Significance of Item Category in Authorization rule?

Dear Experts,

I urgently required your help in understanding the Item Category usage in Approval Group.

My Requirement is, to the existing Approval Group setup i need to Include one Item Category with unlimited Approval.

The Buyer who has the limit of 5000USD need to Approve unlimited If the PO contains PRJ.SER category.

Current Approval Group setup:

Document Total 5000USD

Account Range 5000USD          included all range from 0 to 9

Expectation:

Document Total 5000USD

Account Range 5000USD       included all range from 0 to 9

Item Category     99999999999999USD Included      PRJ.SER

Kindly advise if this works.

Thanks.