Outback Radian AC Coupling Note

Application Note

Precautions Using a Generator When AC Coupling

Most residential generators, and even some commercial grade generators, are not designed to

synchronize with another AC source. They may experience catastrophic failure if the other AC source is

a “stiffer” source and can overpower the weaker AC coupled generator.

To prevent the backfeed from the GTI into the generator, a safety relay can be utilized that disconnects

the GTI inputs from the Radian AC output bus bars when the generator is started, either using the

MATE3s AGS generator start function, or some other method.

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Figure 7 GS-AC-GEN-KIT, Generator Protection Relay from OutBack

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Figure 8 on the next page shows the normal operation with the Radian inverter connected to the GTI

through the 2PDT relay. Should the generator ever start — automatically or manually — the live AC

voltage at the GSLC load center Gen AC Inputs will activate the 2PDT relay coils and force the normally

closed (NC) contacts to the normally open (NO) position which opens the GTI connection so there is no

danger of backfeeding the generator from the GTI.

While the suggested 2PDT relay in this example has been tested by OutBack Power, it has not been

listed with the Radian GSLC load center. The local authority having jurisdiction may require an approval

stamp from a licensed engineer before approving the installation. If this approval cannot be obtained,

then a second solution is shown in Figure 9 and described on page 11.