I am working in a manufacturing facility and am trying to figure where to get power from for some new equipment that will be replacing some existing production lines.

The configuration of the power distribution will be very different, i.e. centralized control panels as opposed to individual branch circuits. I am trying to determine which load center panels to tap for the feeders needed. But since most panels will almost always look overloaded if you just add up the circuit breaker ratings, I am trying to figure out what rules to use (with the help of the NEC Handbook) to determine what capacity I have left in any given panel, once I remove loads that are going away. Even using 80% of capacity one panel looks overloaded all ready. This does not really surprise me in a 10 year old facililty, but I do not know what other criteria I should be using. Most loads on the new equipment are motor loads.

Can anyone point me in the right directions, please?

I will consult an outside expert if I do not get a good feeling on my own. But I am trying to get re-acquainted with, and get a deeper understanding of, the NEC.

Thank you for all suggestions and pointers.