By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
Before 2019, Australia and New Zealand had no dedicated joint standard for the safety of battery storage installations, which meant battery systems were often assessed against a patchwork of general electrical wiring rules never written with lithium chemistries in mind. AS/NZS 5139:2019, Electrical installations, Safety of battery systems for use with power conversion equipment, changed that, and it now sits at the centre of how Battery Energy Storage System (BESS) installations are designed, reviewed, and approved across both countries.
Table of Contents
- What AS/NZS 5139:2019 Actually Covers
- Why a Dedicated Battery Safety Standard Exists
- Scope Boundaries: What Falls Inside and Outside
- Key Technical Themes: Enclosures, Separation, and Ventilation
- Protection, Monitoring, and Fault Response
- How AS/NZS 5139 Interacts With Other Standards
- What This Means for Design and Approvals
- What to Do Next
- FAQ
What AS/NZS 5139:2019 Actually Covers
The standard sets out general installation and safety requirements for battery systems installed in a defined location, such as a dedicated enclosure, cabinet, or room, and connected to Power Conversion Equipment (PCE) that converts the battery’s direct current output into alternating current for use elsewhere in the installation. Its requirements run from the battery system itself up to, but not including, the PCE, and it also applies to pre-assembled integrated battery storage products that bundle the battery and PCE together as a single unit. In effect, it is the standard that governs how the battery half of a BESS is installed safely, regardless of who manufactured it.
Why a Dedicated Battery Safety Standard Exists
Battery systems, particularly lithium based chemistries, introduce failure modes that general electrical wiring standards were never designed to address: thermal runaway, off gassing, and the risk of a fault propagating from one cell or module to its neighbours. A wiring rule written for general low voltage installations has no concept of any of that. AS/NZS 5139:2019 was developed specifically to close this gap, giving installers, designers, and approval authorities a single reference for how to manage those risks consistently, rather than relying on manufacturer instructions of varying quality as the only safety guidance. It also gives insurers and fire authorities a common technical baseline to assess a proposed installation against, which has become more important as battery uptake has grown across both residential and commercial settings.
Scope Boundaries: What Falls Inside and Outside
The standard is written around systems with a rated capacity from around 1 kWh up to 200 kWh, covering the size range typical of residential, small commercial, and many mid scale commercial and industrial installations. It explicitly excludes certain applications: battery systems in premises with critical power continuity requirements such as acute care hospitals, telecommunications applications, and electric vehicles are outside its scope, since those contexts carry their own specific standards. Larger grid scale battery installations often move into territory governed by additional standards covering high voltage installations and switchgear, on top of AS/NZS 5139’s requirements for the battery system itself.
Key Technical Themes: Enclosures, Separation, and Ventilation
A recurring theme through the standard is physical containment and separation: how a battery enclosure or room is constructed, what separation distances apply between the battery system and other parts of a building or installation, and how ventilation is designed to manage any gas release from a cell in distress. These requirements shape decisions that are normally thought of as civil or structural, not electrical, which is part of why BESS design tends to be more cross disciplinary than a typical solar PV installation. Our article on common errors in solar BESS system design covers several cases where these physical siting requirements are missed early and become expensive to fix later.
Protection, Monitoring, and Fault Response
The standard also addresses how a battery system should be monitored and protected during operation, including expectations around disconnection and isolation in response to a detected fault condition. This is closely tied to the Battery Management System (BMS) that most commercial battery products include, which monitors individual cell or module conditions and can isolate the system before a fault escalates. AS/NZS 5139:2019 does not replace the need for a competent BMS, but it sets the installation context that the BMS and its associated protection have to operate within, including how isolation devices are labelled and accessed by emergency responders attending the site.
How AS/NZS 5139 Interacts With Other Standards
AS/NZS 5139:2019 does not operate alone. It sits alongside AS/NZS 3000 for general electrical wiring, AS/NZS 4777 for the grid connection requirements of inverter connected energy systems, and, for larger or high voltage systems, standards covering substation and switchgear design. A compliant BESS design has to satisfy all of the relevant standards simultaneously, not just the one that specifically names batteries, which is a common point of confusion for teams new to storage projects. Getting the interaction between these standards right is also central to a clean connection application, which our guide to DNSP grid connection design requirements explains in more detail.
What This Means for Design and Approvals
For a project team, the practical effect of AS/NZS 5139:2019 is that battery safety cannot be treated as a manufacturer’s problem to solve after equipment is chosen. Enclosure layout, separation distances, and ventilation strategy need to be considered during design, not retrofitted once a product has been selected, because they affect site layout, building approvals, and sometimes insurance requirements. Councils and certifiers increasingly expect to see explicit reference to the standard in design documentation, and its requirements are a routine part of what a certifying engineer checks before sign off. Projects that leave this consideration until late in the process often find that the enclosure they had budgeted for no longer fits the site once the required separation distances are properly accounted for.
What to Do Next
If your project involves battery storage and you are not yet certain how AS/NZS 5139:2019 applies to your site layout or enclosure choice, that is worth resolving before equipment is ordered rather than after. AGILE’s BESS engineering service builds compliance with this standard into the design from the outset, so it does not surface as a late stage surprise during approvals or construction.
FAQ
Does AS/NZS 5139:2019 apply to residential battery installations?
Yes, it applies broadly across the capacity range it covers, which includes typical residential and small commercial battery systems, not just larger commercial and industrial installations.
Does the standard cover the inverter as well as the battery?
No. Its requirements run up to but not including the power conversion equipment. Inverter and grid connection requirements are covered separately, principally under AS/NZS 4777.
Is AS/NZS 5139:2019 mandatory in Australia?
Compliance expectations are generally set through state based electrical safety regulations and building approval processes, which commonly reference this standard for battery installations. Requirements can vary by jurisdiction, so it is worth confirming locally.
Does a grid scale battery project still need to consider this standard?
Aspects of it remain relevant, but very large systems typically sit alongside additional high voltage and switchgear standards, since AS/NZS 5139:2019 is written around a defined capacity range rather than utility scale installations specifically.
What happens if a BESS design does not comply with AS/NZS 5139:2019?
Non-compliance can delay or prevent building and electrical approvals, and in some cases affect insurability of the installation. It is far more efficient to design to the standard from the start than to retrofit compliance later.
