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Branch sizing for Enphase IQ7 microinverters

Enphase Energy Q Relays

There has recently been some changes to the specification for some Enphase Q cables, so it’s worth installers taking a moment to review their branch sizing calculations.

The data sheet for the Australian version of the Q cables can be found on our website here.  Q cables are available in single-phase (2 wire) and three-phase (4 wire) configuration, with connector spacing for portrait as well as landscape 60-cell and landscape 72-cell module layouts.  All Q cables are now rated at 25 amps.

Three-phase circuit sizing
Three-phase Q Relays are rated at 25 amps. The data sheet for these relays can be found here.  With three-phase Q Cable also rated at 25 amps, it is possible to install up to a maximum of 20 x IQ7 or 16 x IQ7+ microinverters per phase.  These microinverters could be on a single branch circuit, a ‘centre tapped’ circuit, or several completely separate circuits. A 25A circuit breaker must be installed upstream to protect the Q Relay and the solar circuit may terminate directly into the PV terminals of the Q Relay, keeping in mind that the Q Relay terminals are suitable for cables up to 6mm2. Where more than 60 x IQ7 or 48 x IQ7+ microinverters are being installed on a three-phase installation, multiple Q Relays and branch circuits must be installed.  For large installations, slaving an appropriately sized three-phase contactor from one three-phase Q Relay is possible and may be attractive where space and/or cost considerations are a factor.

Single-phase circuit sizing
Single-phase Q Relays are rated at 20 amps. The data sheet for these relays can be found here.  So although the single-phase Q Cable is rated at 25 amps, the 20A Q relays are the limiting factor in single-phase circuits.  The single-phase Q Relay must be protected upstream by a 20A circuit breaker.  The solar circuit/s may terminate directly into the PV terminals of the Q Relay, keeping in mind that the terminals are suitable for cables up to 6mm2. A standard single-phase circuit feeding into a 20A Q Relay can accomodate up to a maximum of 16 x IQ7 or 13 x IQ7+ microinverters.  If more than these numbers of modules are required, additional Q relays and branch circuits must be installed.

Three-phase Q Relays rated at 25A can be configured during commissioning for single-phase (or two-phase) operation. So theoretically a three-phase relay could be used in a single-phase application to enable the full 25A rating of the Q Cable to be utilised, but there are cost and space disadvantages to this approach. (Three-phase Q Relays cost approximately twice as much as a single-phase Q Relay and take up 6 DIN spaces compared to 3 for the single-phase relay) In special cases where using the 25A Q relay could alleviate the need for a second circuit having to be run to the roof, this option may be justified. It is important to note that the three phase Q relay can not be used to switch more than one single phase circuit.

Whilst Enphase provide specific guidance around component ratings and recommended number of microinverters per circuit, installers should keep in mind at all times that installations must always comply with all of the regular AS3000 requirements for circuit protection, cable selection, cable joins, voltage drop etc..

AC Solar Warehouse supplies Solar Distribution Boards for single phase and three phase installations. These boards include pre-wired circuit protection, Q Relays, Envoy and production CTs.  

Our staff are happy to assist installers with branch sizing queries – just email us at sales@acsolarwarehouse.com or call 1300 55 44 67.

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