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This website provides information about electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards, residential and commercial electrical wiring, and on proper electrical repair methods for unsafe electrical conditions.

We address safety for the electrical inspector, aluminum electrical wiring hazards, how to determine service voltage and ampacity, how to inspect electrical panels, and significant electrical hazards of Federal Pacific Electric Stab-Lok breakers and panels, Federal Pioneer product warnings, certain Square-D product concerns, Zinsco and Sylvania circuit breakers and panels, multi-wire branch circuit protection, inspection and repair of low voltage wiring systems, and proper installation of lightning protection systems on buildings. Also see ENERGY SAVINGS in buildings.

Critique and content suggestions are invited. Credit is given to content editors and contributors.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

ELECTRICAL HAZARDS, INSPECTION, REPAIRS - Electrical System & Wiring Hazard Inspection, Hazards, Repairs

• ** Safety Hazards and Safe Electrical Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• Aluminum Wiring Information Website Aluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
• Ampacity and Voltage of an Electrical Service: How to determine the electrical service size or ampacity and service voltage (120/240) entering a Building
• ARC FAULT CIRCUIT INTERRUPTERS: what are they, how do AFCI's work, where are they required to be installed? Also includes notes on GFCI's and the 2008 NEC electrical code.
• Cadet Heaters Recall CPSC notice supplemented with identification and heater failure photos
• Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
• Circuits, electrical: electric circuit basics for homeowners, electrical shorts, definitions of AC/DC, watts, amps, volts, etc.
• Code Basics, electrical: electrical code information for homeowners. Can I do my own wiring?
• Conduit, electrical: information for homeowners & home inspectors.
• CORROSION & MOISTURE SOURCES in PANELS, Roger Hankey 2010, and CORROSION in ELECTRICAL PANELS, Daniel Friedman, 1992, 2009, discuss the sources of water or moisture intrusion in electrical panels and causes of rust or other safety concerns.
• Electrical System Classes - (work in process 2010 Power Point Presentations for Milestone Elec. Dallas TX)
  • Aluminum Wiring Class for Electricians - work in process 2010 Power Point Presentation, very large file
  • FPE_Stab-Lok_Class for Electricians - work in process 2010 Power Point Presentation
  • Zinsco_Class for Electricians - work in process 2010 Power Point Presentation
  • Electrical Safety Class for Electricians - work in process 2010 Power Point Presentation
  • Electrical Safety Hazards & Accident Prevention for Home Inspectors, paper presented to the Connecticut Association of Home Inspectors, CAHI 26 March 2008
  • Electrical Panels, How to Inspect in buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
  • "Inspecting Residential Electrical Panels," Daniel Friedman, HVASHI, September 12, 2002 Annual Seminar.
  • "Inspection of Electrical Systems & Special Concerns," Daniel Friedman, ASHI/CAHI/OAHI/IAEI Conference, Toronto, Ontario, 10/19-21/1995
• DEFINITIONS of ELECTRICAL TERMS: Amps, Volts, Watts, Resistance and other electrical terms are defined and illustrated with sketches
• "Determining Service Ampacity," Daniel Friedman, Alan Carson, The ASHI Technical Journal, Vol. 2 No. 1, Winter 1992
• DIRECTORY OF ELECTRICIANS: if you need to hire an electrician with special skills or familiarity with aluminum electrical wiring, FPE Stab-Lok replacement panels, Zinsco replacement panels, etc. here is a directory of professionals.
    DIRECTORY OF ELECTRICIANS - Aluminum Wiring - Specialists in repairing aluminum electrical wiring
    DIRECTORY OF ELECTRICIANS - FPE Zinsco - Specialists in repairing or replacing FPE, Zinsco, and other problem equipment
• ELECTRIC METERS & METER BASES: inspection and problem diagnosis
• Electrical Panels, How to Inspect in buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
• EMF RF FIELD & FREQUENCY DEFINITIONS - defines and explains electromagnetic field (EMF) or electro-magnetic radiation EMR and related terms such as EMF, radio frequency - RF, hertz or cycles, megahertz, medium frequency MF, very high frequency VHF, ultra high frequency UHF, megahertz MHz, gigahertz GHz, terahertz THz .
• Federal Pacific Electric (FPE) Website Stab-Lok Circuit Breaker Panel Hazards Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
• Federal Pioneer NCO15 and NC015CP circuit breaker recalls from Schneider Electric in Canada
• "Ground Fault Circuit Interrupters, How Do They Work?" Daniel Friedman [as Journal Staff], The ASHI Technical Journal, Vol. 2 No. 1, Winter 1992
• Hertz - Definitions of KHz MHz GHz THz
  
• How to Identify FPE Federal Pacific Stab-Lok Electric Panels - is yours one of these? ALSO: A History of the FPE Stab-Lok Issue.
• FPE FIRES: Failures continue: FPE breaker fails, results in fires: field reports
• Federal Pacific Electric Fires Waiting to Happen, Debate Waiting to Be Ended, detailed article
• Federal Pacific Electric Panel Replacements FPE Stab-Lok Panel Replacements: two cost and method options for FPE panel replacement.
• 2004 FPE Stab-Lok Technical Report - St. Louis ASHI Seminar including: Hazard Summary & Independent Tests confirms Stab-Lok failures
• Siemens Electric Panel Fires: field report and possible defective equipment - article withdrawn, field reports wanted
• GFCI PROTECTION,Testing GFCIs AFCIs GFCI Ground Fault Circuit Interrupter Receptacle Defects & Testing procedures for inspectors
• Electrical Grounding Defects [in process]
• KNOB & TUBE ELECTRICAL WIRING: identification, inspection, evaluation, and safety guide advice for home owners & inspectors
• Knob and Tube Wiring & Home Owners' Insurance [Carson Dunlop]
• LIGHTING, INTERIOR GUIDE - in depth detail about indoor lighting requirements, fixtures, bulbs, installation, choices
• Lightning Strike Risk Assessment, Lightning Protection Systems & Services, lightning rods, grounding
• "Lightning and Lightning Protection Systems," Daniel Friedman [as Thomas Misciewicz], The ASHI Technical Journal, Vol. 2 No. 1, Winter 1992
• Low Voltage Electrical Wiring Repair & Replacement Guide for GE®, Remcon, Sweepe, Bryant, Sierra, other brands, and newer Touch-Plate® low voltage wiring systems. Low voltage lighting switches, relays, transformers, transconverters.
• Multi-wire branch circuit inspection and defects
• Outlet, how to install: guide for home owners & home inspectors - it's easy but important details make the difference between a safe installation of an electrical receptacle and one that is both dangerous and illegal.
• Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels
• "Safety Considerations for the Electrical Inspector," Daniel Friedman, The ASHI Technical Journal, Vol. 2 No. 1, Winter 1992
• Safety Hazards [electrical] & Accident Prevention for Home Inspectors, paper presented to the Connecticut Association of Home Inspectors, 26 March 2008
• Square D Electrical Panel Recalls: - Counterfeit Square D Recall
• Square D GFCI Recall
• Square-D & Federal Pioneer AFCI Notice (also Federal Pioneer - Schneider Canada)
• Square D Circuit Breaker Recalls, announced by the US CPSC, recalls include a Square D GFCI circuit breaker distributed by Square D, and a Counterfeit Square-D circuit breaker sold through Scott Electric
• WIND TURBINES & LIGHTNING - lightning protection and extra protection from lightning damage for wind turbine electrical generator systems and their controls and batteries
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
• "Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
• "Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
• Zinsco Electrical Circuit Breaker Failures: overheating, failure to trip, burn-ups involving Zinsco and certain Sylvania electrical panel components
• Zinsco Electric Panel Replacements a discussion of repair (replacement) options for Zinsco Electrical Panels and Zinsco-type Sylvania Electric Panels

Questions & Answers about electrical wiring installation, inspection, diagnosis, & repair

Question: Can I Hook Up Two Power Sources to One Electrical Panel?

Is it possible to connect two sources of Electricity to one Sub-Panel? - Muhammad K., Jordan

Reply: Use an isolation switch to avoid simultaneous (and unsafe) electrical power feeds to an electrical panel or sub panel - use backup electrical generator hookups as an example

By "possible to connect two sources of Electricity to one Sub-Panel" I presume you don't mean is it physically possible to connect two power sources to a single electrical panel since that would be trivial to accomplish; Rather I presume you mean is it acceptable practice or is it "safe" to connect multiple power sources into a single electrical panel or sub-panel.

The basic answer is no. In general it is very dangerous to have multiple sources of power into a single panel or subpanel because of the possibility of backfeeding and shocking someone who thinks power is off from a given source. So we don't hookup simultaneous live electrical power sources to a single electrical sub panel or main panel.

We do not hook up multiple electrical power sources to a single electrical sub panel without using an isolation switch.

In our photograph of an isolation switch hook-up (above left), the main electrical panel (1) is at left. In the photo center is an isolation switch (2) that allows the homeowner to switch individual circuits from being powered either by the main electrical panel's service entry mains or by an electrical generator (located outdoors) that is connected to the isolation switch by a removable plug shown hanging on the wall (3). You can see the receiving plug receptacle at the bottom center of the isolation switch (2).

The sub panel shown at right (next to our client) was an addition to the original electrical system to support central air conditioning and is not part of this discussion. See BACKUP ELECTRICAL GENERATORS for details.

Watch out: Emergency backup electrical generators produce 120V and 240V which may cause fatal electrial shock if precautions are not followed. DO NOT under any circumstances connect your electrical generator to any circuit or receptacle that is receiving electrical power (home, office, etc) from any other sources as this is likely to result in a fire and damage all electrical systems and could also shock someone working on the system.

Our auxiliary electric generator photo at left shows a backup "home" generator that the owner had set up to keep a basement sump pump working. Some owners connect an extenstion cord to the generator's electrical supply receptacle and connect the other cord end to a tool or appliance - which may be safe. But using that same extension cord to "back-feed" a home electrical circuit without an isolation switch is unsafe and should not be done.

Other key safety warnings include the warning that the backup generator should not be operated indoors nor in an enclosed area - there are fire and also potentially fatal carbon monoxide hazard risks. Note that other safety precautions also apply - be sure to see the instructions provided with the generator.

See BACKUP ELECTRICAL GENERATORS.

Questions & Answers and FAQS about Electrical Wiring

Question: History of Electrical Wiring in the U.S. - Split Receptacles or Electrical Outlets?

When were houses commonly built with split outlets/receptacles? I am doing research to find out how many houses in the US may not have them. Thanks! - Maria S.

Reply: A Nano-History of Electrical Wiring Devices in North America - Guessing: 1950 - 1965

You are referring to the practice of providing separate power from separate electrical circuits individually to the upper and lower receptacle openings of a duplex electrical receptacle.

That feature has been technically possible and therefore almost surely was done in some homes from around the time that duplex receptacles were first installed. (See Split Wired Receptacles under MULTI-WIRE CIRCUITSfor details.)

The two-pin electrical receptacle was invented by Hubbell in 1904 as a device that screwed into light bulb sockets (electrical power for lighting was sold at a lower rate! - Wiki.)

Grounded electrical receptacles date to around 1915, though they were by no means in widespread use until much later.

Because sources (Wikipedia and others) note that the dominant way to plug in electrical appliances was by connecting them (using the screw-in adapter) to light bulb sockets into the 1920's (in North America) it is reasonble to argue that it was not until the mid or later 1920's that duplex electrical receptacles began appearing in homes.

Labre patented the grounded plug in 1928. Ten years later, twist-on locking electrical receptacle connectors date to Harvey Hubbell way back in 1938.

Polarized plugs (one blade wider than the other) were not introduced until 1948 and were not widespread before the 1950's. (The neutral wire is connected to the larger slot on the electrical receptacle)

Ring circuits (adopted only in the U.K.) first saw use in the U.K. around 1947 - provided the functional equivalent of our split wired receptacle approach and suggest the history of origin of the idea.

The sum of this history to date (subject to revision as our research continues) is that I'd place duplex receptacles in widespread use by 1935-1940 and it would be fair to assume (barring a code restriction yet to be found) that split wired receptacles, being physically possible, appeared in some uses as early as 1940.

IN sum it is more likely that split wired electrical receptacles were in use by the late 1940's, expanded during the post-Korean ware boom, and began seeing widespread use in North America after 1965-1970. That last OPINION derives from guessing at the onset of surge in use of multiple electrical appliances at once in home kitchens.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
AFCIs ARC FAULT CIRCUIT INTERRUPTERS
ALUMINUM SECs & WIRING
ALUMINUM WIRING HAZARDS & REPAIRS
AMPS & VOLTS DETERMINATION
AMPACITY - the LIMITING FACTOR
APPLIANCE EFFICIENCY RATINGS

BACKUP ELECTRICAL GENERATORS
BOOKSTORE - ELECTRICAL
BUILDING SAFETY HAZARDS GUIDE

Cadet & Encore Heater Recall
BACKUP ELECTRICAL GENERATORS
CIRCUIT BREAKER FAILURE
Classified CIRCUIT BREAKER WARNING
CUTLER HAMMER PANEL FIRE
CONDUIT, ELECTRICAL
CORROSION in ELECTRICAL PANELS
CORROSION & MOISTURE SOURCES in PANELS

DEFINITIONS of ELECTRICAL TERMS

DIRECTORY OF ELECTRICIANS

ELECTRIC HEAT
ELECTRIC METERS & METER BASES
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRIC PANEL AMPACITY
ELECTRIC PANEL INSPECTION
ELECTRIC PANEL MOISTURE
Electric Power Frequency Table
ELECTRICAL BASICS

EMF RF FIELD & FREQUENCY DEFINITIONS

ENERGY SAVINGS in buildings

ELECTRICAL GENERATORS
ELECTRICAL GROUND SYSTEM INSPECTION

ELECTRICAL GENERATORS
ELECTRICAL GROUND SYSTEM INSPECTION

ENERGY SAVINGS in buildings

FEDERAL PACIFIC FPE HAZARDS
FIRE SAFETY Checklist, CPSC

GENERATORS, ELECTRICAL
GFCI PROTECTION,Testing GFCIs AFCIs

HEATING COST FUEL & BTU Cost Table
HEAT, ELECTRIC
HEAT TAPE USAGE GUIDE
Hertz - Definitions of KHz MHz GHz THz

KNOB & TUBE WIRING

LIGHTING, INTERIOR GUIDE

LIGHTNING PROTECTION SYSTEMS

LOW VOLTAGE BUILDING WIRING

MAIN DISCONNECT
MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
MULTI-WIRE CIRCUITS
MURRAY SIEMENS Recall

PHOTOVOLTAIC POWER SYSTEMS
PUSHMATIC - BULLDOG PANELS

REMOTE ELECTRIC POWER, PHOTOVOLTAIC
RUST in ELECTRICAL PANELS

SAFETY FOR ELECTRICAL INSPECTORS

SE CABLE SIZES vs AMPS
SIEMENS MURRAY Recall

SOLAR ENERGY SYSTEMS
SQUARE-D RECALLS

UNDERGROUND SERVICE LATERALS
VOLTAGE MEASUREMENT EQUIPMENT
ZINSCO SYLVANIA ELECTRICAL PANELS
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING

• "Whole-House Systems Approach [to saving on energy costs]", U.S. DOE, describes designing and constructing an energy-efficient home by considering all of the house systems. Original DOE source: www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10370
  • "Appliances and home electronics", U.S. DOE on energy savings suggestions
  • "Insulation and Air Sealing", U.S. DOE describes how to reduce a home's heating and cooling costs by proper insulation and air leak sealing. Moisture control and ventilation are also discussed.
  • "Lighting and Daylighting", U.S. DOE, is a very brief DOE article suggesting how to reduce the cost of lighting in a building
  • "Space Heating and Cooling", U.S. DOE, attacks the biggest energy user in buildings, typically about 56% of energy use in a typical home in the United States.
  • "Water Heating", U.S. DOE, addresses reducing the cost of heating domestic hot water used for washing and bathing - that accounts for 14-25% of home energy usage in the U.S. and includes
    • "Selecting a Water Heater", U.S. DOE
    • "Energy Efficient Water Heating", U.S. DOE includes suggestions to lower hot water heating costs including reducing hot water usage, lowering hot water temperature, insulating the water tank (nonsense), insulating hot water pipes, installing heat traps on the water heater tank, water heater timers, and drain-water heat recovery systems (possibly not cost effective)
    • "Swimming Pool Heating" cost savings suggestions from the U.S. DOE includes suggestions on using a high efficiency (gas-fired swimming pool heater or heat pump swimming pool heater) or solar swimming pool heater, using swimming pool covers, managing swimming pool water temperatures, and installing a more energy efficient swimming pool pump, or using it less.
• "Basic Housing Inspection," US DHEW, S 352.75 U48, p.144, out of print, but is available in most state libraries.
• Thanks to home inspector Larry Olson lomo5202@gmail.com for forwarding the 2010 US CPSC circuit breaker recall information concerning Siemens Murry equipment.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)
• * Safety Hazards and Safe Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• Aluminum Wiring Information Website Aluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
• Ampacity of an Electrical Service: How to determine the electrical service size or ampacity entering a building
• Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
• Electrical Panels, How to Inspect in buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
• Federal Pacific Electric (FPE) Stab-Lok Circuit Breaker Panel Hazards Website - Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
• Lightning Strike Risk Assessment, Protection Systems & Services
• Multi-wire branch circuit inspection and defects
• Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• Safety Hazards and Safe Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
• "Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
• "Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
• "Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
• Electrical System & Wiring Hazard Inspection, Detection, Cause, Remedy, Prevention - Main Electrical Page
• ...