-37301000000CT-ND,18-37301000000TB-ND 37301000000
18-37321000000CT-ND,18-37321000000TB-ND 37321000000
WK3025BK-ND 37300630410
WK3028BK-ND 37301250410
WK3030BK-ND 37301600410
WK3043BK-ND 37306300410
WK3037BK-ND 37303150410
WK3027BK-ND 37301000410
F4492-ND 37311600430
F4498-ND 37316300430
18-37302000000CT-ND,18-37302000000TB-ND 37302000000
18-37314000000CT-ND,18-37314000000TB-ND 37314000000
18-37312000000CT-ND,18-37312000000TB-ND 37312000000
WK3058BK-ND 37312500410
F4499-ND 37318000430
WK3063CT-ND,WK3063TB-ND 37315000000
18-37300500000CT-ND,18-37300500000TB-ND 37300500000
1294-37311250000-CHP,F5485TB-ND 37311250000
1294-37311000000TB-CHP,F5484TB-ND 37311000000
F4497-ND 37315000430
18-37318000000CT-ND,18-37318000000TB-ND 37318000000
F4489-ND 37306300430
WK3026BK-ND 37300800410
F4488-ND 37305000430
F4493-ND 37312000430
F4495-ND 37313150430
F11306CT-ND,F11306TB-ND 37305000000
18-37308000000CT-ND,18-37308000000TB-ND 37308000000
WK3035TB-ND 37302500000
WK3040TB-ND 37304000000
WK3024TB-ND 37313150000
37301250000-ND 37301250000
37303150000-ND 37303150000
37306300000-ND 37306300000
37311600000-ND 37311600000
37301600000-ND 37301600000
37312500000-ND 37312500000
WK3040BK-ND 37304000410
F4486-ND 37301000430
37301250430-ND 37301250430
37301600430-ND 37301600430
37302000430-ND 37302000430
F4487-ND 37302500430
37303150430-ND 37303150430
37304000430-ND 37304000430
37308000430-ND 37308000430
F4491-ND 37311250430
F4494-ND 37312500430
37300800000-ND 37300800000
37300630000-ND 37300630000
37300500430-ND 37300500430
37300630430-ND 37300630430
37300800430-ND 37300800430