Understanding Breakaway Systems

 
Treadway Blog Image Understanding Breakaway Systems (1)

When towing a loaded trailer, safety isn’t just about careful driving — it’s also about making sure the trailer can stop itself if something goes wrong. A breakaway system gives a braked trailer the ability to immediately apply its own brakes if it ever becomes unhitched, without needing driver input, helping prevent a dangerous runaway situation.

In New Zealand, a properly installed and functioning breakaway system is required for trailers that are not fitted with safety chains. However, many operators choose to use a breakaway system even when safety chains are present, as it adds an extra layer of protection.

Let’s take a closer look at how breakaway systems work, what the law requires, and how to make sure yours is ready to do its job.

What Is a Breakaway System?

A breakaway system is a safety mechanism that automatically applies the trailer’s brakes should the trailer become disconnected from the tow vehicle.

Why Your Trailer Needs a Breakaway System

A breakaway system is a critical safety feature. 

If your trailer becomes detached, the breakaway system prevents a runaway trailer from causing serious accidents, or a disconnected trailer from ramming into the back of your tow vehicle. By applying the brakes immediately, it reduces the risk of severe damage and accidents.

Types of Breakaway Systems
 
  • Mechanical breakaway systems: use a cable connected between the trailer and the tow vehicle; if the trailer detaches, tension on the cable directly engages a lever, spring, or cam to apply the brakes mechanically.
 
  • Electric breakaway systems: use a cable connected to a breakaway switch; when the trailer detaches, the cable pulls the switch, activating a dedicated onboard battery to apply electric or electric‑over‑hydraulic (EOH) brakes.

How Electric Breakaway Systems Work

An electric breakaway system works alongside the trailer’s existing electric or EOH brakes. 

Here’s how they interact: 
   
  • The breakaway system operates independently — if the trailer separates, it bypasses the controller and powers the brakes directly from the breakaway battery.  This ensures immediate braking even if the electrical plug or wiring between the vehicle and trailer becomes disconnected. 
For electric and EOH trailer brake safety, this separation between normal braking and emergency braking is critical. It means the trailer can still stop itself safely, even if the tow vehicle loses connection entirely. 

Components of an Electric Breakaway System
 
  • Breakaway Switch and Cable
A small switch mounted on the trailer’s drawbar, connected to the tow vehicle by a thin cable.
 
  • Breakaway Battery
A dedicated breakaway battery (housed in a weatherproof box) that powers the brakes once the switch is triggered. It provides the power needed to activate and sustain the brakes if the trailer detaches. While the trailer is attached, the battery uses the tow vehicle connection to stay charged. This ensures it always has enough energy to work when needed.
 
  • Wiring Harness and Connectors
Transfers power and signals between the battery, switch, and brakes.
 
  • Charging Circuit (via Tow Vehicle Plug)
Allows the tow vehicle to maintain the breakaway battery’s charge while driving.

Operation

When your trailer disconnects — for example, if the coupling had not been seated correctly on the tow ball — the breakaway cable acts as a safety trigger.

This cable is attached at one end to your tow vehicle and at the other end to a small breakaway switch mounted on the trailer. Inside that switch is a plastic or metal pin that keeps the circuit open (off) during normal towing.

If the trailer pulls away, the cable yanks that pin out of the switch.

Once the pin is removed, the circuit closes, sending power from the breakaway battery directly to the electric brakes, putting the trailer to a stop.

This pin is reattached to the breakaway system after the trailer has been secured.

How to Ensure Your Electric Breakaway System Is Working

Like any safety device, a breakaway system should be checked regularly. Here’s a simple step-by-step test you can do safely in your driveway or yard:

1. Check the battery.
Press the test button or use a multimeter to confirm it’s holding a full charge (around 12 V).

2. Inspect the cable.
Ensure the breakaway cable is free of frays or kinks and securely attached to a solid point on the tow vehicle — never to the towball.  

3. Test the switch.
With the trailer parked and wheels chocked, manually pull the breakaway pin. You should hear the trailer brakes engage.

4. Time the response.
Leave the pin out for a few seconds — the brakes should stay engaged until the pin is reinserted.

5. Reset and reconnect.
Replace the pin and confirm normal towing function resumes.

How Mechanical Breakaway Systems Work

Treadway Blog Image Understanding Breakaway Systems Mechanical
A mechanical breakaway system

A mechanical breakaway system is used on trailers using override brake systems. Unlike in electric or EOH systems, the breakaway cable in mechanical breakaway systems directly triggers the braking mechanism or linkage without additional battery and electrical wiring.

With no battery or electrics, there’s little to no risk of failure due to a flat breakaway battery, provided fitment, routing, and cable condition are correct.

Where the Mechanical Breakaway Cable Attaches
 
  • On the towing vehicle side, the breakaway cable is secured to a solid point on the tow vehicle chassis or towbar frame (never the towball).
 
  • On the trailer side, the cable is clipped to the designated breakaway cable attachment loop on the base of the brake lever (outside the coupling, passing through the cable guide underneath).

This linkage is designed so that when the trailer disconnects, the cable is pulled forward and manually engages the brake rod.

Components of a Mechanical Breakaway System
 
  • Breakaway Cable
A strong steel cable attached to the tow vehicle.
 
  • Return Spring
A component of the mechanical brake system that resets the brake lever after activation of the breakaway system.

Operation

If the trailer becomes detached, the breakaway cable pulls forward sharply as it is pulled by the towing vehicle. This action pulls the brake lever or linkage directly, which activates the trailer’s brakes.

Once the trailer is secured and before driving again, the brakes need to be unengaged manually by pressing the return spring switch, which is usually located under the coupling.

How to Ensure Your Mechanical Breakaway System Is Ready for the Trip

Before you tow, make sure that:
 
  • The breakaway cable has enough slack so the brakes aren’t accidentally applied during normal driving.
  • The cable is routed cleanly and does not drag on the ground at any point. For a guide on how to route the breakaway cable, please check your coupling’s manual.

Important Notes on Breakaway Cables
 
The breakaway cable is an essential part of any breakaway system. It experiences the greatest force if your trailer becomes disconnected, which is why it’s important to check its condition before every trip.

Extreme weather, road conditions, or everyday wear can damage the cable, so it should be replaced if you notice any of the following:
 
  • Frayed strands or damage to the outer sheath
  • A damaged clip or carabiner, including a stiff, loose, or misshapen gate
  • Kinks, crushing, or deformation of the cable
  • Rust, corrosion, or any discolouration of the metal

Trailer Got Disconnected? One More Step Before You Hit the Road

In the event your trailer got unhitched and the breakaway system has been activated, there’s one more step to do before getting back on the road: replacing the breakaway cable.

This is because when the trailer detaches, the cable is subjected to extreme tension. In many cases it will snap; in others it may not visibly “break,” but the force applied can permanently stretch or weaken it. Replacing the cable ensures the breakaway system will function correctly if it is ever needed again.

Legal Requirements in New Zealand

According to the NZ Transport Agency (NZTA), trailers must be equipped with functioning breakaway systems, unless they are fitted with an appropriate coupling and safety chains (two safety chains for trailers above 2,000 kg, one safety chain for trailers 2,000 kg or less).

A breakaway brake on a trailer with a laden weight of 2,500 kg or less is not required to be functional if the trailer is also fitted with the required number of safety chains.

If a breakaway brake is fitted to a trailer, safety chains are still recommended but not required.

If using a breakaway system:
  Heavy trailers other than semi-trailers with a rating of TC or TD (above 3,500 kg) are also required to use breakaway systems. Operation of these trailers are governed by stricter requirements.

Failure to meet these standards can result in a warrant of fitness (WoF) or certification failure, and more importantly, compromise towing safety.

TREADWAY TIP: If using safety chains together with your breakaway system:

Make sure the breakaway cable is shorter than your safety chains. This ensures that the breakaway cable will get pulled and activate the breakaway system when the trailer gets detached.

Why This Matters for Safety and Compliance

Beyond compliance, a breakaway system on a trailer:
  • Prevents runaway trailers during detachment incidents.
  •  
  • Protects other road users and property.
  •  
  • Helps maintain your trailer’s certification and insurance validity.
Neglecting the system—or running it with a flat or disconnected battery—means it won’t activate when it’s needed most. That’s why regular checks and proper wiring are very important.

Final Thoughts

Understanding how your breakaway system works and ensuring it is properly connected and/or charged is one of the simplest ways to improve trailer safety in NZ. Whether you’re towing a boat, a caravan, or a work trailer, keeping your setup compliant isn’t just about following the law — it’s about protecting everyone on the road.