"When two inverters are connected to a 120/240 VAC distribution system without using the stacking interface cable, the AC neutral wiring must be capable of handling twice the inverter output. This is due to the lack of synchronization between the inverters. If both inverters are operating in exact synchronization (as opposed to operating 180 degrees out of synch.), then the AC neutral will carry the current of both inverters, which was split among the two AC hot conductors. This often is not a problem since the AC distribution system may be oversized to handle the higher output level of a generator. When an AC source is connected to the inverters, the inverters will synchronize independently and transfer at different times. This is not a problem if no 240 VAC loads are connected to the output of the system."
Comments
I believe the cable you are looking for is discontinued. Here is what I found on the web:
"9/11/08 Discontinued due to UL 1741 NEC-2005. This inverter is code compliant since it was made before the code was changed."
According to SW Owner's Manual, (pg 103), you can stack them without the cable. Here is what it says:
"When two inverters are connected to a 120/240 VAC distribution system without using the stacking interface cable, the AC neutral wiring must be capable of handling twice the inverter output. This is due to the lack of synchronization between the inverters. If both inverters are operating in exact synchronization (as opposed to operating 180 degrees out of synch.), then the AC neutral will carry the current of both inverters, which was split among the two AC hot conductors. This often is not a problem since the AC distribution system may be oversized to handle the higher output level of a generator. When an AC source is connected to the inverters, the inverters will synchronize independently and transfer at different times. This is not a problem if no 240 VAC loads are connected to the output of the system."
You can also try a good off-grid installer. They often stock extra parts and in some cases rebuild and warrantee inverters and generators.
Abney Solar Electrix of Redmond, OR, is offering three rebuilt SWs right now.