This is from the UL White Book:
UNDERGROUND FEEDER AND BRANCH CIRCUIT CABLE (YDUX)
Underground Feeder and Branch Circuit CableYDUXGENERAL
This category covers underground feeder and branch circuit cable, rated 600 V, in sizes 14 to 4/0 AWG inclusive, copper, and 12 to 4/0 AWG inclusive, aluminum or copper-clad aluminum, for single and multiple conductor cables. It is designated as Type UF cable and is intended for use in accordance with Article 340 of ANSI/NFPA 70, "National Electrical Code" (NEC).
Some multi-conductor cable is surface marked with the suffix "B" immediately following the type letters to indicate the usage of conductors employing 90?C rated insulation.
Such cable may also be installed as Nonmetallic-sheathed Cable, per Section 340.10(4) of the NEC. The ampacities of Type UF cable, with or without the suffix "B," are those of 60?C rated conductors as specified in the latest edition of the NEC.
Submersible Water Pump Cable ? Indicates multi-conductor cable in which 2, 3 or 4 single-conductor Type UF cables are provided in a flat or twisted assembly. The cable is Listed in sizes from 14 AWG to 4/0 AWG inclusive, copper, and from 12 AWG to 4/0 AWG inclusive, aluminum or copper-clad aluminum. The cable is tag marked "For use within the well casing for wiring deep well water pumps where the cable is not subject to repetitive handling caused by frequent servicing of the pump units." The insulation may also be surface marked "Pump Cable." The cable may be directly buried in the earth in conjunction with this use.
This cable may employ copper, aluminum, or copper-clad aluminum conductors. Cable with copper-clad aluminum conductors is surface printed "AL (CU-CLAD)" or "Cu-Clad Al." Cable with aluminum conductors is surface printed "AL."
Cable employing compact-stranded copper conductors is so identified directly following the conductor size wherever it appears (surface, tag, carton or reel) by "compact copper." The abbreviations "CMPCT" and "CU" may be used for compact and copper, respectively.
Tags, reels and cartons for products employing compact-stranded copper conductors have the marking: "Terminate with connectors identified for use with compact-stranded copper conductors." For conductor termination information, see Electrical Equipment for Use in Ordinary Locations (AALZ ).
This cable may be terminated at boxes and other enclosures by using nonmetallic-sheathed cable connectors [see Nonmetallic-sheathed Cable Connectors (PXJV )].
Cable suitable for exposure to direct rays of the sun is indicated by tag marking and marking on the surface of the cable with the designation "Sunlight Resistant."
