Advanced Wiring Techniques – SS2 Solar Photovoltaic Installation & Maintenance Lesson Note (Second Term)

Advanced wiring in a solar installation means protecting cables from sunlight, physical damage and rodents by running them through containment: conduits and trunking. On the roof, UV-rated solar DC cables, corrugated pipes, cable glands and drip loops help the system withstand sun and rain. Clear labelling and neat bends complete a professional finish.

Behavioural objectives

By the end of the lesson, students should be able to:

• State three dangers to exposed cables in a solar system.
• Describe PVC conduits and flexible (gooseneck) conduits and say where each is used.
• Explain when trunking is used and how it should be installed.
• List the ways of protecting the DC side of a solar system on the roof.
• Describe good finishing practice: labelling, bending and drip loops.

Why are “naked” wires dangerous?

In a basic science project, you might just tape wires to a wall. In a professional solar system, we never leave wires “naked” (exposed).

The enemies of your cables:

1. UV rays: The Nigerian sun is very harsh. Regular wire insulation will crack and peel off after a few months if left in the sun.
2. Physical damage: People walking, doors closing, or children pulling on wires.
3. Rodents: Rats love to chew on the “sweet” plastic coating of cables, which causes short circuits and fires.

The solution: We use containment. This means hiding wires inside protective pipes and channels called conduits and trunking.

What are conduits?

Conduits are tubes (pipes) that we run cables through. For solar, we usually use two types:

• PVC conduits: These are plastic pipes. They are great for inside walls or underground because they don’t rust.
• Flexible conduits (gooseneck): These are bendy pipes. We use them to connect a solar panel to a junction box because they can handle the curves.

Best practice for conduits

• Don’t overstuff: Only fill a pipe up to 40%. Wires need “breathing room” so they don’t get too hot.
• Use saddles: Use clips (saddles) every 1 metre to keep the pipe straight and firm on the wall.

What is trunking?

Trunking is usually square or rectangular and has a “lid” that snaps on. You see it often in offices or where many wires run together.

When to use trunking

• Inside the inverter room: You have many wires coming from the batteries and panels, so a large trunking keeps them organised and neat.
• Surface mounting: If you cannot dig into the wall (chasing), use neat white trunking on the surface.

Pro-tip: Always use a spirit level when installing trunking. Trunking that is slanted or crooked on a wall looks unprofessional.

How do you protect the DC side (solar cables)?

Solar wiring is different because it sits on the roof in the rain and sun.

1. UV-rated cables: You must use special “Solar DC cables”. These are usually black with thick insulation.
2. Corrugated UV conduits: If you must run wires across the roof tiles, put them inside black corrugated pipes. The black colour resists sun damage better than white pipes.
3. Glands: When a wire enters a junction box, use a “cable gland”. It acts like a rubber seal that stops rain from entering the box and damaging your connections.

What makes a professional finish?

A great solar installer is known by how “clean” their wiring looks.

• Labelling: Use a marker or a sticker to label your pipes, for example “DC FROM PANELS” or “AC TO LOAD”. This helps the next person who has to fix the system.
• Bending: When turning a corner with a pipe, avoid a sharp 90-degree “elbow” if you can. Use a “bend” so the wires can slide through easily without getting stuck.
• Drip loops: When bringing a wire from the roof into the house, make a small “U” shape before it enters the wall. Rainwater then drips off the bottom of the “U” instead of running straight into the house.

Installation checklist

• Is the pipe straight?
• Are the cables loose inside (not cramped)?
• Are the outdoor connections waterproof with glands?
• Is everything labelled clearly?

Evaluation

1. Name three enemies of exposed cables in a solar system.
2. Where would you use a flexible (gooseneck) conduit instead of a PVC conduit?
3. What percentage of a conduit should be filled with cables, and why?
4. Give two situations where trunking is the better choice.
5. What is a drip loop, and what problem does it solve?

Assignment

1. List three ways of protecting solar DC cables on a roof.
2. Explain why corrugated conduits for roof wiring are black.
3. Write two examples of labels you would put on pipes in a solar installation.