Zip ties in cold weather and heat: brittleness, ratings and what to do

Most cable ties are molded from nylon 6/6 (PA66), which is hygroscopic: it absorbs water from the air and gives it back when the air is dry. That water acts as a plasticizer. A tie with normal moisture content is flexible and tough; a dried-out tie is stiffer and much easier to snap.

Molding dries the nylon, so manufacturers typically moisture-condition ties and seal them in plastic bags to keep that moisture in. According to NEMA's cable tie guidance, more moisture makes a tie more flexible and more impact resistant but slightly lowers its tensile strength, while drying out raises tensile strength and reduces impact resistance.

Cold makes the problem worse. Low temperatures reduce the flexibility of the plastic, and winter air is usually very dry. Most brittleness complaints come from ties installed outdoors in cold weather, or from ties stored for a long time out of their bag in an unheated shop, truck or warehouse.

The figures below are typical values published across the industry, not ratings for any particular product. Manufacturers state different limits for different grades, and some quote a lower continuous-use temperature than the headline range. Nirah does not currently publish temperature ratings for its nylon 6/6 ties, so if temperature is critical to your job, use a product with a declared rating on its spec sheet or package.

For ties certified to UL 62275 (the North American standard for cable ties in electrical installations), temperature is not a single number. The package can carry three separate declarations:

• Maximum operating temperature: the highest continuous temperature the installed tie is rated for. Common declarations include 85°C, 105°C, 120°C and 150°C, and it is verified by aging samples above that temperature before strength testing.
• Minimum operating temperature: the lowest temperature the installed tie is rated for, verified with an impact test after cold exposure. Common declarations include -25°C, -40°C and -60°C.
• Minimum installation temperature: the lowest temperature at which the tie can be put on. It only needs to be marked if it is below 0°C, which is why 32°F is the safe assumption for ties without a declaration.

Winter installs on fencing, solar arrays, irrigation lines and construction sites are where ties most often snap. A few habits prevent most failures.

1. 1Keep ties in their sealed bag until you need them, and keep the bag warm: in the cab, a heated trailer or an inside jacket pocket.
2. 2Take out a handful at a time rather than leaving an open bag on a cold surface.
3. 3Pull ties snug, not hard. If you use a tensioning tool, reduce the setting in cold weather.
4. 4Avoid sharp bends in the strap and impacts on installed ties until they have warmed or settled.
5. 5Remember that nylon shrinks more than metal as it cools. A tie cinched tight around a metal pipe or rail on a warm afternoon carries more stress on a cold night, so snug is enough.
6. 6If a tie cracks at the head during installation, stop and warm the rest of the batch before continuing.
7. 7For jobs well below freezing, choose a product with a declared low installation temperature, or install when temperatures rise.

Heat rarely breaks a tie on the spot. Nylon 6/6 melts at roughly 500°F (260°C), so a hot car or an attic will not melt it. The problem is slow: long exposure near or above the rated temperature ages the nylon, and aged ties discolor, stiffen and eventually crack.

Surface temperature is what counts, not the weather forecast. Dark roofs, metal racking and enclosures in direct sun, engine compartments, exhaust and steam lines, and light fixtures can all run much hotter than the surrounding air. Outdoors, heat and sunlight work together, which is why outdoor ties should be UV-stabilized black and inspected periodically.

• Near engines, exhaust, heaters and hot process equipment, use heat-stabilized nylon with a declared maximum temperature above the real surface temperature, or stainless steel.
• Keep nylon ties off surfaces hot enough to be uncomfortable to touch for more than a moment, unless the tie is rated for it.
• On solar arrays and rooftops, use UV-stabilized ties and follow the project specification; many specify stainless or a tie with declared UV and temperature ratings.
• In fire-rated or high-heat routes, general-purpose nylon is not the answer; use hardware specified for that system.

NEMA's guidance on moisture recommends storing cable ties in their sealed plastic bag, out of sunlight, at about 73°F (23°C) and 50% relative humidity. A sealed bag in a typical warehouse should hold its moisture for about a year. Once a bag is opened in a dry environment, the ties may stay flexible for only about three to five days, depending on size and humidity.

• Reseal partly used bags, or move loose ties into a zip-top bag.
• Rotate stock first in, first out.
• Do not store open bags in hot vehicles, on rooftops or in unheated sheds through the winter.
• If old ties feel stiff or snap when bent, NEMA notes that reconditioning can restore flexibility. Follow the manufacturer's procedure, or replace them.