Circuit breakers are usually marked with an interrupting rating as well as an ampere rating. Sometimes the interrupting rating is marked on the side and sometimes it may be on the front. If a circuit breaker has no marked interrupting rating, then it has a default interrupting rating of 5,000 amperes.

NEC Section 240.83 requires every circuit breaker having an interrupting rating other than 5000 amperes to have its interrupting rating shown on the circuit breaker. The interrupting rating is not required to be marked on circuit breakers used for supplementary protection.

The electrician and the inspector will use the marked interrupting rating to verify that the electrical installation complies with NEC^® 110.9 which requires the circuit breaker to have an interrupting rating at least equal to the available fault at the line terminals of the breaker. A circuit breaker with an interrupting rating of 10,000 amperes could not comply with NEC^® 110.9 if the available fault current at the line side of the breaker was more than 10,000 amperes.

See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).

2014-2017 Code Language:

240.83 Marking.

(C) Interrupting Rating. Every circuit breaker having an interrupting rating other than 5000 amperes shall have its interrupting rating shown on the circuit breaker. The interrupting rating shall not be required to be marked on circuit breakers used for supplementary protection.