Introduction to Open Return Wiring
The open return wiring system was an innovative method of wiring homes economically in the 1930s. This wiring system used a common neutral wire that returned all electrical currents to the service panel, allowing each circuit to share the neutral wire.
Prior to open return wiring, homes were wired using knob-and-tube wiring. This involved running individual hot and neutral wires through the walls and ceilings for each circuit. While effective, knob-and-tube wiring was labor intensive and used twice as much copper wire compared to the open return system.
The open return system was cheaper, faster to install, and used less materials. However, it came with some drawbacks that I'll discuss later on. First, let's look at how the open return wiring system worked.
How the Open Return Wiring System Functioned
The open return wiring system consisted of a shared neutral wire that provided a return path for all the electrical currents in the home. Here's a quick overview of how it worked:
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A main service cable brought power from the street into the home. This consisted of two 120V "hot" wires and a neutral wire.
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The neutral wire was connected to all the neutral terminals in the home. This created an open loop back to the service panel.
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Each circuit got its own hot wire that powered lights, outlets, and appliances. The circuits shared the common neutral return wire.
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Electricity flowing along the hot wires went through the devices and returned to the panel via the open neutral wire.
This meant that only one neutral wire could provide the return path for multiple circuits. The neutral wire was often a bare wire that simply ran through holes drilled in the wall studs and floor joists.
The Cost and Labor Savings of Open Return Wiring
The open return system delivered huge savings in materials and manpower compared to knob-and-tube wiring:
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It used 50-70% less copper wire since wires didn't have to be run in pairs.
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Labor costs for installation were far lower because workers only had to run one wire per circuit instead of two.
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The simpler wiring method allowed 3-4 times faster installation compared to knob-and-tube.
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Overall, open return wiring cost half as much per circuit compared to previous methods.
These savings allowed 1920s wiring methods to be adapted for the surge in home construction that took place in the late 1930s. It simply wasn't feasible to wire all the new suburban homes using old-fashioned knob-and-tube.
The open return system brought electrification within the budget of more homeowners. This spurred the spread of electrical appliances beyond just lighting.
Safety and Reliability Concerns with Open Return Wiring
While effective and affordable, the open return system came with some potential hazards:
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Having multiple circuits share one neutral wire meant overloading was a risk. The neutral could overheat if too many appliances were running at once.
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The bare neutral wire had more risk of short circuiting if it came into contact with other wires or grounded metal.
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It provided less redundancy. If the neutral was damaged, multiple circuits could stop working.
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Voltage fluctuations on one circuit could affect others on the same neutral.
The open return system was also less compatible with modern appliances and electronics that produce electrical noise. This electrical interference can cause problems when many circuits share a neutral.
Overall, open return wiring provided adequate safety when properly installed. But it lacked the reliability of having dedicated neutral wires.
The Decline of Open Return Wiring
By the 1950s, the electrical code started prohibiting open return wiring in new construction:
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The updated code required a dedicated neutral for each circuit. This avoided overloading and electrical noise issues.
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Copper prices decreased, making it more affordable to run separate neutral wires.
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Improved wiring insulation allowed bundles of wires to be run through walls more easily.
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Safety concerns motivated a return to grounded electrical systems.
Today, open return wiring is prohibited by the National Electrical Code. But it still exists in many older homes, especially in rural areas.
Identifying and Replacing Open Return Wiring
Here are some signs your home may have open return wiring:
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Frequent tripped breakers when multiple appliances are in use.
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Voltage fluctuations when other devices turn on and off.
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A single bare copper wire instead of a wire pair feeding outlets.
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2-prong ungrounded outlets.
If open wiring exists, it's best to have a licensed electrician inspect and replace it. They can:
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Run new wires and add grounding.
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Replace overloaded circuits.
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Isolate noisy appliances on separate circuits.
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Bring everything up to the current electrical code.
While open return wiring served its purpose in the 1930s, upgrading provides much better safety, capacity, and reliability for modern households.
Conclusion
The open return wiring system enabled affordable electrification of homes in the 1930s. While not as safe as modern wiring, it allowed new suburbs to be wired quickly and inexpensively. The reduced use of copper wire was also important for wartime supply needs in the 1940s.
This little-known wiring method helped bring electricity to the masses. But its limitations and risks eventually led to stricter electrical codes mandating grounded, dedicated neutrals for each circuit. Although mostly forgotten, open return wiring remains an innovative electrical solution that powered the homes and appliances of its era.