How to Choose the Right Electrical Wire Size? A Practical Guide
Choosing the wrong wire size is the most common electrical mistake in Egypt — an undersized wire heats up, degrades, and causes fires, while an oversized wire unnecessarily increases cost. This guide teaches you the correct method for selecting the right size for each load.
Quick Answer
A practical guide for choosing the correct electrical wire size for every application — lighting, outlets, AC units, water heaters. Understanding the relationship between load, voltage, and wire size to avoid common mistakes.
Wire Sizes by Application
1.5mm² wire — For lighting only: standard light points and decorative lighting. Rated up to 15A. Do not use for outlets or any other load — lighting only.
2.5mm² wire — For general outlets: kitchen, bedroom, and living room sockets. Rated up to 20A. The standard in every residential apartment.
4mm² wire — For small to medium AC units (up to 2.25 tons) and electric water heaters. Rated up to 30A. Dedicated circuit for each appliance.
6mm² wire — For large AC units (3–4 tons), electric ovens, and large instant water heaters. Rated up to 40A. Essential for heavy loads.
10mm² and above — For very large loads: 3-phase water pump, small factory, or entire building. Rated 60A+. Requires precise engineering calculation.
Golden rule — The correct wire = one that doesn't heat up under full load. If the wire feels warm to the touch after an hour of operation, its cross-section is too small. This is a hazard that must be addressed immediately.
Quick Reference Table
| Size | Max Load | Application |
|---|---|---|
| 1.5 mm² | 15A / 3,300W | Lighting only |
| 2.5 mm² | 20A / 4,400W | General outlets |
| 4 mm² | 30A / 6,600W | Small AC / water heater |
| 6 mm² | 40A / 8,800W | Large AC / oven |
| 10 mm² | 60A+ | Industrial loads |
FAQ
How do I calculate the right size myself?
Basic calculation: Load (watts) ÷ Voltage (220V) = Current (amps). Then choose a wire rated at least 25% above the calculated current as a safety margin.
Does the wire type and material matter as much as the size?
Yes, significantly. Copper wires compliant with Egyptian specifications (such as El-Sewedy or certified alternatives) are more conductive and longer-lasting. Avoid wires of unknown origin.
What's the risk of using an undersized wire?
An undersized wire heats up under load, gradually degrading the insulation. Over time the insulation burns and creates a short circuit that can cause a fire. This is the most common cause of residential electrical fires in Egypt.
Can a 2.5mm² wire be used for an AC unit?
No. A 2.5mm² wire cannot safely handle a 1.5–2 ton AC unit's current (reaching 10–15A) over the long term. The correct wire for an AC unit is at minimum 4mm² with a dedicated circuit.
Does the required size change with wire length?
Yes. The longer the wire, the greater the voltage drop. For long runs (over 15–20 meters), it's advisable to increase the wire size by one step to compensate for voltage loss.