This page focuses on project-level power distribution systems, including medium-voltage cable (MV-105), feeders, and facility-level electrical infrastructure. It does not cover high-voltage transmission systems typically supplied directly by utilities.
Every commercial, industrial, and infrastructure project depends on a reliable power distribution system — from the utility service entrance through medium-voltage switchgear, transformers, main distribution panels, and branch circuit wiring to the final load. The cable connecting these systems must be sized for the load, rated for the installation environment, and compliant with the applicable edition of the NEC and local codes.
Ramcorp Wire & Cable supplies the full range of cable products used in project-level power distribution — from medium-voltage cable (MV-105) for primary service entrances and substation interconnects through building wire for main feeders and branch circuits, tray cable for cable tray distribution, and underground distribution cable for duct bank and direct burial installations.
Cable Types Used in Power Distribution
Power distribution systems use different cable types at each stage of the distribution chain — from medium-voltage primary feeds down to branch circuit wiring. The table below covers the primary cable types, their function, and where they are installed in power distribution and electrical infrastructure projects.
| Cable Type | Function | Common Specs | Where It's Installed |
|---|---|---|---|
| Medium-Voltage Cable (MV-105) | Primary service entrance, transformer feeds, substation interconnects, campus distribution | 5 kV – 35 kV, 1/0 AWG – 500 kcmil, copper or aluminum, 105°C rated | Underground duct banks, MV switchgear rooms, outdoor pad-mount transformer feeds, utility vaults |
| Building Wire (THHN / THWN-2 / XHHW-2) | Main feeders, sub-feeders, branch circuits, panel distribution | 14 AWG – 750 kcmil, 600V, 90°C, copper or aluminum | Main switchgear to distribution panels, MCC feeders, branch circuits, lighting panels |
| Tray Cable (TC-ER) | Power and control in cable tray, exposed runs in industrial and commercial facilities | 14 AWG – 2/0 AWG, 600V, sunlight resistant | Overhead cable tray runs, mechanical rooms, electrical rooms, generator paralleling switchgear |
| Underground Distribution Cable (URD) | Secondary underground distribution from pad-mount transformers to buildings | 600V, aluminum or copper, concentric neutral, direct burial rated | Underground secondary feeds, residential and commercial subdivisions, campus distribution |
| USE-2 / RHH / RHW-2 | Underground service entrance, wet locations, direct burial in conduit | 14 AWG – 4/0 AWG, 600V, 90°C wet, sunlight resistant | Service entrance from utility transformer to main disconnect, underground conduit runs |
| VFD Cable | Variable-frequency drive to motor connections within power distribution systems | Shielded, symmetrical ground, 600V – 2 kV | Between VFDs and motors on pumps, fans, compressors, and conveyors |
| Portable Cord (SOOW) | Temporary power during construction, portable generators, mobile equipment | 12 AWG – 2/0 AWG, 600V, flexible rubber jacket | Construction temporary power, generator hookups, spider boxes, portable substations |
| Tracer Wire | Underground utility locating for non-metallic conduit runs | 12–14 AWG, solid copper, HDPE jacket | Alongside underground PVC conduit, duct banks, and non-metallic pipe per municipal codes |
Power Distribution Chain — Cable at Each Stage
Understanding where cable fits in the power distribution chain helps engineers and procurement teams order the right products at the right quantities. The table below maps the typical distribution stages from utility service point to final branch circuits.
| Stage | Equipment | Cable Typically Used | Typical Conductor Sizes |
|---|---|---|---|
| Primary Service Entrance | Utility metering, MV switchgear, primary fuses or reclosers | MV-105 (5 kV – 35 kV) | 1/0 AWG – 500 kcmil |
| Transformer Feeds | Pad-mount or dry-type transformers, unit substations | MV-105 (primary side), building wire or URD (secondary side) | Primary: 1/0 – 4/0 AWG; Secondary: 250 – 750 kcmil |
| Main Distribution | Main switchboard, main distribution panel, ATS (automatic transfer switch) | Building wire (THHN / XHHW-2), parallel runs for high ampacity | 250 kcmil – 750 kcmil, often parallel sets |
| Generator & Emergency | Standby generators, paralleling switchgear, emergency panels | Building wire, tray cable, portable cord (during commissioning) | 4/0 AWG – 500 kcmil |
| Sub-Distribution | Distribution panels, MCCs, power panels, RPPs | Building wire, tray cable | 1/0 AWG – 4/0 AWG |
| Branch Circuits | Lighting panels, receptacle panels, mechanical equipment | Building wire (THHN / THWN-2) | 14 AWG – 6 AWG |
| Motor Circuits | Motor starters, VFDs, soft starters | VFD cable (for VFD circuits), building wire (for DOL starters) | 10 AWG – 4/0 AWG depending on motor HP |
Key Considerations for Power Distribution Cable
Medium-Voltage Cable Selection
Medium-voltage cable (MV-105) is the backbone of primary power distribution on commercial, industrial, and infrastructure projects. Cable selection must account for system voltage (5 kV, 15 kV, 25 kV, or 35 kV), insulation type (EPR or TR-XLPE), conductor material (copper or aluminum), shield type, and jacket rating. Copper conductors are preferred in space-constrained installations for their smaller OD and easier termination. Aluminum conductors (AA-8000 series) reduce material cost on long duct bank runs where space is not a constraint. See our MV-105 Cable guide for detailed selection criteria.
Conductor Sizing & Ampacity
Proper conductor sizing is critical for safety, code compliance, and system performance. Conductors must be sized for the load ampacity per NEC Article 310 ampacity tables, adjusted for ambient temperature (NEC 310.15(B)), conduit fill and bundling derating (NEC 310.15(C)), and voltage drop limits (typically 3% for branch circuits, 5% overall per NEC 210.19 recommendation). Oversizing feeders to limit voltage drop on long runs is common practice in campus and industrial distribution. Our AWG Wire Gauge Guide covers standard sizes, ampacity tables, and selection criteria.
Underground Distribution & Duct Banks
Underground power distribution is standard on campus facilities, data centers, commercial developments, and infrastructure projects. Cable installed in duct banks must be rated for wet locations (W suffix — THWN-2, XHHW-2, or USE-2 for 600V; MV-105 for medium voltage). Duct bank installations require ampacity derating based on the number of conduits, soil thermal resistivity, and burial depth per NEC 310.60. Direct burial cable (where permitted) must be installed at the minimum cover depths per NEC Table 300.5. Tracer wire is required alongside all non-metallic underground conduit per most municipal codes.
Copper vs. Aluminum Conductors
The copper vs. aluminum decision affects cost, weight, conduit fill, termination requirements, and long-term reliability. Copper is the default for branch circuits, motor connections, and space-constrained feeders. Aluminum (AA-8000 alloy, not legacy EC grade) is cost-effective for large feeders, service entrance conductors, and MV duct bank runs. Aluminum requires properly rated connectors (AL/CU or AL-only), correct torque values, and anti-oxidant compound at terminations. Mixing copper and aluminum at a junction requires listed bi-metallic connectors to prevent galvanic corrosion.
Emergency & Standby Power Systems
Emergency and standby power systems require dedicated feeders from generators and ATS units to life-safety and critical loads per NEC Article 700 (Emergency Systems), Article 701 (Legally Required Standby), and Article 702 (Optional Standby). These feeders must be physically separated from normal power wiring or installed in fire-rated assemblies. Cable for emergency circuits is often the same building wire or tray cable used for normal distribution, but the routing, protection, and labeling requirements are distinct. Generator feed cables must be sized for the generator's rated output and account for any derating factors.
NEC Compliance
Power distribution systems must comply with the current NEC, including Article 230 (Services), Article 240 (Overcurrent Protection), Article 310 (Conductors for General Wiring), Article 392 (Cable Trays), and Article 300 (General Requirements for Wiring Methods). For medium-voltage installations, NEC Article 328 (Medium Voltage Cable) and the applicable sections of Article 310 Part III govern cable selection and installation. Always verify cable ratings and installation methods against the locally adopted code edition and AHJ requirements.
Common Power Distribution Applications
Commercial Buildings & Campus Facilities
Commercial power distribution typically involves an MV service entrance from the utility, step-down transformers, main switchgear, and multiple distribution panels serving HVAC, lighting, receptacles, and elevator loads. Campus facilities (hospitals, universities, corporate campuses) add MV loop distribution between buildings, redundant feeders, and dedicated emergency power systems. Cable quantities scale significantly with building size — a 500,000 sq ft commercial building can require hundreds of thousands of feet of building wire and thousands of feet of MV cable.
Industrial Facilities & Plants
Industrial power distribution serves high-density motor loads, large compressors, and process equipment requiring dedicated feeders from MCCs and power panels. VFD cable is standard for variable-speed motor circuits. Tray cable in overhead cable tray is the preferred distribution method for long horizontal runs in industrial facilities. Industrial systems often include on-site generation, paralleling switchgear, and complex load-shedding schemes that require careful cable routing and sizing.
Data Center Power Infrastructure
Data center power distribution is among the most cable-intensive applications, with redundant A+B power paths from utility through MV switchgear, UPS systems, PDUs, and rack-level branch circuits. See our Data Centers industry page for detailed cable requirements by distribution stage.
Infrastructure & Public Works
Infrastructure projects — transit stations, airports, highway systems, water treatment plants — require power distribution systems designed for long service life, redundancy, and compliance with agency-specific standards (DOT, FTA, FAA). Underground duct bank distribution is standard, and Buy American / BABA compliance is required on most federally funded projects. See our Transportation & Infrastructure and Construction & Infrastructure pages for sector-specific cable guidance.
Related Guides & Resources
- MV-105 Medium Voltage Cable Overview (5 kV – 35 kV)
- THHN vs THWN Building Wire: Ratings & Applications
- AWG Wire Gauge Guide: Sizes, Ampacity & Selection
- Tray Cable Applications & Selection Guide
- Direct Burial Cable: Types, Depth Requirements & Selection
- VFD Cable: Selection & Applications
- Tracer Wire for Underground Utilities
- Made in USA Wire & Cable: Why It Matters for Export
- How to Choose the Right Cable for Your Project
Frequently Asked Questions
What cable is used for power distribution in commercial and industrial buildings?
Commercial and industrial power distribution uses medium-voltage cable (MV-105) for primary service entrance and transformer feeds, building wire (THHN/THWN-2/XHHW-2) for main feeders, sub-feeders, and branch circuits, tray cable (TC-ER) for cable tray installations, and VFD cable for variable-speed motor drives. Underground secondary distribution uses URD cable or building wire rated for wet locations. The specific cable types and sizes depend on the system voltage, load requirements, and installation environment.
What is the difference between MV-105 and building wire?
MV-105 is medium-voltage cable rated 5 kV to 35 kV, used for primary power distribution from utility service points through transformers and substation switchgear. Building wire (THHN/THWN-2) is rated 600V and used for secondary distribution — feeders, sub-feeders, and branch circuits downstream of the transformer. The two cable types serve different stages of the power distribution chain and are governed by different NEC articles.
When should I use copper vs. aluminum conductors?
Copper is preferred for branch circuits, motor connections, and space-constrained feeders due to its higher conductivity and smaller conductor size for the same ampacity. Aluminum (AA-8000 alloy) is cost-effective for large feeders (typically 1/0 AWG and above), service entrance conductors, and long MV duct bank runs. Aluminum requires properly rated connectors, correct torque values, and anti-oxidant compound at all terminations.
What cable is used for underground power distribution?
Underground power distribution uses MV-105 cable for primary circuits in duct banks, URD (underground residential distribution) cable for secondary feeds from pad-mount transformers, and building wire rated for wet locations (THWN-2, XHHW-2, or USE-2) for 600V circuits in conduit. All underground cable must be installed at minimum cover depths per NEC Table 300.5, and tracer wire is required alongside non-metallic conduit runs.
Does Ramcorp supply cable for power distribution projects?
Yes. Ramcorp Wire & Cable supplies medium-voltage cable, building wire (copper and aluminum), tray cable, VFD cable, underground distribution cable, portable cord, and tracer wire for power distribution systems across commercial, industrial, and infrastructure projects. We support large-volume orders with competitive pricing and delivery coordination for multi-phase builds.
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Disclaimer: This guide is provided for informational purposes only and is not installation advice. Installing wire & cable can be dangerous and pose a risk of possible electric shock or other hazards. Specifications, availability, and pricing are subject to change without notice. Always verify product specifications with the manufacturer's current datasheet before ordering. Consult a licensed professional for installation advice.
The information on this page is provided for general reference only and may contain errors or omissions. NEC® is a registered trademark of the National Fire Protection Association (NFPA®). All other trademarks, product names, and brand names referenced on this page are the property of their respective owners. Ramcorp Wire & Cable is not affiliated with or endorsed by these organizations unless explicitly stated.