What type of wire is commonly used in buildings?

In modern buildings, electrical wiring is an essential piece of infrastructure. Like the building's neural network, it delivers power to every corner, from lighting and appliances to mechanical equipment. Without a reliable wiring system, even the most advanced buildings cannot function properly. Choosing the right wiring not only ensures electrical safety and complies with local regulations, but also directly impacts a building's energy efficiency, durability, and overall performance.
The choice of wiring is often influenced by a variety of factors, including building type, operating environment, power requirements, and regional standards. Wiring preferences vary significantly across countries and regions due to differences in regulatory requirements, climate conditions, and construction practices.
This article will provide a comprehensive overview of the types of wiring commonly used in buildings worldwide, analyzing their characteristics, advantages, applicable scenarios, and usage in different countries to help readers better understand this vital building component.
Commonly Used Wiring Types in North America
Romex (NM Cable)
Romex (non-metallic cable) is one of the most common types of wiring used in North American residential buildings. It consists of several insulated conductors encased in a plastic sheath and typically contains a hot, neutral, and ground wire. It was originally designed to provide a safe, economical, and easy-to-install indoor wiring solution for homes.
In new homes, Romex is typically installed through the gaps between wall studs, floor joists, and ceiling joists, eliminating the need for additional conduit protection. This installation method significantly simplifies the construction process and reduces material and labor costs. Because the sheathing inherently provides some mechanical protection, it can be installed directly in dry environments without worrying about damage from minor friction or contact.
However, Romex's use has significant limitations. It cannot be used in wet areas (such as bathrooms and under kitchen sinks) or outdoors because the sheathing is not sufficiently waterproof. In these situations, specialized cable or conduit systems must be used. Furthermore, Romex's use in commercial or industrial buildings is limited, typically only permitted in certain small commercial spaces.
Despite these limitations, Romex remains a workhorse in residential electrical systems in the United States. Its cost-effectiveness, ease of installation, and compliance with NEC standards have ensured its irreplaceable position in the North American market.
THHN/THWN Wire
THHN (heat-resistant nylon-coated wire) and THWN (heat-resistant water-resistant nylon-coated wire) are the mainstay wire types in North American commercial and industrial buildings. They utilize a copper conductor covered with thermoplastic insulation, then protected with a nylon jacket over the insulation, creating a double layer of protection.
The most significant feature of THHN wire is its high-temperature resistance. It is rated for operating temperatures up to 90°C, significantly higher than the 60-75°C of standard PVC-insulated wire. This makes it particularly suitable for installation in heat-stable locations such as distribution boxes and motor junction boxes. The nylon jacket provides excellent abrasion and chemical resistance, making it less susceptible to scratches during conduit routing and resistant to a variety of industrial chemicals.
THWN wire adds waterproofing to THHN, allowing it to be used in humid environments and even in situations subject to short-term submersion. It excels in applications such as swimming pools, fountains, and industrial cooling systems. However, even THWN is not suitable for long-term burial due to its lack of long-term protection against soil chemicals and microorganisms.
Both types of cable are almost always used in conjunction with a conduit system. In commercial buildings, electricians typically lay a network of metal or PVC conduits before running multiple THHN/THWN cables through them simultaneously. This installation method not only provides additional protection but also facilitates future maintenance and line replacement.
Due to its high performance and versatility, THHN/THWN cable has a wide range of applications. They can be found in everything from office building lighting systems to heavy equipment in factories, from air conditioning controls in shopping malls to powering medical equipment in hospitals.
MC (Metal-Clad) Cable
MC (Metal-Clad) cable is a complex but high-performance wiring solution. It consists of multiple insulated conductors encased in a metal sheath, typically made of aluminum or steel. The metal sheath not only provides mechanical protection but also serves as a grounding conductor, simplifying installation.
MC cable's greatest advantage over Romex is its comprehensive protection. The metal sheath can withstand strong mechanical impacts, prevent puncture from sharp objects, and even provide some resistance to rodents. This makes it particularly suitable for commercial and industrial environments with high foot traffic and frequent equipment movement.
Another key feature of MC cable is its installation flexibility. It can be used in a variety of indoor and outdoor environments, including dry, damp, and even hazardous areas (subject to specific classification requirements). In some cases, it can be installed directly in exposed areas without the need for additional conduit protection, which can significantly save material and labor costs in large industrial facilities.
While MC cable is less common than Romex cable in residential buildings, it has applications in specific areas. For example, MC cable is a safer choice in ceiling spaces requiring additional fire protection, in ceiling junction boxes containing ceiling fans, or in areas where flammable materials may come into contact.
Overall, MC cable represents a higher safety standard and wider applicability. Although it costs significantly more than Romex cable, its investment is irreplaceable in applications where safety is paramount.
Professional Wiring Systems Used Worldwide
Conduit Systems
Conduit systems, a widely used installation method that places wires in protective conduit, are not limited to specific wire types but rather serve as a universal installation standard that can accommodate a wide variety of wire types.
Rigid Metal Conduit (RMC) offers the highest level of protection. It is typically made of galvanized steel with thicker walls, capable of withstanding heavy impact and pressure. In industrial settings, RMC is often used to protect cables connected to heavy equipment or installed in areas where there is a risk of mechanical damage. Its disadvantages are its weight, difficulty in installation, and the need for specialized tools for cutting and bending.
Electrical Metal Tubing (EMT) is the most commonly used conduit type in commercial buildings. It is significantly lighter than RMC and is made of thin-walled, thick-walled galvanized steel, which can be bent manually using specialized conduit benders. EMT is relatively simple to install, is affordable, and provides excellent mechanical protection for wires. It is particularly well-suited for indoor wiring in offices, schools, retail spaces, and other locations.
PVC conduit performs well in wet environments and outdoor applications. It's completely non-conductive, won't rust, is lightweight, and easy to cut and connect. In residential construction, PVC is often used to protect wires in wet areas like bathrooms and kitchens; in commercial and industrial settings, it's widely used for underground wiring and outdoor lighting systems.
Flexible Metal Conduit (FMC) offers a solution for specialized installation needs. Made from spirally wound metal strips, it can bend easily around obstacles. FMC is particularly suitable for connecting equipment that requires minimal movement, such as air conditioning units, pumps, and certain types of motors.
The greatest advantage of conduit systems lies in their flexibility and maintainability. When replacing or adding wiring, electricians simply pull the old wires out of the conduit and pull in the new ones without having to damage walls or ceilings. This makes conduit wiring particularly valuable in commercial and industrial environments where frequent upgrades are required.
Underground Cable (UF)
UF (underground feeder) cable is a specialized cable designed for outdoor and underground applications. It features solid or stranded copper conductors, encased in a specially formulated thermoplastic insulation, and topped off with a weather-, moisture-, and chemical-resistant jacket. The most significant feature of UF cable is that it can be buried directly in the soil, without the need for conduit protection. This greatly simplifies the construction process for outdoor wiring, reducing material costs and installation time. In residential settings, UF cable is commonly used to connect garden lighting, pool equipment, outdoor outlets, and outbuildings such as garages and sheds.
Although UF cable is designed for underground use, it also has specific installation requirements. The NEC stipulates that UF cable must be buried at least 24 inches (approximately 60 cm) deep in the soil, and even deeper in areas where it could be damaged by tilling equipment. Additional conduit protection is often required when crossing roads or other high-traffic areas.
UF cable's applications are not limited to underground use. It can also be used for certain outdoor overhead lines, especially when the lines need to cross areas where they may be exposed to direct sunlight. Compared to standard overhead lines, UF cable's integral construction makes it more durable and less susceptible to weathering.
Armored Cable (AC)
Armored cable is a long-standing type of electrical wiring that is still widely used in certain areas. It consists of an insulated conductor and an outer metal armor, typically made of steel tape or wire, forming a sturdy protective layer.
Traditional armored cable (AC) shares structural similarities with modern MC cable, but there are also key differences. The armor of AC cable typically consists of two spirally wound steel tapes with a paper insulation layer in between. This construction provides good mechanical protection, but bending can cause gaps in the armor, compromising overall protection.
In modern buildings, AC cable is less widely used than it once was, but it remains a preferred option in certain circumstances. For example, in areas where it must pass through fire walls, AC cable's structure allows it to better maintain its fireproof integrity. In some renovation projects in older buildings, electricians may also choose AC cable as a replacement for older cables because its installation method is compatible with the legacy system.
The greatest advantages of armored cable are its excellent mechanical strength and interference resistance. The metal armor not only protects against physical damage but also provides a certain degree of shielding against electromagnetic interference, which is an important consideration in some industrial environments.
Common Wire Types in Europe
PVC-Insulated Cable
PVC (polyvinyl chloride) insulated cable is one of the most common types of wire in the European market, particularly in the UK and Ireland. It features a copper conductor encased in PVC insulation and can be single-core or multi-core, depending on the application.
The main advantages of PVC cable are its cost-effectiveness and ease of installation. PVC insulation offers excellent electrical properties, is inexpensive to process, and can be produced in a variety of colors, facilitating circuit identification. In residential buildings, it is common to use single-core PVC cable in conjunction with a conduit system to route wires from distribution boxes to individual outlets and lighting fixtures.
However, PVC cable also has significant limitations. Its relatively low operating temperature, typically no higher than 70°C, limits its use in high-temperature environments. When burned, PVC releases toxic gases, which is one reason its use is restricted in some locations with stringent fire safety requirements.
To overcome these shortcomings, various improved PVC cables have been developed for the European market. For example, low-smoke zero-halogen (LSZH) PVC cables produce significantly less smoke and toxic gases when burned, making them the standard choice for hospitals, subways, and high-rise buildings. Flame-retardant PVC cables, by adding special flame retardants, enhance their resistance to flame spread.
Despite facing competition from high-performance materials like XLPE, PVC cables maintain a stable share of the European low- and mid-range markets thanks to their affordability and mature manufacturing technology.
XLPE Cables
XLPE (cross-linked polyethylene) cables represent the development trend of high-end wire technology in Europe. Through specialized chemical or physical processes, polyethylene molecules form a three-dimensional cross-linked structure, resulting in performance advantages far exceeding those of ordinary PE materials.
The most significant feature of XLPE cables is their high-temperature resistance. Standard XLPE cables are rated for operating temperatures up to 90°C, while XLPE cables produced using specialized formulations and processes can even operate stably at temperatures exceeding 125°C. This characteristic makes them particularly suitable for connecting high-temperature equipment or installing in high-temperature environments.In addition to high-temperature resistance, XLPE cables also possess excellent electrical properties. Its low dielectric constant and low dielectric loss enable it to maintain stable insulation performance under high voltages. This is one reason why XLPE is widely used in medium- and high-voltage transmission cables.
XLPE cables also excel in mechanical properties. They offer superior tensile strength and abrasion resistance compared to PVC cables, making them less susceptible to cracking due to bending or vibration. This durability extends the cable's service life and reduces maintenance costs.
Another key advantage of XLPE cables is their environmental performance. Halogen-free, they do not release toxic gases when burned and produce significantly less smoke than PVC cables. This makes them a preferred choice for safety-critical locations such as public buildings, transportation facilities, and data centers.
In the European market, the application range of XLPE cables is continuously expanding. From industrial motor connections to residential power distribution systems, from subway tunnel lighting to offshore wind turbine platforms, XLPE cables, with their superior comprehensive performance, are gradually replacing traditional PVC cables and becoming the next-generation mainstream wire material.
Conclusion
Electrical wiring is a vital component of a building's structure. Its selection and use directly impact its safety, performance, and longevity. From Romex and THHN cables commonly used in North America to PVC and XLPE cables popular in Europe, each type of wiring has its own specific advantages and applications.
When selecting wiring, factors such as building type, operating environment, local standards, and cost-effectiveness should be comprehensively considered. With technological advances, new environmentally friendly and intelligent wiring systems are gradually changing the face of building electrical systems, providing safer and more efficient power transmission solutions for future buildings.