Electrical Guides
July 9, 2025

Understanding the Pilot Wire and Ripple Relay Hot Water Control Systems in Auckland Homes

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If you’ve ever wondered why your hot water mysteriously turns off at certain times of the day, you might be experiencing the effects of the pilot wire or ripple relay system — legacy technology still active in many Auckland homes.

In this blog, we’ll explain exactly what these systems are, how they work, why they were installed, and what’s replacing themas Auckland moves toward smarter energy solutions.

What Is the Pilot and Ripple Relay System?

Pilot wire and ripple relay systems are control mechanisms used to manage electrical demand by switching off non-essential appliances like hot water cylinders and night-store heaters during peak times.

You’ll typically find the relay device - a small rectangular unit - mounted next to your electrical meter inside the meter board.

Image of a standard Ripple Relay within a Meter board

Why Were Ripple and Pilot Relays Installed?

Imagine this scenario:

You get home at 5:30pm. You turn on the oven to preheat for dinner, fire up the heater to fight the chill, and throw on the TV to catch The Chase.

All of those devices draw current (electrical energy) from the residential grid.

Multiply this by hundreds of thousands of households in Auckland, and you have a recipe for massive  energy usage.

We call this high-usage time the ‘Peak’ Period.

In winter, Auckland’s residential grid can peak at 700–900 megawatts - that’s equivalent to the energy stored in over 1.5 million car batteries being used all at once.

To reduce this strain, network operators began remotely disabling hot water systems during peak periods, a clever way to curb demand without impacting essential services.

How Do These Systems Work?

The Ripple Control System

This system works by injecting a high-frequency signal (typically 1050–1750 Hz) into the power grid from a local substation.

Modern electricity meters detect this signal andrespond by switching off the ripple relay, which cuts power to your hot water system or heater. Once the peak has passed, the injected signal is removed, the meter disengages the ripple relay, turning your hot water back on.

The Pilot Wire System

This is an older method. A dedicated wire - the pilot wire - runs alongside your standard power supply and carries a control signal (usually 230V AC or 24V DC) directly to the relay.

Pilot wire systems were widely used in older Auckland suburbs in the 1950s–60s but have become largely obsolete due to their infrastructure requirements.

When Were These Systems Introduced?
  • 1950s–60s: Pilot wire systems used in early suburban developments.
  • 1970s–80s: Ripple control gained popularity due to lower infrastructure costs.
  • By the 1990s: Ripple control became the national standard across New Zealand, adopted by networks like Vector, Counties Energy, and Entrust (formerly Mercury Energy).

Are These Systems Still in Use?

Yes — but they’re being phased out.

Why Are They Being Replaced?

  1. Smart Meters: These allow two-way communication and remote load control, making ripple signals unnecessary.
  2. Aging Equipment: Ripple injection units and relays are expensive to maintain and nearing the end of their service life.
  3. Modern Load Control: Systems like smart home automation and demand-response tools provide more flexibility.
  4. Solar, EVs, and Batteries: These modern power sources require more sophisticated control systems than ripple or pilot relays can offer.
What’s Replacing Ripple and Pilot Systems?
  • Advanced metering infrastructure (AMI) with built-in smart load control
  • Time-of-use pricing from your energy retailer
  • Smart home energy systems that respond to real-time energy demands
What Does This Mean for Auckland Homeowners?

If you live in an older property, your hot water may still be controlled by a ripple or pilot relay.

While this isn’t a problem on its own, it could lead to issues if therelay fails or your hot water stops working without explanation.

Modern homes and renovations are moving toward smart meter control, which eliminates the need for ripple systems altogether.

What Happens If My Ripple or Pilot Relay Fails?

If the relay fails, your hot water could stop working altogether. Here’s what to do:

  • Contact your local energy network (in Auckland, that’s Vector). They may be able to repair or replace the relay. OR
  • Call your electrician. If you have a smart meter, they may bypass or remove the relay and connect your hot water directly.

Summary

The pilot and ripple relay systems were once revolutionary, helping to reduce grid strain by remotely switching off high-energy appliances like hot water heaters during peak demand periods.

Today, however, these systems are being replaced by smarter, more flexible technologies that give both consumers and energy companies better control over when and how power is used.

If your home still uses a ripple or pilot relay system and you're experiencing hot water issues, it might be time to talk toyour electrician or energy retailer about an upgrade.

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