AS/NZS 5033:2021 – The Importance in PV Installations

The AS/NZS 5033:2021 standard lays out comprehensive safety and installation guidelines for photovoltaic (PV) array electrical systems, which are critical as the solar energy industry continues to grow. Published in November 2021, the updated standard introduces significant changes aimed at enhancing consumer safety and streamlining system design and installation practices. Here’s a detailed overview of the key updates and requirements.

Key Updates in AS/NZS 5033:2021

Transition and Compliance
  • The updated AS/NZS 5033:2021 was released on November 19, 2021. Installers had a six-month grace period to transition from the 2014 standard, during which they could choose to comply entirely with either the 2014 or 2021 version.
  • After May 20, 2022, compliance with AS/NZS 5033:2021 became mandatory. It’s important to note that you cannot mix and match clauses from both versions; the system design and installation must fully comply with one version.
Voltage Limits
  • The maximum voltage for domestic PV installations has increased from 600V d.c. to 1000V d.c., aligning with international standards. However, due to regulatory stipulations in AS/NZS 4777.1:2016, the 600V limit still applies to domestic dwellings such as houses and apartments until the standard is updated.
  • Commercial and industrial PV systems can now operate up to 1500V d.c., which facilitates the use of larger systems, though temperature adjustments for maximum voltage must still be accounted for using a multiplication factor from Table 4.1 in the standard.
String Current and Array Calculations
AS/NZS 5033:2021 introduces new formulas for calculating maximum string and array currents, defined as ISTRING MAX and IARRAY, respectively. These calculations are crucial for determining proper equipment ratings and ensuring system safety:
  1. Calculate the maximum string current using the formula:
    ISTRING MAX = 1.25 × KI × ISC MOD
    Where KI is typically 1 unless bifacial modules are used, and ISC MOD is the module’s short circuit current.
  2. Check the inverter’s backfeed current (IBF TOTAL) to compare with the calculated string current. Most SMA inverters produce zero backfeed current.
  3. Calculate the maximum array current:
    IARRAY = SA × ISTRING MAX
    Where SA is the number of strings in the array.
  4. Confirm that the maximum array current is less than the inverter’s maximum short-circuit current rating.
String Protection and Fusing
The method for sizing string fuses has been refined. Previously, the lower and upper limits for string fuse size were 1.5 and 2.4 times the module’s short circuit current. The new standard simplifies this:
  • The fuse rating In must be greater than 1.2 × ISTRING MAX and less than or equal to the module’s maximum overcurrent protection rating (IMOD MAX OCPR).
This adjustment may be presented differently in the new standard, but the overall principle remains largely unchanged. Designers should ensure fuse selection complies with these updated parameters, especially when using bifacial modules or d.c. conditioning units (DCUs).
Cable Installation Requirements
The updated standard emphasizes stricter guidelines for cable installations, especially in ceiling spaces:
  • Cables must be secured and must not be installed less than 0.6 meters above the ceiling surface unless they are fixed to the roof structure.
  • Additional restrictions apply to cable placement, such as maintaining a 50mm distance from roofing material and ensuring specific clearances when near external walls or disconnection points.
Signage is required if cables are installed in an accessible roof or floor space, providing clear warnings and labels as outlined in the standard.

Abolishment of Rooftop DC Isolators

One of the most anticipated changes in AS/NZS 5033:2021 is the removal of mandatory rooftop DC isolators. Rooftop isolators have historically been a source of safety concerns, with a high incidence of fire-related issues. However, removing them comes with new requirements:
  • Installers must follow updated guidelines for disconnection points, cable routing, and system isolation.
  • Systems with microinverters, two or fewer strings in parallel, or specific setups with string fusing will have tailored requirements for isolators and disconnection devices.

Restricted Access for Ground-Mounted Arrays

The standard introduces a requirement for restricted access to ground-mounted PV arrays, regardless of voltage. Any ground-mounted system, including small residential installations, must have protective measures such as fencing if the PV modules are less than 2.5 meters from the ground.

Optimisers and Voltage Calculations

AS/NZS 5033:2021 incorporates provisions for using DCUs (like optimisers) in system design:
  • When calculating maximum string voltages, DCU maximum output voltages must be considered. For systems like SolarEdge, additional allowances are made through compliance with IEC 62548, which governs inverter-controlled voltage regulation.

Exemptions and Special Cases

  • PV arrays on vehicles, transportable structures, and boats are exempt from AS/NZS 5033:2021 and must instead comply with AS/NZS 3001 or AS/NZS 3004.
  • Large PV systems over 240 kW must comply with all provisions of the standard, eliminating previous allowances for engineering-based variations.
AS/NZS 5033:2021 represents a comprehensive overhaul aimed at improving safety and future-proofing PV installations. While the updates may require adjustments to design and installation practices, they are essential for aligning with international standards and ensuring consumer safety. Installers and designers must familiarize themselves with these changes to remain compliant and leverage the full benefits of the new standard. Always consult with your state regulator and stay updated on any amendments or additional guidance. The standard can be purchased from Standards Australia, SAI Global, or Techstreet.

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