our electrical contractor installed a 4.16kv 200A fused disconnect switch. The short circuit current that this switch could see would be about 40kAic. The switch is only rated for 22kAic. Does the code require that the equipment be rated for the available fault current or can a current limiting fuse be installed which will limit the current to less than 22kAic?
interrupting ratings
- Thread starter tlona1
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If the avaliable fault current at a piece of equipment is 40kA then the equipment must be rated to withstand or interrupt that fault value. Equipment must always be rated to withstand or interrupt a current value that is greater than the avaliable fault current at that location.
You can try to add impedance in the form of cable, or add a reactor in series to try to bring down the avaliable fault current.
zog
Senior Member
- Location
- Charlotte, NC
I assume you mean there is 40kA of avalible fault current, in which case you have a problem. Did you spec the AIC you required to the EC? Did he ask?
we had spec'd 42kaic min and no he did not ask and yes the first response is to make them change it but our schedule is tight and we trying to determine if a current limiting fuse would resolve the issue. It is my understanding that these fuses trip on the 1st 1/4 cycle and therefore would trip well before the 40kaic peak was reached.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
A current limiting fuse would help if you had documentation of a listed combination between the equipment and the fuse, that showed a series rating of 42kA.
A current limiting fuse by itself has benefit, but the downstream dynamic impedance of other devices opening, make it still under rated, unless there is the series rating mentioned above.
A current limiting fuse by itself has benefit, but the downstream dynamic impedance of other devices opening, make it still under rated, unless there is the series rating mentioned above.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
If there was a series rating with a fuse, the fuse would have to be installed upstream of your switch. This would require a 40K switch to hold the fuse, so what have you gained?
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