April, 2009
Inspection News and Views from the American Society of Home Inspectors

The Word: Subpanel


With gratitude and an apology to Stephen Colbert, we begin an occasional column about words we use as home inspectors. We will discuss words that are sometimes misused, misspelled or, as with today’s word, have a tenuous grasp on existence. This column won’t be as funny as the Colbert Report, but The Word hopes you find it informative and maybe a little entertaining.

The Word’s word today is subpanel. Try to find it in an authoritative reference. It’s not in the National Electrical Code (NEC). It’s not in the International Residential Code, although the term sub-panelboard appears in two Figures in the Commentary. It’s not in the American Heritage Dictionary, nor is it in the Dictionary of Architecture and Construction. While widely used, this word does not exist, at least according to references approved by The Word’s Resident Librarian and Grand High Arbiter of Authoritative References.

This situation creates two questions. If you replace the word subpanel, what term do you use? If you use the word subpanel, how do you spell it? The Word gets a spelling error message in Microsoft Word when he types subpanel.

The word subpanel is a compound word that comes from the words subordinate and panelboard. The problem with the word subpanel is that every panelboard downstream from the service equipment and in the same building is treated as if it were a subpanel. This is true even if there is only one panelboard in the electrical system. If the first panelboard in a system is a subpanel, then what do you call a panelboard downstream from the first? Perhaps it is a sub-subpanel? This confusing situation is, no doubt, why the NEC does not use the word subpanel.

A panelboard (in NEC Article 100) is defined, in part, as a panel including busses and automatic overcurrent devices that is designed to be placed in a cabinet. The NEC (in Article 408.34) uses the terms Lighting and Appliance Branch-Circuit Panelboard and Power Panelboard to classify types of panelboards. A Lighting and Appliance Branch-Circuit Panelboard is one that has more than ten percent of its overcurrent devices protecting lighting and appliance branch circuits. Any other panelboard is a power panelboard. These terms, however, are awkward and do not describe the relationship between panelboards. They are not useful to us in reporting our findings.


The Word recommends the term primary panelboard to describe the configuration when one cabinet contains the service equipment and the first Lighting and Appliance Branch-Circuit Panelboard and the configuration when a cabinet contains the first Lighting and Appliance Branch-Circuit Panelboard downstream from the service equipment. The Word recommends the term secondary panelboard to describe Lighting and Appliance Branch-Circuit Panelboards downstream from the primary panelboard. These terms are not perfect and there may be other good ways to describe the relationship between panelboards without using the non-existent word subpanel.

That being said, however, the word subpanel is widely used (but not in authoritative references) and its meaning is generally understood. If you decide
to use it, how do you spell it? Is it sub-panel, or sub panel, or subpanel, or something else? The ASHI Standards of Practice and Code of Ethics spells it sub panel. The Chicago Manual of Style (15th Edition, Section 7.84) states that closed spelling of a compound word is acceptable if the closed spelling is widely accepted and if pronunciation and readability are not compromised. Thus, the closed spelling of the word subpanel is acceptable, in spite of what Microsoft Word believes. Sub-panel also is an acceptable spelling. Sub panel is probably not acceptable, so we may need to change it in the ASHI standards.

Applause, and cut to a commercial for Square D.

Memo to the Electrical Gods and other authorities:  The Word does not reside on Mt. Olympus and welcomes other viewpoints. Send your lightning bolts or e-mails to inspectorbruce@cox.net. Please cite the authoritative references that support your position. Note that all references are not considered authoritative. Unless you are fortunate enough to have a Resident Librarian, as The Word does, consult your local reference librarian. We will continue this discussion, if warranted.