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.
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.
- Set your multimeter to the continuity setting or the lowest
resistance setting.
- Place one lead on the grounding bus bar in the load center.
- 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.
- Set your multimeter to the continuity setting or the lowest
resistance setting.
- Place one lead on the known good ground.
- 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.
- Set your multimeter to the continuity setting or the lowest
resistance setting.
- Place one lead on the grounded conductor (neutral).
- 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.
Best Answer
Your description of red, black and conduit indicates that you do not have neutral but just ground via conduit. That is NOT a good thing. A little background:
Ovens, cooktops, etc. typically need 240V for heating elements but 120V for lights and controls. In order to get 120V, you need a neutral wire (normally white).
In the old days, there was a neutral but often no ground. So ground would piggyback on neutral. That was OK from the perspective of normal usage but a bit problematic if things go wrong in certain ways. So now (actually for many years), a 4-wire connection - hot, hot, neutral, ground (ground can be via metal conduit though, doesn't have to be an actual wire) is required.
But often stoves (and dryers) are still hooked up to a 3-wire connection. A 3-wire connection wouldn't be so bad if it were "ground piggybacked on neutral". But you have the opposite - neutral piggybacked on ground. That is not a good thing.
The solution is to install a proper cable. It must be the right size for the breaker & device (that would probably be 8 AWG) and include two hots, neutral and ground. Alternatively, if you are running individual wires in metal conduit with the conduit acting as ground then you can use three individual wires, two hots and neutral.
Updating based on pictures:
You have a 4-wire connection on the oven. However, there is a "copper bridge" to connect neutral (white) and ground (green screw). You could do that in the old days. But current code says you should:
Run a new white wire through the conduit. Remove the copper bridge. Connect black, red, white, green to matching places on the oven. Then see if there are any remaining problems. But the current installation (no neutral) is WRONG.
I found the official installation instructions (PDF). Follow the 4-wire instructions in step 6, not 3-wire step 5.
What is a bit strange, which I don't quite understand, is that the 4-wire instructions for a Power Cord specifically say "Cut and discard the ground strap." But the 4-wire instructions for Conduit do NOT say to do that.