Maximum Number Of Half Size Circuit Breakers In A Panel

January 9, 2006

Q: Is there a limit to the number of “piggy-back” circuit breakers that are allowed in a 24-space panel?

A: Yes, a Class CTL panelboard is marked to indicate how many circuit breaker poles can be installed. Class CTL is the designation used to identify a panelboard as ‘circuit limiting.’ In these panelboards, only certain positions in the panelboard will allow the use of tandem, half-size or piggy-back circuit breakers. For example, a 125A, 3-wire, single phase, Class CTL panelboard with 20 full-size circuit breaker spaces may be marked to allow two or more tandem circuit breakers.

Class CTL panelboards are the result of a requirement that appears in 408.15. This is the sentence that requires a limit to the number of overcurrent devices in a panelboard: “A lighting and appliance panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than the number for which the panelboard was designed, rated, and approved.”

Although non-CTL tandem circuit breakers are available and will fit in any space in a CTL panelboard, they are marked “For Replacement Only, Not CTL Assemblies.” These circuit breakers are for use in existing old style non-Class CTL assemblies only.

The number of piggy-back circuit breakers that is permitted in a Class CTL lighting and appliance panelboard is marked on the product, and non-CTL tandem circuit breakers are not permitted.

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Written by Wayne Gilchrist · Filed Under National Electrical Code

Comments

3 Responses to “Maximum Number Of Half Size Circuit Breakers In A Panel”

alan harrell on March 21st, 2007 12:12 pm

Article 408.15 does no longer appear in the 2005 code book. What revision
did it appear in?
Administrator on March 21st, 2007 3:28 pm

Hello Alan,

Thank you for your electrical question.

NEC section 408.15 last appeared in the 2002 code book. It has been moved to section 408.35 in the 2005 code book.
Ron Standley on November 17th, 2009 10:28 am

I applaude your adding warnings about de-energizing equipment BEFORE working on that equipment – but I don’t believe people understand what’s at risk. Most do-it-yourselfers have felt 120v AC and now they simply don’t respect it. I was guilty of this fearlessness before taking the first-year electrical apprentice training. The knowledge I gained has reactivated my respect for electricity.

I recommend adding a paragraph about the hazardsof arc blasts and links to the videos on the Internet so these people can at least visualize what is at risk when they work around electricity. Here’s one link to underscore my point:

http://www.metacafe.com/watch/yt-hWlLoHonf78/arc_flash_accident/

Thanks and keep at it. You’re doing a fine service. Ron.

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