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I just moved into an old apartment and found some interesting looking outlets that I've never seen anything like. I'm trying to figure out more about the history of the house and it's age so I'm wondering if anyone knows more about when these types of outlets were used? I did some research and found out they are called "Nurpolian tandem and parallel receptacle". All of the information on the internet about it is very brief and seems to be copy and pasted around every blog so I was wondering if anyone knew anything more about it and it's age?:whistling2:
 

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Those are the old dual-rated receptacles, which were used for both 120 and 240 Volt applications.

Maybe 100 years old.

The problems developed when someone actually used one for a 240 Volt application, and then someone else accidentally plugged in a 120 Volt appliance -- which resulted in the 120 Volt device getting fried rather quickly.

To avoid such fiascos nowadays, standardized NEMA configurations are used.
 
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The only thing I'd add to this discussion is that all of Hubbell's plug designs were originally rated for up to 250v (6A). The parallel configuration was officially given the rating '125v' in the 30s, and the tandem plug was unofficially left implied for 250v until the 50s, when it was finally given that rating officially, a NEMA rating it holds to this day, even though connection with it on 240v has been "banned" since the 60s. Because almost all general service electrical connections in the U.S. were 120v, almost all tandem plugs ended up being connected to 120v. But the tandem plug was never officially made FOR 120v.

Most general purpose, light duty electrical connections in the U.S. have always been 110-125v, but in the late 19th century into the early 20s, there was in fact some 220v, too. No standards on plug types in those days, so the tandem and parallel blade plugs were used interchangeably as available. As well as a couple other Hubbell designs which were unpopular and soon dropped. Even though the plugs weren't assigned official voltages at this time, I do believe Hubbell's intent in creating multiple plug configurations was ultimately to account for the differing voltages in use at the time
 

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I just moved into an old apartment and found some interesting looking outlets that I've never seen anything like. I'm trying to figure out more about the history of the house and it's age so I'm wondering if anyone knows more about when these types of outlets were used? I did some research and found out they are called "Nurpolian tandem and parallel receptacle". All of the information on the internet about it is very brief and seems to be copy and pasted around every blog so I was wondering if anyone knew anything more about it and it's age?:whistling2:
I removed several of those a few months ago from an old house. They were all wired for 120 volts and did not have provisions for terminating dual voltages.

I surmise that these were installed to accomadate different manufacturers plug configurations. When electricity was coming to mainstream there was no standardization for many things. Manufacturers came out with their own outlet designs and plug configurations. By having the dual configuration outlet, you could plug in appliances from several manufacturers.
 
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