Electrical – safely ground a light fixture if the ceiling box has two hot and one neutral wire (no ground wire)

electricalgroundinglight-fixturelighting

Checking for dupes, I saw this question, but the situation appears different as my box is metal, among other things.

I'm fairly new to electrical projects, so bear with me. I recently installed a new light fixture in a ceiling connection in a new building.

The fixture has black, white, and exposed ground wires, and came with instructions to:

  • Connect the black wire to the black wire
  • Connect the white wire to the white wire
  • Connect the ground wire to the green screw, and then to the ground wire.

So I checked that the power was live on a meter, then re-metered after cutting it to ensure it was safe, and proceeded to connect the wires as described, using the white, black, and brown wires in the ceiling.

When put the power back on, the light turned on. But when I hit the light switch, I got a fireworks display and tripped the circuit. After some research, it would seem that the "brown" wire that I assumed was the ground (by process of elimination) was more likely meant to be red (damn you, burnt sienna!), and was in fact a second "hot" wire, probably for a ceiling fan, or maybe a 240V device. I'd connected the second "hot" wire to the exposed ground on the lamp, which was… not awesome.

So, I reconnected the black and white wires, and since there's no ground in the box, just connected the lamp ground to the green screw on the crossbar that's now screwed to the metal box.

I get that my worst initial mistake was not testing the voltage on each individual wire before connecting the fixture. And I get to apply that next time, since I'm not dead.

But here's my question: Is the lamp still grounded, given that it's screwed to a bar in a metal box, or does the lack of an actual ground wire in the box mean I can't ground it?

If I can't ground it, how concerned should I be when changing the bulb?

EDIT: Some clarification points –

  • The building is very new. I think it was completed in 2008
  • The box in the ceiling (more like a cylinder, really) is metal, but I don't know if it's connected to some kind of ground wire behind it, as it's attached to the ceiling and I didn't try to remove it.
  • There were three insulated wires in the cylinder: White, black, and brownish red
  • The black and red both were "hot" on a meter; the white was not

Best Answer

Sometimes when ceiling boxes are roughed in, they use x/3 with ground cable so that they can supply 1 switched hot, 1 neural, 1 hot/switched hot, and 1 ground to the ceiling box.

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This allows a ceiling fan to be installed in such a way that the fan can be controlled either by a separate switch, or using only the attached pull chain. In this situation the red wire in the cable is usually disconnected and capped at both ends, and is only intended to be connected as needed.

You may be able to verify this by opening the switch box, and verifying the wiring at the switch. If this is the case and the extra hot wire is not needed, it should be disconnected and capped at both ends. Once that's complete, you can move on to determining if you have a proper grounding conductor.

Grounding Conductor

If the building was renovated/built in 2008, it's not likely the circuit does not include an ground conductor. However, there are multiple ways to satisfy the grounding conductor requirement according to NEC 2008 250.118.

  • A copper, aluminium, or copper-clad aluminum conductor.
  • Rigid metal conduit.
  • Intermediate metal conduit.
  • Electrical metallic tubing.
  • Listed flexible metal conduit meeting specific conditions.
  • Listed liquidtight flexible metal conduit meeting specific conditions.
  • Flexible metallic tubing meeting specific conditioins.
  • Armor of Type AC cable as provided in 320.108.
  • The copper sheath of mineral-insulated, metal-sheathed cable.
  • Type MC cable where listed and identified for grounding in accordance with specific criteria.
  • Cable trays as permitted in 392.3 and 392.7.
  • Cablebus framework as permitted in 370.3.
  • Other listed electrically continuous metal raceways and listed auxiliary gutters.
  • Surface metal raceways listed for grounding.

Checking for a Grounding Conductor

The most accurate way to verify whether or not there a proper ground connected, would be to check for continuity between the junction box and the grounding electrode system. In most situations this is not an option, so another test must be performed.

Checking Continuity to the Grounding Electrode System

To run this test you'll either have to be within reach of; or be able to run a lead to, the grounding bus in the main service panel.

  1. Set your multimeter to the continuity setting or the lowest resistance setting. enter image description here
  2. Place one lead on the grounding bus bar in the load center.
  3. Place the other lead on the junction box under test.

If the meter beeps or gives a reading close to 0, the box and the load center are electrically connected. This means there is a proper grounding conductor installed. If the meter does not beep or has a reading of infinity, the box and the load center are not electrically connected. You'll have to install an approved grounding conductor throughout this circuit, if you want proper grounding.

Checking Continuity to a Known Good Ground

If you have a known good ground nearby (from another circuit, for example), you can use this ground to test for an equipment ground at the box in question.

  1. Set your multimeter to the continuity setting or the lowest resistance setting. enter image description here
  2. Place one lead on the known good ground.
  3. Place the other lead on the junction box under test.

If the meter beeps or gives a reading close to 0, the box and the known good ground are electrically connected. This means there is a proper grounding conductor installed. If the meter does not beep or has a reading of infinity, the box and the known good ground are not electrically connected. You'll have to install an approved grounding conductor throughout this circuit, if you want proper grounding.

Check Continuity to the Grounded Conductor

If neither of these options are available, the next best option is to check for continuity between the box and the circuits grounded conductor (neutral). These two conductors should be electrically connected (bonded) at the main service panel, so checking continuity between them can (usually) determine if there is an equipment ground.

WARNING: This method relies on the circuit being installed correctly. If the grounded conductor (neutral) is (incorrectly) connected to the grounding conductor anywhere along the circuit, this test may give invalid results.

  1. Set your multimeter to the continuity setting or the lowest resistance setting. enter image description here
  2. Place one lead on the grounded conductor (neutral).
  3. Place the other lead on the junction box under test.

If the meter beeps or gives a reading close to 0, the box and the grounded conductor (neutral) are electrically connected. This means there may be a proper grounding conductor installed. If the meter does not beep or has a reading of infinity, the box and the grounded conductor (neutral) are not electrically connected. You'll have to install an approved grounding conductor throughout this circuit, if you want proper grounding.

NOTE:
All continuity testing should be carried out while the circuit is dead. Shut off power to the circuit at the breaker before working on the circuit, and verify the circuit is off using a non-contact voltage tester.

Electricity is dangerous and can lead to property damage, injury, and death. If you do not feel comfortable working with electricity, please contact a qualified Electrician.

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