In a multiphase installation using a multiphase phase Q relay and 3-phase wiring, what is the maximum circuit breaker current per PV AC branch circuit?

• A. 20 AMP
• B. 32 AMP
• C. 25 AMP
• D. No maximum

Answer: (C)

In a 3-phase PV setup that uses a Phase Q relay, the amount of current that can flow on each PV AC branch is limited by the rating of the relay’s contacts per phase. The relay is designed to safely carry a specific maximum current on every phase, and you must protect the branch circuits so they do not exceed that rating. The Phase Q relay is rated for 25 A per phase, so the PV AC branch circuit protective device is chosen to be 25 A to keep within what the relay and the conductors can safely handle.

Choosing 25 A ensures proper protection and coordination with the other protection in the system. A 20 A setting would unnecessarily cap the available output, while a 32 A setting could push beyond the relay’s capability and risk overheating or damage. There is a real maximum dictated by the equipment ratings, hence 25 A is the appropriate choice.