My utility company specifies 2" rigid steel conduit for my exterior-mounted, overhead service drop/service entrance. Do I need to use special rainproof fittings when coupling the rigid conduit to the meter box, weather head, and any intermediate couplings? If so, please provide an example. References to the relevant sections of the NEC are also appreciated.
Given that the overhead service drop is likely run outdoors, which'd put it in a wet location, 314.15 applies:
314.15 Damp or Wet Locations. In damp or wet locations, boxes, conduit bodies, and fittings shall be placed or equipped so as to prevent moisture from accumulating within the box, conduit body, or fitting. Boxes, conduit bodies, and fittings installed in wet locations shall be listed for use in wet locations. Approved drainage openings not larger than 6 mm (1/4 in.) shall be permitted to be installed in the field in boxes or conduit bodies listed for use in damp or wet locations. For installation of listed drain fittings, larger openings are permitted to be installed in the field in accordance with manufacturer's instructions.
In general, a fitting labeled "raintight" will be listed for wet location service. Non-raintight, albeit acceptably corrosionproofed, fittings may or may not be -- check with the manufacturer for their suitability.
This appears to be one of those places where things are muddled because the case is not clearly called out specfically - but the contrary case is mentioned.
Threaded RMC connections are tapered pipe threads, designed to hold pressure, as they are used in pipes. Threadless connectors are called out as "needing to be liquid-tight (NEC via conduit maker www.wheatland.com) - Threaded connections are not specifically mentioned, other than the prohibition of leaky threads. In observed practice, ordinary threaded couplings are commonly seen on RMC installions in wet locations, and the "raintight" designation is (almost?) exclusively seen on non-threaded (or non-threaded on one side) connectors.
344.42 Couplings and Connectors. (A) Threadless. Threadless couplings and connectors used with conduit shall be made tight. Where buried in masonry or concrete, they shall be the concretetight type. Where installed in wet locations, they shall comply with 314.15(A). Threadless couplings and connectors shall not be used on threaded conduit ends unless listed for the purpose.
(B) Running Threads. Running threads shall not be used on conduit for connection at couplings.
Part (B) prohibits running (aka straight, untapered, non-sealing) threads on threaded connections. An earlier paragraph specifies taperered threads, and refers to a pipe thread standard:
344.28 Reaming and Threading. All cut ends shall be reamed or otherwise finished to remove rough edges. Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (3⁄4-in. taper per foot) shall be used. FPN: See ANSI/ASME B.1.20.1-1983, Standard for Pipe Threads, General Purpose (Inch).