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Installing Residual Current Devices (RCDs) on Enphase microinverter systems

RCDs vs MCBs on Enphase microinverter circuits

AS3000:2018 which became mandatory in most states of Australia as of 1 January 2019 requires  Residual Current Devices (RCDs) to be fitted to all final sub circuits (Clause 2.6.3.2.2).  The Clean Energy Council has confirmed that grid-connect inverter circuits are not considered final sub circuits.  For further details refer to the CEC Tech Bulletin on this topic issued on 13 July 2018.

RCDs are not required to be fitted to inverters to meet the requirements of AS3000:2018 Clause 2.6.3.2.2. However, there is another new clause in AS3000:2018 that may result in solar installers having to use RCDs on inverter circuits.  This is clause 3.9.4.2, which states:

3.9.4.2  Wiring systems near building surfaces

Wiring systems that are fixed in position by fasteners or held in position by thermal insulation or by passing through an opening in a structural member, shall be protected by one of the methods outlined in Clause 3.9.4.4 if they are concealed within 50mm from the surface of a wall, floor, ceiling or roof.

Clause 3.9.4.4 provides 3 options for protecting cables – options (a) and (b) both involve the use of metal conduit, armoured cable, or an earthed, metal barrier or enclosure. Option (c) is the use of a 30 mA RCD.  If the inverter AC circuit is installed in a wall within 50mm of the surface, and RCD will often be the easiest and cheapest way of providing mechanical protection.

Microinverter AC circuits typically run up a wall, through a ceiling space, through a roof penetration and along the full length of the racking on the roof, so there is an argument for the use of an RCD on all installations as a low-cost way of guaranteeing appropriate mechanical protection at all times and providing piece of mind against future faults of any kind.

If an RCD is to be installed on an inverter circuit, then the device must meet the requirements of AS4777.3.4.5 which states:

3.4.5 Residual current devices (RCDs)

An RCD dedicated for an IES may be used to meet the mechanical cable protection requirements and isolation requirements of AS/NZS3000 for the cable from the switchboard to the IES.

If an RCD is used, the RCD shall—

  1. (a)  disconnect all live conductors (including the actives and neutral); and
  2. (b)  be of the type specified in the inverter manufacturer’s instructions or as labelled on the inverter.

Enphase Energy have issued a tech brief which specifies the requirements for RCDs installed on Enphase microinverter circuits.  A copy of this brief can be found here.  In short, Enphase require the use of a Type A, 30mA, C Curve, Bi-directional RCBO.

C Curve and 30mA are common specifications for RCD’s in Australia and New Zealand, but not all RCDs are Type A and bi-directional. Many of the lower-cost RCDs are Type AC, which is a lower rating than Type A.  Type AC RCDs are not suitable for use with Enphase microinverters.

It is also important to check that the RCD is bi-directional because the use of a directional (polarised) RCD could result in nuisance tripping. Even RCDs with line and load terminals marked on them may not be bi-directional – the only way to confirm this is to review the device specifications and if in doubt to get written confirmation from the manufacturer.

In summary, RCD’s are only required to be installed on inverter circuits where they are needed to provide mechanical protection to the cables under AS3000 Clause 3.9.4.2.  If the inverter circuit is run in a wall cavity within 50mm of the surface (at any point) then an RCD will often be the quickest and easiest way to provide this protection.

The cost difference between good quality single phase 20A Miniature Circuit Breaker (MCB) and a 20A Residual Current Circuit Breaker with Overcurrent Protection (RCBO) can be as little as $25 so we recommend that installers should strongly consider using RCBO’s on all microinverter installations.

For the almost insignificant additional cost, AC Solar Warehouse recommends the use of RCBO’s on all Enphase IQ7 installations.

AC Solar Warehouse supplies ready-made single and three phase Enphase Solar Distribution Boards with appropriate RCBOs pre-installed on the solar circuits.  Please contact our sales team on 1300 55 44 67 for further details.

 

 

References

AS NZS 3000:2018

AS NZS 777.1:2016

CEC Tech Bulletin (13 July 2018)

Enphase Energy Technical Brief (November 2018)

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