Fuse I²t Rating
I²t = I² × t
Quick answer
This calculator solves I²t = I² × t for I²t Value. With Current 2 A, Time 1 s, the result is 4 A²s. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
The I²t (I-squared-t) rating of a fuse represents the thermal energy required to melt the fuse element, measured in ampere-squared-seconds. It is the key parameter for coordinating fuse protection with downstream components like semiconductors, capacitors, and cables. For a fuse to protect a component, the fuse I²t must be less than the component I²t withstand rating. During a short circuit, the fuse must clear the fault before the protected component is damaged by the thermal energy of the fault current.
Variables
- I²t — Thermal energy measure (A²·s)
- I — Fault current (A)
- t — Duration of the fault (s)
Practical Notes
Fuses have two I²t values: pre-arcing I²t (energy to melt the element) and total clearing I²t (including arc energy). For semiconductor protection, the total clearing I²t of the fuse must be less than the I²t withstand of the device. Fast-acting fuses have lower I²t than slow-blow fuses of the same current rating, making them better for semiconductor protection.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| I2t | I²t Value | A²s | — |
| I | Current | A | pA, nA, µA, mA, A, kA |
| t | Time | s | ps, ns, µs, ms, s, min, h |
Step by step
- 1. What you know: Current 2 A, Time 1 s
- 2. The relation: I²t = I² × t
- 3. Substitute: I = 2 A, t = 1 s
- 4. Result: I²t Value = 4 A²s
Worked examples
Minimum range
Given: Current 2 mA, Time 100 µs
Result: I²t Value = 4 × 10⁻¹⁰ A²s
Low range
Given: Current 20 mA, Time 1 ms
Result: I²t Value = 4 × 10⁻⁷ A²s
Typical
Given: Current 2 A, Time 1 s
Result: I²t Value = 4 A²s
High range
Given: Current 100 A, Time 1 min
Result: I²t Value = 600000 A²s
Maximum range
Given: Current 1 kA, Time 10 min
Result: I²t Value = 6 × 10⁸ A²s
Solving for each variable
Solve for I²t Value
Current 2 mA, Time 100 µs → 4 × 10⁻¹⁰ A²s
Solve for Current
I²t Value 0.1 A²s, Time 100 µs → 31.62 A
Solve for Time
I²t Value 0.1 A²s, Current 2 mA → 6.944 h
How I²t Value changes with Current
| Current (input) | I²t Value (result) |
|---|---|
| 0.2 A | 0.04 A²s |
| 0.5 A | 0.25 A²s |
| 1 A | 1 A²s |
| 1.5 A | 2.25 A²s |
| 2 A | 4 A²s |
| 3 A | 9 A²s |
| 4 A | 16 A²s |
| 8 A | 64 A²s |
| 14 A | 196 A²s |
| 20 A | 400 A²s |
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<p><a href="https://vbatpower.com/formulas/fuse-i2t/">Fuse I²t Rating</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Fuse I²t Rating?
Use I²t = I² × t. With Current 2 A, Time 1 s, I²t Value works out to 4 A²s.
How do you calculate i2t fuse rating?
Rearrange for I²t Value: with Current 20 mA, Time 1 ms, I²t Value is 4 × 10⁻⁷ A²s.
How do you calculate fuse calculation formula i squared?
Rearrange for I²t Value: with Current 2 A, Time 1 s, I²t Value is 4 A²s.
What is the formula for Fuse I²t Rating?
The formula is I²t = I² × t. The I²t (I-squared-t) rating of a fuse represents the thermal energy required to melt the fuse element, measured in ampere-squared-seconds.
How do you find Current when you know the other values?
Rearrange for Current: with I²t Value 0.1 A²s, Time 100 µs, Current is 31.62 A.
How do you find Time when you know the other values?
Rearrange for Time: with I²t Value 0.1 A²s, Current 2 mA, Time is 6.944 h.
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