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Electrical Installation Requirements for Dwelling Units

Posted By Michael Johnston, Saturday, March 01, 2003
Updated: Thursday, February 14, 2013

Since 1897 theNational Electrical Code(NEC), the world’s most widely used and adopted code for the built environment, has been the source for electrical installation requirements in all types of occupancies and applications, including dwelling units. The NEC was originally developed as a result of united efforts of various insurance, architectural and allied interests, and in 1911 the NFPA assumed stewardship of the NEC. As stewards of the Code, NFPA is responsible for its development and publishing and promotes its use and adoption as the sole source of comprehensive electrical installation requirements for all occupancies in accordance with its scope as stated in Section 90.2. Within the NEC there are numerous electrical installation requirements that apply specifically to one-, two-, and multi-family dwellings. These dwelling-unit-specific requirements reflect the fact that in most cases, particularly with one- and two- family dwellings the layout and design of the electrical system is the responsibility of the installer. Although Section 90.1(C) specifies that the Code is not intended to be a design document, the fact of the matter is that in all dwelling units, an electrical system that complies with the NEC will be safe and in most cases will be adequate for good service. When one looks at the membership of the NEC code-making panels responsible for the article in which the dwelling unit requirements reside, there are technical expertise and balanced representation that enable the Code to stay current with a dynamic and ever progressing electrical industry.

Photo 1. This fairly large one-family dwelling is served by a 400-ampere service and includes approximately 3800 square feet


Photo 2. Another typical one-family dwelling has roughly 3000 square feet of habitable floor space and is supplied by a 200-ampere service

Some codes and standards are occupancy-based or, in some cases, they are occupancy specific. An example of an occupancy-based code is NFPA 101. The first ten chapters of this document are dedicated to general and specific requirements on subjects ranging from means of egress to features of fire protection. The remaining chapters (11-42) cover various occupancy types and how to apply the requirements of Chapters 1-10 to these occupancies. There are codes and standards, the scopes of which focus exclusively on one specific type of occupancy. NFPA 99, Standard for Health Care Facilities is an example of a sole occupancy set of requirements. In general, Chapters 1-4 of the NEC are not considered to be occupancy specific unless otherwise indicated by a requirement. In other words the majority of the requirements in these chapters apply to electrical installations regardless of where they are installed. Chapters 5, 6, and 7 do provide more focused requirements for special occupancies, special equipment and special conditions and, according to the hierarchal arrangement of the Code specified in Section 90.3, these requirements may amend or modify the general requirements contained in Chapters 1-4.


Photo 3. This typical wiring rough-in using non-metallic sheathed cable has supports provided at outlet box and also at required intervals

There are numerous requirements in the NEC, particularly in Chapter 2 that are only applicable to dwellings. Examples of such requirements include the GFCI requirements in 210.8(A), the receptacle spacing rules in 210.52 and the lighting outlet requirements of 210.70(A). The text of these requirements clearly indicates that their application is to dwelling units only. In some cases there are requirements that apply to one- and two-family dwellings or to multi-family dwellings, but the fact of the matter is that for the most part the requirements in the NEC are not occupancy limited (see photos 1 and 2).


Photo 4. A close view of the device outlet box shows the rough-in stages in a typical dwelling unit

In 1968 under the direction of the NEC Correlating Committee, an ad-hoc committee developed NFPA 70A, Electrical Code for One- and Two-Family Dwellings. This code was developed as a convenience to those members of the electrical industry whose primary focus was electrical installations in one- and two-family dwellings. The requirements in this code covered the most typical wiring methods and materials used in the construction of one- and two-family dwellings. In those cases where a wiring method or piece of equipment was not covered in NFPA 70A, the rules of theNECwere to be applied. The first edition of NFPA 70A was based on the 1968 NEC and revised for each subsequent Code cycle until 1993. The requirements in NFPA 70A were directly excerpted from the NEC with only editorial changes to reflect the limited scope of the document. In addition, the chapter arrangement and section numbering sequence of the NEC was retained for 70A so that the Code had the same look and feel as the parent document. This approach ensured that inspectors and installers were on the same page in respect to technical content, presentation and arrangement.

NFPA 70A was not revised for the 1996 and 1999 NEC cycles. However, for the 2002 cycle NFPA 70A has been revised and like its predecessors is a document containing excerpted text from the current edition of the NEC. The requirements are arranged in the same sequence as they appear in the NEC, an important concept that ensures inspectors and contractors are "”speaking the same language.”" There has been an expansion of the topics covered in this edition of 70A that reflects the changing electrical needs of today’s homeowner. As with the past editions, the default position is to refer to the NEC for those specific installation requirements not contained in NFPA 70A.


Photo 5. In this typical two-family dwelling underground service, two utility meters are shown as well as other utilities supplying each dwelling

The International Codes Council (ICC) has also developed a series of codes that are available for adoption and use in the construction industry. One of the codes included in this family of codes is the International Residential Code (IRC), which was developed in 1996 and is actually referred to as the "”International Residential Code for One- and Two-Family Dwellings.”" The International Residential Code includes the requirements for construction, alterations, repairs, movement, enlargement, replacement, use and occupancy, locations, and removal or demolition of one- and two-family dwellings, and multiple single-family dwellings (townhouses) not more than three stories in height with separate means of egress and associated accessory structures [IRC 2000 R101.2].

The purpose of the IRC is to provide minimum requirements to safeguard life or limb, health and public welfare. The IRC includes minimum code requirements for all of the separate disciplines (trades) including electrical code requirements related to one- and two-family dwelling occupancies [R101.3]. The purpose of the NEC is specific to the practical safeguarding of persons and property from the hazards associated with the use of electricity [90.1(A)]. Both codes are directed to essentially the same purpose of safety. The ability to effectively apply the codes to installations and systems is a vital part of the electrical safety system in North America and beyond.


Table 1. A summary of how the IRC 2000 is organized. Part VIII of the IRC is titled "Electrical" and includes ten chapters 3 through 42.

Table 1 is a summary of how the IRC 2000 is organized. Part VIII of the IRC is titled "Electrical” and includes ten chapters—33 through 42.

It is important to provide a bit of background information related to the electrical provisions contained in the IRC. First, it must be understood by both the installer and the inspector that Part VIII (The Electrical Requirements) of the IRC is produced and copyrighted by the NFPA and is based on the requirements of the 1999 National Electrical Code. In simple terms, the requirements contained in the IRC 2000 are derived from the requirements applicable to one- and two-family dwelling electrical systems contained in the NEC presented in a format that is compatible with ICC developed codes. The technical content of the requirements are based on the NEC but there is a different numbering scheme in the IRC that makes things a bit more difficult to find. There are two real important sections contained in Chapter 33 of the IRC that include vital information about the scope and applicability. A close look at Sections E3301.1 and E3301.2 provide the framework for proper application of the rules in Part VIII.

What’s Covered and What’s Not Covered?

The electrical provisions in Chapters 33 through 42 of the IRC are intended to cover the most typical installations of electrical systems, equipment and components installed indoors and outdoors at one- and two-family dwellings. The scope includes the requirements for services, power distribution systems, luminaires (fixtures), appliances, devices and other electrical appurtenances. The IRC includes the requirements for electrical installations and equipment most commonly encountered in the construction or alteration of one- and two-family dwellings and associated accessory structures. The IRC includes provisions for electrical services rated up to 400 amperes that are single-phase, 120/240-volts. Any electrical service beyond those ratings is required to fall under the provisions of NFPA 70, National Electrical Code. Other wiring methods and materials and subject matter that are not covered by the IRC but are covered by the rules in the NEC are allowed by the IRC. [See photos 3 and 4]

IRC defaults to NEC


Photo 6. Here is a closer view of photo 5

The IRC includes the requirements related to the most common one- and two-family dwelling electrical systems and is intended to be used with the NEC in order to provide a complete set of electrical installation requirements for residential occupancies. If any requirement of the NEC is omitted or not included in the IRC, this omission is not to be construed as prohibiting the use of such omitted equipment or installations. The scope of the IRC clearly indicates that electrical systems, equipment or components that are not specifically covered by Chapters 33 through 42 must comply with the applicable provisions of the NEC. Basically, this means that the provisions of Part VIII apply and where the installation is beyond the scope as outlined in E3301.2 of the IRC, the requirements of the NEC are applicable by default. An example is central air-conditioning equipment covered within the scope of Article 440 of the NEC. One should also be aware of any local amendments that may be applicable in addition to these minimum requirements. Generally, local amendments will exceed the minimum provisions by national codes and standards based on particular conditions that require such amendments.

Comparison to the NEC


Photo 7. A typical combination smoke/carbon monoxide detector in a dwelling

The rules in the IRC are primarily derived from the NEC requirements that apply to one- and two-family dwelling electrical systems. Generally, other than a different numbering system, the requirements are the same but in some cases may be worded a bit differently. There are a few differences between the two codes that should be emphasized. This article is not intended to be all inclusive of differences between the two documents. The differences are primarily limited to the limitations in scope and how the rules are presented to the user. The first major difference is the limitation of service size and voltage to 400-amperes, single-phase, 120/240-volts. The NEC does not limit the size of service for dwellings. Remember the IRC is intended to cover the most commonly encountered electrical installations in one- and two-family dwellings. Another difference between the two codes is that many of the rules found in the NEC sections are presented in the IRC in tabular form; that is, the requirements are the same, they just appear in the form of a table rather than a section. Look at the following comparison as an example. The wiring methods for a dwelling are provided in the NEC in Chapter 3. Each wiring method has an article assigned to it and within that particular article the uses permitted, uses not permitted, support and installation requirements, etc., can be found. In the IRC, specifically Chapter 37 Wiring Methods, there is a table that lists all allowable wiring methods (Table E3701.2). Looking further into this chapter there are three additional tables, E3701.4, E3702.1, and E3703.1.


Photo 8. This smoke detector in a dwelling is connected to a listed fire alarm/burglar alarm system

Table E3703.1 and its applicable notes parallel the requirements of NEC Table 300.5 for minimum cover requirements of underground electrical installations. Tables E3701.4 and E3702.1 include the requirements for wiring methods. Table E3701.4 includes the wiring method across the top of the table and the allowable application for the wiring methods listed in the vertical column on the left. This table provides the uses permitted and uses not permitted for the particular wiring methods. This differs from the NEC but only in how the information is presented. The uses permitted and uses not permitted are the same, just provided in tabular form all on the same page.

Table E3702.1 and its applicable notes provide the requirements for installation and protection of the wiring methods. The wiring methods are included across the top of the table and the vertical column on the left provides the installation requirements. This column includes the general installation requirements and specific rules relating to securing and supporting the particular wiring method allowed, such as bored holes in wood framing members, number of 90-degree bends in a conduit run between junction or outlet boxes, and maximum intervals between supports for the wiring method used. This differs once again from how the NEC presents the requirements, but the rules are the same. They just appear in one table rather than in the individual wiring method article.


Photo 9. This large living space in a dwelling has two large ceiling paddle fans in the center

Another table provided in the IRC is Table E3808.12, which is included in Chapter 38 and provides the minimum size equipment grounding conductor for circuits. This table essentially provides the same minimum sizes that are provided by Table 250.122 of the NEC. The primary difference is that Table E3808.12 is limited to circuits rated up to 400-amperes.

The IRC also provides the requirements for service, feeder, and grounding electrode conductor sizing in Table E3503.1. Essentially, this table is an expanded version of NEC Table 250.66. Table E3503.1 not only includes the minimum size grounding electrode conductor required for the service, but also lists the minimum size service-entrance conductor and allowable ampacity for the service-entrance conductor.

The minimum service load calculation requirements are also provided in a tabular format. The minimum size service is 100-ampere and the load calculation is performed similar to those in Article 220 of the NEC. Table E3502.2 is required to be used for calculating the minimum load for ungrounded service conductors and service devices that serve 100 percent of the dwelling unit load. Ungrounded service conductors and equipment that serve less than 100 percent of the dwelling unit load are required to follow the sizing requirements for feeders provided in Chapter 36.

Other sections in the IRC that include the requirements are presented in tabular format. It takes a bit of referencing back and forth from the NEC to the IRC but once located, the information provided, whether in text or table form, has its technical basis in the NEC.

The IRC also includes definitions in Chapter 34. These definitions are derived from Article 100 and are essentially the same. A few definitions, like authority having jurisdiction, and some that would not apply to one- and two-family dwelling electrical installations are not included. The IRC includes another general definitions chapter that applies to the whole code (see Chapter 2 of the IRC). Administrative provisions are located in Article 80 of the NEC and Chapter 1 of the IRC. Information about the scope, applicability, enforcement, permits and plans, powers of the building official, etc., are also found in Chapter 1.

Provisions for Smoke Alarms

The Building Codes generally require rules for fire protection systems and smoke detectors. Building codes will reference NFPA 72 in addition to the specific requirements of the applicable building code. The IRC is no exception. Although smoke alarms and detectors are not a requirement in the electrical provisions of the IRC, the requirements for smoke detectors can be found in Section R317 of the IRC. This section includes the rules for placement, listing requirements, alterations and repairs, and the required power source. Basically this section requires the equipment to be listed and installed in accordance with R317 and the household fire warning equipment provisions of NFPA 72.

Smoke detectors are required in each sleeping room, outside of each sleeping room, and in each additional story including basements and cellars but not crawl spaces. Where more than one smoke detector is installed to meet these requirements, all smoke detectors within the dwelling unit require an interlock or interconnection in a suitable manner that upon activation of one, all alarms will be activated.

The wiring for these smoke detectors/alarms must follow the applicable provisions of Part VIII (Electrical) of the IRC. Smoke alarm equipment installed in new construction requires a primary source of power supplied by the building wiring and must include a battery backup. Smoke alarms that operate on batteries only are permitted under regulation R317.1.1 for remodels or for buildings that do not have commercial power supplied to them. It is important to consult the local authorities relative to any smoke alarm requirements that may also apply.

Cross Reference Information

Electrical requirements are critical to safety of persons and property and serve as the basis for development of codes and standards for safety. Many involved in the electrical field know and understand the provisions of the NEC that apply to one- and two-family dwelling electrical systems. Where jurisdictions adopt the IRC into law, there will be assimilation challenges for those installers and inspectors involved with one- and two-family dwellings. Hopefully this article will reduce some of the anxiety levels created by fear of having to relearn the arrangement of electrical installation requirements.

There is a built in fast finder in the IRC that is similar to the NEC. It includes a contents and an index. The index references section numbers and the contents references page numbers. The IRC also includes a cross-reference between the IRC sections and the NEC sections. IAEI has also included the IRC-NEC cross-reference information in the 2002 IAEI Ferm’s Fast Finder to assist users of these codes.

In today’s world it is not uncommon at all for a dwelling unit electrical system, particularly the service equipment and first level of feeder distribution, to resemble that of a small to mid-sized commercial occupancy. One-family dwellings supplied by 2000-ampere services, 3-phase 208Y/120-volt services, and special equipment such as large air-conditioning and central heating units are not unusual. Services rated at 400 amperes are no longer a surprise to installers and inspectors. Elaborate communication and computer networking systems serve the needs of today’s home office. With this in mind, installers and inspectors involved with dwelling unit electrical systems of this magnitude are using more of the NEC requirements than ever before. For this reason, abridged sets of electrical requirements, such as the IRC, will inevitably require the inspector and installer to refer back to the NEC in order to access all of the applicable requirements.

IAEI is concerned about electrical safety as one of its primary objectives across all codes and electrical safety standards. IAEI is an international organization that has a responsibility to represent the electrical inspector in national and international affairs. One of the key benefits of being an IAEI member includes the access to critical industry information. This article was put together to provide valuable insight into the prospect of having to face the learning curve inherent to using the reorganized electrical provisions of the International Residential Code (IRC) and to help reduce anxiety levels for those having to install or inspect in accordance with the rules in the IRC. One can rest a bit easier with the understanding that the IRC electrical requirements, although unfamiliar in presentation, have been developed through the technical expertise of the National Electrical Code Committee. Some jurisdictions have adopted the IRC with its electrical provisions while the trepidation of relearning the location of familiar requirements has resulted in a number of adoptions without Part VIII and reference the NEC for the electrical requirements. IAEI feels strongly that information relative to finding and applying the electrical code requirements in both the NEC and the IRC is important in the interest of electrical safety. Providing this information is a continuation of the commitment of the IAEI to provide effective products and information for installers, inspectors, engineers, etc., all in the interest of electrical safety.

Always consult the local authority having jurisdiction for the code(s) that applies to one- and two-family dwellings in your area.


Read more by Michael Johnston

Tags:  Featured  March-April 2003 

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