Okay, let's break down the wire transition from overhead to underground and address your questions.1. Twisted Overhead Wires



Purpose

The twisting of overhead wires is primarily for mechanical strength and minimizing the effects of wind and ice loading. It's common in aerial installations. It also helps to reduce electromagnetic interference (EMI) and radio frequency interference (RFI) by keeping the wires close together and reducing the loop area.

2. Underground Wire Selection and Installation



#8 AWG THHN

#8 AWG THHN is generally acceptable for 20A to 40A circuits depending on local codes, insulation temperature rating, and application (consult local codes).

Specific Wire Type for Underground

THHN can be used underground, but it needs to be inside a conduit for physical protection. Since you're planning on using PVC SCH40, this is acceptable.

However, consider THWN-2

While THHN can be used in a dry or damp location, THWN-2 is specifically designed for wet locations. Since underground conduit often accumulates moisture (condensation, seepage, etc.),

THWN-2 is the better and more code-compliant choice for your application. It's the small additional cost that gives you peace of mind. Most THHN is dual rated as THHN/THWN-2. Check the markings on the wire insulation. UF Cable (Underground Feeder)

UF cable is a direct-burial cable designed to be buried directly in the earth. It is NOT to be used in a raceway because it is not labeled to do so. You can use it from pole to the underground transition point. You would need to make a junction and use a conduit afterwards. You would have to check with local authorities.

PVC SCH40 Conduit

PVC SCH40 is a common and acceptable choice for underground electrical conduit, providing good physical protection for the wires.

3. Ordering Materials



Minimum Essentials



Wire

2 Spools of #8 AWG

THWN-2 (much preferred) or THHN wire. Calculate the total length needed from pole to pole through the underground path, and add extra for connections and slack. Round up significantly - you can always trim excess wire. Conduit

PVC SCH40 conduit. Measure the trench length to determine the amount of conduit needed. Buy extra for cuts and fittings.

Conduit Fittings

Couplings to join sections of conduit. 90-degree sweeps or elbows for transitioning from vertical (pole) to horizontal (underground). End bells or bushings to protect the wire insulation where it enters and exits the conduit. Adapters to connect the conduit to junction boxes or other enclosures.

Pulling Lubricant

Essential for pulling the wires through the conduit. Use a lubricant specifically designed for electrical wire pulling.

Marking

Use colored electrical tape or permanent markers to clearly identify each wire at both ends (e.g., black for hot/line, white for neutral). This is critical for safety and troubleshooting later.

Warning Tape

Bury detectable warning tape a foot or so above the conduit to alert anyone digging in the future to the presence of underground utilities.

Grounding

Make sure the proper grounding is in place. If the neutral wire is also acting as the grounding wire, make sure you are not connecting the grounded wire to the enclosure.

Junction Boxes

Install proper junction boxes at the top of the pole for connections from the overhead wires to the underground wires. The box must be suitable for the environment (weatherproof).

Connectors/Lugs

Appropriate connectors or lugs for splicing the wires in the junction box. They should be rated for the wire size and material (copper to copper).

Highly Recommended Extras



Fish Tape/Pulling Rope

A fish tape or strong pulling rope is invaluable for pulling the wires through long conduit runs.

Conduit Cement

PVC cement for joining conduit sections and fittings.

Duct Seal

To seal the ends of the conduit runs to prevent water and debris from entering.

Grounding Clamps

If a separate grounding wire is required, you'll need grounding clamps to connect it to the poles or grounding electrodes.

4. Key Considerations and Next Steps



Local Codes and Permits

This is the most important point. Guam likely has its own electrical codes based on the NEC (National Electrical Code) but with local amendments. You must obtain all necessary permits and inspections. The electrical inspector will be the final authority on what materials and methods are acceptable.

Don't skip this step! Military Installation Requirements

Since one pole is on a military installation, there will likely be very strict requirements regarding materials, installation methods, and security clearances for the work. Coordinate closely with the base's engineering or public works department.

Voltage Drop Calculation

While #8 AWG may be acceptable, perform a voltage drop calculation to ensure the wire size is adequate for the length of the run and the expected load. Excessive voltage drop can cause equipment to malfunction.

Diagrams and Documentation

Create detailed diagrams of the installation, including wire colors, conduit routing, junction box locations, and grounding details. This documentation will be essential for future maintenance and troubleshooting.

Qualified Electrician

While you're ordering materials, strongly consider consulting with a qualified and licensed electrician in Guam. They will be familiar with the local codes, the specific requirements of the military installation, and can help you avoid costly mistakes. This type of work should be performed by a licensed electrician to ensure safety and code compliance.

In summary, while #8 AWG THHN inside PVC conduit is a common solution, THWN-2 is the safer and generally preferred choice for underground applications due to its moisture resistance. Thoroughly research local codes, coordinate with the military installation, and consult with a qualified electrician before proceeding with the work. Flag for review