The numbers 1-10 before the letter A represents the rating for that A capability. The higher the number, the larger A class fire the unit can handle.
The numbers 10, 20, 40, 60, 80 before the letter B represents the rating for the B capability. Once again, the higher the number, the larger B class fires the unit can handle.
The letter C does not get a rating as the letter only signifies that the unit is electrically non-conductive.