Mains Wiring Flipped? - Page 1
Forum section: electronics / beginners

author: rexxar
author_rank: Frequent Contributor
timestamp: May 14, 2013, 04:51:17 am
content: Hey all, I got a new UPS today, and when I plugged it in, the site wiring fault light was on. Naturally, I went to check what was going on. Not having one of those little testers, I just used my multimeter and measured voltages at the outlet. It seemed like the ground wasn't connected because I got 0 volts from hot to ground, and 0 from neutral to ground. Turns out that was just that one outlet, because when I checked another outlet on the same circuit, I got 120 volts from 'neutral' to ground. Hmm. I pulled out the fuse (yes, I have a real fusebox), and pulled the faceplate off the outlet, after checking a half dozen times to makesureit was off (it doesn't take getting zapped too many times before you start being really careful...).What I saw was not pretty. The wiring was two conductors wrapped in awful cloth that disintegrated when I touched it. There certainly was no ground wire, so they must be relying on the 'armor' on the cable. Now, looking at the fuse box, and another outlet, I'm sure that they have the color coding right, black is indeed hot. So, I fixed the outlets in my computer room, and put the fuse back in. I have no idea what happened, because measuring hot to ground gives me 37V and neutral to ground is 26? I looked at some other outlets in the apartment, and it seems that every. single. one. is wrong. I figured there must be some problem because only these two outlets are 'correct', so I switched them back. But it's still doing it.I have no idea what the hell I've done. Anyone have any ideas?

author: GeoffS
author_rank: Unknown
timestamp: May 14, 2013, 04:55:53 am
content: If it's a new UPS, why did you open it and not just take it back to where you bought it?

author: pickle9000
author_rank: Super Contributor
timestamp: May 14, 2013, 05:27:32 am
content: I'd call an electrician, who knows how old the wiring in your building is and how things are screwed. If I had to guess I'd say you have some melted wires in the wall.

author: eKretz
author_rank: Frequent Contributor
timestamp: May 14, 2013, 05:30:32 am
content: Uhh, either I'm missing something or the problem is with the mains wiring, not the UPS, so there'd be no reason to return it. To the OP, perhaps you're getting low voltage to ground due to poor grounding. The cable armor could be corroded or falling apart or cracked in places and only conducting in a haphazard fashion. Sounds like a firetrap.

author: pickle9000
author_rank: Super Contributor
timestamp: May 14, 2013, 05:37:15 am
content: That was my take as well, the mains wiring has a fault.

author: rexxar
author_rank: Frequent Contributor
timestamp: May 14, 2013, 05:53:46 am
content: Quote from: pickle9000 on May 14, 2013, 05:27:32 amMy landlord said the building is 100 years old, but he's probably exaggerating a bit. I think it's somewhere around 80 or so.Quote from: eKretz on May 14, 2013, 05:30:32 amMy concern was that I'm getting voltage to ground from both hot and neutral. I think you're right, though. I tested continuity between the metal outlet boxes in that room to make sure that there was some sort of ground there. It would work sometimes, and sometimes not, so maybe there is a break in the armor. I would have thought, though that if the hot line had contacted the ground, it'd just blow the fuse? At least that's what's happened every other time I've seen it.Calling an electrician is not going to be fun, but it's better than the fire department, I guess.At least the landlord should be paying for it.

author: rexxar
author_rank: Frequent Contributor
timestamp: May 14, 2013, 06:27:44 am
content: You know, it just now occurs to me that while I was doing the first outlet, I left a surge protector plugged in that was connected to the coax for our modem.Sure enough, there is continuity between the neutral side of the mains and the shield on that coax, but not between the shield and the ground on the outlet. Oddly, there is a few volts between the ground on the outlet and the shield on the coax.I guess that means the outlets aren't connected to mains earth at all, huh?

author: eKretz
author_rank: Frequent Contributor
timestamp: May 15, 2013, 07:31:03 am
content: Perhaps not. That isn't uncommon in older houses like that. They get "grandfathered" so they don't have to be up to code except for new work. Many many people have switched to 3-prong outlets on ungrounded mains systems just so they can plug things in without a converter. My own house was built in 1950 and it has several ungrounded outlets (3-prong). I have been fixing that as I can. The bathroom and kitchen outlets are all rewired with ground now and of course GFI outlets where needed.

author: SeanB
author_rank: Super Contributor
timestamp: May 15, 2013, 11:41:35 am
content: Grandfathered until sold, wherupon you have to rewire, and go to current code partially. Minimum spec here is to have all outlets grounded, and to have earth leakage trip on all standard socket outlets. Often to get the insulation resistance high enough during the test they replace the wiring ( have seen some cheap jobs where only the live has been changed, leaving the old cotton covered neutral in place) and replace the sockets to have ones with switches ( mandatory) and install circuit breakers. If it passes insulation test and needs nothing else the fuses will be left in place and EL installed, as the installation is deemed to be as to spec when installed, and only needs the modern requirement of EL. Can be pretty expensive to pull all the old wire out, pull in new, place a new breaker box ( which has to be visible and cannot be in a cupboard, so very expensive if you have to move it a few metres as well) and replace all outlets, switches and light fittings as well. Easily adds $3000 to the purchase price.

author: eKretz
author_rank: Frequent Contributor
timestamp: May 16, 2013, 05:57:12 am
content: Nope, not everywhere. For instance, my house was built in 1950 and bought by me in 2001. I'm in the U.S. They may have changed code since 2001, but they didn't have to upgrade it at that time.

author: Fuse_Burner
author_rank: Contributor
timestamp: May 16, 2013, 07:10:38 am
content: I had a situation here awhile back where my detached garage blew everything up. Upon inspection, I had 240v on one leg instead of 120v on each of two legs. I finally isolated it to a corroded ground. The aluminum mesh in the supply line turned to white powder. Don't underestimate the need for ground

author: eKretz
author_rank: Frequent Contributor
timestamp: May 16, 2013, 08:02:49 am
content: Oh yeah, I had that situation when I moved in too. They had 2 legs of 120 out to the garage and it was in rough shape. It looked like some kind of cloth insulation on the wire. That was the first thing I fixed...ran a 60A sub-panel out in the garage and ran brand new 4-wires of 6AWG out from the basement panel.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 16, 2013, 09:34:07 pm
content: My brother sold his ~80 year old house in the US just a couple of years ago. Most of the house had 3-prong outlets with no ground connection. Since that has never been allowed by code, he had to replace them with two prong outlets, but he didn't have to rewire. He just left all the 3-prong outlets in a bucket so the new owner could switch them back...

author: commongrounder
author_rank: Frequent Contributor
timestamp: May 16, 2013, 09:41:33 pm
content: Your multimeter has a high input impedance and is reading "phantom" AC voltages. Some meters have a "low-impedance" mode to load down the circuit and give a true reading. You most certainly have a bad neutral and or ground. Very hazardous! The landlord must get an electrician in there to inspect the wiring and establish a properly grounded branch circuit to your UPS location (at the very least!).By the way, we had water infiltrate the meter panel on the side of our house. The aluminum neutral conductor of the service entrance cable was touching the steel meter box (can you say dielectric?). By the time I had the power shut off at the street there was only one strand of the conductor left un"powdered" and we had wild voltage swings going on in the house. Scary!

author: rexxar
author_rank: Frequent Contributor
timestamp: May 25, 2013, 07:49:19 pm
content: Quote from: commongrounder on May 16, 2013, 09:41:33 pmThat's interesting. My POS multimeter doesn't have a low-impedance mode, can I make something up to load down the circuit and get a better reading?I'm having trouble finding any specific information on electrical code here in KY. Are landlords required to update wiring after so long or? If it's going to be very expensive, it's going to be a hassle to get the landlord to pay for it, so I'd like to be able to point him to a section in the NEC or the like. I know there's a lot of 'grandfathering' of electrical code, but I'd think there would be a clause somewhere for 100-year old buildings that are being rented out to multiple tenants.Maybe I should just hire an electrician to come tell me exactly how dangerous the current setup is.

author: Alana
author_rank: Frequent Contributor
timestamp: May 25, 2013, 09:31:40 pm
content: Old and very useful tool for electrician's job is a incandescent light bulb in a socket with 2 wires and old analogue meter. For US I'd recommend 2x 120V bulbs in series - you never know when you find 240V instead of 120V.

author: C
author_rank: Super Contributor
timestamp: May 26, 2013, 01:25:09 am
content: I am not sure of the time frames, but I think it was in the 50-60;s. This is before the two wire with ground wire became standard and also before PVC.The wire I am thinking of there were two versions.The actual coper wire was covered with something like rubber then may have a spiral wound paper layer. This was covered with a woven thread covering and sometimes dipped in something.One version took two wires and covered then with a spiral wound paper layer then This was covered with a woven thread covering and sometimes dipped in something. I have seen black, gray and off white colors of this version. Probably safe if left alone, DO Not move or bend!The second version was two wires covered with a spiral wound paper layer thena spiral wound steel layer so you could bend it. Later versions of this had some bonding between each steel spiral. And for both versions steel boxes were the norm.Problems:When you cut that steel spiral to expose the wires it was very easy to nick the wires. There was a sleeve that you slid under the steel to add some protection for the wires from the steel edge that would at times pop out as you were working on the wires in the steel box.Now if you think about it, spiral wound steel, if you do not have good contact between each spiral is an inductor with high resistance and even if you have good bonding it is a high resistance.Now I do not know if it was in the NEC standard back then that you could use that steel spiral as a ground for the ground wire of a two wire + ground wire standard. I have heard of people doing so and I have heard ofhouses that burnedwhen that steel spiral got hot.Of the old wire I have seen of these types, some with that rubber like stuff ether got hard and cracked if flexed or would crumble. The moisture in the air would cause that steel to rust or corrode.So just by putting in a Three prong outlet in that steel box if it is connected by the spiral wound steel sheath and no ground wire, you increase the chance of a fire. Note, the mounting brackets of a three prong outlet are connected to the ground connection. If a fault happens where the fault current is such that the fuse does not blow you now have a resistance heater in your walls. A simple example would be, a electric 3 wire toaster that fails such that the neutral wire breaks free from the power cord a drops down to contact the medal frame which is ground. You now have a current flow from HOT through the toasters heater element to Ground and the spiral wound steel sheath, and the fuse or circuit breaker in the hot lead thinks every thing is fine.A surge protected power strip or UPS when connected to a two wire system may defeat some or all of the surge protection that the surge protected power strip or UPS provides, This is the reason for the site wiring fault light.Only safe answer, hire an electrician to check, you just moving the wires behind that outlet could cause a problem.And you may not like the electrician's answer to bring it back to code. With grandfathering I would guess no three prong outlets connected to that type of wire.In the past, some shops I worked in had a picture of the results of a very very lucky electrician, someone who should know what they are doing. The picture was of a gold wedding band welded to a steel wrench.Be safe CallC

author: SeanB
author_rank: Super Contributor
timestamp: May 26, 2013, 06:00:51 am
content: Call the electrician in, then give the report to the landlord and ask him to please fix the faults ( you pay for the report yourself unfortunately, you might get the money back but regard it as a sunken cost for your own safety) or look at moving and give the unsafe report to the local fire chief as you leave if the landlord does not want to fix the faults.