What is UL wire? A simple explanation from basic knowledge to types and how to choose

UL wires used in North America are high-quality wires that have cleared strict safety standards. They have different standards and notation methods than Japanese wires, and are characterized by their flame retardancy and voltage resistance.

Products that have acquired the UL mark are proof of their reliability in the North American market and are key to entering that market. This article explains the basic definition of UL wires, their types and characteristics, and how to select the appropriate one.

What is UL wire?

UL wire is wire that has been certified by UL (Underwriters Laboratories), a North American safety standard. It is mainly used in the United States and Canada, and is adopted in a wide range of household and industrial devices.

In North America, strict standards are set to manage materials to prevent electrical fires and electric shock accidents. UL wire meets these standards and is expected to be highly reliable and safe. On the other hand, it is characterized by having a different standard system from safety certification in Asia and Europe.

When manufacturing products for the North American market, selecting UL wires is essential. It is necessary to understand the types and performance of wires and make the right selection according to the requirements of the equipment.

Differences between UL wires and Japanese wires

There are some differences between UL wires and Japanese wires.

Specifically, the following points are the major features:

• specification
• Notation
• Rated voltage notation
• Flame retardance

Because safety standards and technical requirements differ between North America and Japan, knowing the classifications for each will be helpful when selecting a product. Here we will explain the differences in detail.

specification

Japanese electric wires comply with the domestic Electrical Appliance and Material Safety Act and JIS standards, while UL electric wires distributed in North America meet UL standards and other US safety regulations.

The UL standard is a certification system that requires testing for safety and performance, which allows a certain level of confidence in performance such as allowable temperature, flame resistance, and voltage resistance.

Like Japanese standards, UL standards strictly evaluate the quality of conductors and insulating materials. However, if Japanese-specification electric wires are brought into North America as is, they may not be usable because they do not have the UL mark.

When selling products overseas, it is important that the wires used are UL certified. It is important to be aware that without certification, it may be difficult to export the product.

Notation

UL wires are often sized using the "AWG (American Wire Gauge)" format. AWG is the North American standard for conductor size, with smaller numbers indicating thicker conductors.

In Japan, electric wires are generally measured in square millimeters (SQ), which indicates the conductor cross-sectional area, for example, "1.25mm²" or "2.0mm²."

It may be necessary to convert values ​​between AWG and SQ, and the names will change even for the same thickness. For example, 12AWG is roughly equivalent to 3.3mm², so it is useful to check the table when making substitutions.

The markings on the wires are also different: UL wires are marked with the UL mark, number, temperature rating, etc. Japanese wires are often marked with the PSE mark or JIS mark.

 Rated voltage notation

UL wire generally has voltage notation as an integer value, such as 600 V. This number indicates the maximum operating voltage that the wire can withstand continuously.

Japanese electric wires are generally labeled as compatible with 300V or 600V, but this is defined within the JIS standard. There is some overlap in the voltage ranges of both, but there may be slight differences in the test methods and tolerances.

In addition to the rated voltage, the UL mark also includes information indicating heat resistance and flame retardancy. Depending on the usage environment, it is necessary to check not only the voltage but also other performance indicators comprehensively.

It is important to select electrical wires based on the equipment's operating voltage and usage environment at the design stage. To achieve both safety and efficiency, it is necessary to understand the appropriate rated voltage.

Flame retardance

UL wires are required to be designed to be flame-resistant.Specifically, standards such as UL94 define detailed classifications of flame-retardant grades.

There are Japanese electric wire products that emphasize flame resistance, but the North American standards and test methods differ in some ways. UL tests are characterized by strict evaluations that include setting the time for which the flame source is exposed and multiple test environments.

Many UL wires are designed with consideration given to self-extinguishing properties and the amount of smoke generated when exposed to flames. Because of the importance of reducing the risk of fire inside equipment, flame retardant performance is essential.

The higher the flame retardant rating, the safer and more protected the wiring is. UL standards are especially respected in facilities and product development where fire protection is mandatory.

UL Wire Types

UL wires come in many variations depending on the application.

They can be broadly divided into three types, each with different performance and functions:

• General-purpose wire
• Special purpose wire
• Specific standard electric wire

Understanding these classifications will make wiring and designing smoother. It is important to check details such as temperature characteristics and flame retardant grades as necessary when making your selection.

General-purpose wire

General-purpose electric wires are used for a wide range of applications, including home appliances and office equipment. Typical products often have standard numbers such as UL1007 and UL1015.

It is characterized by a well-balanced basic performance, such as withstand voltage and allowable temperature. PVC (polyvinyl chloride) is often used for the insulation material, which is easy to handle and has moderate flexibility.

General-purpose wire is cost-effective and can be used in a variety of environments, but when exposed to high temperatures, strong vibrations or special chemicals, more specialized wire is required.

Also, since there are many different products on the market, it is important to choose the right size for your application. Even if it is a general-purpose product, we recommend that you check to make sure it is UL certified.

Special purpose wire

Special-purpose electric wires are designed to meet specific requirements such as high temperature environments, oil resistance, chemical resistance, etc. For example, UL fluororesin electric wires are products that enable continuous use in high temperature environments that ordinary electric wires cannot handle.

These wires use special materials that have excellent insulation properties at high temperatures and fire prevention properties, and they perform reliably even under harsh conditions. For this reason, they are widely used as cables for automated factory lines and industrial robots.

There are many different materials available for the insulation, including fluororesin and silicone rubber. However, care must be taken to ensure that the material and specifications are carefully selected according to the application, otherwise insulation failure and deterioration of the insulation may occur.

There are also specialized types of wires for specific applications, such as those for medical equipment and those that can withstand extremely low temperatures. In some cases, the pursuit of durability according to the application can result in higher costs.

Specific standard electric wire

Standardized wire is wire that meets additional standard requirements for your industry or environment. An example is "UL/CSA wire" that meets both UL and CSA (Canadian Standards Association) standards.

These wires have acquired multiple certifications and are highly versatile, making them easy to use throughout North America. There are also standards for use in special environments, such as for marine, railroad, and military use.

Compared to general-purpose electric wires and wires for specific applications, specific standard electric wires tend to require more tests and certifications. Because of this, safety and reliability are guaranteed more strictly, so they are often used in important equipment.

Even within the same UL wire classification, specific standard wires may be given their own marks and certification numbers, so checking whether they have the necessary certifications makes it easier to determine whether a product is appropriate.

UL Wire Characteristics

UL wires have excellent characteristics because safety and reliability are emphasized.

The main features are as follows:

• Heat-resistant
• Voltage resistance
• Conductivity
• elasticity

Let's take a look at what situations each of these features is useful in.

Heat-resistant

UL wires can be used stably within a specified temperature range. Many products specify a specific maximum allowable temperature, such as 105°C or 125°C, and are designed to maintain their insulation performance and mechanical properties for long periods of time within this temperature range.

UL electric wires that can withstand high-temperature environments often use fluororesins (PTFE, FEP, ETFE, etc.) as coating materials. These materials maintain excellent insulation performance even under high-temperature conditions, and can effectively prevent problems such as electrical sparks and insulation breakdown caused by overheating.

Such heat-resistant wires are essential for wiring in environments prone to high temperatures, but they may deteriorate if used for long periods of time under conditions exceeding the maximum temperature specified.

Therefore, to ensure long-term reliability, it is important to accurately understand the maximum temperature in the actual usage environment and select wires with an appropriate temperature rating.

Voltage resistance

UL wires are designed to operate safely within the rated voltage range. There is a wide lineup of products, from those that can withstand 600V to those that can withstand even higher voltages.

A distinctive feature of these products is that they pass strict insulation and voltage resistance tests during the manufacturing process. These tests are used to determine whether or not the required insulation strength is maintained.

They can be used reliably in industrial equipment with a lot of external noise and in equipment that handles high voltages. However, proper selection is essential, as danger increases when the operating conditions exceed the rated voltage.

When using in high voltage circuits, it is advisable to pay attention to the quality of the insulation material and the thickness of the coating. Selection that does not match the rated capacity may cause equipment failure or safety risks.

Conductivity

Copper (Cu) is the most widely used conductor material for UL wires. Copper has excellent electrical conductivity and low electrical resistance, which minimizes energy loss and heat generation during signal transmission.

The conductor sizes of UL wires are standardized based on standards, and it is possible to select the optimal conductor diameter according to the required current capacity and wiring distance. Conductors plated with metals other than copper may also be used, which prevents oxidation and reduces contact resistance.

A balance between current carrying capacity and heat dissipation is important to maintain proper conductivity. Efficient power transfer improves overall equipment performance.

elasticity

UL wires include products that emphasize flexibility, designed for wiring in limited spaces inside devices or in moving parts. The softness varies depending on the application, such as general-purpose wires with PVC coating or silicone rubber coating.

Office equipment that is frequently rearranged and robot arms and other moving parts that are constantly in motion require wires with particularly high flexibility. It is important that the insulation material is designed to be resistant to cracking and to withstand repeated bending.

However, highly flexible materials can have reduced resistance to high temperatures and chemicals, so the balance between flexibility and durability must be considered according to the usage environment.

The advantage of UL wires is that they are highly flexible and easy to handle, improving the efficiency of wiring work. They allow smooth wiring even in equipment with limited space, allowing greater freedom in design.

How to select UL wire

When selecting UL wire, you need to check the requirements of the equipment and environmental conditions that will be used.

The first thing to consider is the rated voltage and temperature range. Selecting a wire that matches the operating voltage of the equipment and that can cover the expected operating temperatures is a prerequisite.

Next, check the thickness and material of the conductor. Select the AWG size and insulation material based on the current capacity and length of the wiring to ensure efficiency and safety.

Environmental factors at the place of use (humidity, oil, chemicals, etc.) and whether or not the cable is movable are also important points. For factory lines that require oil resistance and abrasion resistance, special-purpose electric wires may be more appropriate.

If multiple safety standard certifications are required, selecting specific standard wire that has multiple certifications, such as UL and CSA, can reduce the cost and time required for additional testing and design changes.

Price is important, but if safety and reliability are compromised, it is highly likely to lead to future problems. Make a comprehensive judgment and choose an electrical wire that can be expected to reduce costs in the long term.

UL Wire Standards and Certification System

UL wires may be certified not only by UL in the United States, but also by multiple international safety standard organizations. Particularly important are the international standards of CSA in Canada, VDE for the European market, and the International Electrotechnical Commission (IEC). Wires that have acquired these multiple certifications have the advantage of being able to be deployed smoothly in the global market and greatly simplifying the conformity certification procedures required when exporting to each country.

UL certification is divided into two categories: "Listing" and "Recognition." Listing is a certification that verifies the safety of the entire product as a finished product, while Recognition is a certification that verifies the suitability of a part that will be incorporated into a final product.

To obtain UL certification, in addition to testing at a testing laboratory, regular audits of manufacturing plants are required. Even after obtaining certification, maintaining quality control is essential, and if standards are no longer met, a warning or cancellation may occur.

In particular, in the North American market, the UL mark is an important indicator of product safety and reliability. Since some countries may refuse to handle or install electrical products that do not have UL certification, obtaining UL certification has become a de facto requirement for manufacturers looking to enter the North American market.

Summary

UL wires are highly safe wires that are widely used in North America. Compliance with UL standards plays an important role in ensuring the safety and reliability of products in the North American market.

There are various types of UL electric wires, and it is necessary to select the appropriate type depending on the application and environment. By understanding the standards and certification system for UL electric wires, how to obtain them, and the differences between them and Japanese electric wires, you can select the appropriate UL electric wire and perform safe electrical wiring.

Using UL wire not only provides access to the North American market, but also helps ensure product safety from a global perspective.