Wiring and Cabling SS1 Solar Photovoltaic Installation & Maintenance Lesson Note

DC vs. AC Cabling (The Two Different Worlds)

In a solar setup, we have two different types of electricity flowing, and they each need their own type of “road” (cable).

1. DC Cabling (The Solar Side): This is the wire that goes from your Solar Panels to your Inverter/Battery.

• Special Needs: These wires are usually outside on the roof. They have to be “UV-Resistant” so the sun doesn’t bake and crack the plastic cover.
• Color Code: We usually use Red for Positive (+) and Black for Negative (-).

2. AC Cabling (The House Side): This is the wire that goes from your Inverter to your TV, Fans, and Bulbs.

• Standard: This is the same type of wire used in normal house wiring.
• Color Code: Usually Brown/Red (Live), Blue/Black (Neutral), and Green/Yellow (Earth).

Important Rule: Never use regular “indoor” AC wire for your solar panels on the roof. It will peel and cause a fire within a year!

Cable Sizing (The “Water Pipe” Rule)

Choosing the size of a wire is like choosing the size of a water pipe.

• If you try to push a lot of water through a tiny straw, it’s difficult and the straw might burst.
• If you try to push a lot of electricity through a thin wire, the wire gets very hot, and you lose power (this is called Voltage Drop).

How we measure wire size: We measure the “thickness” of the copper inside in Square Millimeters (mm2).

• 2.5mm2: Good for small things like light bulbs.
• 4mm2 to 6mm2: Common for solar panels going to the controller.
• 16mm2 to 50mm2: Very thick wires used for connecting batteries to inverters (because the “Current” there is very high).

Factors Affecting Cable Choice

When a solar engineer is “sizing” a cable, they look at three main things:

1. The Current (Amps): The more Amps you have, the thicker the wire must be. A 5KVA system needs much thicker wires than a 1KVA system.
2. The Distance (Length): The longer the wire, the more electricity gets “tired” and lost along the way. If your panels are very far from your batteries, you must use an extra thick wire to make sure the power actually reaches its destination.
3. The Material: Most solar cables are made of Copper because it carries electricity very well. Avoid “CCA” (Copper Clad Aluminum) wires for solar—they are cheap but they don’t last and they get too hot.

Safety and Neatness

A safe installation is a neat installation. In Nigeria, many solar fires happen because of “rough work.”

• Conduits and Trunking: Cables should never just “hang” or lie on the floor. We put them inside plastic pipes (conduits) or covers (trunking). This protects them from rats chewing them and from people tripping over them.
• Tight Connections: If a wire is “loose” where it enters a terminal, it will start to spark. This “sparking” creates heat and is the #1 cause of solar fires. Always tighten your screws!
• Labeling: It is a good habit to put small stickers on your wires (e.g., “From Panel 1” or “To Battery”). This helps if someone needs to fix it later.

Summary and Class Activity

The “Cable Safety” Checklist

• [ ] Is the cable thick enough for the load?
• [ ] Is the solar cable UV-resistant (for the roof)?
• [ ] Are all the connections tight and firm?
• [ ] Are the cables protected from rats and rain?

Class Activity: The “Wire Detective”

1. The Comparison: Look at the cable on a phone charger and the cable on an electric pressing iron. Which one is thicker? Why?
2. The Calculation: If you have a battery very close to an inverter, you might use a 16mm2 wire. If you move that battery 20 meters away, would you need a thicker or thinner wire to keep the power strong?

Color Check: If you see a Red wire and a Black wire coming from a solar panel, which one is likely the “Positive” (+) wire?