Wire & Cable Type Decoder

How It Works

1. Type the marking

   Enter any wire or cable type as it reads on the jacket. The decoder accepts "THWN-2", the dual-print "THHN/THWN-2", lowercase and spaced forms like "xhhw 2", cords like "SOOW", assemblies like "MC" and "TC-ER", and the common trade names BX, Romex, NM, and UF. The normalizer uppercases, strips a "Type" prefix, unifies the dual-print slash, and turns a trailing " 2" into "-2".

2. Read the temperature and ampacity

   The Temperature and ampacity card shows three separate numbers: the dry/damp insulation rating, the wet insulation rating (or "not wet-rated" for bare THHN, RHH, and AC), and the ampacity basis, which is the NEC column you actually size from. When the ampacity basis is lower than the insulation rating (NM-B and UF-B, both 90 C build but 60 C basis), the card flags it.

3. Check the 110.14(C) callout

   Every building-wire result carries the NEC 110.14(C) termination caveat as a callout box: the 90 C figure is for derating and the build, not the lugs, and the usable ampacity is capped at the lowest-rated termination (usually 60 C at or below 100 A, 75 C above). This is the single most common cause of a conductor that calculates fine on the 90 C column and fails inspection.

4. Read the locations, voltage, and grounding

   The Locations and voltage card lists the permitted locations (dry, damp, wet, direct burial, sunlight-resistant, oil-resistant), the voltage class (600 V for hard-service cord and most building wire, 300 V for SJ cords and tray instrumentation), whether the type is flame-rated, and the grounding arrangement. The grounding line is where AC and MC separate: AC carries a bonding strip, not a full EGC, and is indoor/dry only, while MC carries a full-size grounding conductor and can be wet-rated.

5. Read the construction and the letters

   The Construction and standards card gives the insulation material, the governing UL standard, the relevant NEC articles, and a table that breaks the type into its individual letters with each meaning. This is where the T, H, HH, W, N, X, and the "-2" suffix are spelled out.

6. Export the decode

   PDF export produces a branded report with the decoded properties, the letter breakdown, the field notes, and a building-wire termination reference table (the 60/75/90 C columns and the 110.14(C) rule) so the lesson travels with the page. CSV export packages the same fields, and the share button puts the exact marking in a coworker browser.

Built For

• An electrician reading "THHN/THWN-2" off a reel and confirming the wet 90 C rating comes from the THWN-2 half, so it is legal in conduit in a wet location
• An estimator catching that a run sized on the 90 C column has to be resized from the 75 C termination column per NEC 110.14(C) before the bid goes out
• A maintenance planner confirming that NM-B in an attic is taken from the 60 C ampacity column even though the insulation is built to 90 C
• A panel builder deciding between Type AC and Type MC for a damp location and catching that AC is indoor/dry only with a bonding strip, not a full EGC
• A field tech reading "USE-2" on a reel and confirming it is not inherently flame-rated, so it cannot be pulled bare through a building interior unless it is dual-printed RHH or RHW-2
• A controls tech telling MTW from THHN on a machine and catching that MTW drops to 60 C in wet or oil-exposed locations
• An apprentice decoding "SOOW" on a shop cord and learning the double O means oil-resistant insulation and jacket, and the W means it is rated for outdoor use
• An inspector confirming TC-ER is listed for the limited exposed run between a cable tray and a motor per NEC 336.10

Features & Capabilities

Dry and Wet Temperature as Separate Fields

The decoder keeps the dry/damp insulation rating and the wet insulation rating as two distinct values instead of one number, because that is where the "-2" trap lives. THHN shows 90 C dry and no wet rating; THWN-2 shows 90 C in both columns; XHHW shows 90 C dry but derates to 75 C wet. The card spells out which is which.

Ampacity Basis Called Out Separately

A third field, the ampacity basis, is the NEC column the type is actually sized from, which is not always the insulation rating. NM-B and UF-B are built to 90 C but the NEC requires their ampacity be taken from the 60 C column. The decoder stores and flags that gap so a conductor is never sized off the wrong column.

NEC 110.14(C) Baked Into Every Building-Wire Result

A 90 C insulation rating is not a 90 C ampacity at the terminals. Every building-wire result carries the 110.14(C) termination caveat as a callout, with the 60 C and 75 C thresholds stated, so the most common ampacity mistake is surfaced on every decode rather than buried in a guide.

AC versus MC Grounding, Made Explicit

Type AC (BX) and Type MC look similar and are not. AC uses the armor plus a bonding strip as the ground path and is dry/indoor only; MC carries a full-size insulated equipment grounding conductor and can be wet-rated with the right jacket. The decoder states the grounding arrangement and the location limit for each so the two are never swapped.

Cord, Building Wire, and Assembly Families

The decoder branches on family first, which matters because a leading "S" means Service (a 600 V cord) in one family and Service-Entrance (SE/SER/SEU cable) in another. It decodes flexible cords (the S/SJ, O/OO, W, T/E letters), building wire, armored and tray cable, NM-B and UF-B, and service-entrance cable, each with the right standard and location rules.

Never Dead-Ends: Letter Fallback

An uncommon or mistyped combination that is not in the verified table falls back to a letter-by-letter decode, assembling a best-effort property set from the individual letter meanings and flagging it low confidence with a "verify against NEC Table 310.4(1)" warning. The tool always returns something useful and is honest about how sure it is.

PDF and CSV Export with a Termination Reference

PDF export uses the shared ToolGrit programmatic generator and includes a building-wire termination reference table (the 60/75/90 C columns and which common types sit in each) so the 110.14(C) lesson is portable. CSV export packages the decoded fields, and the share button rebuilds the exact decode in a coworker browser.

Light and Dark Mode, WCAG AA

Standard ToolGrit light and dark theme with WCAG AA contrast on the warning and danger callouts, verified readable in both themes. The matched banner uses an aria-live region so screen readers announce the decode when the marking changes, and the mobile layout at 375 px keeps the letter table readable.

Comparison

References

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Frequently Asked Questions