Take the 2-minute tour ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

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
share|improve this question
1  
What is the nature of the cable going to the box? Is the exterior sheath metal or plastic? –  The Evil Greebo Nov 20 '12 at 1:41
    
I have never heard of any colors other than green and yellow being used for ground wires. –  Brad Gilbert Nov 20 '12 at 6:28
1  
A picture of all the wires in the box might help us explain what's going on. How many wires are in the box; not counting the wires attached directly to the fixture, and what colors are they? –  Tester101 Nov 20 '12 at 12:09
2  
No. It is not grounded if there is not an equipment ground conductor attached to the metal junction box. –  Tester101 Nov 20 '12 at 13:03
    
Are the black and red both hot when the switch is on, and not hot when the switch is off? –  Tester101 Nov 20 '12 at 17:17

4 Answers 4

up vote 6 down vote accepted

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.

enter image description here

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.

share|improve this answer
    
You can also perform a similar test by checking for 120V between hot and the box, although this carries exactly the same disclaimer as you have for "Check Continuity to the Grounded Conductor". This method is fairly easy because you are completely working in the box, but also does require working with live, hot voltage, and is very dangerous if you don't know what you are doing. Hot wires must be treated with great respect. –  gregmac Jul 8 '13 at 20:03
1  
@gregmac No. If the box is not grounded it might read 120V to the ungrounded (hot) conductor when you test, but nothing guarantees it will always be that way. The voltage potential between the not grounded box and the ungrounded (hot) conductor, could be anything at any time. Measuring 120V potential between the ungrounded (hot) conductor and another object, does not, guarantee the object is grounded. –  Tester101 Jul 8 '13 at 20:14
1  
Ah, good point. If it's not 120V (or whatever voltage hot is) it does guarantee that it's NOT grounded, but nothing more. –  gregmac Jul 8 '13 at 20:50

If you do not have a ground wire installed with the other wires do not hook up the ground wire without knowing how the wires were carried to the box. If the house is wired with flexible metallic tubing (flex) your grounding the fixture can create an extremely hazardous situation. Older homes are sometimes wired this way. I have run into this situation a lot in my field work. Untrained electricians think any ground is a safe ground. This is not true. Grounding was required starting in 1962.

share|improve this answer

Since this is a new building, it's almost certain that the wires are inside a metal raceway such as EMT conduit, which is allowed to serve as the ground in lieu of a separate conductor. The other possibility is it was wired wrong, but this isn't especially likely in a new building. Wiring without a ground fault path would be a huge mistake and doesn't seem especially likely for a professional installation.

You can verify that the enclosure is properly grounded very easily by testing a load across a hot lead to the metal enclosure. If it's grounded, you'll get a current, if not, you won't. You will need an electrical tester with leads to do this (the current tester you're using isn't sufficient). But honestly this seems almost unnecessary, it is very unlikely that the box wouldn't be grounded based on what you are describing.

So, grounding your fixture to the enclosure is most likely both correct and safe, but if you are not comfortable, then just test the enclosure for proper grounding to be sure.

The two hot wires are a typical configuration for a ceiling fan where the light and fan are controlled by two separate switches. You don't provide much information about the switch box, though, so maybe you haven't opened it. If there's only one switch, then it's likely that this is just a pass-through hot (e.g. always on) intended to chain to another fixture or switch, that was just never used. It is possible it's switched from a separate location, but if the two leads enter the box from the same hole, this is very unlikely - it's probably just a hot.

share|improve this answer

Without pictures or more information I am going to venture a guess at your situation.

Since the box is metal and there doesn't appear to be a ground wire fed to the box, I imagine it is an older style home where the metal boxes were grounded to the metal conduit behind it. An easy way to test this is to take a voltimeter or comparable AC voltage tester and test the hot wire to the box itself. If you are showing 110+ volts then the box itself is in fact already grounded. In this case you can simply run the green wire from the fan directly to a metal backing screw or grounding screw on the box itself and this will be sufficient to ground the fan.

I believe this is the case because when you flipped the switch and shorted the circuit, you had the red wire go directly to ground which meant that there is a good ground on the box already. If there wasn't a good ground on that fan, then when you flipped the switch, the metal body of the fan itself would have been hot and the breaker would have never tripped. You could have electrocuted yourself by touching it.

(removed)

EDIT: The more I think about this the more I am worried about the fact that flipping the switch would cause it to short. At first I was thinking this box was wired for a three way switch but who would put a three way switch into the ceiling?

It may be also that the red wire is a second hot wire for feeding appliances that require 240v rather than 120v. Test both wires when the flip is switched on to see if they are both hot. Also test to see if they are live when the switch is flipped off. If they both turn off when you flip the switch then it is wired for 240v and does not have a ground supply wire. If this is the case and your fan only requires 120v then you do not need the red wire, so you can cap and tape it.

DISCLAIMER I am only guessing based on your account and what you are seeing. Without pictures then nothing I say should be considered gospel truth.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

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