1. We use NFPA 70E (2004): can ETAP 7.0 software be used to filter out any equipment that meets the following 240 V exception?

Arc flash analysis is not required for low voltage electrical
equipment when all the following conditions apply:

a) The circuit is rated 240 volts or less
b) The circuit is supplied by only one transformer
c) The transformer supplying the circuit is rated less than 125kVA

2. I understand many commercial power companies only perform arc flash analysis down to 480 VAC. What do you think? Does it make sense?

Before the 2009 edition of NFPA was added to ETAP, the only way to filter our this equipment was not to fault the buses. Once NFPA 70E2009 was added to ETAP 7.0.0, the program can automatically determine these locations through the Arc Flash Result Analyzer. There is a flag which can be used to determine which locations fall under the listed conditions of NFPA 70E section 130.1 exception A.

It does not make sense to evaluate Arcs to 480 volts. It is well documented that significant incident energy can be generated by low voltage arcs. Further testing may be performed by the IEEE/NFPA collaborative group to determine energy for circuits rated below the NFPA 103.1 exception. Arc flash results should definitely be calculated below 480 volts. The NFPA 70E 130.1 exception may be removed or modified in the NFPA 70E 2011/2012 version which will further require more investigation into the arcs in low voltage equipment.

ETAP Study Case

ETAP Short Circuit Study Case, Arc Flash tab will allow you to select Hazard Cat for LV Equipment, including voltage, transformer size, and for Cat 0 & 1. ETAP also has the capability of running multiple configurations at once using the Scenario Wizzard (great for analyzing different system variables).

ETAP also gives you the option of analyzing incident energy using a varying bus voltage. i.e. you can choose a minimum percent of bus voltage you deem realistic during a fault for the software to determine if there is a worst-case incident energy at a lower operating voltage. For example you can specify that the software analyze arc flash energy down to 85% nominal bus voltage, the program will generate the worst-case incident energy and provide the voltage level it occurred (it will fall somewhere between 85-100% nominal). You will find that arc-flash results are not as intuitive as you may think.