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Fuse Calculation for Wire single Wire Strip Current Carrying Calculation

3,159 views · Published 2 May 2018 · 3:03 · Indexed 22 September 2026

Channel: Tech Doct · 2018 · Education

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The fusing current in amperes at which a wire will melt can be calculated from the
constant (K) that depends on in the metal used multiplied by the square root of the
wire diameter in inches. Due to the fact there is many factors than can influence the
rate of heat loss, these calculations must be considered as approximates and not
exact.
If the power supply will provide more current (without shutting down or tripping a
curcuit breaker or fuse) than the fusing current listed, it is not a good idea to use
that size wire.
Basic Equations to use for fuses:
Preece Equation: i = A * D^1.5
where A is the constant depending on the metal and D is the diameter if the wire.
I.M. Onderdonk Equation: Ifuse = Area * SQRT(LOG((Tmelt - Tambient)/(234-
Tambient)+1)/Time * 33))
where
Tmelt - melting temp of wire in deg C
Tambient - ambient temp in deg C
Time - melting time in seconds
Ifuse - fusing current in amps
Area - wire area in circular mils
*Circular Mils = the diameter of the wire in thousandths of an inch (mils ) squared.
That is, it is the area of a circle 0.001" in diameter. ( 1 cmil = 0.507E-3 sq mm )
*This equation isn't as valid for non-circular cross sections, or where there isn't free
flow of air around the wire.
Practical Example: Situation is 16 gauge copper wire: Tmelt = 1083, Area = 2581
cmils, Time = 5 seconds, Diameter = .0524 in.
Preece: 10244*.0524^1.5 = 123 Amps
Onderdonk: Ifuse = 2581 * SQRT (LOG((1083-25)/(234-25)+1)/(5*33))
= 2581 * SQRT (LOG(1058/209+1)/165)
= 2581 * SQRT (.0047)
= 178 Amps

For Fuse Rating Link: http://www.litz-wire.com/New%20PDFs/Fusing_Currents_Melting_Temperature_Copper_Aluminum_Magnet_Wire_R2.011609.pdf #relay, #protection, #electrical in tamil, #transformer protection, #generator protection
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