What kind of outlet is this?

[Steve Kraus]

What kind of outlet is this?

Let's see now.

A vertical small prong (hot) and sideways large prong (neutral) would signify 120V / 20A. On the receptacle the sideways opening gets a vertical aspect for a combined T shape so it can accept a common 120V / 15A plug as well.

On the other hand the small opening being sideways while the large is vertical signifys a 208-240V / 20A outlet and the receptacle's vertical side is also given a horizontal aspect for a combined T shape so it can accept the rather rare 208-240V / 15A plug with two flat prongs sideways.

The outlet shown is obviously to some ancient standard. Looks like it will accept anything...except a ground pin. LOL.

[Don Young]

Standard old 20A 120V outlet. Used to use the duplex form for the kitchen outlets. These were used before the days of polarized outlets and plugs so the plug could be inserted either way. I am not sure but I think the in-line slots may have been too short to accept the 240V plugs.

Don Young

[Eigenvector]

The Wiki labels it as a NEMA type 2 socket, no longer allowed.

[Steve Kraus]

Is that all? I was hoping for something exotic like DC!

[Berkshire Bill]

Use your test leads to satisfy your curiosity about the voltage and throw the receptacle away. It will accept a non polarized 120vac plug but doesn't look very reliable.

Bill

[Stormin Mormon]

The picture is too dark for my monitor to show. However, my gut sense, it's a very very old 110 volt household power outlet.