megloff11x
Senior Member
How is the bolted short circuit fault current determined for arc fault calculations?
I work for a utility and can get instatanious information however this doesn't help because it constantly changes. Your utility will give you the maximum avalible fault current. However this is also a future number for things like transformer upgrades ect. What you really want is a realistic value for avalible fault current. I don't have an easy answer on how to get this.Originally posted by don_resqcapt19:
This is the biggest problem with arc flash calculations...you can't get the information that is required to make the calculations
Originally posted by bob:
Therefore never take anything Ryan says as accurate.
Yes, the calculation shown in this thread gives the short circuit current at the secondary of the transformer based on an infinite utility primary. The fault current will always be some what less than this calculated value.Are you saying that the utility company's capacity to supply enough voltage or current to the primary to produce the full kVA rating of the transformer is unknown...
... and constantly changing ...Yes, the actual available current on the line side changes as normal operating changes are made on the utility distribution system.
Yes, in fact, because the duration of the fault (arc) is based on the clearing times of the OCPDs in the circuit, and because these devices trip faster with higher fault currents, the duration of the arc and the total incident energy often goes up when the fault current goes down.... and therefore an arc could last longer, and there could be more heat produced?
Don