From $0.20/ft
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Solid THHN/THWN-2 WireFrom $0.20/ft -
Solid THHN/THWN-2 WireFrom $0.20/ft - Solid THHN/THWN-2 WireFrom $0.20/ft
- Solid THHN/THWN-2 WireFrom $0.20/ft
Parent SKU : THN300CST
SKU : THN300CST-250-BK
"The heavy-duty choice for high-amperage industrial power—engineered with dual-rated THHN/THWN-2 insulation and a friction-reducing nylon jacket for maximum reliability in 600V applications."
Why Electricians Choose 300 MCM THHN/THWN-2 Copper The 300 MCM copper building wire is a high-capacity conductor designed for major power distribution. It is the primary choice for 300-amp commercial services, large-scale HVAC systems, and industrial switchgear. The stranded construction is essential at this massive size, providing the flexibility required to "train" the wire into large enclosures and land it securely in high-torque mechanical lugs.
Dual Rated (THHN/THWN-2): Engineered for dry locations up to 90°C (THHN) and wet locations (THWN-2), providing maximum versatility for indoor and outdoor conduits.
Tough PVC/Nylon Jacket: The high-heat and moisture-resistant PVC insulation is protected by a tough, friction-reducing Nylon outer sheath, making for easier pulls through tight bends.
High-Conductivity Copper: Manufactured with soft-annealed stranded copper to provide maximum flexibility and superior electrical conductivity for branch circuits and feeders.
Oil & Gasoline Resistant: The specialized jacket is designed to resist chemical degradation, making it ideal for industrial environments and service station wiring.
Commercial & Industrial Feeders: Supplying power from main service panels to subpanels, distribution boards, and large machinery.
Industrial Motor Supplies: Ideal for powering mid-to-large sized 3-phase industrial motors and heavy manufacturing equipment.
Commercial Building Mains: Used to distribute power from the main service entrance to large distribution panels in retail and office spaces.
UPS & Battery Systems: Providing the high-conductivity backbone for large uninterruptible power supplies in data centers.
Parallel Power Sets: Frequently run in sets of two or three per phase to handle 600A to 800A commercial services.
ENGINEERING OVERVIEW: 300 MCM STR THHN 600V
APPLICATION: Feeder wire for sub-panels, large appliances, and industrial power distribution.
VOLTAGE: Rated for 600 Volts.
CONDUCTORS: Stranded soft-annealed copper.
INSULATION: Heat and moisture-resistant PVC (Polyvinyl Chloride).
JACKET: Tough, abrasion-resistant Nylon.
TEMPERATURE: 90°C Dry (THHN), 90°C Wet (THWN-2).
Ampacity: 285 amps at 75°C | 320 amps at 90°CÂ
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Technical Note: All values are nominal and subject to industry tolerances and manufacturer corrections. Specifications are subject to change without notice. It is the buyer’s responsibility to verify that all materials meet the specific requirements of the project and comply with local electrical codes.
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| Wire Size (AWG/MCM) | 300 MCM |
| Conductor Material | Copper |
| Conductor Type | Stranded |
| Strand Count | 37 |
| Outer Diameter (OD) (in/mm) | 0.766 in. / 19.456 mm |
| Conductor Count | 1 |
| Shield | Unshielded |
| Insulation Type | (THHN) Thermoplastic High Heat-Resistant Nylon-coated |
| UL Listing Numbers | UL 83, UL 1063, UL 758 |
| Voltage Rating | 600V |
| Ampacity Rating | 320 |
| Submersible | No |
| Standards | UL 83 UL VW-1 Size 1/0 & larger suitable for cable tray use MTW per UL 1063 ASTM B1, B3, B8 Federal Spec A-A-59560 |
| Miscellaneous Information | All values are nominal and subject to correction. *90°C Wet/Dry Per NEC Table 310.15 (B)(16) for not more than three conductors in raceway based on 30°C ambient temperature. |
| Primary Applications | General-purpose electrical wiring in commercial, industrial, and residential structures. It's widely used to supply power to outlets, switches, lighting fixtures, and other electrical loads throughout a building |
| Weight per Foot | 0.985 lb |
In-stock orders placed before 3pm EST typically ship within 1-2 business days. Our business days are Monday through Friday; we do not process orders on Saturday, Sunday, or major US Holidays.
You will receive an e-mail with a tracking number within 1-2 business days from the time its shipped. You will also be able to view your order status and tracking numbers in your account order history.
Expedited shipments are delivered Monday-Friday except on US Holidays. The order must be placed before 12pm CST to ship same day ( Mon-Fri Only).
You have 30 days from the day you receive the item to contact us for a return. Returns are subject to a 30% Restocking Fee.
Please contact us at help@wireamerica.com to request a return authorization. Have your order number or name the order was placed with ready and we will email you an RMA (return) number and instructions for return. Currently, we do not offer exchanges. A new order must be placed if you need a different item. If you provide the new order number at the time of your return request, the restocking fee may be lowered.
Orders on any items with a material value of $50 or less are non-returnable.
Get notified when this product is back in stock
Physical Specifications
Technical Specifications
Usage & Installation:
Packaging & Dimensions:
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300 MCM Copper is rated for 320 Amps at 90°C. However, standard commercial equipment and breaker terminations are typically limited to 75°C, which sets the allowable ampacity at 285 Amps. It is frequently used for 250-amp to 285-amp circuits. We always recommend confirming wire size with a licensed electrician before purchasing.
For a standard 4-wire run (three phases and a neutral), a 2.5-inch conduit is the code minimum. However, for easier pulling—especially if there are multiple bends in the run—most contractors prefer using a 3-inch conduit to prevent damage to the nylon jacket.
Not as a single conductor. At the standard 75°C rating, 300 MCM is rated for 285 Amps. To achieve a 400-amp (or higher) rating, you would typically run two conductors in parallel per phase. This configuration is often easier to install than pulling one massive, rigid 600 MCM cable. Always consult with a local electrician or engineer to see what size is best for your project before purchasing.
No. Like all THHN/THWN-2 products, 300 MCM must be installed in conduit (such as Schedule 40 PVC or Rigid Metal Conduit) for all underground applications. For burial without conduit, you must use a cable rated for direct burial, such as Type USE-2 or Aluminum URD.
Yes. At this size, the wire consists of multiple strands of soft-annealed copper. Our Responsive Stranded Copper is specifically designed to be flexible enough to bend into large mechanical lugs while maintaining the maximum possible surface area for electrical conductivity.
MCM stands for Thousand Circular Mils (1,000 Circular Mils). It is a unit of measure used for wires larger than 4/0 AWG. The larger the MCM number, the thicker the wire and the more electricity it can safely carry.
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