Caravan Extension Leads Explained: 1.5mm² vs 2.5mm² and Australian Standards

Posted by Merry Cadalso on Jun 19, 2026

Do You Have the Right Extension Lead for Your Van?

Choosing the right extension lead for your caravan is becoming more confusing than ever.

Recent changes to Australian Standards have introduced new recommendations for caravan power leads, and at the same time many travellers are discovering that not all 15A leads are built the same. One of the most overlooked differences is the thickness of the copper conductors inside the cable, commonly referred to as the cable's core size.

Whether you're looking at a Flat Out lead or one from another manufacturer, you'll typically come across two common options: 1.5mm² and 2.5mm² cable. While both may be compliant and safe to use, they can perform quite differently depending on how far you're running power and what appliances you're using.

In this article, we'll unpack what the Australian Standards actually require, explain the difference between 1.5mm² and 2.5mm² extension leads, and help you understand when the thicker cable is beneficial and when it may simply be unnecessary overkill for your setup.

The First Question: How Long Does Your Lead Need To Be?

Before thinking about cable size, start with lead length.

If a shorter lead reaches the power point, that's usually the best option. Shorter leads are lighter, easier to handle, easier to store, and experience less voltage drop.

Unfortunately, caravan parks don't always place power outlets where we would like them. Many travellers eventually encounter sites where a longer lead becomes necessary.

For this reason, many experienced caravanners carry both a shorter lead for everyday use and a longer lead for those occasions when extra reach is needed.

What Do Australian Standards Say?

Recent changes to Australian Standards have introduced a recommendation that caravan extension leads over 15 metres use a 2.5mm² conductor size.

This recommendation exists because caravans are classified as inhabitable structures. In simple terms, the standard needs to account for every possible usage scenario, including situations where multiple high-draw appliances are running directly from mains power.

The important thing to understand is that this recommendation is primarily about performance rather than safety.

Australian Standards allow a maximum voltage drop of 5%. Different cable sizes and lead lengths simply affect how much voltage is lost before power reaches your appliances.

Why Does Cable Core Size Matter?

Every electrical cable has resistance.

As electricity travels through a cable, a small amount of energy is lost. This loss appears as voltage drop.

Two factors have the biggest impact on voltage drop:

Lead length
Copper conductor size

The longer the lead, the greater the voltage drop.

The thicker the copper conductor, the lower the voltage drop.

This is why cable size becomes more important as lead length increases.

Leads 15 Metres and Under

For most caravan owners, a quality 15A extension lead under 15 metres in length will comfortably handle any normal caravan application.

At these lengths, a 1.5mm² conductor provides excellent performance while remaining lightweight and easy to manage.

Whether you're charging batteries, running a fridge, using lighting, powering a microwave occasionally, or operating an air conditioner, voltage drop remains well within acceptable limits.

For many travellers, a lead in this length range will be all they ever need.

Flat Out Option

Our Compact 12.5m, and 15m 15A Extension Leads use a 1.5mm² conductor and are designed for all types of caravan use where a shorter lead will reach the power outlet.

Leads Over 15 Metres

Once you move beyond 15 metres, the conversation starts to change.

A longer cable naturally introduces more resistance, which increases voltage drop. This is where conductor size becomes more important.

Many caravan owners assume that because the standard recommends 2.5mm² over 15 metres, every traveller must use the larger cable.

That's not necessarily the case.

The right choice depends on how you use your van.

When is 1.5mm² Enough?

A 1.5mm² lead can still be an excellent choice at 20 metres when your power demands are relatively modest.

Typical examples include:

Charging batteries
Running fridges
Operating LED lighting
Supplying power to an inverter
General caravan use with moderate loads

For many travellers, these applications represent the majority of their power usage.

In these situations, a quality 20m lead with a 1.5mm² conductor can provide perfectly satisfactory performance while remaining lighter and easier to handle than a heavier cable.

Flat Out Option

Our 20m Heavy Duty 15A Extension Lead uses a 1.5mm² conductor and is suitable for many common caravan applications where longer reach is required.

When Does 2.5mm² Make Sense?

A 2.5mm² lead becomes beneficial when you're regularly running high-current appliances directly from mains power.

Examples include:

Air conditioners
Induction cooktops
Microwaves
Coffee machines
Multiple appliances operating simultaneously

The thicker copper conductor reduces voltage drop, helping these appliances receive as much voltage as possible.

If you regularly use your caravan like a small home while connected to mains power, a 2.5mm² lead is often the better choice.

Flat Out Option

Our 20m Extra Heavy Duty 15A Extension Lead uses a 2.5mm² conductor and complies with the current Australian recommendation for caravan leads over 15 metres.

Understanding Voltage Drop

Let's put some numbers to this.

Australian Standards require voltage drop to remain below 5%.

Approximate calculations below:

As you can see, all three options remain comfortably below the 5% limit.

The thicker 2.5mm² conductor offsets the additional distance, which is why it achieves almost identical voltage drop to the shorter lead.

The 20m 1.5mm² lead experiences a little more voltage drop but still remains comfortably within the accepted limits.

A Quick Note About "Heavy Duty" Labels

You'll often see terms such as:

Heavy Duty
Extra Heavy Duty
Ultra Heavy Duty

used throughout the Australian electrical industry.

These terms are not defined by any Australian Standard. In many cases they refer to insulation thickness, but because there is no formal standard governing these descriptions, the wording can mean different things from one manufacturer to another.

When comparing extension leads, always check the actual conductor size. The core size tells you far more about the lead's capability than the marketing label on the packaging.

Which Lead Should You Choose?

If you're using a lead under 15 metres:
A 1.5mm² core will comfortably handle every scenario.

If you're using a lead over 15 metres:
A 1.5mm² core is suitable if:

You run high-draw appliances through an inverter, or
You mainly use lighter loads such as fridges and lighting

A 2.5mm² core is recommended if:

You run your van like a house
You power appliances directly from mains power
You regularly use high-draw appliances such as air conditioning, induction cooking or microwaves

The choice ultimately comes down to how you use your van.