An ITCB (interrupting capacity breaker) used for a branch circuit OCPD has a maximum rating; what is the largest permitted ITCB rating for branch circuit OCPD?

An ITCB (interrupting capacity breaker) used for a branch circuit OCPD has a maximum rating; what is the largest permitted ITCB rating for branch circuit OCPD?

• A. 80
• B. 125
• C. 150
• D. 90

Answer: (B)

Understanding this starts with what an interrupting-capacity breaker does: it must be able to safely interrupt the fault current that could appear on the branch circuit. For branch-circuit protections, there is an upper limit on the ITCB size that can be used, based on how the equipment is listed and coordinated with panelboards and conductors. The largest ITCB rating commonly permitted for branch circuits is 125 A. Using a larger rating would require equipment and paneling rated for higher interruption, which isn’t typical for branch-circuit installations. Ratings smaller than that (like 80 A or 90 A) are simply not the maximum, and a 150 A ITCB would exceed the standard limit for branch-circuit applications.

Understanding this starts with what an interrupting-capacity breaker does: it must be able to safely interrupt the fault current that could appear on the branch circuit. For branch-circuit protections, there is an upper limit on the ITCB size that can be used, based on how the equipment is listed and coordinated with panelboards and conductors. The largest ITCB rating commonly permitted for branch circuits is 125 A. Using a larger rating would require equipment and paneling rated for higher interruption, which isn’t typical for branch-circuit installations. Ratings smaller than that (like 80 A or 90 A) are simply not the maximum, and a 150 A ITCB would exceed the standard limit for branch-circuit applications.