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#47087 01/08/05 07:35 AM
Joined: Jan 2005
Posts: 59
Dawg Offline OP
Hi. Can anyone tell me a little more about the old ungrounded t-slot receptacles used in the older homes?

I have heard these could be wired for 120 volts or 240 volts. The 120 utilizing the vertical slots and the 240 volts utilizing the horizintal, or tandem slots.

I would like to know what kind of appliances, tools, etc. used an ungrounded 240 volts back in the day utilizing a tandem blade plug.

Also would anyone happen to know the dates on when the T-slot was produced?

In case anyone here doesn't know what I'm talking about here's a pic:

[Linked Image from]


#47088 01/08/05 09:33 PM
Joined: Nov 2002
Posts: 794
Likes: 3
I have heard these could be wired for 120 volts or 240 volts.

I don't know if I'd want an outlet that might be either 120V or 240V. The slots are such that a 120V 2 prong plug would fit. Most 120V loads will not like 240V at all :-( Depending on how it blows up, it could be a hazard to the user. Even if no injury occurs, he's gonna be real unhappy if the load is something more expensive than a light bulb and it got smoked....

Outlets and plugs are supposed to not be able to be mated if the voltage and current ratings are not compatable.

#47089 01/09/05 12:07 AM
Joined: Sep 2004
Posts: 86
I understood your question was not regarding installing this type of receptacle, just an interest in what the thought was behind its use. If your rally interested in an answer try the Bryant website where you might be able to contact them and get an answer. Some companies enjoy trivia questions like that and sometimes you may even stump them due to their age.
Most of the old twistlock type cord connectors and plugs were like that with dual ratings. Caused confusion in plants with both 220 volt and 480 volt operation. Thanks to Nema ratings they are a thing of the past.
Good luck on finding an answer

#47090 01/09/05 02:51 PM
Joined: Apr 2001
Posts: 518
These receptacles date from when I was forming my very first forgive me if I am not quite correct.
I seem to recall that these receps were the equivalent of today's 20 amp 110 receptacle. Both slots were "T" type so the plug could go in either way, or different plugs could fit. There were no "standard" plugs at the time, and even polarity (neutral prong being larger) was a sometimes thing.

#47091 01/09/05 08:28 PM
Joined: Apr 2002
Posts: 2,527
It could be stranger, like MattE’s “y-slot” recptacle at

[Linked Image from]

[This message has been edited by Bjarney (edited 01-09-2005).]

#47092 01/10/05 12:46 PM
Joined: Jan 2005
Posts: 59
Dawg Offline OP
I believe this receptacle was the forerunner to the T slot:

[Linked Image from]

Notice how there are 4 sets of slots. Two of the slots could accomodate your typical 120 volt 15 amp plug. The other two slots look like they would accomodate a 15 amp 240 volt plug (like you would find on a window air conditioner) with the grounding prong removed of course.

These are very odd looking may I say the least.

I've seen alot of t-slot receptacles in older homes. My grandfather had a ranch house he bought in the late 50's/early 60's and it had them in it.


[This message has been edited by Dawg (edited 01-10-2005).]

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