THWN vs PV Wire: What Is the Difference and Which Should You Use?
- Kanyarugano tanguy nolain
- 33 minutes ago
- 15 min read
THWN and PV wire can both appear in a solar power installation, but they are not the same type of electrical wire and should not automatically be used interchangeably.
THWN and THWN-2 are primarily building-wire designations. They are commonly used in raceways, conduits, cable trays and other protected wiring systems. PV wire, on the other hand, is specifically designed and certified for photovoltaic applications, including exposed wiring around solar modules and other outdoor DC circuits.
The most important difference is therefore not simply the insulation material or cable price. It is the cable’s intended use, certification, voltage rating, environmental resistance and approved installation method.
This guide explains:
What THWN and THWN-2 mean
What PV wire is
The main differences between THWN and PV wire
Whether THWN can be used for solar panels
Whether PV wire can be installed in conduit
Which wire is more suitable for exposed rooftop wiring
How to select the correct wire for different parts of a solar system
What buyers should check before ordering solar cable
THWN vs PV Wire: Quick Comparison
The following table provides a general comparison. Actual ratings depend on the specific product, cable markings, certification documents and installation conditions.
Feature | THWN/THWN-2 Wire | PV Wire |
Primary product category | Building wire | Photovoltaic wire |
Common standard | UL 83 | UL 4703 |
Main purpose | Building, feeder and branch-circuit wiring | DC wiring in photovoltaic systems |
Typical installation | Conduit, raceway or cable tray | Exposed or protected solar-array wiring |
Common voltage rating | Usually 600V | Commonly available in 600V, 1,000V or 2,000V constructions |
Wet-location performance | THWN and THWN-2 are wet-location designations | Commonly rated for wet and dry PV environments |
Typical temperature rating | THWN: commonly 75°C wet; THWN-2: commonly 90°C wet or dry | Depends on certified construction; commonly 90°C wet |
Sunlight resistance | Only when the specific product is marked accordingly | A core feature of UL 4703 PV wire |
Typical insulation | Thermoplastic PVC with nylon covering | Often cross-linked XLPE or XLPO compounds |
Exposed module wiring | Generally not the default choice | Commonly used |
Conduit installation | Common application | Permitted when the product and installation method allow |
Direct burial | Only when specifically listed and marked | Only when specifically listed and marked |
Common solar use | Protected conduit runs and building-side wiring | Module, string and exposed DC wiring |
Relative cable cost | Usually lower | Usually higher because of PV-specific construction and testing |
UL identifies UL 83 as a standard covering thermoplastic-insulated wire and UL 4703 as the standard for photovoltaic wire. UL also describes PV wire as offering enhanced sunlight resistance for solar applications.
What Is THWN Wire?
THWN is a single-conductor building wire commonly used in residential, commercial and industrial electrical installations.
The letters are generally interpreted as:
T: Thermoplastic insulation
H: Heat resistant
W: Suitable for wet locations
N: Nylon jacket or nylon covering
A typical THWN conductor consists of:
A copper or aluminum conductor
Thermoplastic PVC insulation
A thin nylon outer covering
The nylon layer can improve resistance to abrasion, oil and certain chemicals while making the wire easier to pull through conduit.
UL classifies thermoplastic-insulated building wire under UL 83. THWN and related designations are included within that thermoplastic building-wire category.
Where Is THWN Wire Commonly Used?
THWN wire may be used in applications such as:
Residential and commercial building wiring
Feeders and branch circuits
Electrical conduit
Raceways
Cable trays
Industrial control and power wiring
Wet or dry protected locations
Connections between electrical equipment
Southwire describes its THHN/THWN-2 copper building wire as suitable for services, feeders and branch circuits in commercial or industrial applications, particularly in conduits and cable trays.
THWN vs THWN-2
THWN and THWN-2 should not be treated as identical ratings.
A traditional THWN designation is commonly rated:
Up to 75°C in wet locations
Up to 90°C in dry locations, depending on the complete wire marking
THWN-2 is generally rated:
Up to 90°C in wet locations
Up to 90°C in dry locations
The “-2” designation is therefore important when the wire will be installed in a wet environment at a higher operating temperature.
Many products sold today carry multiple markings, such as:
THHN/THWN-2
This means one conductor has been evaluated for more than one approved use. For example, Southwire lists its THHN designation for dry locations up to 90°C and its THWN-2 designation for wet or dry locations up to 90°C.
When specifying wire for a project, do not rely only on the product description provided by a seller. Check the full surface printing and certification documentation to determine whether the conductor is marked THWN or THWN
What Is PV Wire?
PV wire means photovoltaic wire. It is a single-conductor wire developed specifically for the DC side of solar photovoltaic systems.
Typical applications include:
Connections between solar modules
Module-to-module wiring
PV string circuits
Module-to-combiner-box wiring
Combiner-box-to-inverter circuits
Rooftop solar arrays
Ground-mounted solar farms
Solar extension cables
Pre-assembled PV wire harnesses
In North America, PV wire is generally evaluated according to UL 4703, the Standard for Photovoltaic Wire.
UL describes photovoltaic wire as a single-conductor, insulated and potentially jacketed, sunlight-resistant wire designed for photovoltaic power-system interconnections. Depending on the certified construction, PV wire may be rated at 600V, 1,000V or 2,000V.
Typical PV Wire Construction
A PV wire commonly includes:
Stranded bare or tinned copper conductor
Cross-linked insulation
Single-layer or dual-layer cable construction
XLPE, XLPO or another approved cross-linked compound
Black, red or customized outer color
Permanent cable printing for voltage, temperature and certification
Cross-linked insulation is commonly selected because solar wiring may be exposed to:
Ultraviolet radiation
High rooftop temperatures
Rain and moisture
Ozone
Temperature cycling
Mechanical movement
Cold weather
Long-term outdoor operation
However, not all PV wires use exactly the same material or layer structure. The manufacturer’s technical data sheet should identify the actual conductor, insulation, jacket and certified ratings.
What Are the Main Differences Between THWN and PV Wire?
1. Product Standard and Certification
The clearest technical difference is the standard under which each wire is evaluated.
THWN and THWN-2
THWN and THWN-2 are generally covered under:
UL 83 — Thermoplastic-Insulated Wires and Cables
PV Wire
North American photovoltaic wire is generally covered under:
UL 4703 — Photovoltaic Wire
UL states that photovoltaic cable materials are tested according to UL 4703, while thermoplastic building wire used outdoors or in wet locations is tested according to UL 83.
This means that a THWN-2 conductor with sunlight resistance does not automatically become PV wire. It remains a building-wire product unless it is also certified and marked as Photovoltaic Wire.
2. Intended Application
THWN and THWN-2 are designed primarily for general building and industrial wiring.
PV wire is designed specifically for photovoltaic power circuits.
This affects how each cable is normally used within a solar installation.
THWN-2 may be appropriate for:
Conductors inside an approved conduit
Protected wiring between solar equipment
Building-side DC wiring
Inverter AC output circuits
Indoor electrical distribution
Other wiring methods allowed by the applicable electrical code
PV wire is commonly selected for:
Exposed wiring behind solar modules
Module interconnections
Rooftop PV string wiring
Ground-mounted array wiring
Outdoor solar extension cables
Factory-assembled PV connector harnesses
The correct choice depends on the wiring method, voltage, environment, cable listing and locally adopted electrical code.
3. Voltage Rating
Most standard THHN/THWN-2 building wire is rated for 600V.
For example, Southwire’s general-purpose THHN/THWN-2 copper building wire is a 600V product.
UL 4703 PV wire may be available in:
600V
1,000V
2,000V
The availability of higher-voltage constructions is important for modern commercial and utility-scale photovoltaic systems.
However, the cable type alone does not guarantee a particular voltage rating. Buyers must check the voltage printed on the cable.
A wire marked:
PHOTOVOLTAIC WIRE 2000V
can be considered for a 2,000V application when the complete system and local requirements permit it.
A wire marked:
THHN/THWN-2 600V
must not be assumed suitable for a 1,000V or 1,500V DC array.
4. Insulation Material
THWN commonly uses:
PVC thermoplastic insulation
Nylon outer covering
PV wire commonly uses:
Cross-linked polyethylene
Cross-linked polyolefin
Other qualified cross-linked compounds
Single-layer or dual-layer insulation systems
The difference between thermoplastic and cross-linked insulation influences:
Heat resistance
Mechanical performance
Abrasion resistance
Environmental durability
Cold-temperature behavior
Cable flexibility
Overall cable diameter
Long-term outdoor performance
Material names alone are not enough to prove compliance. A cable should be selected according to its certification and final product ratings, not only because the insulation is described as XLPE or XLPO.
5. Sunlight and UV Resistance
PV wire is specifically developed for solar applications where conductors may remain exposed to sunlight for long periods.
UL describes UL 4703 PV wire as offering superior sunlight resistance for photovoltaic applications.
THWN or THWN-2 may also have sunlight resistance, but only when the specific product is tested and marked accordingly.
Look for markings such as:
SUN RES
SUNLIGHT RESISTANT
Do not assume that every THWN-2 product is automatically approved for continuous sunlight exposure.
A sunlight-resistant THWN-2 conductor may provide more installation options than a product without that marking, but it still does not automatically have the same photovoltaic-wire certification or application scope as UL 4703 PV wire.
6. Wet-Location Rating
Both THWN-2 and PV wire can be designed for wet locations, but the ratings are expressed through different product systems.
THWN-2 commonly permits operation at up to 90°C in wet or dry locations.
UL photovoltaic wire may also be rated for wet and dry locations. UL’s PV-wire application guidance describes PV wire as rated for 90°C wet, while higher dry-temperature ratings may be available depending on the construction.
The final allowable ampacity may still be limited by:
Ambient-temperature correction
Number of grouped conductors
Raceway conditions
Overcurrent-protection rules
Local electrical-code requirements
A 90°C insulation rating does not automatically mean that every connected circuit can be designed using the full 90°C ampacity.
7. Exposed Outdoor Installation
PV wire is generally the more appropriate product for exposed module-level and array wiring because it is designed for photovoltaic use and long-term sunlight exposure.
THWN-2 is more commonly installed inside:
Conduit
Raceways
Cable trays
Equipment enclosures
Other approved protective wiring systems
A sunlight-resistant THWN-2 conductor may be allowed in certain outdoor wiring methods, but its suitability should be confirmed from:
Cable surface markings
Manufacturer’s technical data
Product certification
Installation instructions
The locally adopted electrical code
The authority having jurisdiction
NFPA describes the National Electrical Code as a benchmark for safe electrical design, installation and inspection. Actual requirements depend on the code edition adopted in the project’s jurisdiction.
8. Direct-Burial Capability
Neither “THWN” nor “PV Wire” by itself proves that a cable can be installed directly underground.
For direct burial, the product must be specifically listed and marked for that installation.
A suitable PV wire may carry markings such as:
SUN RES DIRECT BURIAL
Southwire, for example, offers UL 4703 PV wire constructions marked for wet or dry locations, sunlight resistance and direct burial.
However, this does not mean every PV wire has a direct-burial rating.
Likewise, standard single-conductor THHN/THWN-2 building wire should not be assumed suitable for direct burial merely because it is rated for wet locations. Wet-location approval and direct-burial approval are separate considerations.
Before underground installation, check:
Direct-burial marking
Cable type
Installation depth
Raceway requirements
Soil conditions
Mechanical protection
Local electrical requirements
9. Cable Outside Diameter
Two wires with the same AWG conductor size may have different overall diameters.
For example, a 10 AWG THWN-2 wire and a 10 AWG PV wire have approximately the same nominal conductor area, but the PV wire may have thicker insulation or an additional outer layer.
Cable outside diameter affects:
Conduit-fill calculations
Connector sealing
Cable glands
Junction-box entries
Minimum bending radius
Cable pulling
Harness assembly
Shipping weight
This is particularly important when choosing photovoltaic connectors.
A connector may accept a 10 AWG conductor but still be unsuitable because the PV cable’s outside diameter does not match the connector seal range.
Always check both:
Conductor size
Finished cable outside diameter
10. Flexibility and Conductor Construction
THWN and PV wire may both be available with stranded copper conductors, but strand count and conductor class can vary.
PV wire is frequently designed for routing around solar modules and mounting systems. Flexible constructions can make it easier to:
Route cable around module frames
Form service loops
Assemble extension cables
Terminate PV connectors
Produce factory-made harnesses
More strands do not automatically mean a cable is suitable for all connectors. The connector contact and crimping tool must be approved for the conductor’s size and strand construction.
11. Price and Total Installation Cost
THWN-2 is usually less expensive per unit length than certified PV wire.
However, cable price should not be considered separately from installation cost.
Using THWN-2 in an outdoor solar project may require:
Conduit
Fittings
Junction boxes
Cable supports
Additional installation labor
More complicated routing
Additional maintenance access
PV wire may have a higher unit price but can be more appropriate for exposed module wiring where its listing allows that installation method.
The better comparison is therefore:
Total installed cost, not only cable price per meter or foot.
Can THWN Wire Be Used for Solar Panels?
THWN or THWN-2 may be used in certain parts of a solar installation when:
The wire is approved for the circuit voltage
The installation method is permitted
Wet-location and temperature requirements are satisfied
Sunlight exposure is addressed
Ampacity and voltage drop are correctly calculated
Equipment terminals accept the conductor
The locally adopted electrical code permits the application
However, THWN should not automatically be used as a direct replacement for UL 4703 PV wire in exposed module-level wiring.
Where THWN-2 May Be Considered
THWN-2 may be considered for:
PV conductors installed inside approved conduit
Protected runs between a rooftop junction box and inverter
Indoor DC wiring
Combiner-box wiring
Equipment connections
Inverter AC output circuits
Building distribution wiring
Where PV Wire Is Usually More Appropriate
PV wire is generally the stronger choice for:
Wiring exposed behind solar panels
Module-to-module connections
Rooftop PV string circuits
Ground-mounted arrays
Outdoor extension cables
Long-term direct sunlight exposure
High-voltage DC array wiring
Pre-assembled PV connector harnesses
The answer is therefore not simply “yes” or “no.”
A more accurate answer is:
THWN-2 may be used in approved protected wiring methods, while UL 4703 PV wire is generally preferred for exposed photovoltaic-array wiring.
Can PV Wire Be Installed in Conduit?
Yes. PV wire can generally be installed in conduit when:
The cable listing allows it
The conduit type is suitable
Conduit fill is correctly calculated
The minimum bending radius is maintained
Temperature and conductor-grouping corrections are applied
The applicable electrical code permits the wiring method
Southwire lists certain UL 4703 PV wire products as suitable for conduits, ducts, troughs, trays and direct-burial applications.
Because PV wire may be larger than THWN-2 of the same AWG size, designers should use the cable’s actual outside diameter rather than estimating conduit fill from conductor size alone.
THWN or PV Wire: Which Should You Choose?
Solar installation area | More typical wire choice |
Exposed wire behind solar modules | PV wire |
Module-to-module connection | PV wire |
Rooftop DC string wiring | PV wire |
Outdoor solar extension cable | PV wire |
Ground-mounted array wiring | PV wire |
DC conductors inside conduit | THWN-2 or approved PV wire |
Protected junction-box-to-inverter run | Depends on design and code |
Indoor inverter DC connection | Depends on equipment and wiring method |
Inverter AC output | THHN/THWN-2 or another approved building wire |
Direct-burial solar circuit | Specifically listed direct-burial cable |
Factory-assembled PV connector harness | PV wire |
General building feeder | THWN-2 or another approved building wire |
The correct product is determined by the circuit and installation environment—not by price alone.
THWN vs PV Wire vs USE-2
THWN, PV wire and USE-2 can all appear in discussions about solar cable, but they have different primary purposes.
Wire type | General purpose |
THWN/THWN-2 | Thermoplastic building wire for protected wet or dry wiring methods |
PV Wire | Photovoltaic-specific wire for exposed or protected PV circuits |
USE-2 | Underground service-entrance wire that may be permitted in certain PV applications when properly listed |
PV wire generally provides broader photovoltaic-specific application coverage than standard building wire. However, exact permissions depend on product markings and the applicable code.
A cable carrying multiple ratings may qualify for more than one installation method. For example, some products may be marked both:
PV WIRE
RHH/RHW-2
DIRECT BURIAL
The complete marking determines the available applications.
How to Read THWN and PV Wire Markings
Cable markings provide critical information about the wire’s approved use.
Example THWN-2 Marking
10 AWG CU THHN/THWN-2 600V 90°C WET OR DRY SUN RES
This may indicate:
10 AWG: Conductor size
CU: Copper conductor
THHN/THWN-2: Wire designation
600V: Maximum rated voltage
90°C WET OR DRY: Temperature and location rating
SUN RES: Sunlight-resistant construction
Example PV Wire Marking
10 AWG CU PHOTOVOLTAIC WIRE 2000V 90°C WET OR DRY -40°C SUN RES DIRECT BURIAL
This may indicate:
10 AWG: Conductor size
CU: Copper conductor
PHOTOVOLTAIC WIRE: PV-wire designation
2000V: Rated voltage
90°C WET OR DRY: Operating-environment rating
-40°C: Cold-temperature designation
SUN RES: Sunlight resistance
DIRECT BURIAL: Approved direct-burial use
Do not rely only on the letters “UL” printed on a wire. UL’s wire and cable application guide explains that surface printing alone should not be treated as complete proof of UL Listing; the complete certification and Listing Mark should be verified.
How to Select Wire for a Solar Project
Step 1: Identify the Circuit
Determine whether the cable will be used for:
Module wiring
PV string wiring
Combiner-box input
Combiner-box output
Inverter DC input
Inverter AC output
Charge-controller wiring
Battery wiring
Grounding
Indoor distribution
Different circuits may require different cable types even within the same solar installation.
Step 2: Confirm Maximum System Voltage
Check the maximum DC system voltage, including the effect of low temperature on module open-circuit voltage.
The cable voltage rating must be equal to or higher than the maximum calculated system voltage.
Step 3: Calculate Circuit Current
Use:
Module short-circuit current
Number of parallel strings
Required safety factors
Continuous-current requirements
Overcurrent-protection rules
Do not size the wire only from the total wattage of the solar panels.
Step 4: Check Ampacity and Derating
Consider:
Ambient temperature
Rooftop temperature
Number of grouped conductors
Conduit installation
Terminal temperature
Cable insulation rating
Overcurrent-protection requirements
Step 5: Calculate Voltage Drop
A wire may pass the ampacity calculation but still produce excessive voltage drop over a long route.
If voltage drop is too high, consider:
A larger conductor
A shorter cable route
A higher system voltage
Moving the inverter or combiner box
Reconfiguring the array
Step 6: Identify the Installation Environment
Determine whether the cable will be:
Exposed to sunlight
Installed in conduit
Installed in a wet location
Installed underground
Attached behind modules
Used indoors
Exposed to oil or chemicals
Installed in an area with extreme temperatures
Step 7: Verify Connector and Terminal Compatibility
Check:
AWG or mm² range
Conductor strand construction
Cable outside diameter
Connector seal range
Terminal temperature rating
Crimping-tool requirements
Pull-out strength
Voltage and current rating
Step 8: Confirm the Required Certification
Depending on the target market, the project may require:
UL 4703
UL 83
cUL
IEC 62930
EN 50618
H1Z2Z2-K
TÜV certification
Additional project-specific approvals
Step 9: Review the Manufacturer’s Data Sheet
The technical data sheet should confirm:
Conductor material
Conductor size
Strand construction
Insulation material
Jacket material
Overall diameter
Maximum conductor resistance
Voltage rating
Temperature range
Minimum bending radius
UV resistance
Wet-location rating
Direct-burial approval
Applicable standards
How to Specify PV Wire for Procurement
To receive an accurate cable recommendation and quotation, provide the manufacturer with:
Required information | Example |
Cable type | UL 4703 PV wire |
Conductor size | 10 AWG |
Conductor material | Tinned copper |
System voltage | 1,500V DC |
Required cable rating | 2,000V |
Installation | Exposed rooftop array |
Temperature range | -40°C to 90°C |
Color | Black and red |
Certification | UL 4703 |
Packaging | 500 ft reel |
Connector requirement | Cable only or assembled connector |
Printing | FRCABLE or private label |
Destination market | United States |
Order quantity | Reel, pallet or container order |
FRCABLE manufactures photovoltaic cables, energy-storage cables and PV wire harnesses for solar developers, EPC companies, distributors and wholesalers. The company offers customizable conductor sizes, cable lengths, jacket colors, printing, packaging and connector configurations.
FRCABLE’s UL PV-wire range includes single-layer and dual-layer UL 4703 constructions, with bare copper, tinned copper and aluminum conductor options for different photovoltaic projects.
Frequently Asked Questions
What is the main difference between THWN and PV wire?
THWN is primarily thermoplastic building wire intended for protected wiring methods such as conduit. PV wire is specifically designed and certified for photovoltaic circuits, including exposed outdoor wiring around solar modules.
Is THWN the same as THWN-2?
No. Traditional THWN is commonly rated up to 75°C in wet locations, while THWN-2 is generally rated up to 90°C in wet or dry locations. Always check the full cable marking.
Can THWN-2 be used for solar panels?
THWN-2 may be used in certain protected parts of a solar installation, such as conductors installed inside approved conduit. It should not automatically replace UL 4703 PV wire in exposed module-level wiring.
Is PV wire required for solar panels?
PV wire is commonly selected for exposed photovoltaic-array wiring because it is specifically designed for solar applications. The exact permitted wire type depends on the project design, product listing and locally adopted electrical code.
Can THWN wire be exposed to sunlight?
Only when the specific THWN or THWN-2 product is marked as sunlight resistant and the installation method permits the exposure. The THWN designation by itself does not prove sunlight resistance.
Can PV wire be installed inside conduit?
Yes. Approved PV wire can be installed in conduit when conduit fill, bending radius, temperature correction and other applicable requirements are satisfied.
Is PV wire suitable for direct burial?
Some PV wire is suitable for direct burial, but not all. The cable must be specifically listed and marked DIRECT BURIAL.
Is THWN suitable for direct burial?
The THWN designation alone does not provide a direct-burial rating. Use only a cable specifically listed and marked for direct-burial installation.
Is PV wire thicker than THWN wire?
PV wire of the same AWG size may have a larger outside diameter because of its insulation thickness or dual-layer construction. The actual diameter should be confirmed from the manufacturer’s data sheet.
Is THWN cheaper than PV wire?
THWN is generally less expensive per unit length. However, conduit, fittings, labor and other protection requirements can increase the total installed cost.
Can THWN handle 1,000V DC?
Most standard THHN/THWN-2 building wire is rated for 600V and should not be used above its printed voltage rating. Check the specific cable marking rather than assuming that all THWN products have the same rating.
Can THWN and PV wire be connected together?
They may be connected within an approved system when the terminal, connector, enclosure and wiring method are suitable for both conductor types. The connection does not transfer the PV-wire rating to the THWN conductor.
Which wire should be used between solar panels and an inverter?
PV wire is commonly used between modules and for exposed array wiring. THWN-2 or another approved building wire may be used for protected sections inside conduit. The final selection depends on voltage, current, environment and local requirements.
What is the difference between UL 83 and UL 4703?
UL 83 covers thermoplastic-insulated building wires such as THWN and THWN-2. UL 4703 covers photovoltaic wire specifically designed for solar power-system interconnections.
Conclusion
THWN and PV wire can both be used within a solar power installation, but they serve different primary purposes.
THWN and THWN-2 are building-wire designations commonly associated with conduits, raceways, cable trays and protected wiring systems. PV wire is specifically developed for photovoltaic circuits and is generally the preferred choice for exposed wiring around solar modules, rooftop strings and ground-mounted arrays.
When comparing THWN vs PV wire, check:
Product standard
Voltage rating
Wet-location rating
Temperature rating
Sunlight resistance
Direct-burial marking
Insulation construction
Cable outside diameter
Connector compatibility
Approved installation method
Do not select solar cable based only on AWG size or price. The cable’s complete markings, certification and installation environment determine whether it is suitable.
FRCABLE supplies UL 4703 PV wire, TÜV-certified solar cable and customized photovoltaic harness solutions for residential, commercial and utility-scale solar projects. Provide your conductor size, voltage, cable length, certification, installation method, connector requirements and order quantity to receive a project-specific cable recommendation.