Tell me how this works cause I don't see this at all. Turning down the Instantaneous setting does not change the impedance, available fault current, or the trip time. I don't see how it can affect the arc flash energy.
Well maintenance switches are most effective in cases where you do not have INST protection (Which is common on main breakers), so I chose my words poorly there. Having an INST setting greatly reduces trip times over ST and has a huge effect. The arcing current can be very low but typically will not self sustain below 38% (Ibf) on 480V systems and can be as much as 85% (Ibf).
When you already have an INST setting it may or may not be effective depending on where it is set, the key here is the trip unit will see the arcing current, which depending on several variables can be much lower than the available fault current and may not be high enough to trip the breaker on INST if the setting is high. Lets say you have a 1600A feeder breaker in a system with 30kA available fault current, and the INST is set at 10X. Arcing current could be anywhere from 11,400A to 25,500A, if your INST is 10X it won't trip the breaker until 16,000A, so maybe it works, maybe not. In this senario lowering the INST setting to 6X would have the same effect.
Obviusly there is a lot more detail involved in determining these settings and every breaker needs to be looked at carefully to determine what the best solution is.
Don't most maintenance switches lower the short time? I'm thinking the arc flash energy is porportional to integral[i^2(t)], so the short time portion of the curve is probably the place where the energy is highest and can be affected by lowering the setting.
Most systems actually install a trip setting that is similar to the INST trip and another setting similar to a GF curve. Here is URC's version
http://www.utilityrelay.com/PDFs/Data Sheets/QUICK-TRIP Data Sheet.pdf