THHN, THWN and THWN-2 wire: 600 V building wire

What the jacket print decides

THHN and THWN are 600-volt building wire: a copper or aluminium conductor, a thermoplastic insulation, and a thin nylon jacket that lets the wire slide through conduit without scuffing. The jacket is why the wire feels slick in the hand. It is also a label. Nearly every foot carries a repeating print with the size, the temperature ratings, the wet-location marking and the listing mark, so a reel identifies itself along its whole length.

The ratings are not decoration. THHN alone is a dry-location conductor, 90°C dry and 75°C wet. THWN adds a wet-location rating at 75°C. THWN-2 carries 90°C in both wet and dry conditions. A reel printed with THHN and THWN-2 together is the general-purpose wire most supply houses stock. A reel printed THHN only cannot legally be pulled into a wet raceway, and that single difference decides who wants the reel.

Sunlight, oil and a season outdoors

Sunlight-resistant print matters in Ohio because so much of this wire is stored outside. A reel rated sunlight resistant can sit in a rooftop raceway; a reel that spent two summers on a pallet behind a contractor's shop may show it, with the print chalked to grey, the nylon dulled, and the outer wraps of a coil stiff where the sun reached them. The wire under that outer layer is usually sound. A review looks at the outside wraps, then at a cut length taken a few inches in.

Oil resistance is printed too. Wire marked oil resistant has a jacket formulated for it; ordinary THHN dropped into a machine-shop sump or a compressor room will soften and swell. Where print has worn away, the reel tag is the remaining record, and a legible tag settles most of what a buyer would otherwise have to guess.

Where the Ohio over-order comes from

Commercial construction around Columbus is bid on takeoff quantities that round up to the reel. A contractor wiring an institutional or corporate building orders to the drawing, then the field adds home runs the drawings missed, or the owner drops a floor from the programme. What remains is often not scrap: two or three partial reels of 12 and 10 AWG in black, white, green, red and blue, cut ends taped and tagged, standing in a connex against the next job.

This is the most common THHN surplus in the state and the easiest to under-value. A 500-foot coil with most of its length left is still a working coil for a service electrician. A 2,500-foot reel down to 600 feet is a partial, handled as footage rather than as finished goods. Only when tag and print are both gone does the lot fall back to conductor weight, and that is a different conversation.

What to send before a reel moves

Sizes, colours and rough remaining footage first, then photographs. Colour mix changes the handling. A clean pallet of black 12 AWG is one thing; a mixed pallet of eight colours in short lengths is another. Wire that came out of a raceway is still usable but arrives kinked, dirty and short, and that belongs in the description rather than in the surprise at the dock.

• Photograph the reel tag and a stretch of jacket print in one frame
• Give the tag footage and a wrap count from the coil itself
• List sizes, colours and whether the coils are still banded
• Say whether the wire was pulled or never left the pallet
• Separate sun-damaged outer wraps from the sound inner coil