Separated Extra-Low Voltage (SELV)

Separated Extra-Low Voltage (SELV) is an electrical protection system that uses a limited supply voltage and electrical separation to reduce the risk of electric shock. It is particularly relevant to equipment operating in wet environments, including certain swimming pool lights, underwater motors and swim jet systems.

SELV is also referred to as Safety Extra-Low Voltage in some international technical standards. In Australia, AS/NZS 3000 uses the term Separated Extra-Low Voltage.

Although SELV operates within the extra-low voltage range, voltage alone does not determine whether a circuit qualifies as SELV. The electrical arrangement must also provide the required separation from other circuits and earth.

What Is Separated Extra-Low Voltage (SELV)?

SELV is a type of extra-low voltage electrical system designed to provide protection against electric shock under normal operating conditions and specified fault conditions.

Under Australian electrical standards, extra-low voltage (ELV) generally refers to voltage not exceeding:

• 50 V AC (RMS)

• 120 V ripple-free DC

These are the general limits for ELV systems, not universal permitted voltages for underwater swimming pool equipment.

An SELV circuit must remain electrically separated from higher-voltage systems and earth. This separation is designed so that a single fault does not introduce a dangerous electric shock risk.

For example, a 24 V DC circuit supplied through an appropriately designed safety isolating power supply may qualify as SELV. Another 24 V circuit without the required electrical separation may not.

How Does an SELV System Work?

In a mains-powered SELV system, a safety isolating transformer or suitable electronic power supply converts the incoming electricity to the required extra-low voltage while maintaining electrical separation between the input and output circuits.

The separation prevents a direct conductive connection between the mains supply and the output circuit. An appropriately designed supply also maintains the necessary protection under specified fault conditions, reducing the possibility of hazardous mains voltage reaching connected equipment.

A typical arrangement follows this sequence:

230 V AC mains supply → Safety isolating power supply → SELV output circuit → Electrical equipment

The voltage conversion and isolation functions may be incorporated into a single electronic power supply rather than a separate transformer.

SELV can also be supplied by an independent electrical source, such as a battery, provided the complete circuit arrangement satisfies the relevant requirements. Australian Standard AS/NZS 3000, Clause 7.5.3, recognises safety isolating transformers, independent sources and certain compliant electronic devices as possible supplies for SELV and PELV systems.

Why Is SELV Important for Swimming Pool Equipment?

Swimming pools create particular electrical hazards because swimmers are immersed in water and may come into contact with wet electrical equipment or conductive surfaces.

If insulation fails, dangerous voltage differences can develop between parts of the pool, its equipment or surrounding structures. The risk depends on the electrical fault, the current path through the body and the conditions of exposure.

SELV helps address these hazards by limiting the voltage available to the equipment and maintaining separation from higher-voltage circuits.

Possible applications include underwater LED lighting, certain submerged electrical components and compatible swim jet systems. In a mains-powered swim jet designed around an SELV supply, the motor circuit may operate at extra-low voltage while the power conversion equipment remains separate from the submerged assembly.

SELV Requirements for Swimming Pools in Australia

Swimming pool electrical installations in Australia are governed by AS/NZS 3000, commonly known as the Australian/New Zealand Wiring Rules.

Section 6.3 establishes requirements for electrical equipment installed in and around swimming pools, paddling pools, spa pools and tubs. These requirements distinguish between different electrical zones according to their proximity to water.

SELV and Swimming Pool Zone 0

Zone 0 generally includes the interior of the swimming pool basin, where electrical equipment may be immersed.

Under AS/NZS 3000:2018, Clause 6.3.4.5, the general requirements for luminaires and other electrical equipment installed in Zone 0 include:

These Zone 0 voltage limits are lower than the general ELV limits because of the electrical hazards associated with immersion.

AS/NZS 3000 also contains specific provisions for purpose-made pumps installed in accordance with the relevant requirements of AS/NZS 60335.2.41.

How Does This Apply to Swim Jets?

A swim jet system may contain several electrical components, including a submerged motor, power supply, controller and connecting cables. Their locations determine which electrical provisions apply.

For a mains-powered swim jet, the external supply may accept 220–240 V AC while delivering a different voltage to the motor assembly. The relevant distinction is between the mains input, the electrical supply arrangement and the voltage at the submerged equipment.

This is particularly important when assessing systems that incorporate power conversion or separate external control units.

SELV vs ELV vs PELV: What Is the Difference?

ELV, SELV and PELV are related electrical terms, but they are not interchangeable.

The main difference between SELV and PELV is their earthing arrangement. Both can provide protection against electric shock when their respective design requirements are satisfied.

Australian swimming pool electrical standards recognise both systems for specified applications.

Is SELV the Same as RCD or IP Protection?

SELV, Residual Current Devices (RCDs) and IP protection ratings address different electrical hazards.

For example, an underwater pool light may use an SELV supply and an IPX8-rated enclosure. The SELV system addresses electrical shock protection, while the enclosure is designed to resist water ingress under specified immersion conditions.

An RCD provides a different form of electrical protection by disconnecting a circuit when its operating threshold is reached. It does not provide the electrical separation required for SELV.

How to Identify SELV Protection in Pool Equipment

Pool owners can identify whether equipment uses SELV by reviewing its electrical specifications and installation documentation.

The main details to check are:

• Rated output voltage: Identify the voltage supplied to the relevant equipment, rather than relying only on the mains input rating.

• Power supply classification: Look for SELV designation or documented compliance with relevant electrical isolation requirements.

• Circuit arrangement: Check whether the output is identified as SELV or PELV and whether the specified earthing arrangement is appropriate.

• Equipment protection: Confirm that the IP rating and construction are suitable for the intended installation zone.

• Installation requirements: Review the permitted locations of power supplies, controllers, electrical connections and submerged components.

Product documentation should identify the applicable electrical specifications and installation conditions. For swimming pool installations, these must be assessed against AS/NZS 3000, the relevant equipment standards and the manufacturer's instructions.

In Australia, fixed electrical installation work should be carried out by appropriately licensed electrical professionals. Where equipment is intended for underwater operation, the complete electrical system must be assessed for its specific application rather than relying on a voltage rating or SELV label alone.