Why isn't the immediate upstream breaker tripping in my 400V Arc Flash simulation?

[Dvhez]

I'm conducting an arc flash study and encountered an issue when testing a bus failure at 0.4kV (MC-002). The protective device immediately upstream of the bus does not open; instead, the device farther upstream does. In the attached case, and according to the TCC, I would expect the breaker that operates to be INCOMING-MC002. However, according to ETAP, the Source PD is the FEEDER-02 device.

What could be the reason why the breaker for the incoming bus does not operate first?

To check attached images in better quality please check this link.

Thank you very much in advance.

 

[wcaseyharman]

In SKM powertools there’s a check box in the report options to include bus/line side arc flash in the analysis, which gives the same result as you have here. I’m not sure if that’s a thing with ETAP but you might check your arc flash analysis options and see if there’s an equivalent setting.

 

[dpc]

Two possibilities:

1. The device further upstream is faster or same curve as the downstream. In other words, the two devices don't coordinate.

2. For low voltage switchboards and panelboards, the local main breaker is often not included in the arc-flash calculation for that bus due to the issue of arc-flash propagation. If the local main breaker is excluded, the program will look upstream for the fastest device. In SKM this is referred to as line side vs load side; in EasyPower it is referred to as "including or excluding" main device. Not sure how is covered in ETAP, but I'm sure it is an option.