Cable & Wire Tables — Quick Reference
Why you need these tables
An undersized wire doesn't give you "weaker electricity" — it gives you heat. Heat destroys insulation, and failed insulation means a short circuit or a fire. Picking a cable cross-section isn't a detail; it's a safety decision.
This is a quick-reference page: open it on site, take the number, get back to work. The tables follow IEC 60228 (conductor resistance) and IEC 60364-5-52 (current-carrying capacity).
1. Conversion table: AWG ↔ mm²
American and Chinese drawings use AWG; European and Syrian specifications use mm². This table translates between them.
| AWG | Area (mm²) | Diameter (mm) | Typical use |
|---|---|---|---|
| 30 | 0.05 | 0.255 | Winding wire, fine electronics |
| 26 | 0.13 | 0.405 | Signal cable, internal USB |
| 24 | 0.20 | 0.511 | Networking (Cat5/6), signals |
| 22 | 0.33 | 0.644 | Control panels, sensors |
| 20 | 0.52 | 0.812 | Signal circuits, small relays |
| 18 | 0.82 | 1.024 | Light fixtures, control |
| 16 | 1.31 | 1.291 | ≈ 1.5 mm² — lighting |
| 14 | 2.08 | 1.628 | ≈ 2.5 mm² — socket outlets |
| 12 | 3.31 | 2.053 | ≈ 4 mm² — medium loads |
| 10 | 5.26 | 2.588 | ≈ 6 mm² — heaters, A/C |
| 8 | 8.37 | 3.264 | ≈ 10 mm² — sub-feeds |
| 6 | 13.3 | 4.115 | ≈ 16 mm² — sub-panels |
| 4 | 21.2 | 5.189 | ≈ 25 mm² — main feed |
| 2 | 33.6 | 6.544 | ≈ 35 mm² |
| 1/0 | 53.5 | 8.252 | ≈ 50 mm² |
| 2/0 | 67.4 | 9.266 | ≈ 70 mm² |
| 4/0 | 107 | 11.68 | ≈ 95–120 mm² |
Rule of thumb: dropping 3 AWG numbers ≈ doubles the area. And a smaller AWG number means a thicker wire — the opposite of what beginners expect.
2. Current-carrying capacity (ampacity) — copper, PVC insulation
The figure depends on the installation method — a cable buried in an insulated wall can't shed heat the way one hanging in free air can.
| Area (mm²) | In conduit, insulated wall (A1) | In conduit on a wall (B1) | Clipped direct (C) | Free air (E) |
|---|---|---|---|---|
| 1.5 | 14.5 A | 17.5 A | 19.5 A | 22 A |
| 2.5 | 19.5 A | 24 A | 27 A | 30 A |
| 4 | 26 A | 32 A | 36 A | 40 A |
| 6 | 34 A | 41 A | 46 A | 51 A |
| 10 | 46 A | 57 A | 63 A | 70 A |
| 16 | 61 A | 76 A | 85 A | 94 A |
| 25 | 80 A | 101 A | 112 A | 119 A |
| 35 | 99 A | 125 A | 138 A | 147 A |
| 50 | — | 151 A | 168 A | 179 A |
| 70 | — | 192 A | 213 A | 229 A |
| 95 | — | 232 A | 258 A | 278 A |
Reference conditions: two loaded conductors, 30 °C ambient, PVC insulation (70 °C rating).
Derating factors — don't skip these
| Condition | Multiply the ampacity by |
|---|---|
| 40 °C ambient | 0.87 |
| 50 °C ambient | 0.71 |
| 2 cables grouped | 0.80 |
| 4 cables grouped | 0.65 |
| 6 cables grouped | 0.57 |
⚠️ Relevant in Syria: summer ambient passes 40 °C easily. A 2.5 mm² cable "rated 24 A" is really 21 A at 40 °C — and less again if it shares a conduit with other cables.
3. Conductor resistance (ohms per kilometre at 20 °C)
You need this for voltage-drop and heat-loss maths.
| Area (mm²) | Copper (Ω/km) | Aluminium (Ω/km) |
|---|---|---|
| 1.5 | 12.1 | — |
| 2.5 | 7.41 | — |
| 4 | 4.61 | 7.41 |
| 6 | 3.08 | 4.61 |
| 10 | 1.83 | 3.08 |
| 16 | 1.15 | 1.91 |
| 25 | 0.727 | 1.20 |
| 35 | 0.524 | 0.868 |
| 50 | 0.387 | 0.641 |
| 70 | 0.268 | 0.443 |
| 95 | 0.193 | 0.320 |
| 120 | 0.153 | 0.253 |
| 150 | 0.124 | 0.206 |
| 185 | 0.0991 | 0.164 |
| 240 | 0.0754 | 0.125 |
Aluminium needs roughly one size larger for the same current (resistivity 0.0282 vs 0.0175 Ω·mm²/m for copper) — but it's cheaper and lighter, which is why big feeders use it.
Temperature correction: resistance rises ≈ 0.4 % per °C. At 70 °C (a fully loaded cable) it is about 20 % higher than the table value.
4. Wire colours
The modern system (IEC 60445 — current standard)
| Function | Colour |
|---|---|
| Phase L1 | Brown |
| Phase L2 | Black |
| Phase L3 | Grey |
| Neutral (N) | Blue |
| Earth (PE) | Green/yellow striped |
Legacy systems you may still meet
| System | Phase | Neutral | Earth |
|---|---|---|---|
| Old UK | Red | Black | Green |
| US | Black / red | White | Green or bare |
⚠️ Never trust colour alone. In old installations a blue conductor may well be live. Always measure before you touch.
5. Choosing a cross-section — four steps
- Work out the current:
I = P / V(single phase) orI = P / (√3 × V × cos φ)(three phase). - Read the ampacity table for a size that carries it — after applying the derating factors (ambient + grouping).
- Check the voltage drop: keep it ≤ 3 % for lighting and 5 % for power. Long runs are governed by voltage drop, not by current.
- Check the protection: the breaker rating must sit between the load and the cable:
I_load ≤ I_breaker ≤ I_cable.
The classic mistake: sizing from the ampacity table alone and forgetting voltage drop. Over a 60 m run a 2.5 mm² cable "carries" 24 A — but the voltage drop will make the installation unusable.
Work it out yourself
Voltage drop and the minimum cross-section — enter the load and the distance:
voltage-drop
Current from power (to start step 1 above):
power-energy
Expensive, common mistakes
| Mistake | What it costs you |
|---|---|
| Ignoring summer ambient | The cable runs over its limit → insulation cracks within a few years |
| Cramming a conduit full | Cables heat each other → up to 40 % of capacity lost |
| Breaker bigger than the cable | The cable burns before the breaker trips — the most dangerous error there is |
| Aluminium at copper sizes | Overheating and excessive voltage drop |
| Forgetting the return path | Voltage drop is calculated over there and back, not the one-way length |
Key points
- Smaller AWG = thicker wire. Three sizes down ≈ double the area.
- Ampacity is not a single number — it depends on installation, ambient and grouping.
- Voltage drop rules long runs; current rules short ones.
- The breaker protects the cable before it protects the appliance.