The Aged Wiring Project
Understanding the effects of aging on our electrical infrastructure.
NFPA Journal®, May/June 2008
The Fire Protection Research Foundation recently completed two projects that explored the effects of aging on electrical grounding and wiring systems in single-family residences. Both studies stemmed from needs expressed by National Electrical Code® (NEC®) Code-Making Panels.
Electrical grounding systems
NFPA has for decades recognized the practice of grounding, or earthing, electrical systems to buried electrodes as the recommended method of preventing
people and property from becoming accidental electrical connections to the earth.
However, there are many unknowns in predicting how many electrodes will perform their intended purpose over time. Factors that influence performance include earth resistivity, earth chemistry, earth moisture, earth temperature, electrode resistance, weather or seasonal changes in the moisture of the earth, the current-carrying capability of the electrode in earth, and damage through unwanted impressed current, mechanical means, or corrosion.
The Foundation studied the performance of 15 types of passive and active direct-current electrodes in 10 sites across the United States over 10 years. The results provide information on improving grounding practices for optimum long-term performance.
Home wiring systems
According to NFPA, an annual average of 24,200 home fires attributed to electrical distribution systems or lighting equipment from 2002 to 2005 caused 830 injuries, 320 deaths, and $700 million in damage. A 1987 U.S. Consumer Product Safety Commission study indicated that the frequency of fires in residential electrical systems was disproportionately high in homes more than 40 years old.1
The high incidence of fire in older homes can usually be attributed to:
Inadequate and overburdened electrical systems.
Thermally reinsulated walls and ceilings burying wiring.
Defeated or compromised overcurrent protection.
Misuse of extension cords and makeshift circuit extensions.
Worn-out wiring devices not being replaced.
Poorly done electrical repairs.
Socioeconomic considerations resulting in unsafe installations.2
With over 100 years of residential electrification in many cities and towns, the aging residential electrical infrastructure is beginning to raise concerns.
The Foundation’s study surveyed, recovered, and analyzed samples of installed residential wiring systems, wiring devices, and similar distribution and use equipment from 30 homes with electrical systems ranging in age from 30 years to over 100 years, in 10 states across the United States. The study revealed that the quality of the original installation, as well as inappropriate upgrades or additions done by unqualified persons, were major factors in the condition of the electrical systems.
These studies provide critical information to NEC Code-Making Panels and other NFPA committees, authorities having jurisdiction, manufacturers,
testing laboratories, installers, owners, and insurers. The report, which can be found at http://www.nfpa.org/Foundation, will be released this July.
D. McCoskrie, L. Smith, “What Causes Wiring Fires in Residences?,” Fire Journal, Jan/Feb 1990.
Technology for Detecting and Monitoring Conditions That Could Cause Electrical Wiring System Fires, USCPSC, September 1995.
Kathleen H. Almand, P.E., FPFPE, is the executive director of the Fire Protection Research Foundation.