How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What is the maximum number of circuit breakers allowed in an electric panel?
Saturday, June 16, 2018
Not What It Used To Be
The answer to this question was once very simple. The National Electrical Code (NEC) specified that a lighting and appliance branch circuit panelboard could not contain more than 42 overcurrent devices (circuit breakers). That was the absolute maximum, unless the manufacturer specified a lower number, which was often the case for smaller panel boxes.
But the 2008 edition of the NEC deleted the maximum number and the new standard became whatever the manufacturer specifies. That number can be found in the fine print of the data plate on the inside of the panel door and is often near the schematic diagram. Some panels only allow one breaker per slot, while others allow some or all of the slots to accept a tandem breaker, which fits two breakers in one slot. So a “20/30” panel, for example, has 20 slots, but will accept up to 30 circuits, allowing up to half of the slots to be tandems.
CTL Breakers Also Important
The NEC has had an additional requirement since 1965 that “a panelboard shall be provided with a physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and listed.” This is known as Circuit Total Limitation panel or “CTL.” Unfortunately, non-CTL breakers are still manufactured for repair of pre-1965 panels, and are sometimes used in newer panels to get around this limitation. They lack the “rejection” feature that keeps CTL-breakers from being installed improperly. Both CTL and non-CTL breakers are clearly marked, although in very fine print, on the side of the breaker.
Maximum Amps Per Stab
One additional limitation for the breakers in a panel is the “maximum amps per stab” that a manufacturer allows. A stab is another name for a bus bar finger. Panels have half as many stabs as total breaker slots, so a panel with forty slots has twenty stabs, and a typical 150-amp rated panel requires that the sum of the amperages of both the breakers on one bus bar finger not exceed 200 amps. So this means you cannot have two breakers side-by-side with a total amp rating that exceeds 200 amps. This maximum is also listed in the data plate, which may also list limits on the number, rating, or arrangement of the breakers in the panel. To learn more, see our blog post What is a "bus stab" in an electric panel?
So the short answer to the maximum number of breakers question is 42 for pre-2008 panels, and whatever the manufacturer specifies for newer panels—while not exceeding the maximum amps per stab or using non-CTL breakers in a CTL panel.
Also, see our blog posts How often should I exercise the circuit breakers in my electrical panel? and Does a subpanel have to be the same brand as the main panel? and Can the total amps of all the breakers in an electrical panel be more than the amperage rating of the panel? and Can you add circuit breakers by different manufacturers to an electric panel if they fit?
• • • • • • • • • • • • • • • • • • • • •
Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
• • • • • • • • • • • • • • • • • • • • • •
Here’s links to a collection of our other blog posts about ELECTRIC PANELS:
of Blog Posts
Top 5 results given instantly.
Click on magnifying glass
for all search results.
Buying a home in North/Central Florida? for a team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.