Direct answer
A cable size such as 1.5 mm², 2.5 mm² or 6 mm² describes the nominal cross-sectional area of the conductor — not a universal current rating. Safe cable selection depends on the connected load, protective device, cable construction, installation method, ambient conditions, grouping and circuit length/voltage drop. This is why a single “2.5 mm² = X amps” internet table can be misleading when it ignores the installation conditions.
Key facts
- mm² is conductor cross-sectional area, not cable diameter.
- Current-carrying capacity changes with installation method and thermal conditions; the same conductor size does not have one universal permissible current in every installation.
- The circuit protective device must be coordinated with the conductor and connected load.
- Longer circuits can be constrained by voltage drop even when thermal current-carrying capacity appears adequate.
- Cable construction and application matter: fixed-building cable, flexible cord, battery cable and solar DC cable are not interchangeable merely because the conductor areas look similar.
What does 2.5 mm² actually mean?
The notation mm² refers to the nominal cross-sectional area of the conductor. It is an area measurement, not the outside diameter of the insulated cable. Two cables with the same conductor area can have very different external diameters because insulation, sheath, armouring and construction differ.
That distinction is useful in retail: customers often arrive with a physical cable thickness and ask for “the same size”. The safer identification method is to read the cable marking/specification and application rather than estimate conductor area from the outside.
Why cable size cannot be chosen from watts alone
Power gives only part of the picture. For a simple single-phase load, current is related to power and voltage, so a 2,000 W resistive load at 230 V is approximately 8.7 A. But that arithmetic does not select the cable. Cable selection still has to account for how the cable is installed, how heat can escape, conductor material/insulation, ambient temperature, grouping, protective device, length and other design conditions.
ECA(SA)’s August 2026 guidance makes this relationship explicit: the conductor, connected load, protective device and actual installation conditions must be considered together.[1]
The breaker protects the conductor
A circuit-breaker’s job includes protecting the wiring against overcurrent. It follows that the breaker cannot be selected independently of the cable. A breaker that permits more current than the conductor can safely carry under the actual installation conditions can allow overheating before protection operates.
This is why repeated tripping is not permission to increase breaker size. The cause of the trip and the circuit design have to be assessed first.
Installation method changes current-carrying capacity
A cable surrounded by thermal insulation cannot shed heat in the same way as a cable with free air around it. Multiple loaded conductors grouped together can also run hotter than an isolated cable. Ambient temperature, enclosure and routing therefore affect current-carrying capacity. IEC 60364-5-52 addresses selection and erection of wiring systems and includes cable-sizing and voltage-drop considerations.[2]
For public-facing buying content, this is a better lesson than publishing an oversimplified amperage chart. A useful retail guide should help the customer identify the cable type and installation purpose, then direct fixed-wiring design to a competent person using the applicable tables and factors.
Why length and voltage drop matter
Every conductor has resistance. As current and circuit length increase, voltage at the load can fall. Excessive voltage drop can affect lighting, motors, electronics and other equipment even if the cable is not thermally overloaded. IEC 60364-5-52 specifically includes voltage-drop provisions in its wiring-system scope.[2]
Low-voltage systems are particularly sensitive in percentage terms: losing 1 V on a 12 V circuit is proportionally much more significant than losing 1 V on a 230 V circuit. That is why battery and LED-strip circuits often need separate voltage-drop attention.
Do not confuse cable families
Flexible cabtyre/cord, fixed installation cable, armoured cable, solar PV cable and battery cable are engineered for different environments and connection methods. A product page should clearly state conductor size, number of cores, voltage/application rating where verified, insulation/sheath type where known, colour and intended use. If a technical parameter is unknown, leave it unclaimed rather than infer it from a product name.
Cable selection: the factors that change the answer
| Factor | Why it matters | Customer-facing question |
|---|---|---|
| Connected load | Determines expected current and duty | What equipment will this circuit supply? |
| Protective device | Must coordinate with conductor and fault protection | What breaker/fuse protects the circuit? |
| Installation method | Changes how heat is dissipated | In conduit, trunking, insulation, open air or underground? |
| Grouping / ambient temperature | Can reduce allowable current | Is it bundled with other loaded circuits or in a hot area? |
| Length | Influences voltage drop | How far is the run from source to load? |
| Cable construction | Determines environment and mechanical suitability | Fixed cable, flexible cord, PV cable, battery cable, armoured cable? |
Frequently asked questions
How many amps can 2.5 mm² cable carry?
There is no single safe answer without the cable type and installation conditions. Use the applicable South African wiring rules and manufacturer data for the actual installation.
Is 2.5 mm² the diameter of the copper?
No. It is the nominal cross-sectional area of the conductor.
Can I use thicker cable than required?
A larger conductor may reduce resistance, but termination capacity, protective-device coordination, cost, routing and equipment terminals still matter. It is an engineering decision, not simply “bigger is always better”.
Does a long cable need to be thicker?
Sometimes. Voltage drop can become the limiting design factor on long runs, so length must be included in the calculation.
Can I use battery cable for house wiring?
Do not substitute cable types based only on mm². Construction, insulation, voltage rating, approvals and intended installation method matter.
Technical references and further reading
[1] ECA(SA) — Wired to Comply: Understanding the Standard Test Report — August 2026 South African guidance: conductor, load, protective device and installation conditions must be considered together. Source link
[2] IEC 60364-5-52:2009 + AMD1:2024 — Current consolidated IEC standard on selection and erection of wiring systems, including cable sizing and voltage drop. Source link
[3] IEC 60898-1:2015 + AMD1:2019 — Circuit-breakers for overcurrent protection in household and similar installations. Source link
[4] ECA(SA) — SANS 10142-1:2026 Ed. 3.03 availability notice — Current South African wiring-code edition availability. Source link
