551.20 Combination Electrical Systems
All converters and transformers shall be listed for use in recreational vehicles and designed or equipped to provide overtemperature protection. To determine the converter rating, the following percentages shall be applied to the total connected load, including average battery-charging rate, of all 12-volt equipment:
The first 20 amperes of load at 100 percent plus
The second 20 amperes of load at 50 percent plus
All load above 40 amperes at 25 percent
Exception: A low-voltage, appliance that is controlled by a momentary switch (normally open) that has no means for holding in the closed position or refrigerators with a 120-volt function shall not be considered as a connected load when determining the required converter rating. Momentarily energized appliances shall be limited to those used to prepare the vehicle for occupancy or travel.