SORIVO · Cable Application Note · North American Building Wire · 2026-09

THHN vs THWN-2 vs XHHW-2: UL 83 vs UL 44 at 12, 10 and 8 AWG — Jacket Markings, Termination Caps and the Ampacity Columns That Decide

All three are sold as “90 °C building wire.” Two of them can be used wet and one cannot, the one with the thicker insulation is not the one you think, and the ampacity you are allowed to use is usually not the column you looked at. Here is the reading order, straight from UL 83, UL 44 and NEC Table 310.16, at the 12, 10 and 8 AWG sizes most North American jobs actually buy.

Published 2026-09-03Updated 2026-09-03Reading ~10 minLevel: Spec & purchase
Direct answer

THHN is a 600 V, 90 °C-conductor thermoplastic wire to UL 83, and on its own it is a dry-location (damp-location permitted) wire. The wet rating is not THHN’s: it belongs to THWN at 75 °C and THWN-2 at 90 °C, which is why the market prints THHN/THWN-2 on the same jacket. XHHW-2 is a different standard altogether — UL 44 (rubber- and cross-linked-polyethylene-insulated wires) — and it holds 90 °C wet and dry.

Then the part that decides your wire size: NEC 110.14(C) caps the ampacity you may use at the termination. For equipment rated 100 A or less you work from the 60 °C column unless the equipment is listed and marked otherwise; above 100 A the 75 °C column is the working default. Our two code references phrase the small-conductor boundary differently — one says 3 AWG and smaller, the other 1 AWG — which is exactly why the marking on the device, not a rule of thumb, is the deciding document. So a 10 AWG wire with a 40 A insulation rating is a 35 A conductor at 75 °C and 30 A at 60 °C. The 90 °C column is for temperature correction and conduit-fill adjustment arithmetic — not for your final ampacity. And the claim that XHHW-2 saves conduit space because of a thinner wall does not survive the standards’ own dimension tables at the sizes we checked: XLPE is thicker than PVC on 14–10 AWG (30 mils vs 20 mils), so XHHW-2 is marginally larger in diameter.

01What each set of letters commits you to

The type letters are not model numbers; they are a construction plus a set of test results, and each one sits under a specific UL standard. Getting the standard right matters when you audit a certificate: a THHN file and an XHHW-2 file are different products directories.

Table 1 — The three types, their standard, and the ratings the standard assigns
TypeUL standard & insulationRated voltageConductor temp, dryConductor temp, wetCopper sizes, as catalogued
THHNUL 83, thermoplastic PVC with nylon jacket600 V90 °Cdry or damp locations; no wet rating on this line alone14 AWG–1000 kcmil (some catalogues to 2000)
THWNUL 83, thermoplastic PVC with nylon jacket600 V75 °C75 °Cas above
THWN-2UL 83, thermoplastic PVC with nylon jacket600 V90 °C90 °Cas above
THHN/THWN-2 (dual-marked)UL 83 — one wire listed to both type lines600 V90 °C90 °Cthe practical market default; our building-wire range is dual-marked
XHHW-2UL 44, cross-linked polyethylene (thermoset)600 V; 1000 V listings exist90 °C90 °C14 AWG–1000 kcmil (some catalogues to 2000)
Voltage and temperature entries are the type lines as written in UL 83 and UL 44 (scope sections and the type/marking tables). Size ranges are what the two large North American catalogues publish — they disagree at the top end (1000 kcmil versus 2000 kcmil), so treat the upper limit as a question for the supplier’s own UL file rather than a spec you can copy. Edition years intentionally omitted: they conflict across the pages we checked.
What the “-2” doesIt changes the wet-location conductor temperature, nothing else. THWN and XHHW take 75 °C wet; THWN-2 and XHHW-2 take 90 °C wet. Dry-location rating is already 90 °C for every one of those types, so on a dry indoor run the “-2” buys you nothing, and on a wet run it is the only thing standing between you and a re-pull.

THHN cable sizes, specifications and colour code

Three questions account for most of the THHN searches we see, and all three have short answers.

  • Sizes. The catalogued copper range for both THHN/THWN-2 and XHHW-2 runs 14 AWG to 1000 kcmil, with some catalogues listing to 2000 kcmil at the top end. Branch circuits live in the 14–10 AWG band; feeders and services start around 6 AWG and run up through 4/0 AWG and beyond. Solid conductors are common at 14–10 AWG; above that, stranded is the practical default. The two large North American catalogues we checked disagree at the top of the range, so treat anything above 1000 kcmil as a question for the supplier’s own UL file rather than a spec you can copy.
  • Insulation type. THHN/THWN-2 is PVC with a nylon jacket over it — the nylon is the abrasion layer that makes a long conduit pull survivable. XHHW-2 is cross-linked polyethylene with no nylon jacket. The ampacity columns in section 03 apply to both; the diameters do not, which is the whole of section 04.
  • Colour code. Jacket colour is not decorative once a project has a colour schedule. Black, red, blue and white are the usual stocked colours for 120/240 V work; green or bare is equipment grounding, and NEC practice reserves white or grey for the neutral. Our cable core colour guide sets the HD 308, BS 7671 and NEC conventions side by side. If your schedule calls for a colour outside the stocked range, put it on the enquiry early — a non-stocked colour is usually a minimum-order question, not a catalogue one.
Spec sheet shorthandWhen a buyer asks for “THHN specifications”, four lines decide the quote: the type designation as printed (including the wet line), the conductor size and stranding, the voltage and temperature rating, and the optional markings — sunlight resistant, oil resistant, VW-1. Everything else on the datasheet is either derivable from those four or is marketing.

02Wet versus dry is where most orders go wrong

“It is indoors, so it is dry” is the assumption that costs money. Our reading of the code treatment — the same position we took in the UL 83 building wire guide — is that the NEC treats raceways in or under a concrete slab, underground runs, and outdoor conduit where water cannot drain as wet locations, whether or not they look dry on the day of installation. We could not pull the code text itself from a primary source during this check, so verify the wording against the edition your AHJ has adopted before you write it into a specification.

  • Wet and getting 90 °C: specify THHN/THWN-2 or XHHW-2, and make the reel imprint prove it.
  • Wet and stuck at 75 °C: a jacket printing only THWN is a 75 °C wire, wet or dry.
  • Dry, physically tighter install, no UV: plain THHN is a legitimate line item — it is simply not a wet-location wire. The claim you sometimes see that “THHN is rated 75 °C wet” conflates THHN with THWN; we checked the standard’s type tables and 75 °C wet belongs to THWN.
Buying trapA supplier who quotes “THHN” without saying which type lines are printed on the jacket has given you half a specification. Ask for a photo of the imprint off the actual reel, not the datasheet. On the sizes we publish, the jacket carries THHN/THWN-2 — see our product pages for the exact printing.

03The 90 °C you cannot spend

Insulation rating and usable ampacity are two different numbers, and the code keeps them apart on purpose. The terminal is where heat has to leave the conductor; a cable rated 90 °C ending in a lug marked for 75 °C is a 75 °C connection.

The ampacity chart: NEC Table 310.16 in three columns

Table 2 — Copper ampacity columns (NEC Table 310.16) against what a termination typically allows
Size (Cu)60 °C col.75 °C col.90 °C col.What the insulation saysWhat you can usually bill the circuit for
12 AWG20 A25 A30 A90 °C (THHN / THWN-2 / XHHW-2)20 A circuit: 25 A is the ceiling at 75 °C, 20 A at 60 °C
10 AWG30 A35 A40 A90 °C30 A water heater: fine at 75 °C; the 40 A number is derating arithmetic only
8 AWG40 A50 A55 A90 °C50 A range circuit sits on the 75 °C column
6 AWG55 A65 A75 A90 °C60 A feeder: 65 A at 75 °C, 55 A at 60 °C
4 AWG70 A85 A95 A90 °C70 A feeder on the 60 °C column, 85 A at 75 °C
3 AWG85 A100 A115 A90 °CThe classic 100 A service/feeder answer — and it is a 75 °C-column answer
1/0 AWG125 A150 A170 A90 °CAbove 100 A you are working on the 75 °C column by default
4/0 AWG195 A230 A260 A90 °C200 A service: 230 A at 75 °C; the 260 A figure exists to be derated from
Values are the copper columns of NEC Table 310.16, from two published mirrors that agree row for row across 12 AWG through 4/0 AWG. The 14 AWG row is left out on purpose: one reference gives 20/25/25 and two give 15/20/25, which is a 60 °C-column disagreement we cannot settle from open sources, so it stays out rather than being guessed. In the 2014–2020 editions this table was numbered 310.15(B)(16); from the 2023 edition the ampacity, correction and adjustment content sits under Table 310.16 with the correction table as 310.15(B)(1) — the factor values did not move, only the numbering. We do not reproduce the correction and adjustment factors here; the derating guide and the ampacity calculator cover that arithmetic.
STEP 1 · WHERE DOES THE CIRCUIT RUN? Dry / damp attic, panel interior, listed dry locations THHN is enough → 90 °C Wet under slab, underground, outdoor conduit, no drain THHN alone stops here Wet, and you want 90 °C THHN/THWN-2 dual-marked, or XHHW-2 to UL 44 jacket imprint is the proof STEP 2 · NEC 110.14(C) · THE TERMINATION DECIDES THE COLUMN Equipment rated 100 A or less Use the 60 °C column unless the equipment is listed and marked for a higher temperature — most breakers and lugs are marked 75 °C. Above 100 A — and marked lugs Use the 75 °C column as the working default, then apply ambient correction and fill adjustment. STEP 3 · WHAT IS LEFT ON THE TABLE 10 AWG, 90 °C insulation = 40 A  |  at a 75 °C termination = 35 A  |  at a 60 °C-only termination = 30 A The 90 °C column survives only as the base for derating arithmetic: it is where correction factors start, not what you size a breaker from.
Figure 1 — The reading order that keeps a 90 °C wire from being sold or specified as a 90 °C circuit. Location filters the type; 110.14(C) filters the column; the insulation rating is left doing the job it can actually do. Numbers are the Table 310.16 copper values from Table 2. Where the small-conductor boundary sits (1 AWG or 3 AWG) our references disagree, so the figure stops at the equipment rating and points you at the device marking.
So whatUp-sizing because the datasheet said 90 °C is not a safety error, it is a copper bill. The opposite error is the expensive one: buying a 90 °C wire, running it into a wet location under a slab with a jacket that only prints THHN, and finding it out at inspection — or later, at a termination that has been cooking at 90 °C conductor temperature into a 75 °C lug.

04Does XHHW-2 fit more conductors in the same conduit?

This one is worth its own section because it is repeated so often — including by suppliers who should know better — and because the code table that actually governs conduit fill says the opposite at the sizes where it is usually claimed. The story comes from a real fact in the wrong place: XLPE has better dielectric strength per unit thickness than PVC at higher voltage classes, so at MV ratings you get a compact construction. At 600 V building wire, UL 44 simply asks for a thicker wall on small conductors than UL 83 does, and NEC Chapter 9 Table 5 then books XHHW-2 as the fatter wire.

Conduit fill: the NEC Chapter 9 Table 5 areas

Table 3 — Conductor cross-sectional area and outside diameter used for conduit fill (NEC Chapter 9 Table 5, copper)
SizeTHHN area (in²)THHN OD (in)XHHW-2 area (in²)XHHW-2 OD (in)XHHW-2 vs THHNConductors in 3/4 in EMT at 40 % fill
12 AWG0.01330.1300.01810.152+36 % area16 THHN  vs  11 XHHW-2
10 AWG0.02110.1640.02430.176+15 % area10  vs  8
8 AWG0.03660.2160.04370.236+19 % area5  vs  4
6 AWG0.05070.2540.05900.274+16 % area4  vs  3
4 AWG0.08240.3240.08140.322−1 % area2  vs  2
1/0 AWG0.18550.4860.18250.482−2 % area1  vs  1
Areas and diameters are the NEC Chapter 9 Table 5 figures for copper THHN/THWN/THWN-2 and for XHHW/XHHW-2, as tabulated in two public mirrors of the same code table; treat that as one primary source, not two. The fill counts use the 40 % usable area for more than two current-carrying conductors in 3/4 in EMT (0.213 in², NEC Chapter 9 Table 4) divided by the conductor area and rounded down — an illustration of the ratio, not a substitute for your own fill calculation with the real conductor mix. Wall thickness explains the direction: UL 83 asks for 20 mils of PVC on 14–10 AWG against UL 44’s 30 mils of XLPE, and the nylon overjacket is added on top of the thermoplastic.
CorollaryAbove about 4 AWG the two areas are within 1–2 % of each other, so there is no fill argument either way. Below that, THHN wins. If a fill calculation is the reason you are buying XHHW-2 on 10 AWG circuits, the calculation has been done with the wrong table.
What to do with thisFill is calculated from the area column, not from a type letter. So ask for the manufacturer’s published diameter, run the number against NEC Chapter 9 Table 5 or the catalogue value, whichever is larger, and let that decide the conduit — then let the wet-location and temperature requirements decide the type. Two separate decisions, in that order.

05Where each type actually earns its place

  • THHN/THWN-2, small branch circuits: one wire type covering the dry interior runs and the wet outdoor stubs on the same panelboard. That is the inventory-holding answer, and the reason we publish dual-marked wire rather than plain THHN.
  • THHN/THWN-2, 1/0 and up: feeders and services where the 75 °C termination column already decides the size, so you are buying flexibility and pull-ability, not amps. The nylon jacket is what makes a long conduit pull survivable — abrasion and cut-through resistance is exactly what that thin layer is for, and a scuffed jacket is the argument that eats a week of labour.
  • XHHW-2: genuinely better where a wet location and 90 °C have to coexist with oil, chips or repeated heat cycles — machine shops, outdoors in tray, service entrances in damp ducts. It is also the answer when a project specifies thermoset insulation for reasons written by someone else’s engineer. Not in our published range — if your bill of materials calls for XHHW-2, we will tell you plainly rather than quote it.
  • MTW (UL 1063): panel and machine-tool wiring where flexibility and oil resistance matter. Some of our THHN sizes are additionally marked to UL 1063, which is why our product pages list both standard numbers.
  • PV wire (UL 4703 / EN 50618): solar DC. Not a building-wire job. Continuous DC stress and UV in a wet array is a different test regime, and a 600 V AC building wire does not inherit it because it looks similar. That distinction is covered in our H1Z2Z2-K vs PV1-F comparison.
Markings worth asking forPrinted type designation with the wet line included, size and stranding, conductor material, the (UL) listing mark with a file number you can look up, plus the optional markings that matter on your job: sunlight resistant, oil resistant (Grade I or II), and the flame designations a datasheet will happily claim. Where the specification says “sunlight resistant”, insist on those words printed on the jacket — a line in a PDF is not a listing, and the file number is what ties one to the other.

06Six lines that belong on the purchase order

Most disputes at delivery trace back to specification gaps written months earlier. Six lines close most of them:

  1. Type, exactly as it must print: “THHN/THWN-2”, not “THHN type”. If the wet rating matters, the second line of the marking matters.
  2. Standard and file: UL 83 (or UL 44 for XHHW-2) plus the UL file number, verified before shipment rather than after.
  3. Stranding: name it. Our 10 AWG and 12 AWG pages offer solid or Class B stranded; the 8 AWG page is published stranded only. Say which you want rather than letting the warehouse decide for you.
  4. Voltage, temperature and any optional markings: 600 V, 90 °C conductor, sunlight-resistant / oil-resistant as your site needs.
  5. Length per reel and colour list: 100 ft / 500 ft / 1000 ft reels, mixed-colour pallets, printed footage. Mismatched footage is a rework problem on a populated floor, not a paperwork one.
  6. Documentation pack: batch test report, conductor resistance and dimension check, and the imprint photo. Our supplier qualification checklist and the certification verification walkthrough are the audit path we are happy to be walked through.

The reason these six lines are cheap and the alternatives are not: copper is most of your unit cost, so a spec that quietly over-dimensioned a feeder by one size costs more than the whole documentation pack saves. The engineering tools page has the sizing and ampacity calculators we use, and the NEC 2026 vs 2023 changes note covers what actually moved in the 2026 edition for cable specifiers — we did not find a change to Table 310.16 or 110.14(C) in that work, and we are not going to claim one here.

Put it on the enquirySend the type designation, sizes, stranding, colours and quantities and we will quote the range we actually build — with the UL file number on the quotation rather than buried in a datasheet. Request a quote. If you are comparing sizes on cost, the per-metre arithmetic behind any building-wire quotation is set out in our how to audit a cable quote.

07What we publish, and what we will not pretend to publish

Our building-wire pages carry UL 83 THHN/THWN-2 in 600 V, with UL 1063 (MTW) marking on the sizes where we list it, UL Listed with CSA marking on the same jacket, RoHS, and VW-1 flame classification per UL 1581 — that wording is copied from the product pages, and the size range we state there is 14 AWG through 1000 kcmil, solid or stranded. XHHW-2 is not in that range and we do not quote it. If your project needs both types, order the thermoplastic here and buy the thermoset from a UL 44 file holder; that is a better outcome than a substituted cable.

Related product · what Sorivo actually publishes for this comparison
THHN 12 AWG stranded copper building wire (UL 83, 600 V)
Application20 A branch circuits, conduit and raceway wiring, control panels
StandardsUL 83; UL 1063 (MTW); ASTM B3/B8
ConductorBare annealed copper, Class B stranded (19 × 0.47 mm) or solid
InsulationPVC 0.38 mm + nylon jacket 0.10 mm
Ampacity30 A at the 90 °C column; product page publishes 20 A / 30 A
Voltage Rating600 V
Temperature90 °C conductor; 90 °C dry and wet as THWN-2
CertificationsUL Listed; CSA; RoHS; VW-1 per UL 1581
THHN 10 AWG stranded copper building wire (UL 83, 600 V)
Application30 A circuits: water heaters, AC units, small feeders
StandardsUL 83; UL 1063; ASTM B3/B8
ConductorBare annealed copper, Class B stranded (19 × 0.60 mm) or solid
InsulationPVC 0.51 mm + nylon jacket 0.10 mm
Ampacity40 A at the 90 °C column, 35 A at 75 °C; page publishes 30 A / 40 A
Voltage Rating600 V
Temperature90 °C conductor; 90 °C dry and wet as THWN-2
CertificationsUL Listed; CSA; RoHS; VW-1 per UL 1581
THHN 8 AWG stranded copper building wire (UL 83, 600 V)
Application50 A feeder and range circuits, sub-panel drops
StandardsUL 83; UL 1063 (MTW); ASTM B3/B8
ConductorBare annealed copper, Class B stranded (19 × 0.75 mm)
InsulationPVC 0.76 mm + nylon jacket 0.13 mm
Ampacity50 A at 75 °C, 55 A at 90 °C (as published on the page)
Voltage Rating600 V
Temperature90 °C conductor; 90 °C dry and wet as THWN-2
CertificationsUL Listed; CSA; RoHS; VW-1 per UL 1581
HUP series copper tube cable lugs, DT type (the other half of the connection)
ApplicationTerminating power cable conductors at lugs and busbars — where the 75 °C column decision actually gets made
StandardsDIN 46235 (as published on the product page)
Conductor RangeCopper tube, 6–1000 mm²; tin-plated
FinishTin-plated copper; crimp termination
Sizes here are metric because they belong to our power-cable range. AWG building-wire terminations are a different catalogue question — ask us rather than forcing a mm² lug onto an AWG conductor.
Need a custom build? Tell us the type designation you need printed on the jacket, the size and stranding, reel lengths and colours, and we will quote what we actually make: request a quote.
Q1Can I install plain THHN in a wet location?

No, not on the strength of the THHN marking alone. THHN is a dry-location type with damp-location use permitted; the wet-location lines under UL 83 are THWN at 75 °C and THWN-2 at 90 °C. Practically, specify dual-marked THHN/THWN-2 and verify the second line in the jacket printing before the reel is on the roof. If a quote says “THHN, wet rated” without a THWN-2 marking, the claim is unsupported.

Q2Is THWN-2 a different wire from THHN/THWN-2?

THWN-2 is a type line; THHN/THWN-2 is one physical wire listed to two type lines at once, which is how almost all of it is sold and printed today. You are buying the dual marking because it lets one stock item cover dry interior runs and wet outdoor or under-slab conduit. The single-marking versions still exist and are cheaper for a reason.

Q3Does XHHW-2 let me fit more conductors in the same conduit?

No — at small sizes it is the other way round. UL 44 asks for a thicker wall than UL 83 on small conductors (30 mils of XLPE against 20 mils of PVC on 14–10 AWG), and NEC Chapter 9 Table 5 books XHHW-2 at 36 % more cross-sectional area at 12 AWG and 15 % more at 10 AWG. From about 4 AWG the two are within 1–2 % of each other, so there is no fill argument in either direction. Buy XHHW-2 for its wet 90 °C rating, thermoset behaviour and oil resistance.

Q4Why can I not size a 40 A circuit on 10 AWG THHN if it is rated 90 °C?

Because ampacity is limited by the weakest temperature rating in the circuit, and terminations are almost always that point. NEC 110.14(C) sends equipment rated 100 A or less to the 60 °C column unless the equipment is listed and marked for more, and gives 75 °C as the working default above 100 A — so read the breaker or lug, because our code references phrase the small-conductor boundary differently. Either way, 10 AWG is a 40 A conductor thermally and a 30–35 A conductor electrically, and the 90 °C column’s real job is to be the starting point for ambient correction and conduit-fill adjustment.

Q5What should be printed on the jacket, and how do I verify it?

Type designation including the wet line, size and stranding, conductor material, the (UL) listing mark with a file number, and the manufacturer or trademark. Verify by looking the file number up in UL’s own directory and matching the file to the exact type line quoted — a file for THHN is not a file for XHHW-2, since those sit under different standards. Ask for a photo of the imprint off the shipping reel, not a datasheet render.

Q6Can I use THHN/THWN-2 for the DC side of a solar array?

No. PV DC duty is a different test regime — continuous voltage stress, UV and wet heat for decades — and it is covered by solar-cable standards such as UL 4703 and EN 50618, not by a 600 V AC building-wire listing. Use PV wire on the array side, and THHN/THWN-2 where it belongs: inverter AC connections, conduit runs and panels.

Specifying building wire for a North American project?

Send the type designation you need printed on the jacket, the sizes and stranding, and the quantities. We quote the range we actually build, with the file numbers to check us against.

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Senior cable application engineer at Sorivo
Reviewed by Luo Qiang — Senior Cable Application Engineer, Sorivo
15+ years in industrial and renewable energy cable specification. Experienced in cable specification aligned with IEC standards.

Sources checked for this article

  • UL 83, Standard for Thermoplastic-Insulated Wires and Cables — scope, type/marking tables, Table 5.1 (minimum average outside diameter) and Table 7.2 (insulation thickness). Standard text is paid; confirm any specific file number in UL Product iQ.
  • UL 44, Standard for Rubber-Insulated Wires and Cables — scope, Types XHHW/XHHW-2/RHH/RHW/RHW-2, Table 8.1 and Table 10.1.
  • NFPA 70, National Electrical Code — Article 110 Part C (termination temperature limitations) and Table 310.16, as reproduced in Schneider Electric’s published reference table and Mike Holt’s NEC conductor ampacity chart; commentary from Electrical Contractor Magazine (Nov/Dec 2023) and Mike Holt’s 2026 newsletter. The code itself is paid and edition-specific.
  • Manufacturer catalogues for type descriptions and size ranges: Southwire building wire, Encore Wire, Capewell building-wire data, Nassau National Cable product pages.
  • Our own What is THHN Wire? guide for the dual-marking and wet-location position we have already published.

Related reading

Code and standards positions in this article reflect the editions and catalogue data we could verify on 2026-09-03. NEC ampacity tables, table numbering and termination rules differ between editions and between adopting jurisdictions — confirm against the edition your authority having jurisdiction has enforced, and have a licensed electrician or engineer make the final call on any installation. Not legal or code-compliance advice.