Grounded Fixture in an Ungrounded Electrical Box

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Old 12-20-18, 12:23 PM
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Grounded Fixture in an Ungrounded Electrical Box

I hope you can help me correctly install a ceiling light fixture with a ground wire into what APPEARS to be an ungrounded electrical box. I have googled this problem and all the solutions seem to contradict one another.

I am in California and this is a commercial rental and the building was probably built before the 80s.

The fixture I want to install has three wires coming off; black, white, and green.

I have attached photos of the electrical box and the wiring that was USED BEFORE. I don't see any "standard" ground screw in the box. As you can see from the photos, the previous fixture had the ground attached to a mounting screw on the side of the electrical box.

So I have to ask:

1) Is there some ground lug that I just am not seeing in this electrical box?

2) Assuming that there is no ground, can I still mount an electrical fixture that has a ground wire on the fixture?

3) What is the best thing to do with the ground wire? Attach it to a mounting screw as before? (Seems dangerous). Cap it off?

Also, if I remember correctly, the electrical outlets at this place have three-prong sockets. If the electrical boxes are UN-grounded, then shouldn't they have GFCI Outlets on them???

And just for safety's sake, does it make sense to replace ALL the outlets with just GFCI outlets.
 
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Old 12-20-18, 12:34 PM
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In a commercial building, ground is usually provided by metal conduit or metallic cable. Is this building wired with either of these? If so, the box itself is the equipment ground conductor.

To ground the fixture, drill and tap a 10-32 screw into the back of the box and install a box ground screw. Sometimes one of the predrilled holes in the back is already the right size. You can pick these up in the electrical aisle of any hardware store.

If the branch circuits are truly ungrounded, then yes you should install GFCI protection for safety.

 
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Old 12-20-18, 12:37 PM
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And just for safety's sake, does it make sense to replace ALL the outlets with just GFCI outlets
You only need one GFCI outlet on each circuit. The load side of the GFCI will provide protection for all the other outlets on the circuit. Only complication is you'll need to find the first outlet in each particular circuit.
 
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Old 12-20-18, 12:39 PM
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Hi there, Ben and thanks for the note.

I honestly don't know if the ground is provided by metal conduit or a separate cable. Is there any way I can tell?

Can I look at an electrical wall outlet and determine if it is grounded or ungrounded? it would be easier for me to take a clear picture of an electrical wall outlet than it is to take a clear picture of the ceiling electrical box.

Or could I take a photo of the circuit breaker? Would that help?

I am pretty worried about this.
 
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Old 12-20-18, 12:42 PM
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Thank you, Mossman.

When you say, "you'll need to find the first outlet in each particular circuit" how would I do that?

Also, do you have any thoughts on what Ben said in regards to this particular electrical box being grounded (via conduit or a wire) or being an ungrounded box?
 
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Old 12-20-18, 12:43 PM
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Can you see into the unfinished wall or ceiling/plenum areas or around the electrical panels? See if there are metal conduits or spiral metal cables running though those spaces as opposed to plastic or cloth covered cables.

Another test is to run a three-prong extension cord from the unknown receptacle back to the area of the electrical panel. Use your multimeter on ohms/continuity setting to measure between the metal face of the electrical panel and the round prong of the cord. This determines if the main panel ground electrically connects to the ground prong of the receptacle.
 
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Old 12-20-18, 12:54 PM
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I will look around but I don't think there is any exposed area where I could see the exterior of this box (or the panel) or of any other electrical box. I might have to cut a whole in the wall somewhere and patch it

Another test is to run a three-prong extension cord from the unknown receptacle back to the area of the electrical panel. Use your multimeter on ohms/continuity setting to measure between the metal face of the electrical panel and the round prong of the cord. This determines if the main panel ground electrically connects to the ground prong of the receptacle.
This sounds pretty scary...

If I understand what you are saying:

- Plug a three-prong extension cable into a wall outlet
- bring the cable close to the electrical panel
- use one lead of the multimeter on the round plug of the extension cable, and the other lead should touch the face of the electrical panel.

Do I have that correct? What are the chances of me starting a fire / electrocuting myself by doing that?
 
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Old 12-20-18, 01:00 PM
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Yes that's right. The procedure should not be dangerous at all as long as you only stick the lead in the round grounding hole. The multimeter should read continuity or close or zero ohms on the resistance scale if the grounding system is properly installed.
 
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