calculate rated current

hello, i hope somene here can help me. let say i want to calculate max current through brass terminal block like this one:
http://www.cableaccs.com/image/brass_earth_terminals_accs-1.jpg
I understand that brass conductivity is 30% of coppers. But this profile hace wholes where wires come etc. How can u calculate what would the be the rated current?
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I suspect there are too many variable to come up with an accurate calculation. For instance, is the block mounted to a chassis which will heat sink it or not? AC or DC? Determining contact resistance will be a problem.
If it was me I would just assume that I max was approximately equal to the I max of any one wire that will fit into it.
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