The main difference between THW and THHN wire is the insulation construction and the conditions covered by the complete wire marking. Common copper THW building wire has PVC insulation without a nylon covering; THHN has PVC insulation with a nylon covering. For purchasing, compare the required wire designation, conductor size, installation environment and supporting documents. A quotation described only as “THHN” does not establish the wet-location rating, and matching conductor sizes do not make two products interchangeable.
Compare building wire options: View our TW/THW wire and THHN/THWN wire product pages. Include the complete designation from your project schedule when requesting specifications or pricing.
THW vs THHN: Insulation and Nylon Covering
Both types are used as individual building conductors in permitted wiring systems. The comparison below concerns common copper constructions; the approved product data sheet controls the actual supply.
| Purchasing detail | THW wire | THHN wire |
|---|---|---|
| Insulation | Commonly PVC | Commonly PVC |
| Nylon covering | Normally absent | Nylon covering over the insulation |
| Conductor construction | Specify solid or stranded copper | Specify solid or stranded copper |
| Complete designation | Confirm THW; do not combine it with TW or THW-2 | Check whether the product also carries THWN or THWN-2 |
| Finished diameter | Obtain the value for the exact size and construction | Obtain the value for the exact size and construction |
| Installation | Confirm the permitted raceway and environment | Confirm the permitted raceway and environment |
| Documents | Match the data sheet and certification scope to the order | Match the data sheet and certification scope to the order |
The nylon covering is a construction difference, not proof that a wire is suitable for every outdoor or wet application. It also does not establish direct-burial suitability.
For a buyer comparing samples, ask for a construction drawing showing the conductor, insulation and any outer covering. A glossy surface or a larger outside diameter is not enough to identify the wire or assess compliance.
If your schedule includes other cable families, use our electrical wire guide for the Philippines to separate individual building wire from flexible cords and complete cable assemblies.
Read the Complete Marking Before Comparing Ratings
The letters matter. In the general wiring designation system explained by UL Solutions, T identifies thermoplastic insulation, H denotes a 75°C rating, HH denotes 90°C, N identifies a nylon jacket, and W indicates moisture resistance. The full type designation and applicable product requirements must be read together.
For the conventional building-wire types discussed here:
| Wire designation | Temperature and location reference | Buyer action |
|---|---|---|
| TW | 60°C, wet or dry | Keep TW separate from THW on the purchase order |
| THW | 75°C, wet or dry | Verify the exact THW product and supporting documents |
| THHN | 90°C, dry | Do not infer a wet-location rating from THHN alone |
| THHN/THWN | 90°C dry under THHN; 75°C wet under THWN | Preserve both designations in the order |
| THHN/THWN-2 | 90°C wet or dry under THWN-2 | Verify that the supplied wire actually carries THWN-2 |
These are designation references, not a declaration that every listed construction is available from KingForYou. Confirm the proposed product’s marking, data sheet and certificate before ordering.
Our TW/THW product page distinguishes TW at 60°C from THW at 75°C. Our THHN/THWN product page lists 90°C dry and 75°C wet. Do not change a THHN/THWN quotation into THHN/THWN-2 unless the supplied product and documentation support that designation.
A conductor’s insulation temperature rating is not an ambient-temperature limit or an automatic permission to increase circuit current. Circuit selection also depends on the wiring method, terminal ratings, conductor grouping and other applicable design requirements. Have the project designer approve any proposed substitution.
For the detailed wet/dry comparison, see our THHN vs THWN-2 guide. For document and marking checks, see our UL 83 building wire guide.
What if the quotation says only “THHN”?
Ask the supplier to provide the complete proposed surface legend and the matching data sheet. If your specification requires THWN-2, the order should say so explicitly. A sales shorthand should not replace the required product designation.
The same rule applies to a quotation headed “TW/THW.” Confirm which type is being supplied for each line item rather than accepting one combined description.
Diameter, Pulling and Termination Checks
Two wires with the same nominal conductor size can have different finished diameters. Their insulation thickness, covering and conductor construction may differ. This matters when replacing a product already included in a conduit or termination design.
Compare finished diameter at the same conductor size
Ask each supplier for the nominal finished diameter and the applicable tolerance. Keep the conductor material, size system and solid or stranded construction consistent.
Do not compare a diameter in millimetres with a conductor area in square millimetres. Likewise, do not accept a rounded AWG-to-mm² conversion as proof that two products meet the same specified conductor size.
Avoid a blanket claim that THHN is always a fixed percentage thinner than THW. Any dimensional comparison should use the two actual products being offered.
Confirm the installation information
Ask for the manufacturer’s handling and installation guidance, including the applicable bending limits, pulling limits and lubricant compatibility. A nylon covering alone does not establish a permitted pulling force or a guaranteed reduction in installation time.
If the proposed product differs from the approved schedule, have the installer or designer check the effect on raceway capacity and the pulling arrangement before accepting the substitution.
Match the conductor to the terminals
Record whether the order requires solid or stranded wire. The receiving terminal must suit the actual conductor material, size and stranding, with preparation and tightening carried out according to the equipment instructions.
“Stranded” is not a complete specification: ask for the conductor construction where it affects the connection. A sample that feels easier to bend does not, by itself, establish suitability for the intended terminal.
Compare THW and THHN Quotations on the Same Basis
A lower price per coil is useful only when the offers meet the same purchasing requirement. First determine whether each proposed wire is acceptable for the project. Then compare the commercial terms.
Use this checklist when requesting alternative quotations:
| Quote field | What to specify or confirm |
|---|---|
| Required type | THW, THHN/THWN or another complete approved designation |
| Conductor | Material, nominal size and solid or stranded construction |
| Size system | Exact AWG or mm² requirement from the schedule |
| Ratings | Required voltage and temperature/location ratings |
| Standard | Product standard, edition where specified, and project requirements |
| Certification | Required scheme, certificate reference and covered product range |
| Dimensions | Finished diameter and relevant tolerances |
| Colors and quantities | Length required for each size and color |
| Packaging | Length per coil or reel, number of packs and labeling |
| Traceability | Manufacturer identification, batch reference and agreed wire legend |
| Commercial terms | Currency, quotation validity, delivery basis and destination |
| Availability | Proposed lead time and any minimum order requirements |
Do not compare a THW offer against a THHN/THWN-2 offer as though the only difference were price. If both are acceptable alternatives, ask the project reviewer to confirm that before commercial evaluation.
Example: normalize coil lengths before comparing prices
Suppose one quotation is for 100 m coils and another is for 90 m coils. Ten coils would provide 1,000 m and 900 m respectively—a 100 m difference.
For an initial material-price comparison:
Price per metre = quoted coil price ÷ stated coil length
This is an illustrative purchasing calculation, not a claim about standard KingForYou packaging. Confirm actual pack lengths and compare freight, taxes and delivery terms on the same basis. Even an identical price per metre does not make products with different specifications equivalent.
Have a wire schedule or two competing offers? Send your wire schedule for review. Paste the required type, sizes, colors, quantities and destination into your message. Identify any proposed alternative separately so the quotation can address the correct requirement.
Buyer Checklist: From RFQ to Delivery
Before requesting a quote, collect the project schedule and note any details still awaiting confirmation. You can start an inquiry with incomplete information; label unknown fields rather than guessing.
Before approving an order:
- Match every quoted line to the required wire designation and conductor size.
- Resolve differences between the quotation, data sheet, wire legend and packaging description.
- Check that the required certification documents cover the proposed manufacturer, product and size range.
- Obtain approval for substitutions that affect the project specification.
- Agree on colors, pack lengths, labels and the documents supplied with the shipment.
For Philippine projects, state the required PNS specification and certification documentation in the RFQ where applicable. If the project also specifies UL requirements, list those separately. Ask the supplier to identify the evidence available for the actual offered product rather than accepting a general certification claim.
At receiving inspection, compare the wire legend, packaging labels and delivery documents with the approved order. Record discrepancies before the material is released for installation. A photograph is useful for checking visible information, but it does not replace the agreed inspection or testing requirements.
Frequently Asked Questions
What is the main difference between THW and THHN wire?
For the common copper constructions compared here, THW has PVC insulation without a nylon covering, while THHN has PVC insulation with a nylon covering. Their complete designations also identify different temperature and location conditions. Compare the actual products, not just their catalog names.
Is THHN better than THW?
The right choice is the wire that meets the approved specification and installation conditions. A nylon covering or a higher dry-location temperature rating alone does not make THHN the better purchase for every project.
Can THHN replace THW?
Only after the proposed product has been checked against the required ratings, wiring method, dimensions, conductor construction and project approval. If wet-location suitability is required, THHN alone is not enough to establish it; check the additional designation.
Are TW and THW the same?
No. They are different wire designations. Do not accept a combined TW/THW catalog heading as the final purchase specification. Request the exact type and its matching data sheet.
Does the nylon covering make THHN waterproof?
No. Nylon alone does not establish a wet-location rating, submersible use or direct-burial approval. Check the complete wire marking and the requirements for the intended installation.
Which costs less: THW or THHN?
There is no reliable universal price difference. Request current quotations using the same conductor material, size, quantities, documentation requirements, packaging and delivery basis. Evaluate only alternatives that meet the project requirements.
Request a Building Wire Quotation
Preparing an order for a distributor, contractor or construction project? Request a building wire quotation from KingForYou with your schedule or the details below.
Copy this checklist into the contact form:
- Project country and delivery destination:
- Application and installation environment:
- Required product standard:
- Complete wire designation:
- Conductor material and solid/stranded construction:
- Size in AWG or mm²:
- Required voltage and temperature/location ratings:
- Length required for each size and color:
- Certification and inspection documents required:
- Wire marking and packaging requirements:
- Target delivery date:
- Any proposed alternatives requiring review:
If some details are undecided, send the information you have and identify the open questions. A clear schedule makes it easier to quote the required wire and separate any alternatives for approval.
