ICP-S Technical Manual
Overcurrent Protection Elements
Rev.A
5/13
5. Checks with I
2
t-tCharacteristic Graph
If the steady-state current includes a pulse, surge, or inrush-current, use the I
2
t
graph and check that the ICP will not deteriorate regardless of the mode of the
current or the ICP will not break the steady-state current while the ICP is in operation.
• Even though the Joule integral value of the current wave form designed at your end is
within the safety area, it is recommended that you confirm the steady-state current for
the safety of the components
Refer to the next section, calculate the I
2
t value, and check the position of the I2t value
in the graph. If the value is in the safety area, it is okay to use the selected ICP model.
If the value is, however, beyond the safety area, use an ICP model with higher ratings.
• Note: The inspection and selection of the ICP according to the Joule integral value is
absolutely based on the results of the approximation of the current wave form.
Be sure to inspect all the current wave forms of your application, or otherwise the safety
of the application will not be fully ensured.
• Consider a safety margin with the dispersion of component characteristics taken into
calculation when inspecting and selecting the ICP, if it is impossible to check the worst
current wave form.
I
2
t-t Graph
Breaking current area: The ICP breaks the current in this area.
Deterioration area: Although the ICP does not break the current instantaneously,
the ICP may break the current as a result of ICP deterioration.
Marginal area: The area where the risk of ICP deterioration is low.
Basically avoid using this area.
Safety area: The ICP will not deteriorate or break the current.
Precautions
t (s)
I
2
t (A
2
- ms)
Breaking
current area
Safety area
Deterioration
area
Margin area
I
2
t-t Graph