Can I safely power a three-prong electrical device from a light socket?

Question

I have a covered lampholder (light socket) outside my house that I want to use to temporarily power a plug-in string of indoor/outdoor lights. Using CFLs, the total wattage of the string of lights will be lower than the rated wattage (100 W) of the lampholder.

The string of lights uses a grounded (three-prong) plug. Is there a way to safely power this using the lampholder?

• I can't find any lampholder-to-outlet adapters that give you a grounded outlet. Are there any?

• Would it be safe to use a two-prong lampholder-to-outlet adapter with a two- to three-prong grounding adapter? Is there anything I can do to make it safer? Keep in mind that this is outdoors, under small cover.

Answer 1

If you're talking about an E26 lampholder (the medium screw-in base widely used in the US), there are only two electrical contacts: live is at the back of the lampholder and neutral is the screw thread. While the light fixture itself should be grounded, it's not available via an adapter.

In an outdoor situation, ground protection is even more important than indoors; if your exterior circuit also includes exterior receptacles, it should already be covered by a GFCI. As I said in an another answer, that breaks the circuit if there's a ground fault, but without a ground connection, any current is going through you to ground, instead of through the ground lead. So no, it's not safe to use a two-prong to three-prong adapter and leave the ground on your lights disconnected.

I have seen exterior light fixtures with a grounded electrical outlet built into them; if you were able to change the light fixture, that would be the safest way to go.

Answer 2

https://www.amazon.com/GE-Porcelain-Lampholder-Grounded-18305/dp/B008DB3JRY

https://www.amazon.com/Leviton-9726-C-One-Piece-Incandescent-Lampholder/dp/B00002N5FR

These are Amazon links, but you can buy the Leviton one in Home Depot, however it is ceramic, so don't over tighten the screws.

These can fit 4 inch or 3 & 1/4 inch light fixture base. The 4 inch screw holes are opened, but if you need 3 & 1/4 inch, use hammer & nail or very small chisel to open them.

Answer 3

Another option would be to replace the basic lampholder with a lampholder that has a grounded outlet in its base. They fit on the same hole size, and this would give you the grounding that you are looking for as well. Of course, you will need a ground wire already run to the lampholder (which may or may not already be there).

Answer 4

Firstly if the circuit is protected with a RCD (residual-current device) you have a lot less to be concerned about. I would not be very happy having a string of lights not protected by a RCD however they are connected!

The next step is to find out if the earth pin on the lights plug does anything. There may be only a two core cable from the plug to the lights, or the earth core of the cable may not connect to anything in the lights. If this is the case you don’t need an earth.

If you do need an earth (ground), you have to be careful about which earth you use. Depending on where you live you are not allowed to connect outside equipment to the house earth and must put in a separate earth spike. Otherwise if you get a fault in the house, you can export the fault voltage to the case of the outdoor equipment.

If I were you, I would buy a set of low voltage lights, or failing that a set of “double insulated” lights so you don’t need to think about earthing.