Fuse
Fuse
A fuse is a
Embedded Files
various fuses
Fuse construction
End caps or lugs connect the fuse into the circuit.
End caps or lugs connect the fuse into the circuit.
Current flows through the fuse element.
The body holds and aligns the end caps.
The fuse element has small resistance.
Current flows through the fuse element and produces
heat.
Heat in the fuse = Pfuse = Ifuse2 x Rfuse
At or below the fuse rating the heat is insufficient to melt
the fuse
What occurs if the current goes up by 10%
Pfuse = Ifuse2 x Rfuse - at rated current
Pfuse 110% = (Ifuse x 1.1)2 x Rfuse
= 1.21 (Ifuse2 x Rfuse)
= 1.21 Pfuse
A small (10%) increase in current leads to a 21% increase
in heat – the fuse melts.
The right fuse element has melted maybe due to short circuit current.
Overloads make small breaks in the fuse element.
large fuses often use blades for connection into the circuit
Filler in a fuse is often
silicate sand.
The filler helps quench the arc.
satisfy, extinguish
Connecting the fuse The fuse connection to the circuit should have very low resistance.
Low resistance means little heating.
Ensure the Right Fuse is Used Why does the left fuse blade have a slot?
A fuse holder only accept fuses with a slot.
This system only accepts fuses that can handle high fault currents
fuse holder: a component that securely hold a fuse in an electrical circuit, ensuring it's connected for replacement if a fuse blows.
Fuse rejection examples
Plug fuses
Plug fuses
Plug fuses replaceable safety devices for electrical plugs to protect wirings and appliances from overcurrent, which could cause overheating or fire.
They're no longer used in new installations but use note colour coding
They're small cylindrical/rectangular component in a plug, made to break the circuit if current flowing through it passes a safe level.
If overcurrent occurs (e.g. due to short circuit or overload), the metal element in a fuse melts, stopping electricity flow and potential damage.
Non-interchangeable fuses
Non-interchangeable fuses
14-204 Non-interchangeable fuses (in Appendix B)
Where plug fuses are used in branch circuits, they shall be of such a type and installed so that they are non-interchangeable with a fuse of larger rating.
Where any alterations or additions are made to an existing fusible panelboard, all the plug fuses in the
panelboard shall be made to comply with the requirements of Subrule (1).
Plug Fuse Rejectors
Plug Fuse Rejectors
Fuse rejectors installed in the bottom of a fuse holder prevent overfusing
Time-delay fuses
Time-delay fuses
Time-delay fuses are also called slow-blow, dual element, fusetrons, type “D” plug fuses.
Time-delay fuses 1
Fuses are often manufactured in a standard and a time-delay configuration.
These are crucial for motor applications.
Time-delay fuses 2
With the standard fuse, 300 amps open the fuse in 10 seconds.
The time-delay fuses takes ~20 seconds.
Operation sequence
Operation sequence
A 100 amps rated fuse with a 80 amps load.
A common arrangement.
The fuse is cool and should last indefinitely.
Now the fuse rating is exceeded, it heats up.
If current drops under 100 amps, it's fine.
At 150 A, it melts.
Fuse resistance goes up, causing more heat.
Arcing starts, resistance goes up and current drops.
The circuit opens and current stops flowing.
Another possible sequence Normal operation. A short circuit occurs.
If the fuse can’t interrupt the current, this is what occurs.
Equipment damage, conductor failure, injuries....
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