Table 250.122


Senior Member
NEC table 250.122 says word rating or setting of automatic overcurrent device at top left. What does rating or setting referring? Let’s say example I have 250A frame and trip unit of 150A non adjustable which one is rating and which one setting?


Staff member
Basically the same question you asked on Friday. and the same answers apply.


Senior Member
The frame size has nothing to do with the size of the EGC.
To add onto this, what "frame size" means, is that manufacturers typically group a range of breaker ratings into a common product design, with the only difference among sizes within this range being the calibration of the trip setting. The trip rating is what governs wire & EGC sizing, and not the frame size. Just like the rating of the fuses in a fused disconnect govern the wire and EGC sizing, rather than the amp rating of the disconnect blade.

For instance, a manufacturer might group all sizes 60A and less, in the 60A frame size category. Then sizes 70 thru 100 in the 100A frame size category. Then 110 thru 150 in the 150A frame size category, and so forth. The trip ratings within any given frame size, would therefore standardize on the same product housing, the same busbar connections, the same lugs, the same handles, the same internal blade, etc. The essential difference is the way the manufacturer tunes the coil, magnet, and bimetal strip, so that it trips at the amps marked on the handle.