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Getting shocked while ungrounded
July 10, 2005 12:39 PM   Subscribe

Why is it that if I walk up and stick my finger in a wall outlet, I'll get shocked even though I'm not grounded? I can see getting shocked when standing barefoot on wet ground, but come on... on a floor wearing tennis shoes? How does that work?
posted by rolypolyman to Science & Nature (20 answers total)
 
Um, the electricity is seeking the easiest path to ground. Even if you're wearing tennies, you're still better than no path at all, which is the state you're interrupting.

We live with electricity every day, but even skilled professionals underestimate it.
posted by dhartung at 12:57 PM on July 10, 2005


did you try this? in the discussion here it was said that it doesn't happen.
posted by andrew cooke at 12:58 PM on July 10, 2005


C'mon folks: think about it. Your blender (with a two-prong plug) is not grounded, but it runs just fine.

As long as you make contact with both holes in the outlet, your hair will be rearranged.
posted by curtm at 1:52 PM on July 10, 2005


On a floor wearing tennis shoes? If you only touch one hole (a bobby pin is traditional for this) you will not get electrocuted. If the shoes were somehow conductive tennis shoes and the floor was concrete then you might. Electricity flows from the hot to ground. One side of the outlet is at ground potential so the electricity flowing through an appliance grounds to that. When you stand in water . . .
posted by caddis at 1:57 PM on July 10, 2005


How is it? you are getting your finger in a wall outlet!? mine have holes that are 1/8 inch wide 1/3 inch long. Is this a serious question, or a what if?
posted by hortense at 2:43 PM on July 10, 2005


Hypothetical... but of course I'm serious... would you not get shocked if you stuck a nail in an outlet?
posted by rolypolyman at 3:02 PM on July 10, 2005


Caddis is close, but that only works with DC. Most standard outlets worldwide are on AC, as it's easier to transmit and step the voltage. Almost any appliance you plug in will have an AC/DC converter on it somewhere, and if it's a small appliance it may even be external (such as the boxy part of cell phone or laptop charging cables) since they aren't tiny and can generate considerable heat. When you connect to any one of the two primary holes, you will not be shocked unless grounded, and even then it will be a shock at the frequency of the current (I think ~60Hz in America). If you touch both you will be shocked continuously, and the flow pattern would look like a sin curve. This is what can be so dangerous, as alternating signals play more havoc with our body.

Remember, you don't have to be grounded, you only have to complete a circuit. Grounding is only one method of doing so. If there are uneven charges, the current will flow through whatever medium it can, including you.

Also don't forget static shock, which is a release of charge on either side of the spectrum, positive or negative. This is simply a momentary imbalance between your body's charge and that of the object you're touching, and gives you an appropriate shock.
posted by mystyk at 3:20 PM on July 10, 2005


Works with DC too. If you are not sure, check with a voltmeter or better yet an oscilloscope. Neutral is tied to ground and the hot side fluctuates. The 120 Volt AC is actually an average (root mean square) and the actual voltage on the hot side varies between about +170 Volt DC and - 170 Volt DC in a sinusoidal pattern with a frequency of 60 Hz (at least in the US). Also, only electronic appliances like computers, televisions etc. convert to DC inside. Those with motors (your blender) or that merely heat or light do not (although they might for an electronic control panel).
posted by caddis at 3:55 PM on July 10, 2005


good god. it's amazing how clueless people can be and still feel qualified to speak out about things that can kill you.

the theory is that if the insulation is sufficient for the voltage (and frequency, possibly, if you were in some strange situation where the insulating layer was sufficiently thin to make it the filling in a capacitor sandwich) then you shouldn't get a shock. exactly what kind of clothing is sufficient for usa mains (120V, 60Hz) is debatable - i guess running shoes should be fine, but there is no way i would try it myself. most appliances (and a whole pile do use ac directly) are not made out of the same materials as clothing, and i've been shocked several times through my own stupidity without finding it much fun at all.

and, of course, if there's any other way to complete the circuit that passes through your body - say you're touching something with your hand, or you touch both wires - then you will get a shock anyway (unless you're touching something equally well grounded, or wearing suitably insulating gloves).

again, i would not attempt this myself. if you find the desire overwhelming, hold your hand palm upwards, fingers relaxed and curled, and touch with the outside of your fingers so that the muscle spasm will pull your hand away from the source. keep the other hand in your pocket. if you kill yourself, don't blame me.

i have no idea what mystyk is talking about when it comes to the difference between touching one wire and touching both above - it sounds like he's very confused about what ac current is, or how it is generally implemented. in many cases, neutral will be at, or close to, earth (and so won't shock you). if you're thinking of touching neutral well, again, i woudn't trust it myself - it's common for live and neutral to be swapped, for example, even if standards/hardware distinguish between them (and in the usa, i don't think they do, iirc, for domestic wiring).

finally, don't forget that voltages in many places are higher (and way more dangerous) than the domestic standard. at your workplace, or in overhead cables, for example. read some of the stomach-turning cases in dhartung's link above.
posted by andrew cooke at 4:00 PM on July 10, 2005


"equally well insulated", not grounded!
posted by andrew cooke at 4:05 PM on July 10, 2005


andrew, I have had several electricians into the house as of late and they all have worked on the wires live - simple stuff like putting in an overhead light fixture. I asked them about this and they said they were comfortable working with live wires - just don't touch more than one at once and do not ground yourself while working. I personally do not feel comfortable following their lead. Theory suggest they are correct, and they themselves practice this. The folks in dhartung's list are mostly not electricians. The first one obviously was working live and from the report it is surmised that he touched ground with one hand and a live wire with the other. I personally would never try such a thing, but pros and fools might.
posted by caddis at 4:38 PM on July 10, 2005


caddis, I am an electrician. (28 yrs) While we can and do work with live circuits when nessecary, the grand majority of us turn the juice off if possible. On average, I get shocked about once a year.
posted by scottymac at 5:13 PM on July 10, 2005


I am not an electrician, but I played one last year while helping a friend rewire her old home.

I worked on live wires several times very cautiously. At no time did I get electrocuted or even mildly shocked.

If there is no return path to ground, there is no shock. Dry wood floors, good shoes, and being damn sure to not touch other not-hot wires, fixtures, appliances, or anything but the hot wires and marrettes was quite enough protection against electrocution.

I do not advise anyone else being so foolish as to do this.

One pair of pliers did get rather impressive divot when I was momentarily careless once. Oops. I guess that dirty white wire wasn't a black wire after all...
posted by five fresh fish at 5:56 PM on July 10, 2005


And as the saying goes:

There are old electricians.

There are bold electricians.

There are no old, bold electricians.
posted by five fresh fish at 5:57 PM on July 10, 2005


Many years ago, I was working on my old house, which was built in the late 1930's.

The ceiling fixture I was working on (to install a ceiling fan) was downstream from a ceiling box which a licensed electrician had patched into to add a light fixture in my attic above a new air handler. I didn't know that while he was wiring in the new fixture, he reversed the wires on the fixture I was working on.

I was on a fiberglass ladder, and I touched what was supposed to be the neutral. I felt a low buzz, and figured that there was a leak into the neutral somewhere. Then, I had to cut the wire and when I did, I touched the diags to the grounded metal fixture and the explosion was like the fourth of July, leaving about 1/4 inch nick in the diags.

What this says:

1) If sufficiently separated from ground, you won't get shocked *much*. I suspect that the shock that I got was due to the humidity in the air.
2) Grounding yourself is much easier than having your feet on the ground or in water. The neutral or a grounded fixture is the most efficient way to cause the AC to loop through some of your body if you touch both the hot and the neutral or ground.
posted by tomierna at 7:00 PM on July 10, 2005


I had to study that funny electrical stuff in college ... funny how they make electrical engineers do that.
The theory goes that as long as you don't complete the circuit you shouldn't get shocked (much). So I concur with some of the others that working with a single live wire is ok*.
In practice, I always make sure that the power is off before messing around with wiring. After all, theories don't account for incorrectly installed wiring by electrician apprentice Billy Bob following his 3 day bender.

*for those who like to play with Darwin
posted by forforf at 8:51 PM on July 10, 2005


andrew,

I must admit that I'm only familiar with DC from theory, not practice. According to theory, a proper converter should allow a steady, 1 way current push on the wires.

AC however allows for both of the primary holes in a "3 hole" outlet (the "eyes" of the face) to be live, not just one, because of the full oscillation of the current. It is possible to complete a circuit between either one and the (true) ground, or either one and the ground plug. You will get shocked, but it won't be as serious as if you complete the circuit between both primary leads.

For some reason, AC current can really fuck someone up inside in ways DC can't, although in my experience DC is more likely to cause flesh burns. Within AC, completing the "designated" circuit instead of an impromptu one using ground just increases the current flow making it more dangerous.

Also, as briefly mentioned, voltage does play a factor. Some countries are 120, others 240 (don't ask which countries are which, I can't remember and I don't feel like googling). Amperage plays a factor too, but I don't know what they are at all for houses. I can say that I have been shocked by 1 million + volts before (from a jacob's ladder) but the amps were so low that I just had a muscle spasm and it was over.
posted by mystyk at 10:34 PM on July 10, 2005


If you want some real excitement, you *can* touch just *one* side of a transformer isolated (and not electrically coupled) plug and hold on to a grounded object. Note that I could also be wrong and you may die, but feh. I wouldn't prove myself wrong, I'm not that dumb. However, hospitals use this type of safety isolation in their ICU rooms (note the orange plugs).
posted by shepd at 12:30 AM on July 11, 2005


mystyk, your conception of voltages on the outlet are not correct. The neutral wire is at ground potential at all times and carries no voltage. It may have a slight voltage due to differing resistance between the ground wire and neutral wire, but ideally is at zero volts. They are both grounded at the circuit breaker or fuse box making it impossible to carry any significant voltage unless there is some problem in the house wiring. The hot wire varies from +170 V to -170 in a sine wave. Please see the following articles for more information.

Electrical-online.com - Grounding
Electrical Safety
How Stuff Works: The Power Plant: Alternating Current


Also, if you complete the ciruit between the hot wire and the ground wire you will receive the same shock as if you complete the cirucuit between the hot wire and the neutral wire. Why do you comment on this stuff when you obviously do not know what you are talking about?
posted by caddis at 7:53 AM on July 11, 2005


Holy guacamoly don't go around touching live wires if you don't have to. Especially don't trust that neutral is grounded. Even if the wiring is correct (wrong more often than I like to think about) I've seen as much as 80V on a floating ground. And your average person is going to feel 110V unless they are standing on a clean rubber mat at 5%RH or similiar.

mystyk writes "AC however allows for both of the primary holes in a '3 hole' outlet (the 'eyes' of the face) to be live, not just one, because of the full oscillation of the current."

mystyk if your talking about a regular NA household three prung outlet, I'm sorry, your wrong. In a properly wired outlet you can stick a nail in the polarized blade or the ground hole while taking a shower and not get a shock or feel anything at all. There are all sorts of places where theory seperates from practice however so I'd would not be trying it. And like FFF I've seen guys swap out a main panel with out disconnecting the 240V 200A service lines but it's not something I would do, I fully intend to collect my monthly Social Security check however small it may be. I've also had the pleasure of taking out power for an entire city block by accidentally shorting the wrong equipment, a dubious distinction I'd recommend against trying to emulate.
posted by Mitheral at 8:24 AM on July 11, 2005 [1 favorite]


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