Installation Guide

Installation
900-0144-01-01 Rev B 31
Multiple-Inverter AC Installations (Stacking)
Installing multiple inverters in a single AC system supports larger loads than a single inverter can
handle. This requires stacking. Stacking refers to how the inverters are wired within the system and
then programmed to coordinate activity. Stacking allows all units to work together as a single system.
The GS3548E and GS7048E models can stack up to ten units in parallel. For three-phase output, up to
nine models can be stacked, three per phase.
Figure 28 OutBack Communications Manager and System Display
Each inverter must be assigned a stacking mode, “master” or “slave”, depending on the configuration.
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The master provides the primary output phase. Other inverters in the system base their phase on that of the
master. If the master shuts off, all other inverters also shut off. The master must sense and connect to an AC
source before other inverters can connect. In all cases, the master inverter must be connected to port 1 on
the communications manager.
In a parallel-stacked or OutBack-stacked system, the master tends to be the most heavily used unit.
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“Subphase masters” are used in three-phase systems. The A phase master cannot measure output loads and
voltages on any other phase. The subphase masters for the B and C phases perform this monitoring and
allow greater control over the system.
There are two types of slave modes.
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A “classic” slave is used for stacking when the slave operates semi-independently of the master. Although
the master sets the phase relationship, the slave creates an output independent of the master.
Classic-stacked inverters can go into Search mode independently of the master if necessary.
This type of system is used for three-phase stacking with more than three inverters. The primary inverters
are the master (A) and the subphase masters (B and C). Additional inverters are A-, B-, or C-phase slaves.
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An “OutBack” slave is used for parallel systems. All slaves are in phase with the master.
All slave outputs are pulse-width-matched to be precisely synchronized with the master inverter. This
avoids potential backfeed.
OutBack slaves can be placed in Power Save mode when not in use. They are activated by the master
inverter as needed. For this reason, the master is normally the only inverter to enter Search mode.
Port 1
Additional Ports
MATE3
MATE3
HUB4
Stacking Connections
Stacking requires an OutBack communications manager and a system display.
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A system of four or fewer units may use the HUB4 Communications Manager.
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A system of up to ten units requires either the HUB10 or HUB10.3 Communications Manager.
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A three-phase system with multiple inverters per phase requires the HUB10.3 Communications Manager.
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All interconnections between the products are made using CAT5 non-crossover cable.