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SV-07 · Service

Electrical Cable Size Guide: Choosing the Right mm²

A practical electrical cable size guide: typical uses for 1.5mm to 16mm cable and what changes the size. Then get a quote from a local electrician or supplier.

Cross-sections of copper cables from 1.5 mm² to 16 mm² arranged from smallest to largest
Cross-sections of copper cables from 1.5 mm² to 16 mm² arranged from smallest to largest

People search for an electrical cable size calculator because choosing the wrong size can mean tripping breakers, dim lights or a cable that overheats. This guide shows which sizes are typically used for which circuits in South Africa, and explains why the final size must be calculated by a registered electrician. ElectricalCable.co.za doesn't sell cable. Tell us what you need to power and how far, and we pass your request to an independent supplier or electrical contractor near you, who quotes you directly. The request is free.

Typical cable sizes and uses

  • 1.5 mm²: lighting circuits
  • 2.5 mm²: plug circuits
  • 4 mm² and 6 mm²: stoves, geysers, air conditioners and short sub-feeds; 4mm electrical cable and 6mm electrical cable are common for these
  • 10 mm² and 16 mm²: main supplies to a house, sub-DBs in outbuildings and larger inverters; 10mm electrical cable often feeds a cottage or workshop
  • 25 mm² and up: factories, large buildings, shopping centres and long supply runs

These are starting points, not a substitute for a calculation. Solar systems add their own sizing for DC and battery cable, which carry high currents at low voltage.

What changes the size

The electrical cable current carrying capacity depends on more than the cable itself:

  • Length and volt drop: long runs to a borehole or outbuilding often need a bigger cable than the load suggests
  • Installation method: cable in free air, conduit, roof insulation or underground is rated differently
  • Grouping: several cables bunched together run hotter
  • Ambient temperature: hot roof spaces reduce the rating
  • Protection: the breaker must suit the cable
  • Conductor: aluminium needs a larger size than copper for the same load

Why online tables aren't enough

An electrical cable size and current rating table from a website or manufacturer is based on specific conditions that may not match your installation. Online calculators often ignore volt drop, grouping or derating, or use overseas standards. In South Africa, cable sizing for fixed wiring is done to SANS 10142-1 by a registered electrician, who is responsible for the circuit when they sign the COC. Undersized cable can pass a quick look but overheat under load, damage equipment or trip breakers. Oversizing every circuit wastes money, so a proper calculation pays for itself.

Getting the right size quoted

The quickest way to get the right cable is to describe the job: what the cable will feed, the breaker or load if known, the length of the run and how it will be installed. An electrician or supplier can then size the cable, list the accessories and quote. Photos of the DB board and the route help too, especially for underground runs and outbuildings. Send those details with your request and get a free quote.

Comparing quotes for cable size guide

The lowest price is not always the best value. When your quote arrives, check:

  • Scope: exactly which cable, size and length is allowed for, and who supplies it.
  • Civil work: trenching, sleeves, chasing and making good, and reinstating paving or lawns.
  • Terminations and testing: glands, lugs, joints, insulation and earth-loop tests.
  • Compliance: that a registered electrician issues a COC under SANS 10142-1, and the guarantee on workmanship.

What to include in your request

  • What the cable will feed (geyser, stove, borehole, sub-DB, inverter)
  • Breaker size or appliance rating, if known
  • Length of the cable run in metres
  • How it will be installed (roof, conduit, underground)
  • Single-phase or three-phase supply

Frequently asked questions

What size cable do I need for a geyser or stove?
Geysers and stoves are commonly wired in 4 mm² or 6 mm² cable, but the correct size depends on the appliance rating, the length of the run and how the cable is installed. A registered electrician must calculate it and match the circuit breaker to the cable.
What size cable is used for the main supply to a house?
Main supplies are often 10 mm² or 16 mm², sometimes larger for long runs or three-phase supplies. The size depends on the supply rating, the distance from the meter and the installation method. Your electrician and the municipality or Eskom confirm the supply details.
Can I use an online electrical cable size calculator?
It can give a rough idea, but many calculators ignore volt drop, grouping and local standards. Final sizing for fixed wiring must be done by a registered electrician to SANS 10142-1, who takes the whole installation into account.
Does a longer cable need to be bigger?
Often, yes. Long runs lose voltage along the cable, so equipment at the end may not get enough. Pumps, boreholes, gate motors and outbuildings far from the DB board frequently need a larger cable than the load alone would suggest.

Cable Size Guide by province

Cable Size Guide by city

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