110.24(A) in 2011

[Ponchik]

As I read 110.24(A) i am assuming the field marking is only for the service equipment. It does not apply to SDS?

Also, short circuit calculation must be done by a PE, correct? I have never done one and California will be enforcing the 2011 next year.

Thanks

 

[don_resqcapt19]

Correct, the rule only applies to service equipment. You get the fault current information from the power company. The only calculation would be the reduction in available fault current as a result of the impedance of the circuit between the service equipment and the point that the power company used for their fault current number. That point is typically the secondary side of the transformer that supplies the power to the service equipment.
If the number the power company gives you is less that the rating of the service equipment, many just put that number on the required sign.

 

[templdl]

From a selling point of view what I have always advised my customers was to is start out by going with the max available fault current available on the primary of the transformer is with 100% motor contribution and see where you end up. It may be that that it isn't worth the extra effort to go through the addition calculations and studies to fine tune what the actual available fault current is.
Then if you see that it would benefit you to get the actual available fault current from the POCO that mat allow you to go from 100kaic equipment to 65kaic equipment then it may pay off. But going from 90 to 75 you are still having to us 100kaic equipment..
Then if you get down to 75 it my pay to get a study done to get you to the 65 and under category and what the equipment needs to be braced for. There may be a significant savings in doing so.
It is of my opinion that what it amounts to a cost of a study to what you may benefiting by reducing the cost if the distribution gear. Before and after a study you may gain nothing but the addition cost of doing the study.

 

[Ponchik]

Thank you gentleman.