UPS warning light says "building wiring fault"

[aurmer]

I noticed this warning LED on my backup battery, and looked into it. I ended up testing the voltages between the hot wire, neutral, and ground. Can I get help interpreting the results? I was surprised because I expected nearly 0V from N=>GND and a full 120V hot=>GND, but I got neither.

Should I tell my landlord that we need an electrician?

[Monkeh]

Should I tell my landlord that we need an electrician?

Yes. You have a bad ground.

[aurmer]

Thank you, I am having a bit of difficulty figuring out how this happens. Can anyone shed some light or share a resource for me to read about it? What measurements should I expect for each of the three?

[Monkeh]

Thank you, I am having a bit of difficulty figuring out how this happens. Can anyone shed some light or share a resource for me to read about it? What measurements should I expect for each of the three?

Someone didn't connect it, the wire broke, something gnawed through it..

You should see ~120V L-N, ~120V L-E, and <10V N-E (should be much less, but it can get to a notable value).

[amspire]

If the unit has metal pipes for plumbing, take a wire from a pipe and measure the voltage to the Active. If you get 120V, then you know definitely that the Neutral is properly grounded nearby, and that your ground wire is not grounded.

Also try other sockets - it might be just this socket.

[Ian.M]

Old buildings (pre 1968) in the USA can have un-earthed wiring 'grandfathered' in and it is even code compliant to replace a 2 pin socket with no ground to the wall box with a three pin one. However *EVERY* such socket *MUST* be marked "NO EQUIPMENT GROUND"


http://ecmweb.com/code-basics/article-406-receptacles

As such, your best course of action is to stop using that socket and go to the hardware store and get a neon socket tester that will indicate whether or not a socket has a ground, and also detect miswiring.  If only a few sockets are missing their ground its probably a real wiring problem that your landlord will be obliged to get fixed, but if a lot of the sockets are ungrounded, and its an old building so that the circuit was originally legal to install without ground then its possible that all you may get is the code required warning label affixed to each socket, and if you actually require a grounded circuit it will be at your expense

[Seekonk]

You never said if there are actually 3 wires going to the socket. Some older wiring used BX metal sheathed cable.  That sheath acted as the ground.  Often this will pull out of some connector box and you will loose the ground.  Your chance of having landlord fix it is about nil.  As said before check all the other outlets to see if they are grounded.  Run a wire to some water pipe.

[Nusa]

Old buildings (pre 1968) in the USA can have un-earthed wiring 'grandfathered' in and it is even code compliant to replace a 2 pin socket with no ground to the wall box with a three pin one. However *EVERY* such socket *MUST* be marked "NO EQUIPMENT GROUND"


http://ecmweb.com/code-basics/article-406-receptacles

As such, your best course of action is to stop using that socket and go to the hardware store and get a neon socket tester that will indicate whether or not a socket has a ground, and also detect miswiring.  If only a few sockets are missing their ground its probably a real wiring problem that your landlord will be obliged to get fixed, but if a lot of the sockets are ungrounded, and its an old building so that the circuit was originally legal to install without ground then its possible that all you may get is the code required warning label affixed to each socket, and if you actually require a grounded circuit it will be at your expense

You focused on the labeling requirement and skipped over the far more important GFCI requirement! Even though your picture and link explain it correctly. Without the GFCI protection, it's only LEGAL to replace a worn-out 2-prong outlet with another 2-prong outlet on existing installations.

That said, it's common to find ungrounded 3-prong outlets installed in older 2-wire systems without any labeling, usually by someone who lived in the place at the time and were tired of dealing with 3-prong adapters. Doesn't make it code compliant, but it is a cheap practical solution.

So to the original poster, yes you may have an issue with the landlord if you want to raise it, and depending on whether its one outlet or all of them.

The landlord can say no, at which point you can contact the local authority with the power to inspect and force code compliance. This all takes time. One possible outcome is for the landlord to replace all the three-prong outlets in your place with two-prong ones, which brings it back into compliance with the original code it was built under. Which probably won't make you happy...