To me, "branch fault current" implies that this is the fault current downstream of the overcurrent device (i.e. at the load). The fault current available at the load could be much lower than the fault current available at the breaker.
You should use the fault current that is present either at the overcurrent device, or on an upstream bus if you want to be conservative.
If you're looking at a single source, radial system then bus fault is clearly the only value to look at.
But in a multi-sourced, networked system then you have to look at what the maximum is from each side and base your choice on that. For instance, if you consider a generator breaker; it needs to interrupt the system contribution for a generator fault or the generator contribution for a system fault, but it can't see the total fault current.
I think using of branch fault current will be more appropriate in case of evaluation of devices. The branch fault current will be a pass through current passing through the respective devices in case of Fault. The devices 'KA' rating, can be compared with the branch fault current & devices can be evaluated.
Can anyone elaborate more on this topic with the help of attached single line diagram.
If we want to evaluate KA rating for PD-3, then which fault current should be considered, the one appearing at the bus PANEL or the fault current going through the branch i.e. CBL-4?
Branch fault would be most appropriate, I would think. The current produced can be compared with the ratings of the devices and the protective device settings modified accordingly.
I use the bus fault level . At the cable terminal of the PD-3, fault current will be essentially the same at the available bus fault current which is the worst case scenario.
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Yes. Generally you use the fault current available when shorting the input terminals to a device. In your single line, it shows the breaker PD-3 connected directly to the bus called Panel so the fault current at this bus is used.
