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AS-NZS 5033 Installation and Safety Requirements for Photovoltaic (PV) Arrays

Page history last edited by wilbo666 4 years ago


 

Introduction

This page lists some notes regarding AS/NZ 5033 the Australian and New Zealand standard for the Installation and Safety Requirements for Photovoltaic (PV) Arrays.

 

These notes are intended for my own personal use, and in no way should be used to contradict the published standards.

Potential readers should study, understand and base all of their actions on the published standards and not the text on this page.

 

Extra Low Voltage (ELV):

Voltage not exceeding 50 V a.c. or 120 V ripple-free d.c.

 

Maximum Array Voltage:

PV array maximum voltage = Voc array + (Y x (Tmin - Tstc ) x M)


Where: (4.2: 2014)
     Voc array = Open circuit voltage of the array at STC, in volts
     Y = Voltage temperature co-efficient, V/°C/module supplied by the manufacturer (negative value for crystalline silicon)
     Tmin = Expected minimum daily cell temperature, in degrees Celsius
     Tstc = Cell temperature at standard test conditions, in degrees Celsius
     M = The number of series-connected PV modules in a string

 

Notes:

  1. "the lowest expected operating temperature." / "Expected minimum daily cell temperature" is NOT clearly defined in the standard to my knowledge. It would seem prudent to use the lowest recorded minimum for the installation location. I would be inclined to also add some further headroom to this if any element in the system was close to its rated limit.

 

Equipment Selection Notes:

The standard covers this in detail, however from the follow section provides a quick summary. The following points apply to all equipment, with subsections of this page detailing specific requirements.

 

All equipment,

  • Shall be rated for DC use
  • Shall have a voltage rating equal to or greater than the PV array maximum voltage determined in Clause 4.2 (see "Maximum Array Voltage" section on this page above).
  • Be rated for the required current (see notes below / standard)

 

PV Modules (4.3.2.1: 2014)

  • PV modules including a.c. modules shall be qualified to either IEC 61730-1 or EN 61730-1 and either IEC 61730-2 or EN 61730-2.

 

Circuit Breakers (4.3.4: 2014)

  • Shall be certified to either AS/NZS 60898.2 or IEC 60947-2
  • Shall not be polarity sensitive
  • Shall be rated to interrupt full load and prospective fault currents from the PV array and any other connected power sources such as batteries, generators and the grid if present
  • Shall be rated for overcurrent according to Clause 3.3.5

 

     Note: Circuit breakers are not recommended for string overcurrent protection.

 

Disconnecting devices

  • Shall comply with the requirements of IEC 60947 (series) (4.3.5: 2014)
  • Shall have a utilisation category of at least DC21B (4.3.5: 2014)
    • See AS/NZS 60947.3-2015
    • DC = Direct Current
    • 21 = Switching of resistive loads including moderate overloads
    • B = Appropriate for devices which, due to design or application, are only intended for infrequent operation.
  • Shall be derated in regards to temperature as required (4.3.5: 2014)
  • Shall have a current rating equal to or greater than the associated overcurrent protection device, or in the absence of such device, have a current rating equal to or greater than the minimum required current carrying capacity of the circuit to which they are fitted according to Table 4.2.a (4.3.5: 2014)

 

  • Load breaking switch-disconnectors shall be capable of being secured in the open position (4.3.5.2: 2014)
  • Each PV array shall have a switch-disconnector to provide isolation of the inverter. The provisions of multiple switch-disconnectors in Clause 4.4.1.4 applies and a warning sign as required in Clause 5.5.2 shall be provided. (2.1.4.1: 2014)
  • For PCE's it shall be possible to isolate the PCE from all poles of the array such that maintenance of the PCE is possible without risk of electrical hazards. (4.4.1.2: 2014)

 

  • Fuse systems used for overcurrent protection are acceptable non-load breaking disconnecting means if they have removable fusing elements

 

Cables (4.3.6: 2014)

  • Shall be rated for 1.25 times the maximum possible current (e.g. 1.25 x Isc Mod, Isc sub-arry, Isc array) if no overcurrent protection is provided, otherwise rated for the protected current.
  • Shall have a temperature rating according to the application (derating maybe required)
  • If exposed to the environment, shall be UV-resistant, or be protected from UV light by appropriate protection, or be installed in UV-resistant conduit (refer to IEC 61386-1)
  • Shall be flexible (multistranded) to allow for thermal/wind movement of arrays/ PV modules.
  • Shall comply with
    • PV1-F requirements (TUV 2 PfG 1169/08.2007);
    • UL 4703; or
    • VDE-AR-E 2283-4.
  • Cable current ratings according to AS/NZS 3008.1.1:2009 Table 11

 

     Note: TPS cables complying with AS/NZS 5000 are not suitable

 

Fuses (4.3.8.1: 2014)

  • Shall (4.3.8.1: 2014) be of an overcurrent and short circuit current protective type suitable for PV complying with IEC 60269-6 (i.e. Type gPV).


Fuse Holders(4.3.8.1: 2014)

  • Shall have a current rating equal to or greater than the corresponding fuse; and
  • Shall provide a degree of protection suitable for the location and not less than IP 2X, even when the fuse link or carrier is removed.
  • Shall have a warning label to not withdraw fuse under load. (5.6: 2014)

 

Connectors (4.3.7: 2014)

  • Shall conform to EN 50521 Connectors for photovoltaic systems. Safety requirements and tests.
  • Shall only be mated with those of the same type from the same manufacturer

 

Blocking Diodes (4.3.10: 2014)

Blocking diodes can be used to prevent the back flow of current through a panel / string which could occur under fault of shading conditions however the standard states that "they are not a replacement for overcurrent protection", however A2.5 of the 2005 version of the standard states "Blocking diodes are not a reliable protection against reverse current because they often fail in short circuit mode. The use of blocking diodes is currently restricted to preventing battery discharge to an un-energized PV array at night. Their use should be avoided for other purposes because they are sources of failures and power loss."

 

If blocking diodes are used they must meet the following requirements,

  • Have a voltage rating at least 2 × PV array maximum voltage determined in Clause 4.2; (see "Maximum Array Voltage" section on this page above).
  • Have a current rating of at least 1.4 times the short circuit current at STC of the circuit

 

     Notes:

  1. I am unsure exactly as to why the voltage rating of blocking diodes must be "at least 2 x PV array maximum voltage", seems quite robust.
  2. In AS/NZS5033-2005 Appendix A was "CHARACTERISTICS OF PV ARRAYS AND SYSTEMS (Informative)", however this useful information appears to have been removed from future revision of the standard which is disappointing.

 

Installation Notes:

 

Switch-Disconnector Devices Location Requirements

  • Disconnecting means shall be provided in PV arrays according to Table 4.3 to isolate the PV array from the PCE or application circuit and vice versa, and to allow for maintenance and inspection tasks to be carried out safely. (4.4.1.1: 2014)

 

  • Where the PV d.c. cabling is arranged in such a way that multiple circuits of either subarray cables and or string cables are brought to the PCE separately, there shall be a load breaking disconnection device for each separate circuit located adjacent to the subarray or string (4.4.1.4: 2014)

 

  • In LV PV arrays in Australia, switch-disconnectors as specified in Table 4.3, shall be installed adjacent to a PV array on the PV array cable or on multiple circuits according to Clause 4.4.1.4, so as to provide safe disconnection of the array from the PCE (refer to Figures 2.5, 2.6 and 4.4).

    In cases where the PCE in LV systems is not in sight of the array or more than 3 m from the array, switch-disconnectors shall also be installed adjacent to the PCE or within the PCE, according to Clause 4.4.1.2. All PV switch-disconnectors shall be readily available. (4.4.1.5: 2014) 

 

Fuses (3.3.6: 2014)

  • In LV arrays, overcurrent protective devices, where required, shall be placed in all current carrying conductors not directly connected to earth.
  • In ELV arrays, overcurrent protective devices, where required for string and sub-array cables, shall be placed in either the positive or negative conductor (the number of current carrying conductors minus one). Where the extra-low voltage array is earthed, the protective devices shall be installed in all unearthed current carrying conductors.
  • The location of overcurrent protection devices shall be at the end of the cable that is electrically most remote from the PV modules. (4.4.1.3: 2014)
    • Note: The reason for this location is that fault currents in parts of an array originate from other parts of the array, for example if an array was composed of 4 sub-arrays (a, b, c and d) then if sub-array cable (a) was to experience overcurrent it could not originate from sub-array (a) as this is inherently current limited, the overcurrent would have to come from the sum total of sub-arrays (b), (c) and (d). The most effective place to interrupt that fault current is from the point where the sub-arrays are brought together, that is at the end of the sub-array cable most electrically remote from the PV modules. Similar principles apply to string cables.

 

Cable Installation

  • All conduit and ducting exposed to sunlight shall be of a UV resistant type (refer to IEC 61386-1). (4.3.6.3.1: 2014)
  • Plastic cable ties shall not be used as a primary means of support. (4.3.6.3.1: 2014)
    • Note Typically plastic cable ties exposed to UV will degrade within 2 to 5 years. Higher quality in 7-9 years (i.e. Carroll), however this is for direct sunlight)
  • Where PV DC. cables are installed within a ceiling space, in wall cavities or under a floor, they shall be installed in such a manner as to reduce the risk of short circuit to a minimum, and be enclosed in metal or heavy duty insulating wiring enclosure to IEC 61386-1 or other equivalent AS/NZS Standards. In all other locations within buildings, it shall be installed in medium duty conduit as a minimum in accordance with AS/NZS 3000. (4.3.6.3.2: 2014)
    • Note: An alternative to this is to run cables external to a building. 

 

Earthing

  • In PV arrays with a PV array maximum voltage greater than ELV and in systems which include a.c. modules and microinverters with LV outputs, all exposed metal PV module frames shall be earthed and the array mounting frames shall also be earthed. (4.4.2.1: 2014)
  • Minimum earth cable size is 4mm²; or 16mm²; if earthed for lightning protection

 

PV Module Frames

  • Support structures and PV module mounting arrangements shall comply with applicable building codes, regulations and standards. (2.2.1: 2014)
  • PV modules, PV module mounting frames, and the methods used for attaching PV modules to frames and frames to buildings or to the ground shall be designed to resist the ultimate wind actions. Attachments shall be appropriate for the importance level, classification and location, calculated in accordance with AS/NZS 1170.2. (2.2.5: 2014)

 

Notable Changes to Standard:

 

Scope of Standard:

Scope of Standard in Regards to Power and Open Circuit Voltage

The 2005 standard in section 1.1, Addendum 1 stated:

This Standard does not apply to photovoltaic systems or arrays operating at less than 25 V d.c. and with a power of less than 25 W.

 

The 2012 standard in section 1.1 stated:

"PV arrays of less than 240 W and less than 50 V open circuit voltage at Standard Test Condition (STC) are not covered by this Standard."

 

The 2014 standard in section 1.1 states:

"PV arrays in portable equipment of less than 240 W and less than 50 V open circuit voltage at standard test condition (STC) are not covered by this Standard.

"PV arrays of greater than 240 kW at STC are not covered by this Standard."

 

Scope of Standard in Regards to Maximum Array Voltage

Since 2012 the maximum PV open circuit voltage for a domestic installation has been limited to 600VDC, where in 2005 it was 1000VDC.

 

The 2005 standard in section 1.1 stated:

"This Standard sets out the general installation requirements for photovoltaic (PV) arrays with d.c. open circuit voltages up to 600 V between positive and negative conductors or up to ±600 V with respect to earth and a maximum power of 30 kW."

 

Mention of the specific voltages covered by the standard appears to have been removed in the 2012 standard updated from section 1.1. The following has been added in the 2012 standard in section 3.1. Of note is that fact that systems above 600V has been forbidden for domestic installations.

"PV arrays for installation on domestic dwellings shall not have VOC ARRAY maximum voltages greater than 600 V. For non-domestic installations where the PV array maximum voltage VOC ARRAY exceeds 600 V the entire PV array and associated wiring and protection, shall have restricted access to allow access by only authorized persons."

 

Calculation of Maximum Array Voltage

Amendment A1 to the 2012 version of the standard changed the method of determining the "Maximum Array Voltage"  detailed in section 4.2 (2012) from

 

     1.2 x Voc array

 

to

 

     PV array maximum voltage = Voc array + (Y x (Tmin - Tstc ) x M)


     Where:
          Voc array = Open circuit voltage of the array at STC, in volts
          Y = Voltage temperature co-efficient, V/°C/module supplied by the manufacturer (negative value for crystalline silicon)
          Tmin = Expected minimum daily cell temperature, in degrees Celsius
          Tstc = Cell temperature at standard test conditions, in degrees Celsius
          M = The number of series-connected PV modules in a string

 

Notes:

  1. "the lowest expected operating temperature." / "Expected minimum daily cell temperature" is NOT clearly defined in the standard to my knowledge. It would seem prudent to use the lowest recorded minimum for the installation location. I would be inclined to also add some further headroom to this if any element in the system was close to its rated limit.

 

Cable Ties

Cable ties (since 2014) cannot be used as the primary means of support regardless of the quality of the plastic and the manufacturers stated lifetime.

 

  • The 2005 revision makes no specific notes of prohibiting the use of cable ties.
  • The 2012 revision, section 4.3.6.3.1 states "Cable ties shall not be used as a primary means of support unless they have a lifetime greater than or equal to the life of the system."
  • The 2014 revision section 4.3.6.3.1 states "Plastic cable ties shall not be used as a primary means of support."

 

Conduit within Buildings

The requirements for conduit within buildings (i.e. Roof cavities and wall cavities) has increased considerable since the 2012 revision of the standard.

 

  • The 2005 revision makes no specific note of requiring conduit
  • The 2012 revision, section 4.3.6.3.2 states "PV array cables within buildings shall be constructed in such a manner as to reduce the risk of short-circuit to a minimum; and be enclosed in heavy-duty insulating conduit to AS/NZS 2053.1."
  • The 2014 revision, section 4.3.6.3.2 states "Where PV DC cables are installed within a ceiling space, in wall cavities or under a floor, they shall be installed in such a manner as to reduce the risk of short circuit to a minimum, and be enclosed in metal or heavy duty insulating wiring enclosure to IEC 61386-1 or other equivalent AS/NZS Standards."

 

     Notes:

  1. While I can understand reasons for the requirement to install PV DC cables in conduit, for example the fact that if an arc is allowed to develop, due to the current limited nature of PV panels it is unlikely to self extinguish, the requirement does seem above what is required in some other wiring rules. i.e. 230VAC lighting circuits which are not required to be on RCD, or a 230VAC, 50A CB feeding to a stove are able to be installed without heavy duty conduit within the walls and ceiling. Surely the given examples also include the risk of arcing and hence fire in these associated instances also? Why then not the requirement to also install these in heavy duty conduit?
  2. There is no differentiation given between ELV and LV DC cabling. ELV cable must also be enclosed in HD conduit according to the standard.

 

Connectors

Section 4.3.7 of the 2012 revision of the standard introduced the requirement that connectors conform to EN 50521 Connectors for photovoltaic systems. Safety requirements and tests. The 2012 revision also required that connectors shall "only be mated with those of the same type from the same manufacturer."

 

     Notes:

  1. While there are obviously some benefits in requiring that connectors only be mated with those of the same type and from the same manufacturer I personally would have to question the practicality of this.
    1. Panels are often supplied with MC4 connectors already fitted, identifying the exact type and manufacturer of these to comply with the standard could be difficult and could likely result in perfectly suitable connectors being replaced to comply with this standard (wasteful?).
    2. Given that there is a requirement to use connectors that conform to a particular standard, is the standard that the connectors must conform to so poor that interoperability of connectors cannot be guaranteed? If that is the case (and one could possibly draw this conclusion from the information provided) then what is the point of the connector standards?

 

Isolator / Switch-Disconnector / Disconnector Location Requirements

TO DO

 

Questions

  1. What specific benefits are gained from fusing the positive and negative leads of PV strings above LV? (Fusing is only required in one conductor for ELV strings if required for string overcurrent protection).

    Fusing both conductors allows the detection of a short from one strings positive to another strings negative (as a result of the negative string fuse fuse operating), however the cable is rated for this current so the benefit is to disconnect the string which would stop any arcing that was occurring and also make the owner aware of the fault so it could be rectified providing increased safety.

    The next question one could ask is why is increased safety only required at LV as opposed to ELV? The fault condition required seems quite unlikely (two insulation faults required).

    Of further interest is that in the 2005 version of the standard floating arrays that are double insulated with respect to earth require protection in one active conductor for PV Strings and PV sub-array cables (Table 2.2: 2005), not both conductors regardless of the voltage (ELV or LV) as is the case in 2012 onwards for LV. I do believe that the 2012 revision of the standard introduced the requirement to earth all LV modules which affects this however.

  2. Why is the scope of the standard so broad? In particular why is the array Voc limit (as STC) for which the scope applies to so low? 50VDC is well below the 120VDC of ELV. In my opinion this forces individuals undertaking installations that are ELV to adopt some aspects of the installation that may seem excessive given the arguably reduced risks associated with ELV. Some of these requirements I believe are roof top isolators and HD conduit, etc which according to the standard are still required even if the system is ELV.

  3. Why are DC conditioning units restricted to 350W and ELV?

    In practise most individual PV modules are now larger than 175W, so this statement effectively limits the use of DC conditioning units to one per PV module. If the power restriction was removed then two 250W, 60 cell PV modules for example would be able to be connected to a single DC conditioning unit while still being ELV. Why is this not allowed?

  4. Stating that semiconductor devices cannot be used for string over current protection (3.3.2: 2014) seems limiting to future technology. If a fail safe, self monitoring semiconductor based from of over current protection was to be developed it would not be able to be used following the standard.

  5. The requirement to install a  switch-disconnector adjacent to each PV string or sub-array seems excessive. (See Table 4.3 and section 4.4.1.4, 4.4.1.5 (2014)).

    Looking at the Australian requirement this effectively requires a "roof top" isolator for each string / sub-array on the roof. I am unsure exactly what specific tangible benefit that this requirement provides? It most definitely adds cost, and additional points of failure to the system in my opinion. My understanding is that the PV cabling could be disconnected if desired from the PV string / sub-array cable by turning off the isolator located adjacent to the PCE, and then disconnecting the PV module (i.e. disconnect the PV module MC4 plug, or remove the PV string over current protection fuses) to de-energise the PV cabling. Given how irregular this requirement is, I believe the fitment of an isolator is excessive, and the above steps would achieve the required outcome. That said I strongly support the requirement for an isolator at (or as part of) the PCE.

    Further my understanding is that "roof top" isolators have been responsible for a number of issues, and I also believe that Germany once required the fitment of "roof top" isolators and now no longer do so as a result of similar resulting issues.

    In addition I find the standard somewhat confusing in the way that Table 4.3 and sections 4.4.1.4, 4.4.1.5 and 4.4.1.6 (2014) are worded.
    Surely this section of the standard could be explained more clearly with the additional use of example diagrams, such as were provided in the "APPENDIX J CASE STUDIES DIAGRAMS (Informative)" of the 2005 version of the standard?

    The wording "The ability of these devices to break load current needs to be according to the Table." in regards to Table 4.3 (2014) is not particularly clear to myself. I interpret that if the table states "load-breaking switch-disconnector" it must be a load breaking switich-disconnector, otherwise a disconnector is suitable...

    4.4.1.5: 2014 states "In LV PV arrays in Australia, switch-disconnectors as specified in Table 4.3, shall be installed adjacent to a PV array on the PV array cable", does that mean that in ELV cases switched-disconnectors (which are specified as required in Table 4.3) do not need to be installed adjacent to the PV array on the PV array cable? In the ELV case where should they installed given that table 4.3 requires that one be install

 

References

  • AS/NZS 5033-2014
  • AS/NZS 5033-2012
  • AS/NZS 5033-2005

 

 

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