URD or Underground Residential Distribution cable is the backbone of below-grade power delivery. This direct burial cable has the same basic construction across all types: aluminum conductor, cross-linked polyethylene (XLPE) insulation, and concentric neutral. The only change is how many conductors are bundled together, and that single variable determines where each type belongs in the distribution system.

Let's break down the differences between all of these, with a specific focus on how homeowners use URD cables.

Single URD

Single Conductor Configuration

1 insulated conductor

One hot conductor that carries a single phase. It is installed as individual runs, typically in sets of three for primary distribution or in pairs for secondary distribution. Running a single conductor allows for custom phasing layouts and individual sizing. Each conductor is pulled and terminated independently.

Applications

• Utility primary distribution lines (15 kV, 25 kV, 35 kV class)

• Large commercial and industrial service runs where conductors must be sized independently

• Replacement or repair work where only one conductor needs to be swapped

• Any project requiring custom phasing arrangements or non-standard configurations

• Utility-scale solar and wind farm underground collector systems

Homeowner context

Homeowners rarely purchase a single URD directly. Single-conductor URD is what the utility pulls to your neighbourhood before the transformer. If you see a crew boring under your street and pulling large individual cables, that's a primary single URD going in. You interact with its downstream product, not the cable itself.

Duplex URD

2 Conductors Configuration

1 phase + 1 neutral

A duplex URD has two conductors helically twisted together: one is an insulated phase, and the other is a bare or covered neutral. It has the simplest complete circuit in a single cable and is designed for single-phase service only.

Applications

• Transformer secondary to a single-family home — the last leg of the distribution chain

• Single-phase service entrance for small commercial buildings, outbuildings, sheds, and pump houses

• Rural residential feeders where single-phase power is all that's available

• Short underground runs across a single property (detached garage, pool equipment)

• Private developments with simple single-phase load requirements

Homeowner context

If you're running power underground to a detached garage, a backyard workshop, a well pump, or a shed, and you only need basic 120V outlets, duplex URD is likely what your electrician will spec. One phase is more than enough for small outbuildings, and a duplex keeps it simple and cost-effective.

Triplex URD

Three conductors Configuration

2 phase + 1 neutral

Three conductors twisted together: two insulated phase legs and one bare neutral. It carries 120/240V single-phase, split-phase power, which is the standard residential voltage in the U.S.

Applications

• The workhorse of residential underground distribution that connects the transformer to the meter base in single-family homes

• Subdivision feeders serving multiple homes from a single transformer bank

• Residential developments converting from overhead to underground service

• Mobile home parks, RV parks, and seasonal community hookups

• Secondary distribution across private residential campuses or multi-unit housing

Homeowner context

Triplex is the cable most directly tied to your home's service. When the utility converts your neighborhood from overhead lines to underground, or when you build a new home in a buried-service subdivision, triplex URD is what runs from the transformer pad to your meter base. It also applies to homeowners running power to a large detached garage, a guest house, or any structure that needs a full 120/240V panel with both hot legs, such as EV chargers, dryers, electric ranges, and HVAC.

You would use it instead of copper analogues because aluminium URD provides the same function at a significantly lower cost and is standard for underground utility distribution.

Quadruplex URD

4 Conductors Configuration

3 phase + 1 neutral

Quadruplex URD consists of four conductors: three insulated phase legs plus one bare neutral, all helically stranded. It carries three-phase power: 208Y/120V or 480Y/277V, depending on the system. This is the only URD type capable of true three-phase delivery.

Applications

• Light commercial and retail sites: strip malls, gas stations, small office buildings

• Industrial facilities and manufacturing plants require three-phase motor loads

• University and hospital campuses with distributed three-phase infrastructure

• Large private properties: sports complexes, data centers, warehouse distribution hubs

• Agricultural operations: irrigation pump systems, grain elevators, processing facilities

• Underground service runs where three-phase power must be delivered in a single pull

Homeowner context

Most single-family homes never need quadruplexes, but they come up more than you'd expect. Homeowners with a large hobby shop or woodworking setup running 3-phase machinery, a small farm with irrigation pumps, or a property-level solar-plus-storage system tied to a three-phase inverter may find their electrician specifying quadruplex for the service lateral or a sub-panel feed. It's also the answer when a homeowner converts a commercial property or barn for residential-adjacent use.

Wire color convention:

Blue indicates the insulated phase conductor, and grey indicates the bare or covered neutral conductor.

Nassau National Cable carries all of these URD cable types, including single, duplex, triplex, and quadruplex, and URD remains one of our flagship product categories.