In the UL Whitebook, in the section ELECTRICAL EQUIPMENT FOR USE IN ORDINARY LOCATIONS (AALZ), page 47:
A Type 3R enclosure may be marked ??Rainproof??
For equipment designated ??Rainproof,?? testing designed to simulate exposure to a beating rain will not interfere with the operation of the apparatus or result in wetting of live parts and wiring within the enclosure.
Therefore, by the definition of rainproof, the interier of a NEMA 3R enclosure is a damp location. Type NM cable is not permitted but this may not be enforced in your area.
The next higher standard device rating (above the ampacity of the conductors being protected) shall be permitted to used. provided all of the following conditions are met:
1) the conductors being protected are not part of a multioutlet branch circuit
2) the ampacity of the conductors does not correspond with a standard ampere rating without trip adjustments
3) the next higher device does not exceed 800 amps.
240 is overcurrent protection which allows you to go to the "next higher"
The following commentary from the Handbook explains: Table 210.24 summarizes the requirements for the size of conductors and the size of the overcurrent protection for branch circuits where two or more outlets are required. The first footnote indicates that the wire sizes are for copper conductors. Section 210.3 indicates that branch-circuit conductors rated 15, 20, 30, 40, and 50 amperes must be protected at their ratings. Section 210.19(A) requires that branch-circuit conductors have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. These specific requirements take precedence over 240.4(B), which applies generally. Tables 310.16 through 310.86 list the ampacities of conductors. Section 240.6 lists the standard ratings of overcurrent devices. Where the ampacity of the conductor specified in these tables does not match the rating of the standard overcurrent device, 240.4 permits the use of the next larger standard overcurrent device. All three conditions in 240.4(B) must be met for this permission to apply. However, if the ampacity of a conductor matches the standard rating of 240.6, that conductor must be protected at the standard size device. For example, in Table 310.16, 3 AWG, 75?C copper, Type THWN, the ampacity is listed as 100 amperes. That conductor would be protected by a 100-ampere overcurrent device. The provisions of 240.4(B) do not modify or change the allowable ampacity of the conductor — they only serve to provide a reasonable increase in the permitted overcurrent protective device rating where the allowable ampacity and the standard overcurrent protective device ratings do not correspond. For circuits rated 600 volts and under, the allowable ampacity of branch circuit, feeder, or service conductors always has to be capable of supplying the calculated load in accordance with the requirements of 210.19(A)(1), 215.2(A)(1), and 230.42(A). For example, a 500-kcmil THWN copper conductor has an allowable ampacity of 380 amperes from Table 310.16. This conductor can supply a load not exceeding 380 amperes and, in accordance with 240.4(B), can be protected by a 400-ampere overcurrent protective device. n contrast to 240.4(B), 310.15(B)(6) does permit the conductor types and sizes specified in Table 310.15(B)(6) to supply calculated loads based on their ratings from that table that exceed their allowable ampacities specified in Table 310.16. The overcurrent protection for these residential supply conductors is also permitted to be based on the increased rating allowed by this Article 310 table. Application of 310.15(B)(6) and its table is permitted only for single-phase, 120/240-volt, residential services and main power feeders. The increased ratings given in Table 310.15(B)(6) are based on the significant diversity inherent to most dwelling unit loads and the fact that only the two ungrounded service or feeder conductors are considered to be current carrying. (thank you, Charlie I posted over you as I was busy looking up the documentation)
