This week's question is the second part regarding arc flash mitigation.

Judging from the responses to last week's question, many DO attempt to lower the incident energy.
Since people visit the forum from around the world, the answers will not be for a specific cost/denomination of money but rather focus on the scope in terms of: Minimal, Moderate and Major costs.
I know this will be open to some interpretation but we'll give it a try.

This week's question:

What would be a typical cost/scope for reducing the incident energy?
- Minimal Cost - i.e. setting changes, fuse changes, minor modifications
- Moderate cost - i.e. addition of relays, current liming devices, remote operation and similar items
- Major cost - replacement of major equipment, arc resistant equipment, major upgrades

The typical approach I have seen is to do all three of these things, in turn. Start off with the "freebies", adjusting breaker settings, fuse sizes, etc. Move up to upgrading of relays and equipment. And, if there is still some unacceptable values out there, move on to some major capital investments to fix them.

I have found that mitigation can require changes that fall in all 3 categories, but the "moderate cost" category has been implemented most successfully.

There is a preference for changes in the "minimal cost" category, but those solutions can create coordination concerns. Increasing the sensitivity of upstream devices may sacrifice selectivity and result in larger than necessary outages or devices operating under normal conditions like motor starting.

As I described in my post in last week’s question of the week, our company does not have a policy yet on what is acceptable as incident energy or how much we should spend on it.

Personally I would push for getting incident energy under 8 cal/cm2 and go up to moderate cost to get the energy under 8 cal.
If the energy is already under 8 cal then I would go for the minimum cost mitigation (but still do it).
If the energy is over 25 cal after doing/calculating/simulating the moderate cost mitigation I would push for major costs. But then again I would do my own risk assessment with experienced engineers on how big the change is that someone would cause an arc flash under those circumstances. The idea being that someone should not even open the doors/covers when that situation is possible (most worst case arc flashes I found are on the MSB (main switch board) when the ship is in ‘full speed ahead’ mode).
When the energy is over 40 cal I would always push for the major costs.

Funny how powerful a few numbers become when you draw a line… (4 8 25 & 40)