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Ohio building history, hazards and the rules

What wiring a Central Ohio house has, era by era

A house is wired to the rules in force where it stands when the wiring goes in, which is not always the year it was built. This page sets those rules out edition by edition, from knob-and-tube to arc-fault protection, with the dates Ohio put each edition of the National Electrical Code into its residential code, from the state's own filings. It carries the federal agencies' own words about aluminum branch wiring and about one manufacturer's breakers, with the qualification each agency attached. It does not say which code any one house was built under, because that depends on a permit it does not have.

Last updated September 2026 · The code's edition years from the inspectors' association, the Consumer Product Safety Commission and the homebuilders' association, Ohio's adoption dates from the Board of Building Standards' own filings, and the 1940 Census lighting tables were read September 2026 · No prices on this page; the Estimate Builder carries those · Part of the knowledge base

What dates a house's wiring

The National Electrical Code's first edition was published in 1897 as the rules and requirements of the National Board of Fire Underwriters. The International Association of Electrical Inspectors says in its own magazine that the code is revised every three years, and the Consumer Product Safety Commission says the same in a footnote to its ground-fault fact sheet.

This page therefore dates editions and adoptions, not houses, and never says which code any one house was built under. Which building rules were in force in Columbus, the Franklin County townships and the suburbs between which dates is on the page about which building code a house was built under. What a bathroom's receptacles, circuit, fan and lights must satisfy today is on the bathroom electrical page, permits are on the Columbus permit page, and smoke and carbon monoxide alarms are on the page about the fires, floods and collapses behind Ohio's rules.

Knob-and-tube, the 1890s to about 1930

The Rehab Guide of the Department of Housing and Urban Development describes knob-and-tube as two wires held about an inch off the surface of studs and joists by nonconducting porcelain knobs, with porcelain tubes where a wire passes through framing; the electrical inspectors' association describes it the same way. The guide says the system contained no ground and the outlets were not polarized.

The department's two guides, one publisher, do not end the method in the same year. Nationally, the Rehab Guide calls knob-and-tube the first widely used electrical system and dates it from the 1890s to 1920, while the department's Residential Rehabilitation Inspection Guide says it is still found fairly often in houses built before 1930.

The inspectors' association says the code still allows the method in existing locations, and by special permission, at Section 394.10; that section number is the association's, because no government host publishes the code's text. The same magazine says that beginning with the 1987 edition the method cannot be used in wall or ceiling cavities that have loose, filled or foamed-in-place insulating material that envelops the conductors. Asked whether insulation may be installed over live knob-and-tube wiring, the Department of Energy's weatherization program answers not in all cases and sends the question to local code.

Armored cable, nonmetallic cable, and where the ground came from

Armored cable, long sold as BX, was recognized by the code in 1899 and did not become widespread until 1920, the Rehab Guide says. It and a column in the American Society of Home Inspectors' magazine both say early armored cable contained no ground and that the armor itself was used as a ground, and both say the code required all armored cable to contain a slender aluminum bonding strip from 1959. Nonmetallic-sheathed cable, the type the code calls NM, was first recognized by the code in 1926, the Rehab Guide says, and began as two rubber-insulated conductors in a cloth sheath.

Four dates from two publishers describe how a grounding conductor arrived, and they do not agree. The Rehab Guide says that in 1928 the code required that ground conductors be installed in nonmetallic-sheathed cable, and that ungrounded cable went on being used in some places into the mid-1960s. The inspectors' association dates grounding-type receptacles and the equipment grounding conductor in cable and raceway to the mid-1950s; says the 1959 edition, at Section 210-22(b), first required grounding-type receptacles in named places, among them laundry rooms, breezeways, basements, workshops, garages and outside walls; and says the 1962 edition moved the rule to Section 210-21(b) and made all 15-ampere and 20-ampere receptacles on branch circuits the grounding type. The inspection guide says instead that it is best that all circuits be grounded to the panelboard, and that the code did not require it before 1965. All four print here and none is reconciled.

The size of the service

The Rehab Guide's service-size figures are national. In the early 1900s houses were usually equipped with 15-ampere and 20-ampere services; as appliances arrived in the 1930s and 1940s, 40-ampere and 60-ampere services became common. The same guide, written in April 2000, states that 100-ampere service is the minimum required by code for new construction; no source read for this page names the edition in which that minimum first appeared, so it is given no year here. The inspection guide adds an observation about circuits rather than amperes: a building built before 1980 may be considered to have an inadequate number of them, because current codes call for a separate laundry circuit and a separate circuit for the bathroom receptacle.

Aluminum branch wiring, and one maker's breakers

The Consumer Product Safety Commission says a shortage of copper in the mid 1960s caused builders to increase the use of aluminum wire on general-purpose 15-ampere and 20-ampere circuits, and the inspection guide independently dates that residential use to the 1960s and early 1970s. In 1978 the Commission told a House subcommittee that it was addressing residential aluminum wiring systems manufactured between 1965 and 1973; that span is the Commission's, and it describes when the systems were manufactured.

The Commission says the fire hazard it investigated occurs at connections with aluminum wire, including receptacles, switches, junction boxes and major appliances. Its publication records the sizing difference: aluminum branch conductors were run one gauge larger than copper, No. 10 and No. 12 for 20-ampere and 15-ampere circuits against copper's No. 12 and No. 14. The Commission also says it approves of only three methods for a permanent repair, complete replacement with copper cable, the COPALUM method and the AlumiConn connector, and that those repairs do not apply to the larger gauge aluminum wire circuits and connections used for service entrance cables, electric clothes dryers and cooking ranges. That list is reported as the Commission's; this page recommends nothing.

One manufacturer is named here because a federal agency named it. On March 3, 1983 the Consumer Product Safety Commission announced that it was closing its two year investigation into Federal Pacific Electric Stab-lok type residential circuit breakers. The reason it gave was that the data then available to it does not establish that the circuit breakers pose a serious risk of injury to consumers. The same release says the Commission was unable at that time to link the calibration failures its testing had confirmed to the development of a hazardous situation, and that the Commission staff believes that it currently has insufficient data to accept or refute the position of Reliance Electric, the parent company. A note the Commission added to that release on February 18, 2011, addressed to electricians, homeowners, home inspectors and real estate agents, says the Commission closed the matter without making a determination as to the safety of FPE circuit breakers or the accuracy of the manufacturer's position on the matter. Those statements travel together; the first without the last inverts the agency's meaning.

Ground-fault and arc-fault protection, edition by edition

Ground-fault protection entered the code in the 1968 edition, for underwater lighting in swimming pools, which is also where the code first defined the device; the inspectors' association, the National Association of Home Builders and the Consumer Product Safety Commission all put it there. The inspectors' association says the 1971 edition reached receptacles within 20 feet of a pool, construction site receptacles and outdoor receptacles; the Commission's fact sheet lists receptacles outdoors since 1973, under a heading that calls its years effective dates. This page does not choose between them.

The bathroom came next. The inspectors' association says the 1975 edition required bathroom receptacles to be provided with the protection and the 1978 edition added garages, and the Commission's fact sheet gives the same two years. The 1980s are the association's alone: spas and hot tubs in 1981, then in 1987 hydromassage bathtubs, boathouse receptacles, basement receptacles, and kitchen receptacles within 6 feet of the sink and above the countertop. The Commission's list corroborates only the kitchen, at 1987.

The association's account then runs to crawl spaces in 1990, with the basement rule narrowed to unfinished basements; wet bars in 1993, together with protection when a receptacle is replaced in a place the code now covers; accessory buildings and kitchen countertop receptacles in 1996; electrically heated floors in 1999; laundry, utility and boat hoist outlets in 2005; receptacles at sinks other than kitchen sinks in 2011; every receptacle within 6 feet of a sink, with bathtub and shower areas and laundry areas, in 2014; and receptacles from 125 volts through 250 volts in 2020. The Commission's fact sheet independently gives 1990 for crawl spaces and unfinished basements, 1993 for wet bar sinks and 2005 for laundry and utility sinks. Why a Central Ohio basement takes water is on the page about what goes wrong in a Central Ohio house, and what the plumbing code asks of one below the sewer is on the floods, dams, levees and floodwalls page.

Arc-fault protection is younger. The first arc-fault circuit interrupter reached the market in October 1997, and the 1999 edition first required the protection for branch circuits serving dwelling unit bedrooms, with an enforcement date of January 1, 2002; the homebuilders' association, the inspectors' association and a Commission staff paper all say so. The inspectors' association says the 2005 edition stopped accepting the first branch-feeder device and that January 1, 2008 was established as the date the industry would transition to the combination type. The homebuilders' association says the 2008 edition carried the protection out of the bedroom into family rooms, dining rooms, living rooms, closets, hallways and similar rooms, that the 2014 edition added kitchens and laundry areas, and that the list stayed put in the 2017 and 2020 editions.

What Ohio adopted, and when

Ohio's residential code has exactly one electrical chapter, Chapter 4101:8-34, and no chapters numbered 35 through 43: the chapter list at codes.ohio.gov runs 1 through 25, then 29 Plumbing, then 34 Electrical, then 44 Referenced Standards. Chapter 4101:8-34's current version, per codes.ohio.gov, took effect April 15, 2024, and its prior effective dates are January 1, 2013, January 1, 2016 and July 1, 2019. It now says it incorporates the National Electrical Code including the amendments (1) through (8) listed below it.

The edition itself is named in a different chapter, Referenced Standards 4101:8-44-01, which took effect May 27, 2006 and has been amended ten times since, most recently on April 15, 2024. The Board of Building Standards' own filings at the Register of Ohio show which edition each version named. That record begins with a rule filed new in March 2012, so the sequence below starts there and nothing is said here about the editions behind the earlier effective dates.

EditionIn force in Ohio's residential code fromThe Board of Building Standards filing
2011January 1, 2013Filed May 29, 2012; 70-11 on the National Electrical Code row
2014January 1, 2016Filed December 7, 2015; 11 struck out, 14 inserted
2017July 1, 2019Filed December 14, 2018; 70-17, the row underlined as new
2023April 15, 2024Filed for that date; 17 struck out, 23 inserted

The last change was filed twice. A final filing of January 29, 2024 would have taken effect March 1, 2024, was withdrawn on February 26, 2024, and was refiled to take effect April 15, 2024, which is why the March date is absent from the rule's prior effective dates. Houses and other buildings run on the same wiring standard in Ohio but under separate rules: the Ohio Building Code's electrical rule, 4101:1-27-01, took effect March 1, 2024, with prior effective dates of March 1, 1998, January 1, 2002, July 1, 2007, November 1, 2011, January 1, 2016 and November 1, 2017.

Two Ohio amendments differ from the national text. One excuses branch circuits supplying receptacle outlets installed to serve only the kitchen countertop surfaces from arc-fault protection, and it was already in the rules effective July 1, 2019. The other is Ohio's own outdoor ground-fault rule, which carries Exception No. 1 for lighting outlets and Exception No. 2 saying that GFCI protection is not required for listed HVAC equipment. That exception is new in the 2024 filing, and the equipment behind it is on the page about heating a Central Ohio house.

When the wires reached Central Ohio houses

The City of Columbus says Columbus gets its first streetlights, which are gas powered, in 1844, and that by 1880 the first workable lighting system is unveiled at the Ohio State Journal newspaper offices. It says the city's power plant goes on line in 1899 with a 264 horsepower engine, and that by 1910 the division began making power available to public buildings and commercial businesses downtown. Columbus Landmarks says the Columbus Municipal Light Plant was constructed in 1903 and ran until it closed in 1977; the city's page says that by the end of the 1980s it had ceased to produce power at the Dublin Avenue plant. Both closing dates print. Nothing read here says when a Columbus house, as opposed to a street or a downtown building, could first buy electric service. The City of Columbus gave the inspection of electrical wiring to its inspector of buildings by an ordinance of 1923, dated on the page on how Columbus came to inspect its houses.

Outside the city the wires came later. South Central Power Company's own history says that in 1936 nine farmers from rural Fairfield, Perry and Pickaway counties came together to form the cooperative, that it set its first pole in Fairfield County in September 1936, and that it began providing power to 288 members at Christmas of that year, when the first lines were energized.

The 1940 Census of Housing counted lighting equipment. Of Ohio dwelling units reporting lighting equipment in 1940, the Census Bureau counted 90.6 percent with electric lighting, 8.2 percent still using kerosene or gasoline and 0.8 percent gas. The state figure hides a divide: in 1940, 98.2 percent of Ohio's urban dwelling units reporting had electric lighting, against 86.8 percent rural-nonfarm and 59.3 percent rural-farm.

Franklin County was ahead of the state. Of its dwelling units reporting lighting equipment in 1940, 97.5 percent had electric lighting, and in the City of Columbus 98.4 percent. Inside the county in 1940 the early suburbs were finished and the countryside was not: Bexley and Grandview Heights read 100.0 percent, Upper Arlington 99.9 and Westerville 99.3, against 93.3 percent of the county's rural-nonfarm dwelling units and 87.2 percent of its rural-farm units. Every percentage here is taken on units reporting lighting equipment, not on all dwelling units. How those suburbs got their water and sewers is on the early suburbs page, and Westerville's record is on the Westerville page.

The short version. Ohio's residential code has referenced the 2011 National Electrical Code from January 1, 2013, the 2014 edition from January 1, 2016, the 2017 edition from July 1, 2019 and the 2023 edition from April 15, 2024, by the Board of Building Standards' own filings. A house carries the rules of the edition in force when the work was done.

Sources

Every figure, date and quotation on this page comes from one of these documents, read on the date given. Where two of them disagree, the page says so.

Common questions

Which edition of the National Electrical Code did Ohio's residential code use before 2019?

The Ohio Board of Building Standards' own filings at the Register of Ohio give the sequence. The rule filed May 29, 2012 and effective January 1, 2013 put standard number 70-11 on the National Electrical Code row, so Ohio referenced the 2011 edition from that date. The rule filed December 7, 2015 struck 11 and inserted 14, effective January 1, 2016. The rule filed December 14, 2018 named the 2017 edition, effective July 1, 2019. That record begins with a rule filed new in March 2012, so earlier editions are not stated here.

Why did Ohio's residential code change electrical editions on April 15, 2024 rather than March 1?

Because the first filing was withdrawn. The Register of Ohio's filing table for the referenced standards rule, 4101:8-44-01, shows a final filing of January 29, 2024 that would have taken effect March 1, 2024, a withdrawal on February 26, 2024, and a refiling that took effect April 15, 2024. That is why the March date is absent from the rule page's list of prior effective dates. The Ohio Building Code's own electrical rule, 4101:1-27-01, did take effect March 1, 2024, so the two codes changed on different days that year.

How many Columbus houses had electric lighting in 1940?

The Census Bureau's 1940 Census of Housing counted lighting equipment and reported that 98.4 percent of dwelling units in the City of Columbus reporting lighting equipment had electric lighting. Franklin County as a whole read 97.5 percent and Ohio 90.6 percent. Inside the county, Bexley and Grandview Heights read 100.0 percent, Upper Arlington 99.9 and Westerville 99.3, against 93.3 percent of the county's rural-nonfarm dwelling units and 87.2 percent of its rural-farm units. Every figure is taken on units reporting lighting equipment, not on all dwelling units.

Is knob-and-tube wiring still allowed under Ohio's residential code?

Ohio's residential code has one electrical chapter and says it incorporates the National Electrical Code including the amendments numbered one through eight listed below it, so the model code's own rule governs the method. The International Association of Electrical Inspectors says that code still allows the method in existing locations, and by special permission, at Section 394.10, and that beginning with the 1987 edition it cannot be used in wall or ceiling cavities that have loose, filled or foamed-in-place insulating material enveloping the conductors. This page states the record and judges no house.

When did the National Electrical Code first require GFCI protection in bathrooms?

The 1975 edition. The International Association of Electrical Inspectors says bathroom receptacles were first required to be provided with ground-fault circuit interrupter protection in that edition, and the Consumer Product Safety Commission's own fact sheet lists bathrooms since 1975. The protection had entered the code earlier, in the 1968 edition, for underwater lighting in swimming pools, which is also where the code first defined the device. Both publishers put garages at 1978 and kitchens at 1987, and the Commission gives crawl spaces and unfinished basements at 1990.

When did the National Electrical Code start requiring grounding-type receptacles?

The sources give different answers and this page prints all of them. The International Association of Electrical Inspectors says the 1959 edition, at Section 210-22(b), first required grounding-type receptacles in named places including laundry rooms, open porches, breezeways, basements, cellars, workshops, garages and outside walls, and that the 1962 edition made all 15-ampere and 20-ampere receptacles on branch circuits the grounding type. The Department of Housing and Urban Development's Rehab Guide dates ground conductors in nonmetallic-sheathed cable to 1928, while its inspection guide says grounding to the panelboard was not required before 1965.

Does Ohio require arc-fault protection on a kitchen countertop circuit?

No, and that is one of Ohio's own amendments rather than the national rule. The Residential Code of Ohio excuses branch circuits supplying receptacle outlets installed to serve only the kitchen countertop surfaces from arc-fault protection, and that exception was already in the rules effective July 1, 2019. The National Association of Home Builders says the 2014 edition of the National Electrical Code added kitchens and laundry areas to the rooms the model code covers. So a national article about kitchen arc-fault protection is describing something Ohio has changed in its own text.

What size electrical service did houses have before the 100-ampere minimum?

The Department of Housing and Urban Development's Rehab Guide, written in April 2000, gives national figures. In the early 1900s houses were usually equipped with 15-ampere and 20-ampere services, and as appliances arrived in the 1930s and 1940s, 40-ampere and 60-ampere services became common. The same guide states that 100-ampere service is the minimum required by code for new construction. No source read for this page names the edition that first set that minimum, so it is stated as a current requirement without a year.

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