Guide to UL Wire Specifications & Standards

Few markets face greater risk than the electronics industry.

That’s why organizations like UL (Underwriters Laboratories) exist. UL evaluates 70+ wire and cable categories worldwide for safety, performance, and use of ethical materials. By following the right UL wire specifications for your specific needs, you can avoid retesting and redesign, improve product safety, and go to market sooner.

UL Wire Specifications Explained

These are the UL wire standards that matter most to industrial electronic designs:

1. Voltage rating
2. Temperature rating
3. Flame test
4. Special criteria

There’s also a dedicated UL 758 standard for appliance wiring we’ll cover below.

It’s challenging to sort through the hundreds upon hundreds of UL wire types, plus the array of UL tests for various use cases. 

Common Industrial & Commercial Wire Types

AWG (American wire gauge) is important to keeping the integrity and performance of the wire on track. For example, excessive current flow can damage an amplifier, while a lack of voltage could prevent optimal performance.

Insulation thickness plays a huge role in a cable’s electrical performance. A thicker insulation layer blocks the heat radiation that can short-circuit or burn a cable. In general, the more electrical power your application needs, the thicker cable insulation you’ll need.

Insulation material determines the level and type of protection a wire receives. Depending on the application, wire insulation may need to resist extreme temperatures, flames, moisture, chemicals, mechanical stress, or other factors.

We’ll cover temperature and voltage ratings separately below.

UL 758 for AWM

UL 758 deserves its own section because it’s a big part of so many industrial wiring solutions. This standard is solely for appliance wiring material (AWM) in factory and production settings, laying out specs for suitable single-conductor, multiconductor, and fiber-optic materials. The wiring is usable:

• Internally, within the enclosure – only requires insulation
• Externally, interconnecting appliances – sheathed for UV, oil, & moisture resistance
• As components, in multiconductor cables

All wires in this category can withstand at least 60°C heat, though some can survive in much hotter climates.

Appliance wiring material isn’t just for factories. It’s a category that covers a huge swath of wire and cable products. 

General AWM Categories

UL assigns a different AWM number for each approved wire and cable type and publishes a “style page” (example here) outlining the build of that product. The information provided includes voltage range, temperature rating, insulation type and thickness, shielding, and conductor stranding.

4 Types of UL Wire Specifications & Ratings

Now, on to the key specs to watch out for in evaluating wires:

1. Voltage Rating

Unsurprisingly, voltage rating is one of the most important UL wire specs for evaluating suitability for a particular application.

Voltage rating indicates the maximum continuous current a wire can carry without sustaining damage or becoming a safety hazard. 

The rating is based on:

• Insulation material
• Operating temperature
• Wire gauge

Ignoring a wire’s voltage rating can result in overheating, degraded insulation, and other safety and performance issues.

The spark test is a well-known way to measure a connection’s safety. This inline voltage check typically happens during the manufacturing and rewinding phases of a cable’s life. It’s primarily used for low-voltage insulation and medium-voltage nonconductive jacketing and sheaths.

2. Temperature Rating

All UL-rated wires carry a temperature rating for dry locations. Some have a second rating for temperature in wet locations.

Wire temperature ratings determine the maximum how hot a wire’s working environment can be without it degrading or becoming a fire hazard.

UL uses two main criteria for wire thermal ratings:

• Insulation material – determines max temp wire can withstand without breaking down
• Installation environment – accounts for exposure to heat from nearby equipment and sunlight

UL uses a variety of testing methods to determine wire temp ratings:

• Thermal aging – monitors degradation of insulation over a long period when exposed to heat, cold shock, mechanical stress, & humidity
• Insulation resistance testing – measures ability to resist current flow over product’s lifetime
• Flammability testing – more below

The higher its temperature rating, the better a wire is at withstanding heat. can safely withstand. However, using a wire with a rating of 105°C can be a waste of money if your project’s end-use environment will never surpass 60°C.

3. Flame Test Requirements

A burning wire is, obviously, pretty problematic. They can produce a surprising amount of:

• Smoke
• Heat
• Harmful fumes
• Falling flaming material (called “burning droplets”)

UL can provide two types of fire tests for cables and busways:

• Resistance to fire – Evaluates a cable’s degradation and burning in a fire environment, including fires involving water and mechanical shock hazards
• Reaction to fire – Measures a cable’s behavior if it actually catches fire, including vertical flame growth, smoke emission, and acidic gas emission 

UL’s flammability standards for wiring products is a bit of a tangled mess. Your application will determine which ones you should worry about:

• UL 1666 – Also called the riser cable flame test, it measures the flame height on cables vertically installed in shafts or multi-floor runs
• UL 1685 – Analyzes flame spread and smoke release in industrial control and power cables in a vertical test chamber
• UL 1061 – A small-scale, vertical flame test for appliance wiring cables carrying currents up to 500W
• UL 910 – A flame-spread test necessary for all plenum cables in a building’s tight, air-circulated spaces
  
  

4. Special Criteria

It’s rare that UL rates every industrial wire for every situation, because some products are clearly not intended for those situations.

Depending on your project, you may need to meet more niche UL wire and cable standards for these environmental factors:

• Outdoor – Resistance to moisture, wind, dust, etc.
• UV – Has a metallic or suitable nonmetallic cover to repel direct radiation from the sun
• Cable tray use – Endurance when exposed to flames, mechanical stress, and extreme temperatures
• Oil – Exposure to oil at up to 60°C
• Gasoline – Exposure to liquid and vapor gas and similar solvents
• Direct burial – Able to be buried in the earth
• Submersible pump – Use in submersible or non-submersible pumps
• Other – Uses, exposures, and build features other categories don’t cover

Material type and thickness of protective layers are the top factors in a wire succeeding or failing in these environments.

Other UL Tests by Wire/Cable Type

Electric industrial wires couldn’t be further from “one-size-fits-all.” They serve nearly every market in existence, so there are a wide variety of standards necessary to cover the seemingly endless use cases.

Some key standards by wire type include:

There are many, many other obscure UL standards for highly specific use cases. All the way down to Christmas lighting.

Spec-Based UL Standards

There are also UL wire standards specifying certain traits of a component(s) of the cable. These determine the materials, dimensions, and other qualities suitable for your wire application:

Labeling? 

Industrial wire labels help users determine the product’s specs before installation.

Different wire types come with different requirements for their marking – both what’s displayed and where it’s displayed. 

This list of UL standards labels includes many for the wiring of appliances, control panels, telecom equipment, and more.

Some wires may have markings for multiple Type designations. This means UL has approved their use in all Type designations on the label.

(Related Resource: Guide to UL-Friendly Cable and Wire Marking)

Building to UL Wire Specifications & Standards

Boasting a “UL-recognized component” mark on your wire assemblies doesn’t automatically make it safe and effective for your product. Carefully choose components that meet all of your project’s specs and requirements. The top factors in designing a UL-friendly product are temperature resistance, flammability, and voltage capacity – and whether your components will place nicely in these environments. 

Pair what you’ve learned so far with the experience of an established distributor (bonus points if it also has manufacturing expertise). The good ones will recommend products that are sufficiently rated for your project, yet don’t inflate your bill of materials cost.

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