My boyfriend and I just moved into a house together* …said house was built in 1952. The electrical stuff was updated at some point, and there are areas of the house, such as the kitchen and the finished basement, which have grounded outlets. Other rooms, such as the bedroom we want to use as an office, and the living room, have regular 2 prong outlets. We want to know if the outlet box inside is grounded or not (we figure they may have done this when they updated the house’s electrical stuff, but not bothered changing the actual outlet receptacles to
the 3 prong kind). How can we check? We have a volt/ohm meter if that’s of any use.
Most hardware stores carry a device for this purpose. I costs less than $5. You plug it into a socket and will display lights telling if it is grounded. I am not sure two prong plugs can be grounded. The testers I have seen all have three prongs.
ETA: I was just trying to be helpfull didn’t see CM’s much more helpfull and informative post when I hit submit.
Use the ohm meter touching a prong to the neutral and one to the box. A low resistance and it’s grounded. It doesn’t mean that they ran a second ground wire, they may have wired the box to the neutral wire. I don’t think somebody would run a ground wire to the box and then not install a grounded outlet.
In case they have the wires reversed, you had better be sure that you turn off the breakers before checking with the ohm meter. You don’t want 120 volts applied to the ohm meter.
They can’t, but the box itself may have a ground line going into it, which is what they’re looking for. (This is why 2-3 prong adaptors often have a little lead that you’re supposed to attach to the faceplate screw, which might be grounded if you’re lucky.)
In case they have the wires reversed, you had better be sure that you turn off the breakers before checking with the ohm meter. You don’t want 120 volts applied to the ohm meter.
**Crafter Man’s ** method is superior to using an ohmmeter. Just one thing, it might be that the romex cable to the two prong outlets wasn’t upgraded when the kitchen and basement were redone. If that’s the case the old cable will not have the safety ground wire in it.
This, by the way, is a problem and needs to be fixed (ditto for the other case where Crafter_Man said the wires are reversed). If you end up in this situation, you need to determine where the wires got reversed. If you open up the outlet and black is where white should go and vice versa (a surprisingly common problem) then it’s easy to fix. But, if you open up the box and the wires are in the right place on the outlet, then someone has the wiring really screwed up and you might want to contact an electrician at that point. Don’t just flip the wires around if you’ve got a hot neutral.
Older wiring like this was often pre-romex, installed in flexible metal conduit. That conduit itself was generally properly grounded, and can legally function as the ground path.
If that’s the case, it’s a real simple fix for the OP: replace the outlets with 3-prong grounded ones, and connect the ground terminal to the box itself. (Indeed, sometimes the outlet mounting screws themselves are rated to serve as a connection!)
Heehee!! That made me giggle far more than it should have
Thanks everyone, for your answers. Dan tried it and he thinks that at least in the living room, the outlets are not grounded. Haven’t tested elsewhere yet.
It does work if the breaker is off. Throwing the breaker breaks the circuit path so between hot and ground is infinite resistance. A low resistance is present if the neutral and box are connected. Either the box is wired to the neutral wire along with the socket for a short path, or in the neutral wire connects up with the ground in the breaker box via a second path in the breaker box. The short route will be almost no resistance, and the longer route will have a slightly higher resistance. You can make a judgment of weather you have two separate paths back to the circuit breaker box or only a connection between the box and neutral at the box.
There’s an advantage and disadvantage to using the ohmmeter approach:
Possible Advantage
Properly done, using an ohmmeter may give you an idea of the *integrity * of the ground circuit. The lower the resistance, the better. If the resistance is abnormally high (e.g. 4 ohms), it indicates there’s a poor connection somewhere. However, in order to do this measurement, you need a high precision digital ohmmeter. In addition, you need to carefully zero it or use a 4-wire resistance measurement. If you don’t carefully zero your meter or use a 4-wire resistance measurement, then there’s no real advantage to using an ohmmeter.
Disadvantage
You run the risk of frying your ohmmeter. Even if the breaker for the outlet is tripped, there may be “shared neutrals,” which means there might be a volt or two on the neutral relative to ground. This voltage could screw up the reading on the ohmmeter.
Unless the house is completely dead, I wouldn’t use an ohmmeter.
If you have a lot of them to do- consider a Circuit Analyzer Product Description
Tests for open grounds, open hots, open neutrals and reversed polarity. Wrap-around indicator lights. 110-125V AC. UL listed.
7 bucks or so. Any decent hardware store should have one.
I was just answering the additional comments from later. I didn’t intend for Opalcat to get into analysing by resistance beyond an open or closed circuit. There are multiple ways to check and I wouldn’t have posted had the first response been there already when I read the thread.
Several methods of grounding the boxes were used in the 1950s. 2 wire type NM (nonmetallic cable), a.k.a. Romex supplied hot and neutral to the device, and a separate bare traveling ground started at the panelboard, and daisy chained to all device boxes. Not a good plan, as a break removes ground from the remainder. Another method was what t-bonham referred to, that being type AC (armored cable), a.k.a. BX. The grounding conductor is wound back around the corrugation on the exterior, and is attached to the device box with an approved clamp. DIYers often incorrectly terminate this type of cable, as they don’t know better. Unfortunately, the quality of ground is only as good as the poorest connection. Lastly, there was the early 3 wire type NM which was terminated by winding the grounding conductor around one of the device box clamp screws. This was the best of the three, but still is dependent on the device mounting strap being tightly secured to the box, as well as the mounting strap being listed for use as grounding path. As such, the ground quality remains dubious.
If you’re looking for good, low-impedence grounding to supply electronic equipment, contacting an electrician is advisable.
