42 Circuit Rule in Electrical Panels (PanelBoards/Load Centers)

Wenatchee Home Inspections

This subject of how many “Circuits” are allowed in residential electrical panels has come up in a recent discussion. I have had this exact discussion before with other home inspectors as well as electricians.

Note: this rule applies in commercial settings also if more than 10% of the overcurrent protection devices are for lighting and appliance branch circuits.

The rule often called the “42 Circuit Rule” was often a bit misleading. Because what it really was saying how many pole positions in a panel can there be. For example you could have a 240v circuit, that is just one circuit but has two pole positions.

• From Article 100- Definitions

•  

• Branch Circuit.

• The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

From a Schneider Data Bulletin in 2008

“The National Electrical Code (NEC) 2008 edition no longer distinguishes between lighting and appliance panelboards and power panelboards.

In prior NEC editions, panelboards were required to have no more than 42 overcurrent protective devices (OCPDs) when used for lighting and appliance branch circuits (as defined in the 2008 NEC edition).

This white paper covers the following topics to assist you with future panelboard installations:

• Definition of the 42 Circuit Rule

• Application Impact

• Applications Still Requiring the 42 Circuit Rule

• 2008 NEC Panelboard Changes

• 2008 NEC Adoption and Enforcement Reminder

The 2005 NEC edition, Article 408 defines a lighting and appliance branch circuit panelboard as

“. . . having more than 10 percent of its overcurrent devices protecting lighting and appliance branch circuits.  Such circuits have a connection to the neutral of the panelboard and overcurrent protection of 30 A or less in one or more conductors.”   

The scope of application areas for lighting and appliance panelboards include residential, commercial, retail, and industrial (depending on the type of loads connected). The maximum number of 42 overcurrent protective devices in one lighting and appliance branch circuit panelboard is specified in NEC 408.35.

Article 408 also defined “power panelboard” as a panelboard having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch circuits. Power panelboards are allowed more than 42 branch circuits.

The elimination of the 42 circuit rule will be reflected in the product standards for panelboards, allowing manufacturers to build 42+ circuit panelboards for lighting and appliance branch circuit applications. Installations that previously used a two section panel due to the 42 circuit rule may be able to install all of the necessary overcurrent devices in a single panel. This may benefit those applications where the number of circuits required were slightly more than the 42 circuits installed.”

Here is the link to the bulletin -

42 Rule Link: https://wp.me/aaTg4l-hO

The defining parameters of this will always be based on the specific panelboard/load center listing and labeling. This will define how many total pole positions and if tandems breakers are allowed and where they can be installed.

Example 1-  What is referred to as a 16/24 panel where you have 16 full sized breaker positions (number spaces) but allows half sized breakers to be installed in the bottom half positions giving it a total of 24 pole positions (number circuits).

Siemens Panelboard

Example 2 - Here is a legend from Square D. What is referred to as a 30/40 panel where you have 30 full sized breaker positions but allows half sized breakers to be installed in 10 positions giving it a total of 40 pole positions. Quite often the half sized breaker position is at the opposite end of the bus from where the main breaker/conductors are.

Example 3- Here is several legends from Square D. You can see where some of the load-centers allow tandem breaker and some do not. Often the the part number will give you a clue to what the number of full sized breakers and total poles allowed.  Such as the QO12024L125G(bottom left). This allows 20 full sized breaker and 4 Tandem Breakers for a total of 24 poles.

So if you have a panelboard installed prior to 2008 NEC adoption there will be the 42 limit. Post 2008 NEC you may have a panel that allows more poles than 42 but will still be dependent on how the panel is listed which the label will define.

“Somewhere, something incredible is waiting to be known.”

Carl Sagan

If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

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Instructor- Fundamentals of Home Inspection-  Bellingham Technical College

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