How is it possible to be zapped by a manhole cover?

The manhole cover is generally mounted in a concrete lined manhole. Cured and dry concrete is a poor electrical conductor, so if there was a fault that allowed current to flow to the metal cover and a person were to bridge between the cover and a good ground then it would certainly "zap" the victim.

Yeah, I imagine the cement case acts as an insulator in some way. If it's possible. I mean if you bury a wire in the ground with an exposed top sticking out, and then touch that, zap.

eric, cephyn: Except that the manhole cover is also in contact with the same pavement the person is walking on. There are remarkably few (we couldn't find any) documented cases of a manhole cover event.

OK well then lets get a little more hypothetical and put some conditions on this - IF the manhole cover is indeed in contact with the actual ground, ok, you shouldn't get shocked.

but if the manhole cover is set in some sort of concrete or insulative tube, not in contact with the ground, it could hold a charge. This would be if the manhole was in its own separate concrete block that is sunk into the ground. Hypothetically speaking, if its 10 ft deep, inside a concrete tube (that has a bottom) and there's a generator down there and a wire going up to the manhole, it could hold a charge.

now that's a very specific case, obviously. I'm not saying it has happened, i'm just saying that maybe it could. I've seen manholes set in concrete blocks that are separate from the general asphalt around them. Don't know what happens under them of course. I'd never heard of manhole electrocutions until i read this blog post btw, so if you say it's never happened, i believe you.

Come on Revere!!!!!!!! We all know that man hole covers are really listening devices planted there by aliens. Really Revere!!!!! Not again!

but if the manhole cover is set in some sort of concrete or insulative tube, not in contact with the ground, it could hold a charge.

Out of curiosity I looked up the conductivity of concrete, and while completely dry concrete is a good insulator, apparently that's not so true of concrete exposed to moisture. This site gives a figure of 30-90 Ohm-meters. Which means that to maintain a voltage difference of, say, 120 V over, say, 10 cm, a current density of 13+ Amperes / square meter would be required. Offhand I don't think such a situation would be strictly speaking impossible, but I suspect most ground faults wouldn't fit the bill. But I am not an electrician.

Yes, theoretically this can happen. Ground (dirt, particularly if it is wet) can indeed pass a charge.
I recall my father telling me about a demonstration of electricity at a Pasadena College event (pre WWII) in which a generator was set up and a conduit was run into the ground. Alas, they found that the electrical conduit was not long enough to run the outdoor lighting. So, they rigged some type of terminal to the conduit feeding into the ground. 15 feet further away, they rigged some type of terminal to collect the electrical charge and then fed it to the lighting system. There was an actual gap of 15 feet of ground that the electricity passed through. Luckily no people were zapped that evening, but they did indeed fence off the area to prevent something like that.

Another situation has presented itself in San Francisco recently. An inordinate number of homes along the Muni electric train route have been reporting serious leaks in their fresh water pipes into their homes. On investigation the water company is positing that some 'stray current' from the Muni electric railway does cross into the ground, where it is picked up by metal pipes, which then proceed to corrode at a much more than normal rate.

Finally, if you can find any EE's that have worked for real live power transmission companies, they can tell you tails of seemingly impossible electrical events occuring -- linemen with no connection to anything metal becoming fried, people walking across paved power generation sites picking up charges enough to spark fires, fireballs out of nowwhere rolling along transmission lines -- people getting shocked when their electrical system somewhere connects with a sewer pipe -- electricity doesn't do everything 'by the book'

Pogo's mom: Still doesn't make sense. If the cover is in contact with the ground then there is no voltage difference with the ground and no current will pass. "stray voltages" can occur in some circumstances but it isn't clear manhole covers are one of them. So far a search has not found any documented evidence it has ever happened despite the commonn belief it has happened. But I'm open to both an explanation and documentation of a case.

I've never heard about a manhole specifically, but I do remember reading stories about people being electrocuted (sometimes to death) by metal plates or gratings in New York. Again, hard to take me seriously with no cite on hand, but I really DO remember reading those stories in a real newspaper (the NYTimes I think) and they were about incidents that had just happened, not something vaguely referenced.

But wait, I do have a cite, sort of.

http://select.nytimes.com/gst/abstract.html?res=FB0F1EFB3F550C778CDDAA0…

Can't get through their firewall to see the whole article, but the summary says enough to at least confirm that someone did get it from a plate, and that "stray voltage" is something that electricians were at least looking for.

plunge: I think your cite is the doctoral student who stepped on the service box plate and was indeed electrocuted. Also stray voltages around lamp posts have been shown. The wiring of each of these is different than where manholes are used. The manhole meme is pretty common in my experience, although surprisingly many commenters here so far seem never to have heard it.

My manhole cover guy at MLGW weighed in on this particular gig. He said something along Pogo's mom can happen easily, especially if the water is acidic. It apparently turns the older concrete caisson's into Leyden Jars. What is a battery he said? Two dissimilar metals with an acid. Connect them with the old cast iron pipes and have a stray current feeding into the ground. E.g. he said it happened here only it resulted in not an electrocution but a methane gas explosion in the 1960's (wouldnt have wanted to be on the jar that day). Something happened to discharge it and kapoomp went the methane. Lifted covers off for four blocks in what was then mid-town and stood the water in the toilets up about 4 feet was the account. When they dug it up they found electrolysis but no direct connection. So was it the electrocute the student or was it helped along by the voodoo of a 220 line that was found up the street six blocks that was grounding prior to going into a building? Not something you want to test as a normal lunch project. That is unless you are going to MIT and need a senior thesis in E/engineering.

Randy: Checking with other electric company engineers, there seems to be quite a bit of doubt about manhole covers because of the way electrical manholes are built. Exploding manhole covers are common. But electrified ones seem to exist mainly as anecdotes and not (so far) anywhere else. If the water becomes conductive then the voltage difference will disappear that way and in any event become a path of less resistance than a body. The more I think about it the more this seems like an urban legend. Can anyone find a credible report?

Are we talking about round manhole covers or triangular?

I can recall having seen more than one story in the newspaper about people being electrocuted when stepping on metal plates in the sidewalk, but I doubt these involved true manhole covers. But wouldn't the logic about "grounding" also apply to the metal service boxes? They are also set in the ground/concrete/pavement/whatever. I think the only reason you're not finding instances involving manholes "proper" is simply that you don't normally have loose wiring in close proximity to the metal lid of a true manhole.

No electrocution, just an explosion in 00.

http://media.www.gwhatchet.com/media/storage/paper332/news/2000/12/11/N…

Kurt: Yes it clearly happens with metal plates on service boxes. I assume they are different in some way from manholes where I haven't been able to find anything but anecdotes. But your question of how it is possible with other "metal plates" is a good one. Anyone have an answer? Hivemind?

Ahhhh.... Mental masturbation at its best.

Andrew said 13A/meter. There's very few things around a manhole cover that produce 1A (I actually can't think of any, but I'm being generous) let along 13A. You only need 100mA to seriously interrupt heart rhythm and cause potential death.

Additionally, Revere, you say zap. Zap could mean voltage with "no" amperage a la static electricity. Not that I could think of any situation where a manhole cover could hold a charge...

I often tell my wife who freaks out random bacteria spawning on our counter-top that spontaneous creation didn't explain life 500 years ago and it doesn't explain how bacteria would magically spawn on our counter either. My point is that whether a manhole cover could carry current or hold a voltage, where exactly are these electrons coming from???

I think it's actually happened a few times in Boston over the last couple of years, mostly to dogs in the winter (I'm guessing hot manhole covers aren't easily noticed in snow boots). I don't know if the problem has been solved per se, but it did get quite a bit of press in '04 and '05 if I remember correctly. I don't recall it ever happening to a human though.

The deaths of the dogs in Boston were caused by "stray voltage" from frayed wires near street lamps. The dogs then stepped on nearby metal plates and were killed instantly. This happened all over the city, and the problem was supposedly fixed by tracing down the electrical problems and by placing plastic plates under the metal lids. I believe a total of 4 or 5 dogs were killed.

Dari: The problem of how a current source could get to a manhole cover is an important question, given the way those boxes are built. But even if you assume some cable or wire made a connection to the cover, why wasn't it grounded immediately?

Brain, Lori: Yes, we've all heard that. And street lamps can definitely be a source of stray voltage because of the way they are built and set in ground. But we keep hearing "manhole covers" and finding an instance of it is pretty difficult. In fact we can't find any. We were also sure we'd read it in the paper. But a search turned up nothing. Has it ever happened?

Revere,

I think it is time to acknowledge that your son inherited some of your intelligence genes, and is probably right about this one.

It is an interesting mental exercise, but I have also not been able to find any real sources as well.

I've been poking around on this topic for a little while now... here's what I understand about electrified manhole covers. Please note -- I have no formal training to speak of in electrical engineering!

Any manholes with live wires are required to keep those wires at least 12 feet below ground. The enclosed manhole is constructed of insulating concrete with a long metal rod driven into the earth to provide adequate grounding. The insulated sheathing on the wires should be resistant to corrosion and protected from mechanical failure. For these reasons, a joint utility-city-neighborhood task force in Boston concluded that it is very unlikely an injury would occur from an electrified manhole cover (see pp 9-11 especially top of p 11):
http://www.cityofboston.gov/electricalsafety/pdfs/safety_report.pdf

Service boxes are placed to provide easy access to street-level wiring (e.g. traffic lights, street lamps). In this case there are live wires at ground level, and so the potential for stray voltage is higher. My guess is that many (all?) of the anecdotal reports of injuries are actually related to service boxes and not manholes.

Revere,

I have never been able to find anything on this subject that I felt was more than urban legend, so I think your son is probably right.

However, theoretically speaking, there is a way that a manhole cover could shock someone, but along the reverse path, not with the cover itself being electrified.

Basically, if someone had built up a large static electrical charge and then stepped on the manhole cover (say from a car, off a sidewalk, or from some insulated surface onto the cover), then the current would pass into the metal of the manhole, much like what can sometimes happen when you walk across a carpet in winter and then touch metal, or when getting out of your car and the door zaps you. I've been zapped that way many times (my electric personality, I guess). Here we are talking about a shock that might hurt, but wouldnt kill someone.

On the other hand, if a person had developed a strong enough electric charge (not from static but from some other source) and then bridged the gap by way of the manhole, then the charge would seek to discharge into the manhole cover through the person. Zap..., dead person. While I cant see this as being very likely to happen, I think its probably more likely than the cover itself being electrified.

What if it's not the manhole cover that's holding the charge? What if it's providing the path to ground? Would that change the story (or at least, the search terms)?

No Nym: If it's the path to ground, then, as a conductor, it is at zero potential. If you step on it no current will flow (unless, as in Lenn's scenario, you are charged).

http://www.pulp.tc/html/dog-walking_new_yorkers_fear_e.html

Quote:
In 1999 a carriage horse was killed when it stepped on an electrically charged manhole cover in midtown Manhattan.

Now, it says "manhole" - so I assume that's what they mean. So obviously it can hold a charge somehow? It talks about service boxes in the article too, so I imagine if the horse stepped on a service box, it would say so.

http://www.chicagoreader.com/features/stories/strayvoltage/

There's a story about electrified wet concrete electrocuting dogs. Wires in the ground are cause, but they aren't specifically touching the concrete. So even in contact with the ground, dogs on the surface are catching the current. Does this make it any more possible that a manhole cover could hold a charge?

also in that chicago article -
"Four years prior, a dog was killed and its owner hospitalized after they stepped on an electrified manhole cover at the intersection of Lincoln, Sheffield, and Wrightwood."

cephyn: What we haven't been able to find is any documentation that these things really happened. Almost all the accounts are like this one, second or third hand accounts. My question has two prongs: the first is, has it really happened? Urban legends typically have second and third hand accounts, so I am not persuaded by these. The reason has to do with the second prong. How is it possible for it to happen? That's actually of more interest to me. If it does happen (and it might), I'd like to know how, given the fact that a manhole cover seems to be well grounded.

Revere, even if it is lying flat on the ground, road, beach, lawn, whatever, it is not "well grounded". Dirt, asphalt, etc are not good conductors of electricity, not usually as good as people, in turn not as good as metals.

Ground, the earth, is generally regarded today more as a theoretical reference potential (voltage) than as a conductor. It can carry electric currents because there is so much of it. However, your electric utility runs a separate wire. It works better and is cheaper despite the price of copper. Even the "ground wire" on your computer or autoclave is "ground" only because all the nearby "ground wires" are connected at one place AND because there is normally no current in any of them.

Radio amateurs maintain a large literature on the subject. Strategies vary from the easy (connect to the water line where it enters your house, if your city still uses metal pipes) to the difficult (dig a ditch down into the watertable and bury a lot of connected metal).

If a "hot" wire came loose and contacted a manhole cover, electric current would leak into the surrounding "ground". DON'T TRY THIS AT HOME! However, if you ran a metal wire over to something "properly" grounded, eg trolley tracks or a lamppost or another (grounded) manhole cover, you could make healthy sparks. A casual pedestrian probably would not notice the tiny potential difference (voltage) between their foot on the pavement and their foot on the manhole, especially not if shod. Perhaps the dog pulled forward onto an electrified manhole cover, while the owner held a lamppost or stepped in a puddle, with a metal leash between them.

Depends on the potential, too. Ordinary 120/240v lines storm-downed on your lawn are safe enough, if dry, if you don't touch them. However, high-tension lines would have dangerous potential gradients around them. A dog with wet feet nosing a high-tension line is asking for trouble.

Depends on the victim, too. They used to tell the cautionary tale of a researcher experimenting with the effect of mild electric shocks on heart rhythms, found dead one morning hooked up to his own apparatus, which the tellers insist was incapable of delivering a fatal shock. Non-lethal stun-guns continue to kill people, some of them healthy respectable bourgeois citizens.

While not as complicated as viral evolution, electric circuit theory is complicated enough, especially when it is indistinguishable from magic. (Just like evolution.)

In summary, an electic circuit requires a circuit, a circle, a conductor to 'there' and back. A living thing will often die if inserted into the circuit, if .. well a lot of conditions.

"Ground" is not usually a good conductor. Animals may die when they offer themselves as alternate (and better) conductors.

Media stories rarely provide circuit diagrams, generally presenting electricity as heap-big magic.

An electified manhole cover "could kill" a person or a dog if they offered themself as a conductor and if they were connected to another conductor. Theoretically yes, practically unlikely, but we have lots of people and dogs. The newspaper will not tell you the most significant part of the story, the circuit.

Greg: Yes, "ground" is a reference point. Granted. My point, however, was that the manhole cover is "conncected" to the surrounding pavement and both are "connected" to earth. It's hard to see how you could get a meaningful potential difference between them that would find a dog a better pathway. And in fact it is very hard to find non second hand reports of this happening with a manhole cover. As commenter Al notes above, to add to it, those vaults are built so it is very unlikely a power cable could get anywhere near the cover, but if it did would seem it would be an immediate short to "ground."

Where to post this one? High traffic one for sure I think. More than 10 and less than 20 requests have come in for me to "spill","out", "stick it up" Revere's identity and some of those were the more polite ones. This is because they feel I think that the right side of the aisle is automatically discounted here for the better part. Republican means wrong. That could be right, or wrong.

As for releasing his identity boys and girls it aint going to happen and for several reasons. I stumbled onto his very likely identity about a month or two ago when I was trying to trace a linked virus that was floating around every time I logged onto EM. It was a pesky little buzzard and I pulled out the old language files that allows for the tracking/tracing of everything on the net. Had to write program to get it but I wasnt looking for his address, I was looking for that dirty sunavabitch that kept on putting spyware on my computer. Turns out it wasnt his server but one over in Minnesota that was mirroring on his server. I mentioned it to one or two and didnt say who it was. It didnt take long for the pressing to find out started.

In fact I copied Revere(s) in on one of the emailed request and while its a valid request, its not up to me to honor. Revere is in a position of authority with likely dozens of more bright and shiny right and left wing minds that depend on research grants to get the job done. Be it bird bug or the common cold he is on the front lines with those kids on getting shit fixed. They cant do it without money and that money is controlled by a shall we say less than funny about it right wing extreme right now. This too will pass and the true Republicans will knock the Tail Gunner Joes out of those positions sooner or later. We may diametrically oppose each other on many things, but this is not one of them. To a certain extent I am a Gunner Joe, but not to the point of the 1950's. Mine is based on getting hit slightly two or three times and it hurt like hell. Everytime someone gets popped in Iraq I more than sympathize, I physically feel it. I think that my right wing buddies who are more arm chaired commando's than I was feel my pain. Thanks.

This country was founded on many rights and one of those is privacy. Even though I think he is full of shit on many things, it is that and other tenets of our country which I fought for in many places that I hold sacred. I am not in the business of suppression of thought and that would indeed be the end result of this if I did all of the above suggested to the Revere's. This Administration doesnt play well with others and I am well aware of that even though I personally believe that many of them have their hearts in the right place. On the other hand I as a right winger wouldnt go hunting with Dick Cheney on a bet.

So for those of you who want Revere's identity, ask HIM/THEM for it. He has all of your email addresses and could do so with a flick of the BCC on an email. Remember, unlike most of you here I took an oath to defend the country and abide by the Constitution and that includes all of the amendments and that means his privacy. If it ever came down to a right wing witch hunt looking for a Revere, they would have to go thru me to get to him. Bottom line. Dont ask me, you aint going to get it.

So help me God.

Revere, I was answering, "How is it possible for it to happen?".

Replying directly to your most recent, the pavement is a poor conductor, the ground (dirt) is usually a poor conductor. The manhole cover is physically near ground (dirt), but it is not electrically "well grounded". "well grounded" is a hypothetical good conductor located near the electric generator.

If an electrical wire contacts a manhole cover, the potential difference is between the manhole cover and the other side of the power line. If the manhole is "hot", the other side of the power line will likely be connected to actual dirt ground somewhere (but probably not physically nearby).

If we have only manhole, pavement etc, then the potential difference will more or less evenly (proportional to instantaneous electrical resistance) distributed along the length of the path between manhole cover and the other side of the powerline, or the nearest good conductor connected to it. The path could be quite long, so that the potential difference per metre near the manhole would be quite small. Also since the pavement and dirt are poor conductors, the current would be limited by their resistance, too. A person or a dog walking would not notice the potential.

However, if there is (say) a nearby properly grounded metal lamppost, then the potential difference is distributed between the manhole and the post. Taking the example of a dog, a metal leash, and a man, if the dog touches the manhole cover and the man touches the lamppost, then almost all of the potential difference is shared between the dog and the man. The the manhole cover, the leash, the lamppost, and whatever electrical wiring involved, being a good conductors, would experience little electric potential. The pavement etc, being poor conductors, are insignificant.

So it is possible, if somehow the manhole cover becomes electrified, and if nearby there is a suitable electrical return path. If there is no return path there is no danger.

I have said only how it is possible.

The probabilities must be tiny, but there are lots of people, lots of dogs, lots of manhole covers, lots of electrical wires (not all to modern code). There are lots of freak accidents in this huge old freaky world.

I expect the stories are urban legends.

Part of the cognitive problem here is that the legends treat the electrified manhole cover as magic. They fail to mention the necessary electrical return circuit. At first glance, that makes them more reasonable : electricity,, Wotan's Hammer. Then, you think, where is the return circuit, and they become unreasonable. If they would specify the circuit they would become much more credible.

Without getting into the science, I had a neighbor who put up a retaining wall for her garden with railroad ties, and the ties were driven in (many years ago) with metal posts. When the posts were driven in, one of them nicked the electrical service and eventually (not immediately) became energized. Many years later, her lawn guy was using a string trimmer and got shocked by an arc from the embedded post (which similarly was "grounded"). The power company had to shut down her power to fix it- very costly.

I know it's anecdotal but it's true.

Dunno, doc, here's a NY story that specifically ties a dog's death to a "manhole cover."

THE NY TIMES
Dog Dies on a Downtown Sidewalk, Possibly Electrocuted
By ANTHONY RAMIREZ and EMILY VASQUEZ
Published: February 15, 2007

A small dog being walked along a downtown sidewalk yesterday was apparently electrocuted moments after crossing an icy manhole cover, according to a veterinarian who examined the animal after a dog-walker brought him in.

The police quickly cordoned off the sidewalk where the dog died, on Rector Street near Greenwich Street. A crew from Consolidated Edison began testing the area for stray voltage, but Con Ed officials could not immediately confirm that the manhole cover or another metal object in the area had been electrified.

The dog, a 1-year-old 16-pound Boston terrier named Bob, was crossing the manhole cover when he suddenly lifted his paws, yelped in pain and went limp in the dog walkers arms, according to Seth Edelstein, owner of Walkee Doggie, the TriBeCa dog-walking company that employs the walker.

If the cause of Bobs death is determined to be electrocution, his death would be the latest in a string of episodes in which pet owners or their pets were harmed by stray voltage in metal plates or other objects on the citys streets and sidewalks.

The most serious accident occurred in 2004, when Jodie S. Lane, a graduate student, died while walking her two dogs on a wet street in the East Village. The utility later found that a metal service plate Ms. Lane had walked on had been accidentally electrified because of insufficient insulation.

Mr. Edelstein, who would not identify the dog walker, said she gave the dog mouth-to-mouth resuscitation after Bob went limp. She called the police, then dashed to a nearby animal clinic. The two other dogs being walked were uninjured, he said.

At the clinic, the Battery Park Veterinary Hospital, a veterinarian, Mary Xanthos, said Bob was dead on arrival.

It really sounded like an electrocution, Dr. Xanthos said, noting that the salt spread on sidewalks to melt ice can increase electrical conductivity.

Bobs owners, Beth Boyer, 33, a hospital nurse in Manhattan, and her fiancé, Joe Cardiello, 36, a funeral director from Paramus, N.J., said they were distraught by their pets death. They said they had not decided whether to have a necropsy performed to help determine cause of death.

Ms. Boyer said Bobs death was especially wrenching because Bella, a pet cat who belonged to Ms. Boyers roommate, just died on Saturday after a long illness. The cat and the dog were best friends, she said, and often played together. They even looked alike, Bellas dark gray and white almost matching Bobs black and white coat.

This is the worst Valentines Day, Ms. Boyer said.

Cara Buckley contributed reporting.

DeadAhead: This report raises all the usual questions. None of the people quoted actually saw the dog zapped by a manhole cover; the cause of death is still undecided; how is it possible for a manhole cover to be electrified (note that ConEd didn't confirm stray voltages). The string of incidents does includes all sorts of metal plates, not just manhole covers. So I remain agnostic on this.

Not sure if you see new comments on old threads, but...

Now it's actually happened. Dog electrocuted by manhole cover. The story is rather sad, it's about how 911 told the owner to drag the dog('s corpse) off the manhole by his leash. But no one denies that electrocution by manhole cover was the cause of death.

It also mentions a terrier being electrocuted the day before and surviving, but it doesn't specify if it was by the same manhole. (If so, why wasn't it fixed?)

caia: Thanks for this. If you see any more about this case, pass it on. I find this very intereseting. And yes, as a dog owner, it is sad.

My dog got shocked repeatedly by a manhole cover, buried under leaves and dirt on the ground. In the winter, there was snow on it and later on when it had rained and the ground was wet.
I told the electric co. about it and they said there was stray voltage there.
She (my dog) was very scared.

As this thread is showing no signs of dying, I'll add this latest, from Toronto:

Two dogs dead, one injured after electrocution in the city's east end

The problem was caused by a faulty insulator in a span cable that holds up the mass of streetcar wires over the intersection. When the insulator failed, it caused an electrical current to pass from the streetcar wire into the span cable and from the cable into a metal pole it happened to be touching.

From the pole, the current travelled into the sidewalk, conducted by the rain.

Dogs were electrocuted during the winters of 2009 and 2010 in Toronto, also. Perhaps salt is a contributing factor.