I have a light fixture to install that is pre-wired with only the black and white wires (see 2nd pic). The box in the ceiling (3rd pic) is plastic and has black, white, and bare copper wire -- the bare copper wire is grounded to a screw in the box (bottom left of picture).

The fixture comes with a separate ground wire (see 1st pic). Also in the 1st pic is the light fixture bracket to connect to the box.

My 2 questions are:

  1. Do I need to use the separate ground wire at all? If not, what do I do with the bare copper wire in the box?

  2. If I do need to use the separate ground wire, does the 4th picture look correct in terms of how to install the separate ground wire to the light fixture bracket?

Separate Ground Wire

Light Fixture Wires

Plastic Box

Possible Install

  • 1
    Have you looked at the instructions? Regardless of what we say, the instructions have final authority.
    – KMJ
    Commented Mar 15, 2023 at 19:36
  • No instructions were included unfortunately.
    – Carolyn
    Commented Mar 15, 2023 at 22:36

3 Answers 3


Plastic is not a good conductor of electricity.

The only way to ground that light is to connect the extra ground wire to the ground wires in the box with a wire nut or wago connector.

One pro of metal boxes is that the metal can double as a ground path. The extra wire is probably provided for use in plastic boxes.

As @KMJ comment mentions, the instructions are what you go by.

  • I understand that I'll need to connect the extra ground wire to the ground wire in the box with a wire nut, but does the last picture look correct in terms of having attached the extra ground wire with the metal nut (before it then ends up connecting with the box ground wire)? As noted in response to @KMJ, no instructions were included.
    – Carolyn
    Commented Mar 15, 2023 at 22:39
  • @Carolyn The screws connecting the fixture should ground the fixture to that holder/brace. The round ring seems like it fits the attachment for the light, so it seems correct. There are quite a few electrical devices sold online that do not have a UL/ERLT(?)/CSA listing(maybe a fake CE), that are not legal(not in code) to use. Lack of instructions make this seem possible.
    – crip659
    Commented Mar 15, 2023 at 22:52
  • thanks so much!
    – Carolyn
    Commented Mar 16, 2023 at 0:38
  • 1
    @crip659 ETL, but yeah Commented Mar 18, 2023 at 12:46

Yes that looks correct assuming you also use metal screws to screw the canopy to the cross bar and connect the other end of the light's ground wire to the loose end of the ground wire in the box using a wire nut.

The ground screw terminal in the plastic box is meant to help but it is covered in paint and fairly useless. Maybe the metal cross bar is meant to be grounded by contact with that part? But forget that, use a wire nut.

The end effect is the cross bar and canopy, all the metal parts, will be connected to ground.


In most older homes none of the fixtures are grounded and you do not need to ground this one either provided that is not going to be inspected for Code Compliance

  • 1
    The photo clearly shows that this fixture does have a supply line with a ground wire. Commented Mar 18, 2023 at 14:17
  • As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.
    – Community Bot
    Commented Mar 18, 2023 at 15:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.