As confirmed in a recently published article by the Principal Technical Advisor at Energy Safety, WorkSafe NZ, AS/NZS 3000:2018 requires a “true isolating switch” to be installed for fixed-wired hot water heaters (Clause 4.8.2.3). A “true isolating switch” refers to a switch disconnector (ON-load isolator) as defined in AS/NZS 60947-3—the product standard for switches.

What is a switch disconnector (ON-load isolator)?

A switch disconnector is designed to make and break electrical load under both normal operating conditions and specified overload scenarios. It also meets the mechanical requirements for effective isolation. For installations such as hot water heaters, a switch disconnector offers a practical and cost-effective solution, as it performs both switching and isolation functions in a single device.

How can you identify a switch disconnector?

According to WorkSafe New Zealand’s Energy Safety Bulletin and AS/NZS 60947-3, a true switch disconnector is not just a basic isolating switch—it must be capable of making and breaking load under normal and specified overload conditions, while providing mechanical isolation. Always refer to the product's data sheet or technical specification to confirm compliance.

Other key identifiers include:

• Look for compliance with AS/NZS 60947-3 on the product label or datasheet. This standard specifically covers switch disconnectors.
• A true switch disconnector must clearly indicate its position—ON (I) and OFF (O)—ensuring visible confirmation of isolation.
• The device may display a disconnector symbol (a switch with a horizontal line and break) or be explicitly labelled as a "Switch Disconnector" or "Isolator."
• The device must be rated to make and break load currents, not just isolate. This will be stated on the technical specification or rating plate.
• Switch disconnectors are typically designed to lock in the OFF position, enhancing safety during maintenance or servicing.
• Datasheets, product brochures, or catalogues will confirm whether the device is a switch disconnector in line with AS/NZS 60947-3. 

Always consult the product’s datasheet or certification documents to confirm the device’s classification and capabilities.

What is a disconnector (OFF-load isolator)?

Disconnectors, also known as OFF-load isolators, are a separate product classification under AS/NZS 60947-3. They are rated to carry the specified current once the contacts are closed in the ON position but are not designed to make or break load. Therefore, additional measures must be taken to interrupt the load current before the disconnector is operated. This is typically achieved using electrically interlocked equipment that safely breaks the load prior to disconnection.

While disconnectors offer a cost-effective and practical solution for high-current applications, they are uneconomical for low-current installations, such as domestic water heaters.

How can you identify a disconnector? 

A disconnector (OFF-load isolator) can be identified by the following characteristics:

• It is marked and classified according to the AS/NZS 60947-3 standard as a disconnector or OFF-load isolator.
• It is designed to carry current only when closed but is not rated to make or break load, meaning it must only be operated when the circuit is de-energised, or the load is already interrupted.
• It usually lacks the robust switching mechanism required to safely interrupt current under load, distinguishing it from a switch disconnector.
• It is often used in conjunction with additional switching devices (such as contactors or circuit breakers) that break the load before the disconnector is operated.
• Physically, disconnectors commonly feature lockable open positions to ensure isolation and safety during maintenance.
• Manufacturer labels and technical datasheets will explicitly indicate whether the device is a disconnector or switch disconnector, along with its rated utilisation category. 

Always consult the product’s datasheet or certification documents to confirm the device’s classification and capabilities.

What are the essential safety and performance requirements for isolators?

Isolators, including switch disconnectors and disconnectors, must be rated according to their designated utilisation categories and must also meet the following stringent isolation requirements:

• Must only indicate OFF when all contacts are physically open (verified by the 3F Handle Test).
• Must clearly and reliably show the isolation position; the international symbols ‘O’ (OFF) and ‘I’ (ON) meet this requirement.
• Must disconnect or isolate all active conductors.
• Must be capable of withstanding impulse voltages likely to occur at the point of installation.
• Must be designed to prevent unintentional operation due to impact, vibration, bumping, or brushing.
• Must provide the ability to be secured in the open position (lockable); note: it must not be possible to secure the device unless all contacts are open.
• Must be clearly marked with the appropriate symbol identifying it as a switch disconnector or disconnector (OFF-load isolator).

What are the functions of a switch?

A switch is designed to make, break, and carry current according to specified utilisation categories and can come in various contact configurations and positions. Switches come in various contact configurations and positions, such as Man–OFF–Auto control switches, spring-return switches, UPS bypass switches, and motor reversing switches.

Unlike switch disconnectors, switches do not have to meet isolation requirements such as ensuring all contacts are physically open when in the OFF position. Identification is often made by the manufacturer’s marking and symbols, which are utilisation. The specific symbol for a switch is typically documented in technical standards and product datasheets. The symbol for a switch can be found in relevant standards and regulatory publications (for example, in the Q&A section of technical guides or product manuals).

What are utilisation categories and their typical applications?

Utilisation categories describe the electrical conditions under which a device can safely operate, including voltage, current, load type, and switching frequency. They help specify what kind of loads the switch or isolator is designed to control.

Water heaters fall into utilisation category AC-21.

How can you ensure your installation is complaint and that an isolation switch suitable for a water heater was installed?

To ensure your installation complies with regulations and that an appropriate isolation switch is installed for a water heater:

• Verify the isolation switch is a true switch disconnector (ON-load isolator) compliant with AS/NZS 60947-3 and meets the requirements outlined in AS/NZS 3000:2018.
• Confirm the switch is rated according to the utilisation category appropriate for the water heater’s electrical load.
• Ensure the isolator can disconnect all active conductors, clearly indicates the ON and OFF positions, and is lockable in the OFF position for safe maintenance.
• Check for manufacturer certification, product datasheets, or testing documentation verifying compliance with relevant standards.
• Engage a qualified and licensed electrician to inspect and certify the installation meets all safety and regulatory requirements. 

For complete details and information on the requirements for water heater isolation and product standard requirements for isolation switches please refer to AS/NZS 3000:2018 (incl A1 & A2) and AS/NZS 60947-3.

This article is intended for general informational purposes only and does not constitute professional advice. While we aim to provide accurate and up-to-date content, readers should conduct further research and consult relevant industry bodies or training providers if they are considering becoming a qualified electrician. Requirements and regulations may vary by region and are subject to change. This article is an adaptation of an article published by Kraus & Naimer.

by Sean Aucamp, 16 June 2025

Sources:

AS/NZS 3000:2018 Electrical Installations (Wiring Rules) including Amendments A1 and A2

AS/NZS 60947-3:2022 – Low-voltage switchgear and control gear – Part 3: Switches, disconnectors, switch-disconnectors, and fuse-combination units

Kraus & Naimer. (2023, May 1). EnergySafe state, “Isolators required for hot water heaters.” https://www.krausnaimer.com/fileadmin/user_upload/Kraus_u_Naimer/Pdfcat/Local/NZ/Isolators_for_Hot_Water_Heaters.pdf

WorkSafe NZ – Energy Safety Bulletin (2024): www.worksafe.govt.nz