Standard for 12 volt DC Edison sockets

September 2, 2013

I recently decided to create a 12 V DC lamp for emergency lighting. I started with a 120 V AC desk lamp from a big box store ($5.99) and added one of the 2W 12V DC bulbs that use the Edison E26/E27 socket.

Of course, I needed to remove the existing NEMA 1 plug and replace it with something that can’t be plugged into household current. I chose PowerPole connectors. That brought up the question: what should be the positive terminal and what should be the negative?

I did a lot of searching in RV and boat wiring, but couldn’t find anything regarding polarity of Edison E26 / E27 sockets. So in the end I just went with what seemed sensible. I wired what used to be connected to the wide blade of the 120 V plug (neutral) to negative, and what used to be connected to the narrow blade to the positive terminal.

This means that in the E26 / E27 socket, the brass projection ends up connected to the + terminal and the shell ends up connected to the – terminal.

That seems to make sense to me – but if anyone knows a better standard I’d love to hear about it.