How I almost killed myself - Page 1
Forum section: electronics / general

author: TNb
author_rank: Regular Contributor
timestamp: October 01, 2016, 10:00:14 pm
content: Well, I don't know why I am writing this, maybe to remind others about safety, but you can just feel free to laugh and write "what an idiot you are" below.So I came back home from a walk and my feet were tired of walking in crappy shoes, so I decided to take "feet bath", don't know how to call it in English, basically put your feet in a bowl with hot water to relax. While taking the bath I was repairing some crap with a glue gun. You guessed right. So I put the glue gun on the table to fiddle around with other crap, then bam - glue gun, turned on into 220 V mains falls off the table to the bowl of water where my feet are. Who knows for what reason, but nothing happened - circuit breaker is not turned off, I am not electrocuted, I just pull out my feet and glue gun out of the mains socket.Have no idea why nothing happened, because that glue gun is absolute cheapest chinese crap, I wonder if it is so well insulated inside, if it is - I would like to send some thankful money to engineer who designed it.So the moral of the story - don't be a fucking idiot and don't do stupid shit like that, safety first and so on. But really, even very experienced people like to screw safety, seen many factory workers just spitting on every safety aspect. Don't be those guys, and don't be like me for certain.And while we are at it, if somebody has time to answer some related questions it would be nice:1) It seems I don't have residual current device(at least I don't see it in this appartment), but if I would have it - does it save from this kind of shit? I guess not, since I am basically in the middle of the circuit or something... don't know much about RCD, would be interesting to know.2) How the hell it didn't do anything? Is it insulation? How can such a good insulation be in glue gun? Let alone 1$ shit like this. I can do a teardown probably, not now though, too tired.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 01, 2016, 10:03:15 pm
content: What was the bowl made of ?if plastic, then you could probably stick 240V live in the water and unless another part of you had a path to ground you wouldn't feel a thing.

author: TNb
author_rank: Regular Contributor
timestamp: October 01, 2016, 10:04:41 pm
content: It is plastic, but glue gun has both live and neutral wire in it, isn't it enough to conduct through water? I mean, at least I would feel something, no?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 01, 2016, 10:17:08 pm
content: Quote from: TNb on October 01, 2016, 10:04:41 pmOnly if a part of you was between the live and the neutral

author: TNb
author_rank: Regular Contributor
timestamp: October 01, 2016, 10:19:58 pm
content: Quote from: mikeselectricstuff on October 01, 2016, 10:17:08 pmBut my feet are technically in between, though of course the resistance and distance is much greater than from leads themselves.If all that is not so dangerous - how is there so many stories about people killing themselves in a bathtubs with a hairdryer?

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: October 01, 2016, 10:23:03 pm
content: Electroboom has a video basically explaining the same thing, but with his finger. With Live and Neutral so close, and you not providing a path (being in parallel) you were fine. May have been different if you touched something with a path to ground/neutral, though!

author: TNb
author_rank: Regular Contributor
timestamp: October 01, 2016, 10:32:59 pm
content: Quote from: RGB255_0_0 on October 01, 2016, 10:23:03 pmOh, interesting, thanks!I guess all those stories about people committing suicide in bath with hairdryer are myths, unless they are touching grounded tubes.Anyway, I am not going to repeat the experiment

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2016, 10:48:30 pm
content: A bath is completely different from the bowl.A bath usually has any metal parts like taps bonded to earth, so mains current has a path through the water (and potentially through you) to ground. If you get between a live wire and a path to ground then you could be electrocuted.Your plastic bowl was insulated from earth and there was no path to ground through your body (unless you were to touch something metal while your feet were connected to mains).

author: helius
author_rank: Super Contributor
timestamp: October 01, 2016, 10:55:35 pm
content: Unless the water contained salts, its resistance was higher than the heater in the glue gun. Also consider the spatial distribution of current within the bowl: it will be highest in the immediate vicinity of the input wires, and lower with increasing distance.Electrocution in bathtubs is much more likely when there are grounded fittings in contact with the water (like brass drains). There is then a path from the live wires to ground that passes around a bathing person. The danger is even higher if they are lying in the water along the same direction as that path: because voltage difference across the body is what causes current to flow inside the body. If they touch the grounded fitting it is even worse.

author: TNb
author_rank: Regular Contributor
timestamp: October 01, 2016, 11:01:57 pm
content: What about residual current device? Does it help if person in a bathtub with a hairdryer?

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: October 01, 2016, 11:05:04 pm
content: RCD would only help if current was going back via the protective earth/other than the neutral and exceeded the leakage rating. RCD wouldn't protect you if you stuck your hand in an insulated bowl powered by a 2-wire mains device and you were isolated also.Again there are videos about this on YouTube.

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2016, 11:06:14 pm
content: Quote from: TNb on October 01, 2016, 11:01:57 pmIt should do. However, if you were in the UK you would have nowhere to plug in the hairdryer close to the bath, so the combination of hairdryer and bath would be very unlikely.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 01, 2016, 11:11:12 pm
content: Can we see a teardown of the glue gun? If they used heatshrink to insulate the electrical connections, there might not have been any electrical connection between the water and the power.Mythbusters investigated this idea and found that you can definitely get killed this way. Remember that their tests were done with 110 VAC. You'd be twice as dead at 220 V!Are there any countries where there must be a ground connection to a bathtub? In North America, all the pipes are now plastic and the tubs are plastic, so there might not be a ground to trigger our GFCIs. With a two wire appliance, you could easily die.Ed

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2016, 11:16:02 pm
content: Water pipes should definitely be copper. There have been lawsuits over house floods caused by burst or broken plastic water pipes.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: October 01, 2016, 11:18:07 pm
content: Pretty sure all new work in the US must now have GFCI and bonding in new installations for basins/baths since at least 2014 because of 2-wire appliances.

author: TNb
author_rank: Regular Contributor
timestamp: October 01, 2016, 11:18:36 pm
content: Quote from: edpalmer42 on October 01, 2016, 11:11:12 pmTomorrow, it's quite late here, gonna hit the sack soon.Quote from: edpalmer42 on October 01, 2016, 11:11:12 pmIn Finland and Russia you can easily find grounded water tubes, I am not sure if this is required by law, but most houses are like that.

author: helius
author_rank: Super Contributor
timestamp: October 01, 2016, 11:31:40 pm
content: All hairdryers in the US have GFIs built into their cords. They should have a ground wire in the cord even if there is none in the electric outlet, so they should still trigger if dropped into a bathtub. Filling the bathtub with DI water might prevent that.

author: amyk
author_rank: Super Contributor
timestamp: October 02, 2016, 12:23:12 am
content: I'd say you were very far from killing yourself as the current would've far preferred to go through the heater or the water immediately surrounding the wires than through the water, you, and whatever else before it reaches ground. Unless the water had salts (conductive ions) in it, it would not be very conductive either.Some more discussion on safety (and perhaps a distorted perception of such) here:https://www.eevblog.com/forum/projects/suicide-shower-hear-teardown/tl;dr: electricity can be dangerous but only if a lot of it passes through you... which doesn't happen that often.

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 02, 2016, 12:28:45 am
content: Path of lease resistance. I'd say the heat element in the glue gun would be it, even when it's in the water, especially if there was no salt in the water, but if you added salt then it does make it a bit more dangerous. Basically some current will travel through water and back to gun but most of it will be going through the element.

author: rdl
author_rank: Super Contributor
timestamp: October 02, 2016, 12:47:34 am
content: These apartments were built around 2001-2002, and all the plumbing that I can see is plastic. Under both the kitchen and bath sinks, about 3" of white PVC comes out of the wall. There's a fitting of some kind on the end where flexible tubing is attached that runs on up to the faucets. I can see down the drain in the tub and it's white plastic also. I can't see the supply there though because it's inside the wall. The pipes to and from the water heater are red and blue plastic.

author: IanB
author_rank: Super Contributor
timestamp: October 02, 2016, 12:55:00 am
content: Yes, plastic definitely gets used for water pipes, but it is a cost cutting measure and is something you should complain about.If copper pipes fail you tend to get pinhole leaks which can be spotted and repaired while the damage is still localized.if plastic pipes fail they tend to split or break which will cause a huge amount of water damage if you don't manage to shut the water off immediately. This is especially true of PVC pipes.My house was originally built with plastic water pipes and they were all replaced with copper piping after a class action lawsuit.

author: Macbeth
author_rank: Super Contributor
timestamp: October 02, 2016, 01:31:00 am
content: Quote from: IanB on October 01, 2016, 11:06:14 pmThis is where you are wrong. I regularly plug in my mains cable extension reel in the hallway and roll it out to the bathroom where I leave it precariously dangling near the taps. My hairdryer will be in one socket and my beard trimmers in the other, or else a bar fire in the winter months that I jam in the corner between the shampoo bottles.I know I'm safe because a proper electrician has rewired the house to BS 7671:2008+A3:2015 (Yes, a metal consumer unit is now mandatory instead of plastic).I also have all those 99p shop battery chargers and night lights plugged in at all times, the ones Big Clive tears down that seem to go up in smoke.

author: JoeN
author_rank: Frequent Contributor
timestamp: October 02, 2016, 01:57:29 am
content: Quote from: TNb on October 01, 2016, 10:00:14 pmCan you describe the circuit that was created that made you part of the circuit and took the mains current through the core of your body?I can't either.

author: Brumby
author_rank: Unknown
timestamp: October 02, 2016, 02:14:01 am
content: Yes.The danger is NOT that voltage isbeingsomewhere ... it is is that current isgoingsomewhere - and that the path it takes goes through your body. (Only IF it goes through your body does it matter WHERE it goes through your body.)

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 02, 2016, 04:18:54 am
content: On subject of mistakes, I was just messing around with a 555 timer, trying to figure out the best combination with the parts I have to max it out (it's a 100khz one so trying to at least get close to 100) and I smelled something funny, without thinking, I checked to see if the resistors were hot. One of them was. Very very very hot. That left a nice resistor shaped mark on my finger. Going to feel the burn for a while.

author: ez24
author_rank: Super Contributor
timestamp: October 02, 2016, 05:00:21 am
content: Quote from: rdl on October 02, 2016, 12:47:34 amPEX pipe red is hot blue is coldit is sure a pleasure to work with, not to code where I live but I use itNever had even one drop leak

author: IanB
author_rank: Super Contributor
timestamp: October 02, 2016, 05:14:31 am
content: Quote from: ez24 on October 02, 2016, 05:00:21 amHmm, PEX looks like a good system.

author: Falcon69
author_rank: Super Contributor
timestamp: October 02, 2016, 06:03:39 am
content: I like using PEX also. It can stretch instead of bursting like copper pipes do when they freeze.Here, you can either use PEX or Copper...I think Galvanized piping is a thing of the past, not used very much in residential, at all anymore,,,maybe for only being buried?Anyway, Pex is super easy and quick too. No need for a torch and solder like with copper/brass pipes. Just a crimping tool, maybe a stretching tool, and a clamp. You can even do with the water running. Try doing that with copper pipe. I so hated trying to sweat pipes. Never could get a good solder joint on them. I'm not a plumber, just fix pipes of my own house.They also have slide on quick connect fittings which don't require a crimping tool, but you'll pay a MUCH higher cost for those fittings. Only worth it for the caps, so you can cap off plumbing like if you were replacing a shower, then uncap them and save the caps for the next job.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 02, 2016, 06:10:15 am
content: Only thing with PEX is it can break the earth bond to any remaining copper pipes in your house. Never seen it done though.I was talking to a plumber and he said PEX is good but he just puts copper in anyway as isn't much more expensive and he finds it easier to work with.

author: Falcon69
author_rank: Super Contributor
timestamp: October 02, 2016, 06:17:59 am
content: you are right about the grounding. We had a new service panel put in. Since the house plumbing was upgraded to PEX, the electrician (aside from the ROD put in the ground), had to string a line under the house and out (under ground) to the water main at the curb.He said normally grounding to the rod is sufficient since the interior of the house had copper at the time and the pipes were grounded to the rod. But, since the house was upgraded, he had to do that. Cost us extra money.If he used Copper anyway and said it was easier, that's only because he has done copper for many many years and is used to the process. Every plumber I've talked to prefers to run the Pex.I could see it becoming standardized in the future. Think of how much money the insurance companies potentially save from pipes bursting in the winter time - PEX vs. Copper.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: October 02, 2016, 09:09:52 am
content: Unless you are russian, russians dont give a single f*ck about safety.because why not use an angle grinder without a shirt cutting some steel hah.

author: VK3DRB
author_rank: Super Contributor
timestamp: October 02, 2016, 09:30:24 am
content: Quote from: ZeTeX on October 02, 2016, 09:09:52 am...especially the safety of babies, toddlers, and hospital patients.

author: SeanB
author_rank: Super Contributor
timestamp: October 02, 2016, 11:16:20 am
content: I have a liking for copper pipe, but where it is outdoor and exposed to the thieves, I will use either a plastic or galvanised pipe, even though I have to go to the local plumbers store with exact measurements of each pipe length so they can thread it, as I do not have a set of pipe taps. For some pipes I had to put the copper pipe inside a cast iron pipe, which actually cost more per metre than the copper pipe inside it. If you really want a long lasting pipe use hard drawn stainless steel pipe, even though every joint would have to be a brass compression fitting.

author: tatus1969
author_rank: Super Contributor
timestamp: October 02, 2016, 11:38:27 am
content: three things that happened to me, and I appear to still be alive:- played around with electrolysis, with one hand deliberately behind my back, and using the other to move around one of the (ground isolated) electrodes. The second electrode got loose and fell into the salt water. My other hand twirled around and caught that electrode before I could even realize what I was doing. I couldn't move my arms or loosen my grip anymore because of the current flowing through my body, and paniced. After an endless time I realized that I could, of course, move my legs, and pushed away. When I mention how I created the high voltage for my experiment you will probably only shake your heads: I had an adjustable model railway transformer that could do 0 ~ 12VAC. To its output I connected a small bell-ringing transformer, but with reversed input and output. That gave me an adjustable 0 ~ 230VAC or thereaboutsHave to say, I was 14 years old or so then.- I was busy cleaning my apartment and put away my mop around the corner. I felt some warmth at the back of my wet hand holding the mop, and it started smelling burnt. I realized that I touched both L and N sticking out of the flush-mounted box after I had removed the light switch. Should I mention that we have 230V here?- working on the power stage of a motor inverter, realizing that it suddenly felt hot. I first thought that some parts had not cooled down enough, but had to realize that the DC bus supply was still on. Now I know that 130V DC does not immediately kill you, it only feels strange.

author: TNb
author_rank: Regular Contributor
timestamp: October 02, 2016, 04:45:32 pm
content: Teardown as promised, though there is not much interesting going on here. I wouldn't destroy it further to know how it is inside, but I don't think it is well insulated, leads are enameled and go inside wrapped in kapton tape, not proper isolation of course, but at least something.

author: IanB
author_rank: Super Contributor
timestamp: October 02, 2016, 04:51:31 pm
content: Quote from: SeanB on October 02, 2016, 11:16:20 amIn industry such pipe would be welded, or would use flanged joints

author: SeanB
author_rank: Super Contributor
timestamp: October 02, 2016, 05:00:00 pm
content: We are talking potable water use here, where you use a really thin walled pipe, so it is either a compression fitting or a very high silver content hard solder instead. Industry will use a laser weld or a TIG or MIG weld, but hard to do that under a kitchen sink or next to a wall.You can use such thick wall pipe with flanges, but only in water treatment plants, not in the home.

author: SeanB
author_rank: Super Contributor
timestamp: October 02, 2016, 05:05:09 pm
content: Quote from: TNb on October 02, 2016, 04:45:32 pmStandard PTC glue gun, they are pretty reliable ( aside from the lead blowing where it enters the body as the strain relief is poor there, and the PTC element will eventually shatter to powder) and the current flow path inside is really short, so there is a low chance of you, sitting in a chair isolated from ground by either a plastic seat or plastic rollers, and with your feet in a plastic bath, from completing a path to earth to get a shock.Birds sit on power lines and do not get a shock, along with live line workers doing maintenance, simply because they are not completing a path to the ground. Bridge across the isolator ( or come within arc over distance) and you will be a very poor light bulb for a second.

author: gamalot
author_rank: Super Contributor
timestamp: October 02, 2016, 05:37:55 pm
content: This glue gun has just saved your life, you should not call it cheapest chinese crap!

author: aandrew
author_rank: Frequent Contributor
timestamp: October 03, 2016, 02:34:10 am
content: Tangential story... back in my former life I worked at an industrial power electronics manufacturer. Three phase reduced-voltage (SCR) soft starters and drives, that kind of thing.We had a beast of a transformer that we used for load testing; 575V in, something like 9V out with enormous lugs on the output due to the increase in current. We would usually run this low voltage, high current source through our equipment and then terminate the equipment with resistive load elements in a 55gal plastic barrel that we kept a stream of fresh running water flowing in to (and draining out the bottom).One night my boss comes up to my office with this funny grin on his face and asks me to come down to the unit under test. My curiosity piqued, I followed.He then tells me to stick my hand in the barrel. I declined, but he convinced me to do it. With only my hand in the barrel of (fairly warm) water, nothing much. But when I got to elbow-depth, I had the oddest feeling in my forearm, like someone was grabbing and releasing my arm 60 times a second.My only explanation is that I was getting some kind of capacitive coupling through my shoes to the concrete. It was a pretty stupid thing to do, especially after reading about how some electrocution damage isn't apparent until many hours after the event, but it was pretty interesting to feel. I can only imagine that if it really was being capacitively coupled that it was not passing through my heart on the way to the ground.

author: IanB
author_rank: Super Contributor
timestamp: October 03, 2016, 02:58:44 am
content: Quote from: aandrew on October 03, 2016, 02:34:10 amWhen I have experienced electric shocks from the mains, I have likened it to golf balls rolling up the inside of my arm.Quote from: aandrew on October 03, 2016, 02:34:10 amNot every mains shock will kill you. While the risk of death is ever-present, the probability of death is fortunately much less than 100%.

author: CJay
author_rank: Super Contributor
timestamp: October 03, 2016, 08:40:04 am
content: Quote from: IanB on October 01, 2016, 11:16:02 pmNo, I think it's perfectly legitimate to use plastic in the UK, there are systems I've seen here which are plastic from the utility entry to every point in the property that needs water, apparently suitable for potable water and also heating systems.http://www.johnguest.com/speedfit/

author: IanB
author_rank: Super Contributor
timestamp: October 03, 2016, 02:28:08 pm
content: Quote from: CJay on October 03, 2016, 08:40:04 amAs long as the pipe is the above mentioned PEX system that should be OK. Where I get worried is if PVC is used.

author: aandrew
author_rank: Frequent Contributor
timestamp: October 03, 2016, 02:37:51 pm
content: Quote from: IanB on October 03, 2016, 02:58:44 amOh, I've received many, many shocks from the 120VAC in the house in my earlier years as both a child and as a teen learning the ins and outs of electronics. The feeling with my arm in that barrel of water was unlike any kind of shock I'd received before.It's funny. I spent the first 13 years of my professional career around three phase low voltage (230-575VAC) and medium voltage (up to 4kV)... I have no fear of them, but that little kid inside of me is still fairly nervous around 120VAC.The high voltage (~50kV), high frequency (and super low current) experiments were the most fun. Lots of ozone and everything around me being statically charged. Those shocks were far more surprising than they ever were painful, even if I'd touched the HV lead directly. :-)

author: SteveyG
author_rank: Unknown
timestamp: October 04, 2016, 09:58:32 am
content: Quote from: Red Squirrel on October 02, 2016, 12:28:45 amWhat's the point you're trying to make here? If there was no heating element present do you think the result would be different?Quote from: helius on October 01, 2016, 10:55:35 pmAgain, what's the point you're trying to make here? If there was no heating element present or the load was different do you think the result would be different?

author: SteveyG
author_rank: Unknown
timestamp: October 04, 2016, 10:01:23 am
content: Quote from: edpalmer42 on October 01, 2016, 11:11:12 pmThe Mythbusters "test" was flawed in so many ways. It also assumed you have a bath waste that is conductive, however in the majority of the world we have plastic wastes and plastic waste pipes.

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 04, 2016, 10:43:19 am
content: Quote from: IanB on October 03, 2016, 02:28:08 pmYeah pex is fine and is pretty much what goes in now days. I don't think I would trust PVC or anything that is glued for pressurized applications such as water supply. I've heard of CPVC being used and that kinda makes me cringe. It's not really designed for high pressure applications.

author: CJay
author_rank: Super Contributor
timestamp: October 04, 2016, 10:53:56 am
content: Quote from: SteveyG on October 04, 2016, 10:01:23 amWould be interesting to know if metal taps and wastes have to be supplementary bonded though...

author: SteveyG
author_rank: Unknown
timestamp: October 04, 2016, 12:42:49 pm
content: Supplementary equipotential bonding is only needed where conductive items may introduce a potential in the event of a fault. Normally the main bonding is sufficient if all circuits in the bathroom are protected with a 30mA RCD. If supplementary bonding is needed, it'd only be required where the water or waste pipes are metallic. You don't need to bond metal taps on plastic pipe, just like you don't bond the door handle or the toilet roll holder.

author: CJay
author_rank: Super Contributor
timestamp: October 04, 2016, 01:56:46 pm
content: Quote from: SteveyG on October 04, 2016, 12:42:49 pmMakes absolute sense and is exactly what I'd expect but y'never know.

author: rrinker
author_rank: Super Contributor
timestamp: October 05, 2016, 02:32:15 pm
content: Quote from: SteveyG on October 04, 2016, 10:01:23 amMaybe on all new construction. But my house was built in 1972, and the main waste pipes from the bathrooms are cast iron pipe, same as was in the house I grew up in, which was built in the 50's. Though it's not the electrical properties that really worry me, it's the way it weakens as it ages and then leaks, so at some point I may have them replaced as a preventative measure. Most of my under sink traps are that crappy metal, too. I much prefer plastic there as well, as it tends to not have major failures, just leak around the connections.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: October 05, 2016, 05:36:54 pm
content: How about this?

author: helius
author_rank: Super Contributor
timestamp: October 05, 2016, 10:50:34 pm
content: Quote from: SteveyG on October 04, 2016, 09:58:32 amIt's not warranted to assume that water acts as a purely ohmic load in these cases. In order for current to flow at all, there is some polarization (capacitance) in the ion gradient, which isn't easily separated from the heating element since it has area which alters that capacitance. You can't really model it as two parallel loads.

author: zl2wrw
author_rank: Regular Contributor
timestamp: October 05, 2016, 11:46:12 pm
content: Quote from: aandrew on October 03, 2016, 02:34:10 amWas the 9V secondary of that transformer floating? (or was it earth referenced?)Did that transformer have an earthed electrostatic screen between the 575V primary and 9V secondary windings?I suspect that what was happening was that high frequency common mode was capacitively coupling through the insulation between the transformer primary and secondary windings and your arm was a path to earth!I have had a plumbing related "shock". House was built in the 1940's, plumbed with Cu pipe and a galvanised iron connection to the old cast iron city water mains, and in NZ, conductive water pipes are bonded to protective earth, which is bonded to neutral (MEN variant of TN system). It was a hot summers day, so I was barefoot, washing the car and playing with the dog with the hose - when I was done with this, my hands and feet were thoroughly wet (pruned skin etc). When I grasped the handle of the brass outside tap to turn off the hose, I felt a rather noticeable 50 Hz tingle - thought "that shouldn't do that!".After I got dried myself off and got changed, I got my trusty Fluke DMM and found that there was about 15 Vac RMS touch potential between the outside tap and local ground. A clip on amp meter indicated that there was a couple of amps flowing in the PE bond to the galv. iron water pipe coming into the front of the house. The power company came and had a look and basically said that there was nothing wrong with the wiring in the house (ie neutral hasn't gone open) and that the fault was somewhere else and that this house was just in the return path for the fault wherever it is (they basically gave up as no one had any idea where the fault was). A couple of years after that, water started leaking out of the old galv iron water pipe under the front lawn. The plumber replaced it with plastic pipe, and as a result, the touch potential on the outside tap at the back of the house went to zero

author: IanB
author_rank: Super Contributor
timestamp: October 06, 2016, 12:52:45 am
content: Quote from: zl2wrw on October 05, 2016, 11:46:12 pmGalvanic corrosion due to the fault current, perhaps?

author: zl2wrw
author_rank: Regular Contributor
timestamp: October 06, 2016, 08:03:41 am
content: Quote from: IanB on October 06, 2016, 12:52:45 amYes, I assume that is what happened to the pipe.Somewhere in my neighbourhood, there probably was (and maybe still is?) a house with an open circuit neutral conductor, resulting in most of their return current flowing through the neutral-earth link in their switchboard, to get to the metallic city water mains, to get to the neutral-earth links in all the other houses, and thus back to the neutral conductor and the distribution transformer.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 06, 2016, 08:22:27 am
content: Quote from: zl2wrw on October 05, 2016, 11:46:12 pmDo you have RCDs on your house?How good is your Earth?Do you have a shed or outbuilding with a separate Earth stake?If it was a neighbours house, I am guessing it would have to be pretty close. Or else something of yours, pool or a sump pump?Where did the galv pipe go? Was it only attached to your house or was it incoming?

author: zl2wrw
author_rank: Regular Contributor
timestamp: October 06, 2016, 11:05:44 am
content: Quote from: HackedFridgeMagnet on October 06, 2016, 08:22:27 amYes, the house has 30 mA RCCBs for sub-circuits as per ASNZS 3000:2007 (hot water cylinder, range and heat pumps excluded).Turning off the main switch made no difference to the current flowing in the bonding wire connected to the water pipe.The people that the power company sent to investigate said that there was nothing wrong with the wiring of this house (yes, they did look at/test the main earth rod, and inside the switchboard too).In any case, replacement of the metal water main to this house with plastic pipe eliminated the touch potential and stray current (if we had a bad earth rod and a bad neutral, I'd expect that replacing the metal pipe with plastic would make the touch potential much higher, not lower).

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 06, 2016, 12:43:30 pm
content: Quote from: zl2wrw on October 06, 2016, 11:05:44 amJust trying to think through how you got that tingle.The only thing I can think of is, as you said before you have some non zero remnant voltage on the incoming Gal pipe but that this pipe has was not electrically well bonded to your water pipe and therefore your main earth.Maybe your soil type is not very conductive, and it only became conductive with all the water.Also bear in mind it is easy to have a good earth stake but not a good earth, all the power guys would have done is test the resistance to the earth stake, not to the ground as you need a special meter for this.But I guess in those situations the earth itself becomes less important.Ps. If you could be bothered, you can get some 2 part compound to improve an earth cant think of the name. But unfortunately I think plants don't like it.

author: SteveyG
author_rank: Unknown
timestamp: October 06, 2016, 12:48:32 pm
content: Quote from: HackedFridgeMagnet on October 06, 2016, 12:43:30 pmIt's the typical PEN failure on a TN-C-S system. The mass of earth and the earth derived from the PEN conductor end up at dissimilar potentials. This is the reason TN-C-S supplies should not be exported to outbuildings any significant distance from the property.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 06, 2016, 09:12:27 pm
content: Quote from: SteveyG on October 06, 2016, 12:48:32 pmWell it probably isn't a typical PEN failure because AFAIK they found no broken PEN when they checked the premises.