The best wire conduit to install in the United States is typically a combination of PVC (Polyvinyl Chloride) and metal conduits, depending on the specific application and environment. PVC conduits are widely used due to their cost-effectiveness, ease of installation, and resistance to chemicals and moisture. Metal conduits, such as steel or aluminum, are preferred in environments where higher durability and fire resistance are required.

PVC conduits are ideal for general-purpose electrical installations, as they are lightweight, flexible, and offer good protection against physical damage and moisture. According to the National Electrical Code (NEC), PVC conduits are suitable for most residential and commercial applications. They are also easy to install, which can save time and labor costs. For instance, the 2021 NEC states that PVC conduits can be used for "all types of wiring methods where the conditions of use are not detrimental to the conduit material" (Article 300.4).

On the other hand, metal conduits, such as steel or aluminum, are more durable and provide better protection against fire and extreme temperatures. They are often used in industrial settings, underground installations, and areas where the conduit may be exposed to harsh conditions. According to the 2021 NEC, metal conduits are required for "wiring methods where the wiring is subject to physical damage, where the conduit is to be installed in a corrosive environment, or where the conduit is to be used as a raceway for communication conductors" (Article 300.4).

A study by the National Fire Protection Association (NFPA) found that metal conduits can provide up to 3 hours of fire protection, compared to only 1 hour for PVC conduits. This makes metal conduits a safer choice for environments where fire safety is a priority. Additionally, metal conduits are more resistant to corrosion, which can be a significant concern in coastal areas or areas with high humidity.

In conclusion, the choice between PVC and metal conduits depends on the specific application and environment. PVC conduits are generally more cost-effective and easier to install, making them suitable for most residential and commercial applications. Metal conduits, on the other hand, offer greater durability, fire resistance, and corrosion resistance, making them ideal for industrial settings and areas with harsh conditions.