What Cable Size Do You Need for a Geyser? (South African Guide)

Why Cable Size Matters for Geysers

A geyser is one of the largest electrical loads in most South African homes. It runs for long periods, draws a high current, and if wired incorrectly can be a serious safety risk. Choosing the correct cable size is not just about performance — it’s about preventing overheating, fire hazards, and ensuring compliance with South Africa’s wiring code (SANS 10142).

Homeowners often ask: What cable size do I need for a geyser? The answer depends on the geyser’s power rating, the length of the run, and the protection devices used — but there are standard practices that most qualified electricians follow.

Typical Geyser Cable Sizes in South Africa

While the final decision should always be confirmed by a registered electrician, these are the most common sizes used in South Africa:

  • 4mm² Surfix cable – Used for most standard domestic geysers (150L–200L, 2–3kW heating elements).

  • 6mm² Surfix cable – Required for larger geysers (200L+, 3–4kW elements) or where longer cable runs are involved.

  • Beyond 6mm² – Only required in special cases such as very long distances from the distribution board or unusually high loads.

These cable sizes are paired with appropriate circuit breakers and isolator switches, ensuring both safety and compliance with regulations.

Factors That Influence Geyser Cable Size

Several factors affect the correct cable size for a geyser installation:

1. Geyser Power Rating

Most residential geysers fall between 2kW and 4kW. The higher the wattage, the more current it draws, which increases the required cable size.

2. Distance from the DB Board

Voltage drop becomes a concern if the geyser is far from the distribution board. Longer runs may require a thicker cable to compensate.

3. Circuit Protection

The breaker size installed in the DB board must match both the cable size and the geyser’s rating. For example:

  • 20A breaker for a standard 3kW geyser on 4mm² cable

  • 25A breaker for a larger geyser on 6mm² cable

4. Installation Method

Cables run through conduit or areas exposed to higher ambient temperatures may require upsizing, as heat reduces current-carrying capacity.

5. Compliance with SANS 10142

All geyser installations must comply with South Africa’s wiring code. Even if a cable “works”, if it does not meet SANS standards, the installation is non-compliant and will not pass inspection.

Common Mistakes to Avoid

Unfortunately, many unsafe geyser installations are discovered during inspections. Here are some of the most frequent mistakes:

  • Using undersized cable such as 2.5mm² Surfix, which cannot handle the load of a geyser.

  • Skipping the isolator switch, even though SANS requires one to be installed within 1 metre of the geyser.

  • Running Surfix unprotected outdoors, instead of in black UV-rated conduit.

  • Ignoring the breaker rating, which can lead to nuisance tripping or, worse, fire hazards.

  • DIY installations without a Certificate of Compliance (CoC), leaving homeowners at risk of failed insurance claims.

FAQs

What is the minimum cable size for a geyser in South Africa?
Most domestic geysers require at least 4mm² Surfix. Anything smaller is not recommended and may not be compliant.

Can I use 2.5mm² Surfix for a geyser?
No. It is generally undersized for the load a geyser draws and would not be considered safe.

Do all geysers need 6mm² Surfix?
Not always. 6mm² is normally used for larger geysers (3–4kW) or when the cable run is longer than usual.

What breaker size is used with a geyser?
A 20A breaker is standard for a 3kW geyser with 4mm² cable, while a 25A breaker may be required for larger units on 6mm².

Does a geyser need an isolator switch?
Yes. South African regulations require a local isolator switch within 1 metre of the geyser.

Can I wire a geyser with cabtyre?
No. Geysers must be wired with fixed wiring cables such as Surfix. Cabtyre is only for flexible, portable appliances.

Choosing the Right Cable with Lite-Glo

At Lite-Glo, we stock a wide range of Surfix cable in 4mm², 6mm², and larger sizes, available by the metre or full rolls. We also supply geyser isolator switches, breakers, and conduit to ensure your installation is safe, compliant, and built to last.

⚠️ Safety & Compliance Notice

All electrical installations in South Africa must comply with SANS 10142-1 (Wiring Code) and the Occupational Health & Safety Act. Work must be carried out by a qualified, registered electrician.
This article is for general educational purposes only. It does not replace professional advice, and Lite-Glo accepts no liability for how this information is used. Always obtain a valid Certificate of Compliance (CoC) for any electrical work.

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