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I haven't found any advice on my specific predicament, so I'll ask here. First, some background.

I just moved into a house with old electrical wiring (read: ungrounded outlets). Unfortunately, the area where I'll be working with static-sensitive devices (microcontrollers and similar devices) is in a carpeted area and the humidity here is very low. In other words, I will likely want to start using a wrist strap and anti-static mat for my work. However, I don't have anything to ground to.

While I know connecting ground to neutral in an actively used outlet is a silly idea, I'm wondering if it would be alright to use the neutral connection of an unused outlet to ground my mat and wristband. Since the outlet is unused the neutral wire should never be energized and always grounded.

If this is not a reasonable idea, does anyone have any better suggestions? (Rewiring is not an option for me as it's not my house.)

If it is a reasonable idea, I'm curious if it would also be safe to ground an active outlet with the neutral wire of an unused outlet. Not that I plan on doing that, I'm just curious if that makes sense (it seems like it would theoretically be fine given my understanding of how individual outlets are wired).

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Are their any exposed copper water pipes that you can ground your static mat to? –  mikes Dec 30 '12 at 22:10
    
Not near the workspace, and I'm hoping to avoid lengthy cables weaving around the house. I understand for this application that would probably be a safe approach, but I'm curious if my theory that the neutral line on an unused outlet would be a safe option is a correct assessment. –  Anthony Dec 31 '12 at 3:06
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No. You can/should not EVER use the grounded (neutral) conductor as an equipment grounding conductor. –  Tester101 Dec 31 '12 at 4:15
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It's not just if the outlet is unused, but if the entire circuit is unused. Even so, you still should not do it. For the sake of discussion though, a question for anyone: What if Anthony killed the circuit and disconnected the power conductor? Now there's a wire at his workbench bonded to the service entrance equipment, but has no formal grounding means. Is this of any use. In theory? –  bcworkz Dec 31 '12 at 23:27

3 Answers 3

This is a bad idea! Don't do it! If I were you I would just run a green ground wire along baseboards all the way to whatever good ground you can find.

That said, for the sake of theory and imagination, I think one could also do the following hack:

  • Find the circuit breaker that corresponds to the outlet you want to repurpose as a ground
  • Disconnect the hot from the breaker so it is impossible to use anything on the entire circuit. Maybe just remove the entire breaker.
  • Disconnect the neutral from its bus bar too
  • Connect both the hot and neutral wires to a bare-wire pigtail with a wire nut
  • Connect the pigtail to the ground bus

As far as I can see, this would be safe because you will have completely disabled the entire circuit by repurposing both wires to be grounds. Now you have to go around to all other receptacles on that circuit and remove them or at least label them as non-functioning.

However, this is still unsafe because it violates the principle of least astonishment. Modern electrical systems are safe in part because they all follow the same conventions. Any electrician can come into a home, look at part of the wiring, and make reasonable assumptions about how it is wired based on the colors of the wires (for example). Violating these conventions will mislead them, and that's unsafe.

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For the sake of theory and imagination, also tag all of the wires at both ends. –  Steven Jan 5 '13 at 2:47
    
@Steven +1 Good idea, and include the URL of this thread. :) –  lukecyca Jan 6 '13 at 22:44

There are different forms of grounds.

Earth ground is obvious and what you'd wish for and what you should tie your anti-static system to if you want absolute ground potential on it.

A ground plane can establish an equal potential for everything that's attached to it. While it's floating above or below absolute ground potential, it establishes a neutral differential level to all that touches it.

It's how you work with computers that aren't plugged into the mains power. You clip your wrist strap to the metal casing which neutralizes any charge you may have in relation to the electronics and then set the packaging for the item you're working with on the metal case so it discharges to neutral potential. Once you've created that situation, you're not going to have any static differential that will zap anything.

Expand that a little and cover the desktop with an antistatic mat. Jumper the computer case to the mat and your surface work area of equal potential is now as large as the mat is.

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Building a ground plane was another idea I had but I'm not sure if that wouldn't just slowly build up a surface charge and what effect that might have. My understanding of working on computers was that connecting to the case was okay while working on it for a bit as any built charge would be dissipated the next time you plug it in. But if my ground plane builds a charge and there is a large enough potential difference relative to power ground, it seems like I could build a situation to zap something any time I want to add or remove components to my circuit which has a different ground. –  Anthony Dec 31 '12 at 18:36
    
Any mucking around with micro-controller boards and peripherals I've ever done, you need to tie grounds together anyway so you have signal reference. Do that first and the situation never crops up. Everything lives on the mat. 4' x 6' was a sufficient work area, you just keep it clear so all your work occurs on it. –  Fiasco Labs Jan 1 '13 at 4:31
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YMMV time. In a rental, I once drilled a hole just large enough to run a #4 ground wire down to a 4' ground stake driven at an angle in the crawl space. When I left, the wire and stake came out, a piece of dowel went in and nobody knew what had gone through the carpet. It helps to have the kind of landlord that doesn't frown on minor repairs, we always took care of stuff. –  Fiasco Labs Jan 1 '13 at 4:37

Do not do this.

If you ever ended up with a break in the neutral between the outlet and the panel, you would have electrified your workbench and wrist band.

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At which point, you will have the possibility of finding the real ground you should have used in the first place. There's a reason why the NEC does things. Empirical evidence supports it. You don't want to become a negative statistic from attempting to disprove it. –  Fiasco Labs Dec 31 '12 at 5:48
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Even if you don't break the neutral somewhere, neutral is the path that hot current takes to get back to ground. If you happen to be a better ground path than the neutral wire, it will travel through you instead. –  BMitch Dec 31 '12 at 14:21
    
Yes, also any resistance (long runs, etc.) that creates a difference in potential between the two ends of the wire will make the neutral hot in relation to ground as well. Another is, especially in an old house with no grounding, miswiring a branch circuit, which in the days of cheap tube radios with a hot chassis, could be fatal. Remember those big Bakelite knobs and all that wood? It could be there for a very good reason. –  Fiasco Labs Dec 31 '12 at 16:40
    
My understanding of grounded outlets is that the ground wire goes to precisely the same place the neutral wire goes to (they're bonded at the breaker). The difference is that, while the outlet is active, no current runs through ground (assuming everything is normal) so it is never live like the neutral line (thus your casing never zaps you). Given this, it would seem to make sense that on an outlet where the live terminal is never connected, the neutral would have the exact same effect as the ground wire. Why this would not be true is what I'm interested to know. –  Anthony Dec 31 '12 at 18:22
    
@Eric: Why would a break between the outlet and the panel give me an electrified workbench? This would be an unused outlet, i.e. there would be no connection between the live and the neutral. Then the only worry would be the live somehow shorting with neutral to electrify the line, which I would think is about as worrisome as the live shorting with ground on a grounded outlet. –  Anthony Dec 31 '12 at 18:41

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