con- nects to the unit circuits. If located outside the park trailer, the device shall be protected against weather and physical damage.
Exception: External low-voltage supply shall be permitted to have the overcurrent protective device within 450 mm (18 in.) after entering the unit or after leaving a metal raceway.
(F) Switches. Switches shall have a dc rating not less than the connected load.
(G) Luminaires. All low-voltage interior luminaires rated more than 4 watts, employing lamps rated more than
1.2 watts, shall be listed.
III. Combination Electrical Systems 552.20
Combination Electrical Systems.
(A) General. Unit wiring suitable for connection to a battery or other low-voltage supply source shall be permitted to be connected to a 120-volt source, provided that the entire wiring system and equipment are rated and installed in full conformity with Parts I, III, IV, and V requirements of this article covering 120-volt electrical systems. Circuits fed from ac transformers shall not supply dc appliances.
(B) Voltage Converters (120-Volt Alternating Current to Low-Voltage Direct Current). The 120-volt ac side of the voltage converter shall be wired in full conformity with Parts I, III, IV, and V requirements of this article for
120-volt electrical systems.
Exception: Converters supplied as an integral part of a listed appliance shall not be subject to 552.20(B).
All converters and transformers shall be listed for use in recreation units and designed or equipped to provide over-temperature protection. To determine the converter rating, the following formula 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 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 unit for occupancy or travel.
(C) Bonding Voltage Converter Enclosures. The non- current-carrying metal enclosure of the voltage converter shall be connected to the frame of the unit with an 8 AWG copper conductor minimum. The grounding conductor for the battery and the metal enclosure shall be permitted to be the same conductor.
(D) Dual-Voltage Fixtures Including Luminaires or Ap- pliances. Fixtures, including luminaires, or appliances
having both 120-volt and low-voltage connections shall be listed for dual voltage.
(E) Autotransformers. Autotransformers shall not be used.
(F) Receptacles and Plug Caps. Where a park trailer is equipped with a 120-volt or 120/240-volt ac system, a low-voltage system, or both, receptacles and plug caps of the low-voltage system shall differ in configuration from those of the 120-volt or 120/240-volt system. Where a unit equipped with a battery or dc system has an external connection for low-voltage power, the connector shall have a configuration that will not accept
120-volt power.