I am just getting started in this and my company has already done a study. Most of our equipment is marked but with a ATPV value not in HRC. My question, is a easy table to convert one to the other. Some tables say that HRC 2 for example is a min of ATPV 8. Is this the lower limit of a HRC 2 or is it the upper limit? Does HRC 2 go from 4 to 8 or 8 to 25? Tried reading thru 70E and it does not seem to be clear to me.

Look at Table 130.7(C)(11).

It provides the minimum ATPV rating per HRC.
For your example: HRC2 requires clothing with a minimum Arc Rating (ATPV) of 8 cal/cm².

The Arc Thermal Performance Value (ATPV) is presented in calories per square centimeter and represents the maximum capability for arc-flash protection of a particular garment. This value is usually sewn onto the outside of the garment in large letters. If your company has done an arc flash hazard analysis and the equipment label displays the ATPV you need to wear FR clothing that is rated that many cal/cm2 or higher.

If you want to relate a given ATPV to a HRC I would do so as follows:

HRC 0 = 0 - 1.1 cal/cm2
HRC 1 = 1.2 - 4 cal/cm2
HRC 2 = 4.1 - 8 cal/cm2
HRC 3 = 8.1 - 25 cal/cm2
HRC 4 = 25.1 - 40 cal/cm2

If you are not performing an arc flash hazard analysis and you’re instead following T130.7(C)(9) then the PPE is assigned based on task and voltage level, not the calculated incident energy (IE). Since the IE is unknown when an analysis is not done, these tasks are assigned a Hazard Risk Category (HRC). The HRC then dictates the minimum PPE ATPV which must be worn when using this method to determine PPE; see T130.7(C)(11).

HRC 0 = N/A
HRC 1 = 4 cal/cm2
HRC 2 = 8 cal/cm2
HRC 3 = 25 cal/cm2
HRC 4 = 40 cal/cm2

Another thread on this topic to check out:
http://www.arcflashforum.com/showthread.php?t=655&highlight=mixing+tables

Thanks A King, I think that is where I was getting confused. I was trying to use both at the same time to figure out what was the right PPE to put on.

I also read the link, I think, although good discussion, people are forgeting that what the code states is a mininum, you must do atleast this. They are not stating that you cannot do both just that you must make sure that the hazard is clearly stated in form "A" or "B". I just received a 70E handbook, I looked this up and the blue explaintion is just as I was thinking.