Need help with a home electrical wiring problem.
January 1, 2014 6:26 PM   Subscribe

I am attempting to add one electrical outlet to my attic wiring. After installation there is enough power to the outlet to set-off a wire tester but not enough power to run anything plugged into the outlet. If there are any electricians or experienced DIY'ers around who could take a look at the wiring diagrams I made and see if anything is obviously wrong it would be much appreciated. Or, if you know of any forums where I could post the diagrams for help that would be good too.

The current attic wiring has one switch that controls one hanging lightbulb. Everything works properly.
Here is a link to the "before" wiring diagram.

After adding the outlet, the light switch and light bulb continue operate correctly but the outlet does not. There is not enough power to the outlet to run anything plugged into it but it will set off a wire tester. Multiple things have been tested in the outlet. Nothing works. The outlet itself is connected properly. I know how to do that. I double-checked all the connections. They are tight and secure.
Here is a link to the "after" wiring diagram.

I am assuming it is a circuit problem but I cannot see what the problem is. This is a 1920s home with older wiring but definitely not knob-and-tube. Thank you very much for any help you might have.
posted by pixlboi to Home & Garden (15 answers total)
 
If the light bulb works, that suggests the white wire is live and you're using the ground wire as "neutral." You are running that live white wire and the mystery disconnected black wire to your outlet. If they're both live wires, there's no potential difference and the outlet won't work.
posted by Huffy Puffy at 6:46 PM on January 1 [1 favorite]


Well, that's terrifying. It's wrong on several layers:
* The incoming white isn't neutral (unless there's a 3-way switch somewhere? -- if so, under no circumstances can you have an outlet there)
* The lightbulb uses ground for the return path
* You have two different wire colors to that switch (either lazy or wrong, depending on 3-way or not)

Please run new wires to a new breaker for your outlet; you have no idea what other scary things are connected before this light.
posted by flimflam at 6:48 PM on January 1 [6 favorites]


Yeah, the way you did it is wrong. White (neutrals) always connect together except on a switch. The switch should be connected to the black wire coming from the breaker panel, and the other wire from the switch (probably white) should connect to the black wire on the light fixture. The white wire from the light fixture connects to the white wire coming from the breaker panel.

The black from the outlet should connect to the black wire coming from the breaker panel, and the white from the outlet to the white wire coming from the breaker panel.

The copper grounds should get connected to a copper ground coming from the breaker panel - if there is no copper ground from the breaker panel the whole shebang isn't grounded.
posted by BillMcMurdo at 6:48 PM on January 1


On second look the "before" wiring was all screwed up too (the switch ground shouldn't be connected to the light's neutral). I'd be worried about other things nearby and plan to redo more than just this box, as flimflam suggests.
posted by BillMcMurdo at 6:52 PM on January 1


Just to clarify, the "before" wiring was not something I did. That is the way it was when we purchased the house.

The "after" wiring is what I added. There does not appear to be anything else nearby on this circuit. There is just the one main line in the attic, coming from the panel, and, seemingly, only providing power to the one lightbulb. There are no other electrical devices in the attic.

Thanks for the suggestions so far.
posted by pixlboi at 6:57 PM on January 1


The wires coming into the light fixture are wrong: the white should be neutral, but appears to be hot. To properly wire a grounded outlet box, you need three wires, all connected properly to your panel: black is hot, white is neutral, and bare is ground (also neutral, but not intended to carry current). From your "before" diagram it's clear that this is not how the circuit is actually wired, and you need to figure out why.

What kind of wiring do you have in the house? Is the house very old? Pre-WWII wiring often lacks a separate ground, and really old knob-and-tube wiring can be very sketchy.
posted by mr vino at 7:33 PM on January 1


Agreed with everything flimflam said. Taking the issues one at a time

1) There appears to be no neutral wire, and the light bulb uses ground as a neutral (connecting the white wire from the bulb to the junction box). That's pretty disturbing and probably the most dangerous thing you have going there. It means that the electrical box and the entire path to ground is part of the circuit (and hot) when the lightbulb is on, which is a big no-no. WRONG AND DANGEROUS.

2) Either the black wire is neutral (and mis-colored) or there really isn't a neutral. The best case scenario is that the black and white wires were reversed somewhere upstream and the black is actually a neutral. That isn't very likely though, since whoever installed the lightbulb probably would have just used the black wire instead of capping it off. Sending either wire through the switch and connecting both to the lightbulb would have worked, so the fact that they didn't do that pretty much tells me the black wire is hot.

3) There appears to be no connection between the box ground and the main house ground. This depends somewhat on whether the wiring connecting the box to the main panel is plain wire (like an extension cord, also known as Romex), metal conduit with metal boxes (EMT) or flexible metal conduit (often called BX). With Romex this is always wrong, but in some jurisdictions metal conduit with metal boxes and mechanical fasteners can be considered a ground so I would defer to a local electrician on this one.

As pure speculation - is this circuit extended from an electric dryer or an electric stove, or was there ever anything high draw in the attic (e.g. an AC unit)? A circuit with two hot wires and no neutral could have originally been a 240V circuit to run an AC unit, stove, or dryer; those circuits have two hot wires in opposite phases and no neutral. Someone entirely uninformed could have extended that circuit into the attic for a light and then found themselves stuck with no way to wire a 120V bulb fixture other than the insane way they did it. What else turns off when you switch the breaker?

With the current setup there really is no way to run an outlet safely. I can think of some next steps but none that I'm comfortable recommending over the internet beyond slowly backing away and calling a pro on this one.
posted by true at 7:37 PM on January 1 [5 favorites]


n'thing flim flam - just because nothing is "nearby" doesn't mean there aren't other things on that circuit somewhere - i.e., in my 1930's house, which had the wiring seriously mucked with before I got it, a receptacle downstairs w side of house is on the same circuit as one 2nd floor E end of house. Only two I can find on that circuit - so far.

I've found other things that have lead to the inescapable conclusion that the previous owner had absolutely no business doing anything more complicated than changing a light bulb. I think he must have owned your place at one time as well.

Put it back like you found it, and get a pro, whether you want the outlet or not. Returning the circuit through a ground is seriously bad stuff, but that's just one of the issues.
posted by rudd135 at 7:53 PM on January 1


I was going to upload a corrected wiring diagram, but I realized I'd need to make assumptions that may be completely incorrect.

The wiring you show - both before and after - is all kinds of messed up.

This is a job for a pro. Given the age of the home and whatever mistakes others have made before you got to it, it's time to call an electrician. It's not worth endangering your loved ones or your property to save a few bucks by doing it yourself.
posted by under_petticoat_rule at 7:58 PM on January 1 [1 favorite]


The original wiring is wrong. The white wire from the keyless shouldn't be grounded. The after wiring is wrong though what you added on should have been right. You need someone with a meter to check the incoming power wires (Hot to ground, hot to neutral, and neutral to ground); and continuity of the switch wiring. Then depending on what they find out they need to fix the wiring. That may involve running a new circuit if you've got something whacky like a California three way up stream of the ceiling box. In a house this old that has undoubtedly been worked on multiple times you often have to fix several wiring problems before everything is hunky dory. This is probably one of those cases because of the keyless being wired to ground in the original circuit.

BillMcMurdo: " The switch should be connected to the black wire coming from the breaker panel, and the other wire from the switch (probably white) should connect to the black wire on the light fixture."

In Canada where the OP is this isn't the legal way of connecting a switch where the power goes to the ceiling box and the wire going to the switch is a switch leg. You need to have the BLACK wire coming from the switch and going to the BRASS screw on the keyless fixture. Therefor the WHITE wire going to the switch is connected to the BLACK incoming power wire in the ceiling box. The incoming WHITE power wire then connects to the silver screw on the keyless. Having anything but a white wire going to the silver screw on the keyless is illegal here.
posted by Mitheral at 8:15 PM on January 1


Looking again at your diagram I see you don't actually have a keyless fixture (or at least that isn't what is pictured). Substitute Black fixture wire for Brass screw and White fixture wire for Silver screw in my previous comment.
posted by Mitheral at 8:19 PM on January 1


Jesus, a hot neutral AND flowing out through ground. YIKES, be careful, please.
posted by intermod at 9:12 PM on January 1


Others have explained what's wrong fairly well and how there is a problem with the incoming wire, but I want to explain why the light wiring is unsafe even if you sort out the incoming wire. In short, there's a decent electrocution hazard there. Using ground for a return path, as others noted, is dangerous.

Electrical current flows in loops (hence the word "circuit"), and every light, appliance, TV, and snowcone maker in your house has its own loop. For something like a lightbulb or other devices with a two-prong plug, it's simple:
Hot ------+
          |
         bulb
          |
Neutral --+
The hot and neutral lines connect back to your distribution board / circuit breakers and from there back to the power company that closes the loop. Imagine a loop of wire extending from the power company all the way out to your lightbulb. (All kinds of details make that not really the case, but for the sake of understanding this, it will work.)

Grounded devices with three-prong plugs look more like this:
          +----+
Hot --------+  |
          | |  |
          |load|
          | |  |
Neutral ----+  |
          |    |
Ground ---+----+
There is still a loop from hot to neutral through the load (whatever in the device uses electricity), and the ground is just connected to the metal chassis (if it has one), not to either hot or neutral. The idea is that the ground is there as protection. If something inside were to short out to the chassis, the ground connection would carry the charge away, and hopefully a circuit breaker would trip due to the high current flowing with no load. Without the ground connection, such a short would just energize the case but otherwise leave things working, waiting for you to come along, touch the case, and make a connection to ground through your body (bad).

The ground connection is not supposed to carry current; it's just there as a backup. It can form part of a loop from the power company to your device (the current can literally flow through the earth back to the power plant), but it shouldn't. The bare copper wires for ground are uninsulated because they're not supposed to be live in any way; metal electrical boxes, conduit, etc. is all connected to ground but exposed to their surroundings; ground often connects back to your plumbing, as metal pipes make a decent connection back to the earth.

But what happens if ground does carry current? That's what's happening in your light wiring:
Hot ------+
          |
         bulb
          |
Ground ---+

Neutral --??
Here, the light works fine. Like I said, ground can make a return path for the current to flow and the bulb to light up. But now you've energized your ground whenever that light is on. Current is flowing back to the power company through a suboptimal path, and it will happily take other paths if offered. It's not clear where that ground connection goes from your diagram, but it's clearly not through the insulated wiring. So all sorts of exposed metal might be energized when the light is on. If someone touches any of that metal in a way that gives the current another path, it might just take it through their body.

Wiring can be "correct" meaning it works or "correct" meaning it's up to code. Your light bulb is wired correctly in the first way. But that's just because the light bulb doesn't care if anyone is electrocuted, while the code does.
posted by whatnotever at 8:22 AM on January 2 [8 favorites]


Using the grounding conductor as a neutral: totally against the Canadian Electrical Code, Rule 10-200 (the current is very "objectionable"; since V = RI, your ground isn't at ground potential anymore). Fixing this mess: a job for a professional.
posted by Monday, stony Monday at 9:16 AM on January 2


My guess is that at some point that black wire running up to that box either got disconnected or broken. A previous owner then patched around this problem by changing the connections at the other end (wherever that wire comes from) to use the white wire as a live conductor, and the ground wire as a substitute for the neutral wire. Which works, but as noted amply above, is all kinds of wrong.

You've now added an outlet that is connected correctly based on the wire colours. However because of the incorrect way the existing wires are used, what you have an outlet with its "live" terminal connected to a broken/disconnected wire, and its "neutral" terminal connected to what is now the live wire. There is no complete circuit there, thus it doesn't work for anything that draws real current. The tester, that responds to the presence of voltage on even a single wire, still beeps.

Do you have an AC voltmeter you can use to safely measure voltages on the incoming wires to that original box? What you would see if this was the case would be the normal 120-ish volts between the white wire and ground, and some lower (but not necessarily zero) voltage between the black wire and ground.

There are other, weirder possibilities, but the above seems like the most likely course of events that would lead to the horrible mis-wiring job that the previous owner left you to work with.
posted by FishBike at 2:38 PM on January 2


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