Noah wrote:
Could anyone help me to elaborate this description?
"In certain cases, such as for switchboards, it is possible that the fault may occur or propagate to the line-side of the local protective device."
By the way, how do you deal with the arc flash study for a project only contains single phase service? Even it could be a 200A 240V service?
Thanks!
What their getting at is that the plasma in the arc flash is conducting and the arc itself can travel down the bus. If an arc flash is large enough (a.k.a. huge fireball) it could reach the line side of the protective device and continue arcing ahead of the protective device - even if the device itself trips.
This is why the "limiting" over current device (i.e. the one that you consider will trip to end the event) is a device upstream in a separate enclosure. Unless the equipment is designed so the arc does not propagate to another area i.e. arc resistant equipment.
For low voltage single phase, there are still no official equations yet.