Electrical Codes and Regulations – SS2 Solar Photovoltaic Installation & Maintenance Lesson Note (First Term)

Electrical codes are written rules that tell an installer how to wire a building safely.

Behavioural objectives

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

1. State what an electrical code is and give three reasons for following it.
2. Name the new cable colours for live, neutral and earth, and the colours used in solar DC wiring.
3. Explain the current rating, voltage drop and 125% rules for sizing wire.
4. Describe the work of circuit breakers, surge protective devices and fuses in a solar system.
5. Explain why solar panel frames must be earthed.

What are electrical codes?

An electrical code is a set of rules that sets the minimum safe standard for wiring and installing electrical systems.

• Simple picture: a code is like a recipe book. Follow it exactly and the result is good. Skip steps and the house may catch fire.
• What the codes cover: cable colours, wire sizing, protective devices and earthing.
• Nigerian Code of Practice (NCP): the main local code followed by installers in Nigeria.
• IET Wiring Regulations: an international standard, formerly called the IEE Wiring Regulations.

Why do installers follow electrical codes?

Installers follow electrical codes for three main reasons: standardisation, fire prevention and legal protection.

1. Standardisation: any electrician who comes to the house later understands exactly what was done.
2. Fire prevention: many electrical fires come from ignoring the code, for example using thin wires for heavy loads.
3. Legal protection: after a failure or damage, an insurer or investigator may ask: “Did the installer follow the code?”

What are the cable colour codes?

A cable colour code is an agreed set of insulation colours that shows what each wire does.

• Old colours: Nigeria once used red, black and green.
• New colours: the country has moved to the IEC colours to match international standards.
• Rule for students: know both sets, but always use the new colours for new solar installations.

What are the new standard colours (IEC)?

The new standard uses brown for live, blue for neutral and green/yellow stripes for earth.

What colours are used in solar DC wiring?

Solar panels produce direct current (DC), and DC wiring uses red for positive and black for negative.

• Red: positive (+).
• Black: negative (−).
• Why it matters: joining positive and negative the wrong way can damage the inverter or battery.

How do we size wire correctly?

Wire sizing means choosing a cable thick enough to carry the current safely without overheating or wasting power.

• Common mistake: using a thin wire for a large current.
• Water picture: forcing a large flow through a small pipe causes damage.
• In wiring: an overloaded wire gets hot, and its insulation can melt and start a fire.

What are the key code rules for sizing wire?

Three rules guide wire sizing: current rating, voltage drop and the 125% rule.

1. Current rating: every wire has a limit, measured in amperes (A), and the load current must stay below it.
2. Voltage drop: a long, thin wire loses some voltage along its length, so less power reaches the battery. In solar wiring, the loss is commonly kept to 3% or less.
3. The 125% rule: choose a wire rated for at least 1.25 times the maximum current the panels can produce.

How does the 125% rule work in practice?

• Reason: strong sunlight can push panel current above its rated value, so the wire needs extra room.
• Step 1: find the maximum panel current from the panel label (for example, 8 A).
• Step 2: multiply by 1.25 (8 × 1.25 = 10 A).
• Step 3: choose a wire rated at 10 A or more.

What causes voltage drop?

• Long cable runs: more length means more loss.
• Thin cable: a small conductor resists the current more.
• Remedy: use a thicker cable or place the panels, inverter and battery closer together.

What protective devices does a solar system need?

A protective device is a “gatekeeper” that cuts off power or diverts danger when something goes wrong.

A solar system needs three protective devices: circuit breakers, surge protective devices and fuses.

What is a circuit breaker (MCB)?

• Meaning: a switch that trips (turns off) automatically when too much current flows.
• Reusable: it can be switched back on after the fault is cleared.
• Where fitted: one between the panels and the inverter, and another between the battery and the inverter.

What is a surge protective device (SPD)?

• Meaning: a device that catches a sudden voltage surge and sends it safely to the ground.
• Why needed: lightning is common in Nigeria and can destroy an expensive inverter.
• Connection: it must be joined to the earthing system to work.

What is a fuse?

• Meaning: a protector with a thin wire inside that melts when current is too high.
• Single use: once the wire melts, the fuse must be replaced.
• Replacement rule: use a fuse of the correct rating, never a wire or a bigger fuse.

How do the three devices compare?

Why is earthing important in a solar system?

Earthing (grounding) is the connection of metal parts of a system to the ground so that fault current has a safe path.

• Importance: it is often ignored in local installations, yet it is one of the most important safety measures.
• The earth rod: a copper rod driven deep into the ground.
• What is connected: all the metal frames of the solar panels are joined to the rod.

Why must panel frames be earthed?

• Accident: a live wire may touch the metal frame of a panel.
• With earthing: the current flows down to the earth rod instead of through a person.
• Without earthing: the frame stays live and shocks the next person who touches the roof.

What is on the safety compliance checklist?

• Conduits: are all wires inside conduits (pipes) to protect them from rats and sun?
• Labels: are switches clearly labelled, for example “CAUTION: SOLAR DC LIVE”?
• Battery box: is the battery kept in a ventilated box?

Evaluation

1. What is an electrical code, and why must an installer follow it?
2. State the new colours for live, neutral and earth wires.
3. Which colours are used for the positive and negative wires in solar DC wiring?
4. Explain the 125% rule for sizing wire.
5. Why must the metal frames of solar panels be connected to an earth rod?

Assignment

1. List the three protective devices used in a solar system, and state what each one does and where it is fitted.