Arc withstand vs short circuit withstand capability

[RRaghunath]

Hai friends,

The subject is switchgear. Short circuit withstand capability is specified as 25kA, 1sec (some utilities specify it to be 3sec).
How about Arc withstand - does the above also mean that the arc withstand shall be for 1sec??

To me, it appears that it is not practical. But, I am not aware of any codal stipulation on the subject. Could you please help.

Thanks.

 

[dpc]

In general, electrical equipment is not tested for arcing faults and have no rating related to arc energy. Short circuit testing is based on bolted faults that have, by definition, no arcing.

So when subjected to an arcing fault, almost anything can happen, including doors flying off, panels blown off, etc. You should not depend on closed door for protection against arcing faults.

There are standards for arc-resistant metal-clad switchgear. That equipment is tested for withstanding forces related to arcing faults.

 

[davidbeach]

To add to what dpc said, arc-resistant gear is arc-resistant only to the extent that when the doors are closed the blast energy is directed elsewhere away from someone who might be standing in front of the gear. In some cases the LV controls are accessible without opening the blast containing doors. The gear itself will still be severely damaged by an arcing fault and will require substantial repair following any arc event.