Multiplex Cables Guide for Overhead and Underground Work (2023 NEC)

Updated: August 20, 2025

TL;DR

Pick the right multiplex set for the environment and scope. Use listed products, size from Table 310.16 with terminal limits per 110.14(C), respect clearances in 230.24 and burial rules in 300.5, and coordinate with PSEG Long Island before you trench or hang a mast. For temp power gaps, stock rugged portable cords. When in doubt, verify with your AHJ and the latest utility service manual.

Why it matters

Multiplex cable sets keep projects moving. They combine two, three, or four conductors into a compact assembly that installs fast, reduces splices, and holds up in tough environments. On Long Island, where utility coordination and site logistics can slow a job, choosing the right set up front saves time, inspection cycles, and callbacks. If you’re weighing overhead service-drop versus underground residential distribution (URD), this guide explains how to size, select, and install according to the 2023 NEC, with local notes for PSEG Long Island and township building departments. Browse our in-stock multiplex cables to match your next service or feeder.

Always verify requirements with your Authority Having Jurisdiction and the current manufacturer instructions before you order or install.

Fundamentals

• What “multiplex” means. A factory-twisted set of insulated phase conductors with, in many overhead sets, a bare or insulated messenger that often serves as the neutral. Common sets: duplex (two conductors), triplex (three), and quadruplex (four). “URD” typically refers to triplex or quad sets for underground distribution.
• Typical materials. Conductors are often AA-8000 series aluminum for light weight and cost efficiency. Insulations you will see include XLP/XLPE (marketed as XHHW-2 or USE-2 depending on listing). Overhead service-drop sets usually include a messenger for mechanical support; URD sets are direct-burial rated and omit the messenger.
• Voltage classes. Most jobsite multiplex products for buildings are 600 V rated. Medium-voltage URD exists for utility distribution, but that falls under separate specs and the National Electrical Safety Code. Building-side work follows the NEC. The service point divides the utility and premises scope; coordinate early with the utility’s service handbook.
• Where they shine.
  • Overhead service-drops/feeders: Triplex with messenger from the utility or from a masthead to the service point where allowed by the AHJ and utility standard.
  • Underground laterals/URD: Direct-burial triplex or quad sets feeding residential service equipment, pedestals, or transformers through sweeps and short risers.
  • Temporary power: For site power, you’ll often pair devices and assemblies with rugged cord sets. See our stocked portable cords for temp applications.
• Listings and markings. Look for USE-2 or XHHW-2 markings for wet locations per 310.10(B) and sunlight-resistant marking where exposed per 310.10(D). Terminations must match the conductor material and temperature rating shown on the equipment.
• Local note, Long Island, NY. PSEG Long Island service requirements and local building department amendments can change attachment heights, mast hardware, and meter location expectations. Get the current utility booklet and clear it with the inspector before trenching or setting a mast.

Next, we map the specific NEC 2023 rules that govern listing, wet-location use, direct burial, and clearances, then step through a practical selection workflow. Keep your spec handy and compare with your site conditions while you review options in multiplex cables.

Code & compliance (NEC 2023)

• Listed and installed per listing. Follow 110.3(B). Match conductor material, lugs, and any oxide inhibitor to the manufacturer’s instructions.
• Termination temperature limits. Most service equipment and panels are 75°C. Size from Table 310.16 using the 75°C column unless 110.14(C) allows otherwise. Use 90°C values only for adjustment/correction math; final ampacity cannot exceed the terminal rating.
• Wet locations and direct burial. USE-2 and XHHW-2 are permitted in wet locations per 310.10(B). Direct-burial assemblies must be listed for that use per 310.10(C) and installed with required cover and marking per 300.5(A) and 300.5(D).
• Sunlight resistance. Where exposed, use conductors marked sunlight resistant per 310.10(D).
• Overhead clearances and attachments. For services above roofs and near openings, comply with 230.24(A) and 230.9, and set the point of attachment per 230.26. For outdoor feeders that are not services, see 225.18 and 225.19.
• Grounding and bonding. At service equipment, comply with 250.24(A)(1) through (A)(5). Keep neutral isolation and bonding in the correct location.
• Pools and similar hazards. Extra separation applies around pools and spas; see 680.9(A) for overhead conductors.
• Interior use of Type USE. Article 338 (see 338.12) limits interior use of Type USE. Choose dual-rated conductors (for example USE-2/XHHW-2) where you must continue inside.
• Local adoption on Long Island. PSEG Long Island and township AHJs may add requirements for mast hardware, meter locations, and clearances. Verify before you trench or set the mast.

Compare listings and ratings while you review stocked options in multiplex cables.

Selection steps

1. Confirm system and scope. Is it premises wiring under the NEC, or utility-side work under the NESC? The service point divides responsibilities.
2. Pick conductor count and construction. Duplex for two-wire, triplex for 120/240 V single-phase with neutral, quadruplex where three-phase or separate neutral/ground are required. Overhead sets often include a messenger that may serve as the neutral; URD sets are direct-burial without a messenger.
3. Choose insulation/listing for the environment. Select USE-2 or XHHW-2 for wet locations per 310.10(B), and sunlight-resistant where exposed per 310.10(D). Confirm 600 V rating for building services/feeders.
4. Size for ampacity and terminations. Use Table 310.16 with the 75°C column for typical equipment per 110.14(C). Apply ambient correction 310.15(B)(1) and any adjustment 310.15(C)(1) if more than three current-carrying conductors are bundled.
5. Check mechanical details. For overhead, verify point of attachment, drip loops, and clearances per 230.26 and 230.24. For underground, verify cover and marking per 300.5 and route around other utilities per local rules.

Need material on site fast? Check current size availability and cut sheets in multiplex cables.

Sizing & configuration examples

Example A: 100 A residential feeder using triplex aluminum URD

• Design: 120/240 V single-phase feeder to service equipment. Conductors are AA-8000 aluminum XHHW-2/USE-2 in a direct-burial set with short risers at each end.
• Terminations: Equipment rated 75°C per labeling. Use Table 310.16.
• Ampacity path (ambient 40°C):
  • Candidate size: 1/0 AWG Al, 90°C ampacity = 135 A (for adjustment/correction).
  • Ambient correction: 90°C factor at 40°C = 0.91. Adjusted = 135 A × 0.91 = 122.85 A.
  • Terminal limit: 1/0 Al at 75°C column = 120 A. Final allowable cannot exceed 120 A.
  • Result: 1/0 Al supports a 100 A feeder, assuming no additional adjustment for more than three current-carrying conductors.
• Burial: Install the direct-burial set per 300.5(A). Typical residential cover for 0–600 V direct-burial cable is 24 in. Install warning tape per 300.5(D) at least 12 in above the cable (coordinate with local standards).

Example B: 200 A dwelling service conductors, underground lateral

• Design: 120/240 V single-family dwelling service lateral, direct burial to the meter then into service equipment.
• Sizing method: Where permitted, apply 310.12 for dwelling service or main power feeder sizing.
• Selection: 4/0 AWG aluminum USE-2/XHHW-2 is commonly acceptable for 200 A under 310.12 when installation meets the article’s conditions. Verify with the AHJ and the utility before ordering.
• Burial and marking: Provide cover per Table 300.5 and install marking tape per 300.5(D) at least 12 in above the cable.

Installation & wiring notes

• Overhead attachment. Use a listed point of attachment at the proper height per 230.26. Maintain clearances above roofs per 230.24(A) and from building openings per 230.9. Form drip loops and keep messenger tension per the manufacturer. Do not attach to trees.
• Messenger/neutral. On many triplex sets the messenger is the neutral. Bond and terminate exactly as shown on the cut sheet. Do not use the messenger as an equipment grounding conductor unless specifically permitted.
• Aluminum terminations. Use Al-Cu rated connectors, clean as instructed, apply oxide inhibitor if the lug maker requires it, and torque to specification per 110.14. Re-torque only if the manufacturer says so.
• Underground transitions. For URD, use long-radius sweeps, seal conduit risers to shed water, and maintain cover per Table 300.5. Install warning tape per 300.5(D) at least 12 in above the cable (or per AHJ/utility standard). Keep separation from gas and other utilities per local rules.
• Sunlight and wet ratings. In exposed areas, select conductors with sunlight-resistant marking per 310.10(D), and USE-2 or XHHW-2 insulation for wet locations per 310.10(B). Confirm the exact listings on the print.
• Inside-the-building question. Many URD sets are marked USE-2/XHHW-2. If the set is only USE-2, Article 338 (see 338.12) limits interior use; typically you may only enter and terminate at the service equipment. Choose dual-rated conductors when you need to continue in raceway indoors.

Testing, commissioning, and documentation

• Pre-energization checks. Verify conductor IDs, phasing, and neutral continuity. Inspect jackets for nicks at bends and terminations.
• Insulation checks. If the manufacturer allows, perform an insulation resistance test at a conservative voltage for 600 V insulation. Record values by conductor. Do not over-test.
• Termination proof. Record torque values, take clear photos of lugs, and capture equipment labels showing temperature ratings per 110.14(C).
• Utility release packet. For service work, prepare trench photos, depth measurements, and a one-line. Keep the inspector and PSEG Long Island requirements front and center.

Troubleshooting

• Excessive sag. Check messenger tension and the point of attachment. Verify clearance per 230.24(A). Rehang with correct hardware if needed.
• Hot lugs. Usually poor termination. De-energize, clean per instructions, re-terminate with Al-Cu lugs, apply oxide inhibitor if specified, and torque correctly.
• Nuisance breaker trips. Recheck ampacity math. Confirm you sized from the 75°C column for 75°C terminals and applied 310.15(B)(1) ambient correction and any 310.15(C)(1) adjustment.
• Water ingress at risers. Add proper sealing fittings and rain-tight connectors. Ensure drip loops are present and oriented correctly.
• Open or high-impedance neutral. Inspect messenger/neutral splices. Replace corroded connectors with listed components and re-torque.

Common mistakes

• Sizing from the 90°C column without applying terminal limits from 110.14(C).
• Using a direct-burial URD set above grade where sunlight resistance is not marked.
• Skipping warning tape or required cover depth from Table 300.5.
• Using connectors not listed for aluminum, or omitting oxide inhibitor where required.
• Assuming the messenger is an equipment grounding conductor. It usually is the neutral.
• Buying USE-2 only cable, then trying to run it indoors for a long distance. Choose dual-rated conductors for clean transitions.
• Forgetting local requirements. PSEG Long Island and township AHJs may add rules for meter location, mast size, and clearances.

Parts to stock + “Shop at Revco”

• URD triplex and quadruplex aluminum sets, 600 V rated, direct burial.
• Overhead triplex with messenger neutral, sunlight resistant.
• Al-Cu mechanical lugs and splice kits rated for aluminum, plus oxide inhibitor.
• Mast hardware, service heads, points of attachment, strain clamps, and drip-loop fittings.
• Conduit sweeps, expansion fittings, raintight connectors, and duct seal for risers.
• Underground warning tape and tracer wire where required.
• Pulling lubricant and compatible electrical tape and heat-shrink.
• Temporary power gear including rugged portable cords.

Get same-day pickup or delivery. Browse current sizes and cut sheets in our multiplex cables category.

When to call the AHJ or an engineer

• Service point location, meter placement, mast sizing, and attachment height disputes.
• Roof clearance exceptions, proximity to windows, decks, or pools.
• Parallel sets, ampacity adjustments beyond Table 310.16 basics, or unusual ambient conditions.
• Shared trenches with gas or telecom, or reduced cover proposals under 300.5.
• Medium-voltage distribution or anything on the utility side of the service point.

Long Island note: Coordinate early with PSEG Long Island service standards and your township building department. Requirements may exceed the NEC.

Safety disclaimer

This guide is for qualified electrical professionals. Follow the 2023 NEC, local laws, and manufacturer instructions. Use listed products, PPE, and test before touch. Always verify requirements with your Authority Having Jurisdiction and the current utility service manual before you order or install.

FAQ

• Can I run a URD triplex indoors? Only if it carries an indoor rating like XHHW-2 and the installation meets the listing. USE-2 alone is not for extended runs inside buildings.
• Is the overhead messenger a neutral? Often yes, but verify the cut sheet. Do not use it as an equipment grounding conductor unless specifically permitted.
• What burial depth should I plan? Many residential 0–600 V direct-burial installs require 24 in of cover with marking per 300.5(D). Check Table 300.5 and local rules.
• How do I size aluminum for 200 A dwellings? 4/0 Al is commonly acceptable under 310.12 when conditions are met. Confirm with the AHJ and utility.
• Do I size from the 90°C column? Use 90°C values for correction/adjustment math, but final ampacity cannot exceed the terminal rating, often 75°C per 110.14(C).
• What about temporary power on site? For flexible drops and devices, pair devices with rugged portable cords. Keep multiplex for feeders and services where listed.

Credits

Author: Revco Editorial Team — Electrical Content Editor
Technical review: Pending — add approved name/credential
Contact: Revco Lighting & Electrical Supply, (631) 283-3600

About Revco Lighting & Electrical Supply

Since 1978, Revco Lighting & Electrical Supply has been helping professionals bring their projects to light—literally. As a go-to source for lighting and electrical products across Long Island, NY and nearby areas, we specialize in supporting contractors, builders, and industry experts with practical solutions and dependable service. Whether it’s a complex commercial build or a simple residential upgrade, we’re here to make sure you have what you need, when you need it.

Sources

1. [1] NFPA. “NFPA 70, National Electrical Code, 2023 Edition.” nfpa.org. Retrieved 08-2025.
2. [2] IAEI Magazine. “Reorganization of Article 310 and Conductor Ampacity Tables.” iaeimagazine.org. Retrieved 08-2025.
3. [3] EC&M. “Overhead Service Drop and Lateral Clearances Explained (NEC 230.24).” ecmweb.com. Retrieved 08-2025.
4. [4] Manufacturer Data. “Triplex Aluminum URD, 600 V, USE-2/XHHW-2.” prioritywire.com. Retrieved 08-2025.