| Recap |
| In
this lecture we have learnt the following: |
 |
Available Fault Current: This is the maximum rms short circuit current that flows to a faulted node or point. The |
| |
magnitude is limited by the ac impedance to that specific point. The impedance is the sum of the utility source impedance and the in-plant circuit impedance. |
|
Continuous Current Rating: As with all overcurrent devices, most fuses are limited to a continuous loading of 80% of |
| |
their label rating. This is due to the mutual heating between switch, fuse and adjacent devices. |
|
Current limiting Fuse: First generation fuses, e.g. expulsion type, only limit the duration (time) of the fault. The modern |
| |
current-limiting fuse, however, not only limits the duration of the fault, but also limits the magnitude of the fault. |
|
Interrupting Rating: This is the maximum current that overcurrent device can safely interrupt at a stated voltage, |
| |
frequency, and short circuit power factor. Interrupting ratings are expressed in rms symmetrical amperes. It is common for a device rated 200 000 A to have an abbreviated marking such as 200 KA IR. |
|
Voltage Rating: The rms alternating current voltage at which the fuse is designed to operate. Fuses of the 600 V class |
| |
will always function safely on a lesser voltage. For example 600 V fuses are typically used on 480 and 208 V. |
| |
Congratulations, you have finished Lecture 14. To view the next lecture select it from the left hand side menu of the page |
