To verify a series rated system was properly installed, specific marking on the overcurrent devices is needed along with the series rating label or book inside the panelboard enclosure.

In the image, the Siemens panelboard can be installed where the available Fault Current (AFC) is as high as 22,000 amperes as long as specific circuit breaker types are used. This installation is an all-in-one service panelboard with a 200-ampere main breaker ahead of the branch circuit breakers. The main breaker is a 200-ampere type EQ 9685 with an interrupting rating (AIC rating) of 22,000 amperes. The branch circuit breakers are type QP with an interrupting rating (AIC rating) of 10,000 amperes.

These circuit breaker types match up with the series rating information on the label to show that even if there is up to 22,000 amperes (22kA) of available fault current at the line terminals of the breakers, the entire panelboard has a short circuit current rating of 22kA even though all of the branch circuit breakers only have a stand-alone AIC rating of 10kA. This installation complies with NEC^® 110.9 because the combination of the main and branch circuit breakers has been tested and listed as a team to have an overall interrupting rating at least equal to the available fault current at their line terminals.

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).

2017-2023 Code Language:

110.22(C) Tested Series Combination Systems. Equipment enclosures for circuit breakers or fuses applied in compliance with the series combination ratings marked on the equipment by the manufacturer in accordance with 240.86(B) shall be legibly marked in the field to indicate the equipment has been applied with a series combination rating. The marking shall meet the requirements in 110.21(B) and shall be readily visible and state the following:

CAUTION — SERIES COMBINATION SYSTEM RATED ____ AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.