I want to install new z-wave light switches that require a ground, but it appears that none of the electrical boxes in my house have ground wires and the previous light switches didn't use a ground.
Is it legal to have no ground wires? Im in Chicago and my condo was built in 2001, so it's not super old.
Can I simply connect a wire to the screw on the metal box for ground? how do I know if the box is grounded?
Congratulations, you have EMT conduit or better. This is the good stuff, much of the "pipes" you see in commercial and industrial buildings are this. Look at the ceiling at CostCo.
Your box looks exactly like it's supposed to. All my boxes look like that. The metal conduit serves as the ground wire.
How do you attach a device ground? Look in the back of the junction box. There are several holes, but one of them is different. It is tapped for a 10-32 screw. Often, it sits on a little "dimple" to give the screw threads somewhere to go.
Any short 10-32 screw will do, but for a professional flair, they make green screws for the purpose, and even will sell them with pigtails attached. Do not use sheet-metal screws.
However, this may not be necessary. The device has metal tabs (ears) where you screw it into the box. Pay close attention - if the ears "bottom out" on the metal of the box, you do not need that ground wire. If they bottom-out against drywall, you need a ground.
Unrelated, one more tip on the device-mounting screws. Some are shorter. Look behind the lower right mounting screw on your box. See where a pipe is coming in? That screw needs to be shorter, or it'll hit the pipe. (the screw will suddenly get stiff to turn; stop or you can strip out the threads on the junction box, a painful repair even when it's not in drywall.) The old screws may be captive on the old device; they are held on by a square of cardboard or plastic, easy to move. Or you can buy short ones (1/2") at the hardware store, or cut them to length with the screw shear on the a multi-strip tool (that's what it's for).
Chicago is an oddity Code-wise in that they require the use of metal conduit for wiring instead of allowing nonmetallic-sheathed cables. Note the threaded entrance and locknut in the bottom right, along with the lack of any ground wires in the box -- that's a dead giveaway that this was done in metal conduit.
Since the box is grounded through the conduit (which is as good a ground conductor as any), you don't even have to terminate the ground wire to the box as long as the Z-wave switch has a metal yoke that contacts the box, although you can get a grounding screw (any 10-32 machine screw will do in a pinch), screw it into the back of the box (there is a hole there tapped for a 10-32 screw just for that job), and terminate the Z-wave switch's ground wire to that if you wish. NEC 404.9(B) point 1 allows the mounting-yoke of the switch to be part of the ground-fault current path:
(B) Grounding. Snap switches, including dimmer and similar control switches, shall be connected to an equipment grounding conductor and shall provide a means to connect metal faceplates to the equipment grounding conductor, whether or not a metal faceplate is installed. Snap switches shall be considered to be part of an effective ground-fault current path if either of the following conditions is met:
(1) The switch is mounted with metal screws to a metal box or metal cover that is connected to an equipment grounding conductor or to a nonmetallic box with integral means for connecting to an equipment grounding conductor.
That looks like wire in conduit feeding that box, however I cannot tell the type of conduit from the picture. Some types of conduit are effective grounding paths. If the condo was built in 2001, in order to pass inspections, all boxes would have needed to have been grounded.
Assuming you are the original owner and no friends, relatives, or handyman types have done uninspected electrical work to the property, I would say it is a safe assumption that the box is correctly grounded.
However, if you are not the original owner or if there is potential for some uninspected electrical work, all bets are off without tracing the circuit ground path all the way back to the panel through your walls (which would mean opening the walls to find out). However, that is a bit extreme and likely unnecessary. As a quick sanity check, you could measure the voltage difference between the box and the neutral (white) wire that feeds from the panel--make sure you have turned off all breakers feeding this connection first (if you do not know or do not feel comfortable doing this safely, please contact an electrician for further investigation). The voltage difference should be on the order of a couple of volts or less if there is an effective grounding path. Note: This is only a sanity check and you cannot know the true ground path continuity without more drastic measures because there are ways for dirty-rotten prior homeowners to unsafely fake the appearance of a correctly grounded connection that cannot be easily detected with tools priced for a homeowner's use.
I may missed sometbing. I would connect a regular 3-prong receptical, with hot and neutral, and ground pigtail with 2 green screws to the metal box. There are testers $10-$20 which can tell you if erything is ok, or what is wrong. Like "no ground" . you may even see a piece of emt pipe, but with such message you can assume it is not continuous all the way. Kitamer
