Building Code Glossary
Voltage, Nominal: Building Code Definition
How the IRC 2009 define voltage, nominal, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Voltage, nominal is a defined term in the International Residential Code (IRC) 2009, in Electrical Definitions. The code's own words are: “A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 2 chapters of this corpus, most often in Building Services and Systems (IFC 2009), Electrical Definitions (IRC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Voltage, Nominal — IRC 2009, Electrical Definitions:
A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.
What must be verified before using this guidance?
Voltage, Nominal is defined once in this corpus, in the Electrical Definitions chapter of the International Residential Code (IRC) 2009:
A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.
Where voltage, nominal is used in the code
The term appears in 2 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Building Services and Systems | IFC 2009 | 4 |
| Electrical Definitions | IRC 2009 | 1 |
The term in use
How the code actually writes about voltage, nominal, quoted from the 2009 text hosted here:
A group of electrochemical cells interconnected to supply a nominal voltage of DC power to a suitably connected electrical load, designed for service in a permanent location.
— IFC 2009, Building Services and Systems
The terms voltage, nominal is built out of
The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what voltage, nominal covers:
- Equipment — IRC 2009: All piping, ducts, vents, control devices and other components of systems other than appliances that are permanently installed and integrated to provide control of environmental conditions for buildings.
- System — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.
Voltage, Nominal: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IRC | Electrical Definitions | |
| Re-check the requirement that uses it | Building Services and Systems (IFC 2009) | |
| Re-check the requirement that uses it | Electrical Definitions (IRC 2009) | |
| Confirm the dependent definition | Equipment | |
| Confirm the dependent definition | System | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of voltage, nominal?
The International Residential Code (IRC) 2009 defines it in Electrical Definitions as: “A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on voltage, nominal?
In this corpus the term is used across 2 chapters, led by Building Services and Systems in the IFC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What is the definition of nominal voltage?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Electrical Definitions: “A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.” It is defined in IRC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
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