Check panel capacity and instantly determine if an MPU or derate is needed.
(Busbar Rating × 1.2) − Main Breaker = Max Solar Breaker
You can install up to a 40A solar breaker on this panel without an MPU. Enter a specific system size at left to check compatibility.
Where to look:
Find the largest single breaker switch in the panel. It is usually physically separated from the smaller breakers, located at the very top or very bottom of the stack.
What to look for:
The rating (e.g., 100, 125, 150, 200) is stamped directly onto the physical plastic switch handle itself.
Where to look:
Look for the manufacturer's specification sticker. This is almost always glued to the inside of the metal panel door or on the interior side wall.
What to look for:
Scan the fine print on the sticker for "Max Amps," "Mains Rating," or "Bus Rating."
Tip: The busbar rating is often the exact same number as the main breaker, but sometimes it is higher (e.g., a 200A Bus with a 150A Main).