This is a little embarrassing but I have been in the trade a long time and never became prfeicient at load calcs. What book could take the rocket science out of it for me.
Write down a list of the connected load, on a lined paper. On each line put the demand factor in per-centage. On same line write the result of multiplying the percentage times the load. This is the calculated load for each item. Add all these, the result is the total calculated load.