Week 3 Flashcards
What is a Fuse
A fuse is intended to safely isolate a fault preventing damage to equipment
Overcurrent…
Is excess current resulting from either a short circuit or an overload
Overload…
An overload is a current that is in excess of normal current but confined to normal conducting paths. An overload current is typically 1 to 6 times the normal current. An example of a sustained overload is a defective or overloaded motor
Short Circuit…
A short circuit current is not confined to normal conducting pads and current can be several hundred times greater than normal current levels
Voltage Rating…
The max circuit voltage in which the fuse can safely be applied
If the voltage rating is exceeded…
…restrike is possible across the open fuse element
The continuous current rating on the fuse is…
The current that the fuse is intended to normally carry
The interrupting rating…
Is the maximum short circuit current that a fuse can safely interrupt without rupturing
A fuse is said to be current limiting if it…
Operates quickly under short circuit conditions typically in less than 1/2 of a cycle
If distribution systems protective devices are selective…
Only the protective device nearest the faulted system will open
Safety and standards
US is underwriters Labs and Canada is CSA
Fuses operate…
From increased fuse element temperature caused by an over current flowing through them
On a short circuit (Elements)
Several sections of the link melt instantly
The total operating time of current limiting fuses during short circuit conditions can be…
Less than half cycle (8/1000)
Delta
Connected in parallel
