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[Jonathan Johnson]

If you see an outlet with two T-shaped slots, be very, very wary. Often designated "NEMA 2-15" it was designed to be used with EITHER 120V or 240V. This means that someone could plug in a 120V device into 240V, with potentially disastrous results.

[Jonathan Johnson]

I'll add that most installations of this style of receptacle were done before a grounding conductor was required. If the center coverplate screw is grounded, it is likely incidental through the use of conduit or the jacket of armored cable (which is not considered a reliable grounding conductor) and not intentionally grounded by the installer. For this reason, the ground should not be trusted as it may be an unreliable or high-resistance/high-impedance ground.

[Mike Sokol]

I'll add that most installations of this style of receptacle were done before a grounding conductor was required. If the center coverplate screw is grounded, it is likely incidental through the use of conduit or the jacket of armored cable (which is not considered a reliable grounding conductor) and not intentionally grounded by the installer. For this reason, the ground should not be trusted as it may be an unreliable or high-resistance/high-impedance ground.

My grandparents had receptacles like these in the 60's, and I've seen a few of them in an old school just a few years ago. I told the custodian they needed new wiring installed, but they probably ended up as bootleg grounds since the boxes were too small for a GFCI.

[Kevin Graf]

Now there are smaller form-factor/footprint GFCI's available.

http://www.leviton.com/OA_HTML/SectionDisplay.jsp?section=47134&minisite=10251

[Frank DeWitt]

If you see an outlet with two T-shaped slots, be very, very wary. Often designated "NEMA 2-15" it was designed to be used with EITHER 120V or 240V. This means that someone could plug in a 120V device into 240V, with potentially disastrous results.

It is a old outlet, and of course any outlet should be checked before plunging in any thing you value,  Most of the outlets that look like that were made to accept the standard plug we all know and love often called an "Edison plug" OR old Hubbell plugs that look like this.

http://en.wikipedia.org/wiki/File:Hubbell_Tandem_cap_base.JPG

A little history.  Edison invented not just the light bulb but the entire home lighting system.  Bulbs, sockets, wiring, fuse boxes,  Every thing a home needed EXCEPT outlets.  Small appliances and floor lamps simply did not occur to him.  The first plugs had the Edison screw base Just like light bulbs.  If you are a strange collector, you will have outlets that look like light sockets but mounted in the wall with a little brass door over the open socket.  Later a number of manufactures came out with "plugs"  some were very scary.  The VHS and batamax of the industry turned out to be the Hubblell and the one we have today.  For many many years, outlets were made to accept either one.

Here is another design http://electrical-contractor.net/forum/el/lstrecps.jpg

No,  I don't know why I collect this stuff.
 

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