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Wednesday, September 29, 2021
Question:
Hello Code Question of the Day.
My question is about installing half-size breakers in a panelboard to make room for additional breakers. Is this allowed by the NEC? An electrician has indicated that a sub panel needs to be installed. I'd appreciate any insight you can provide.
Thank you.
Sam Price
A
Answer:
Greetings Sam,
Thanks for participating. Section 408.54 addresses maximum number of overcurrent devices in panelboards. This rule indicates that a panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and listed. For the purposes of this section, a 2-pole circuit breaker or fusible switch shall be considered two overcurrent devices; a 3-pole circuit breaker or fusible switch shall be considered three overcurrent devices. So knowing the requirements of this section it is clear that the design, rating, and listing have an impact on the number of OCPDs that can be installed. Section 110.3(B) says follow the manufacturer's installation instruction provided. The may be limitations on installing half-size breakers or tandem breakers. Also these smaller breakers need to be listed for installation in the particular panelboard, typically by the same manufacturer. Be aware that there are also circuit limiting panelboards that exist and usually that are identified as a CTL panelboard.