Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
ACCURACY vs PRECISION of MEASUREMENTS
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
CIRCUIT BREAKER FAILURE
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
Classified CIRCUIT BREAKER WARNING
CORROSION in ELECTRICAL PANELS
CORROSION & MOISTURE SOURCES in PANELS
CUTLER HAMMER PANEL FIRE
DEFINITIONS of ELECTRICAL TERMS
Definition of Amps, Electrical Current
Definition of Electrical Circuits, shorts
Definition of Volts
Definition of Watts
How a Building Gets 240V and 120V
How many Watts in a Circuit
Definition of AC Alternating Current
Definition of DC Direct Current
Definition of Electrical Ground Terms
Definition of Electrical Potential
Definition of Ohms, Electrical Resistance
Definition of Power Factor, Real Power
Efficiency of 120V vs 240V Equipment
DIRECTORY OF ELECTRICIANS
DMM Digital Multimeter, How to Use
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
Electricity Basics - how it works
Electrical Circuit ID, Map & Label
Electrical Circuits, shorts
Electrical Code Basics
Electrical Grounding Basics
ELECTRICAL OUTLET, HOW TO ADD & WIRE
Electrical Splices, how to make
Electrical Tools & Tests
Electrical Wire Stripping Tips
Electrical Wiring Books & Guides
Electrical Wiring in Old Houses
OLD HOUSE ELECTRICAL GROUNDING
ELECTRICAL DISTRIBUTION PANELS
ELECTRICAL GROUND SYSTEM INSPECTION
ELECTRICAL SERVICE DROP
ELECTRICAL SERVICE ENTRY WIRING
EMF RF FIELD & FREQUENCY DEFINITIONS
ELECTRICAL GROUND SYSTEM INSPECTION
FEDERAL PACIFIC FPE HAZARDS
FIRE SAFETY Checklist, CPSC
GFCI PROTECTION,Testing GFCIs AFCIs
HEAT TAPE USAGE GUIDE
Hertz - Definitions of KHz MHz GHz THz
KNOB & TUBE WIRING
LIGHTING, EXTERIOR GUIDE
LIGHTING, INTERIOR GUIDE
LIGHTNING PROTECTION SYSTEMS
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MANUALS & PARTS GUIDES - HVAC
MAIN DISCONNECT AMPACITY
MOISTURE SOURCES in PANELS
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
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
UNDERGROUND SERVICE LATERALS
VOLTS / AMPS MEASUREMENT EQUIP
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING
ZINSCO SYLVANIA ELECTRICAL PANELS
Building electrical system installation, troubleshooting & repairs & electrical hazards. How to install, inspect, & troubleshoot building electrical systems, appliances, components. How to detect & report electrical hazards, defects in residential and commercial electrical panels, switches, fixtures, electrical wiring & grounding systems. Proper electrical repair methods for unsafe electrical conditions. 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 are addressed.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
See the article links listed at Related Topics for a complete index to building electrical systems & components: inspection, diagnosis, & repair guides.
Frequently Asked Questions (FAQs) about electrical wiring installation, inspection, diagnosis, & repair
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.
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 CIRCUITS for 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 reasonable 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.
Questions & answers or comments about building electrical systems, panels, breakers, wiring installation, inspection, diagnosis, & repair.
Ask a Question or Enter Search Terms in the InspectApedia search box just below.
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.