[RE-wrenches] Connecting Two Grid-Battery Backup Inverters to 120/208

[William Korthof]

You could use a 120:120volt, with both the first and second inverters using the same phase, but the xfmr secondary used to supply 120 volts out of phase from the primary for the slave. Voila, auto-transformer 120:240 split phase power. Downsides are the heavy loading all on one phase and neutral, and xfmr losses... 

Alternate option is to get an isolation transformer with 208 primary and 120/240 secondary. Bond the midpoint. 
Better phase balance, but xfmr losses.

/wk

William Korthof
714.875.3576
Sustainable Solutions
#956904 

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From: Christopher Warfel 

We were asked to replace two failed Trace SW4048 inverters with two 
Outback GT3048 inverters. Upon start up the slave inverter would not 
connect.  We did not realize that the building service is 208, 3 phase. 
The bypass is 120/240 which the SW4048s could connect to without a 
problem. Outback says their inverters will not connect to this system 
because of the phase angle of 120 and their software.

The phases are always going to be at this rotation, so I don't see a 
transformer helping solve the problem, but this is something I am really 
unfamiliar with.

So the input at the inverter panel is two 120 volt phase at 120 degrees. 
The output to the EP is 120/240.

I am asking if anyone has an idea of how to fix this problem? 
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