When you specify a NEMA rating for an equipment connection, the value is displayed automatically on the drawing.
If you do not want the NEMA rating to be displayed on the drawing, but want to include it in the schedule, use one of the Schedule Notes fields. Manually type in the NEMA rating there. Leave the NEMA Rating field blank.
When you insert the schedule, press the Edit Title, Column Labels, and Column Order button. Change the header for the notes column from the default value to NEMA or whatever you prefer.
More generally, the extra notes columns are included for exactly this purpose. They are there so you can schedule information that we do not have a field for. If you run out of notes and need more fields, you can use other fields the same way. You have to be careful to fill in the fields properly when creating the equipment. Make sure to communicate with any other designers working on the project about how you are scheduling equipment so everyone does it the same way.