Electrified Water Detector - Page 1
Forum section: electronics / projects

author: ianxtreem
author_rank: Contributor
timestamp: April 24, 2016, 03:12:12 pm
content: Hey everybody, I recently purchased an old marina and one of my biggest concerns is that one of my customers will fall off a dock, or a child will jump off a dock into electrified water. I want to build a series of sensors around the marina to monitor the water and report to me if any part of the water is electrified so that I can take action to effect repairs. The biggest cause is worn power cords from the dock to the customers boats, but sometimes its hard to tell that they are bad. Electrified water is either from 115v or 220v ac. 60hz.So, on to my questions... Do you have ideas for the construction of a sensor. I would imagine I am simply detecting an AC voltage at 60hz... But, the question is between the water and what? Maybe this is just a non-contact voltage sensor? I'm not exactly sure of the properties of electrified water, but I am researching. Also, I would like to set up a test bed without killing myself. My thoughts there are a large power resistor between my AC source and the water. Any thoughts?

author: Marco
author_rank: Super Contributor
timestamp: April 24, 2016, 03:34:57 pm
content: Wow, I didn't even know that wasa thing...Unless you have idiots throwing their own cables around powered by a generator "all" you need is ground fault protection devices for each plug on the marina.

author: SeanB
author_rank: Super Contributor
timestamp: April 24, 2016, 03:53:54 pm
content: They also require regular maintenance and checking, which many marinas and boat owners will not do as it is seen as a cost that has no benefit - they see the power is still on even with a fault, but with the GFCI installed any fault results in a no power trip and a repair, which they see as a nuisance cost and a waste of time. Also an expensive retrofit, you might have to replace every cable on a dock, and install new outlet boxes to replace the old ones, which still allow power through, even though they are half full of water from damaged cases and torn out cable glands. As well you need a GFCI per socket outlet, not a single 100A breaker at the shore end, so those who are drawing 40A over a single socket outlet to power the AC, sauna, cooker, enough light to do a stadium and such will complain the power trips at 20A.

author: ianxtreem
author_rank: Contributor
timestamp: April 24, 2016, 03:57:52 pm
content: Quote from: Marco onTodayat 07:34:57 PMUnfortunately its not as simple as that. Sometimes ground fault plugs dont always work. Sometimes a muskrat eats through the insulation on the supply line. Sometimes someone is running an inverter off of a 12v source. Last week a child near here drowned after jumping in the water into electrified water. And lastly, the world is full of idiots.... So i think prevention is part of the answer, but detection is another part.

author: ianxtreem
author_rank: Contributor
timestamp: April 24, 2016, 04:00:05 pm
content: Yep, all of this is true, but prevention is just one part of the solution.... detection is another.Quote from: SeanB onTodayat 07:53:54 PM

author: Marco
author_rank: Super Contributor
timestamp: April 24, 2016, 04:17:45 pm
content: Quote from: ianxtreem on April 24, 2016, 03:57:52 pmIf they use their own generator/inverter and there is a circuit from say something at the back of the boat to the prop there is very little you can do about it ...

author: sarepairman2
author_rank: Frequent Contributor
timestamp: April 24, 2016, 04:22:57 pm
content: search my threads, i made a thread about this for pools. I think people posted some stuff there that might be relevant.you probobly want 2 electrodes to detect a Efield.i am very curious about how things are in the ocean though....also, someone should link that video of that indian guy who made the video about water/electricity.he does some experiments with a beaker of salt water and a lamp cord, that should not be replicated, but are VERY relevant.

author: dmills
author_rank: Super Contributor
timestamp: April 24, 2016, 05:42:49 pm
content: Ah, shore power hookups, **always** good for a giggle...You do not say which country you are in, but Marinas are often treated as 'special locations' in the wiring regs (I believe 7671 and the US NEC do this as a minimum).It is actually a much hairier problem then it at first appears, not just from the life safety perspective, but also from the perspective of managing electrolytic corrosion of sub surface fittings and structures. from a life safety angle, the problematic fields can be very localised, so better to take steps to avoid the problem then try to detect that you have it.What are the earthing arrangements for the incoming neutral (TN-C-S/PME/MEN and variants can be particularly troublesome), and are there isolation transformers in play? TN-C-S style supplies are troublesome because the IR drop in the common neutral/earth results in a 'earth' at the shore power box that may be meaningfully different to the body of earth.The smart approach is individual isolation transformers with the output side neutral 'earthed' to the water and an earth leakage trip fitted to the output side after the earth bond, if you want to get clever you can use a small CT to measure the earth leakage directly in the earth bond (Or use an earth leakage relay with a display, but this is probably overkill).At a bare minimum every outlet in a marine environment should have an earth leakage (GFI) breaker fitted and it should cut all poles when it trips.Regards, Dan.

author: helius
author_rank: Super Contributor
timestamp: April 24, 2016, 06:47:59 pm
content: I'm picturing some kind of RC model boat with submerged plates fore and aft, with a buzzer circuit that begins wailing when there is more than 2 VAC per foot across the plates. Then you just have to use it...

author: Kilrah
author_rank: Unknown
timestamp: April 24, 2016, 06:51:58 pm
content: Except you would need hundreds of those - that's the problem I'd see with detection. Given the issue is likely to be localized you'd need hundreds of the sensors everywhere in the water, and they'd have to be where people are likely to be in the water - i.e. in the way of said people and the boats that come and go, and cut them in pieces.

author: Ian.M
author_rank: Super Contributor
timestamp: April 24, 2016, 07:09:13 pm
content: Any responsible marina has a strict no swimming in berths or fairways policy. Enforce it!As both swimming and the greatest voltage differential usually occur at the stern of craft berthed bow in (because of acccess and because the sterngear is usually the largest area of underwater metal within 6' of the surface), it is extremely difficult to monitor voltages in the water. Maybe put sensors either side of a workboat that are always on, with a GPS linked data logger, and do a regular patrol, close in both sides of each fairway, which also enhances security. If you check for DC as well you'll have far fewer cases of electrolysis damage caused by proximity to idiots who've grounded their battery positive, which will improve your marina's reputation.

author: Marco
author_rank: Super Contributor
timestamp: April 24, 2016, 08:09:45 pm
content: Quote from: dmills on April 24, 2016, 05:42:49 pmSo a 3+ kW isolation transformer per dock? That's a bit expensive.

author: dmills
author_rank: Super Contributor
timestamp: April 24, 2016, 08:50:06 pm
content: Not cheap, but very, very effective, and it is actually what many vessels that move around a lot fit on their end of the cables anyway, just to ensure they are isolated from whatever insanity the dock you are visiting has come up with (And trust me on this, there is **EVERY** sort of insanity out there, even before you get to the other guys messed up cathodic protection).Certainly the first thing shore power hit when I was doing sea going things was a sodding great iso transformer down in the machinery spaces, the ability to tap change to trim voltage was also rather nice.Regards, Dan.

author: ianxtreem
author_rank: Contributor
timestamp: April 25, 2016, 02:19:53 pm
content: Quote from: dmills on April 24, 2016, 05:42:49 pmI am in the US. Thanks for the input. Yes, this problem is more complex than first glance. The problem is also made much harder given the magnitude of the repairs to be done and the simple economics of having to repeat the solution for over 200 slips.

author: ianxtreem
author_rank: Contributor
timestamp: April 25, 2016, 02:22:26 pm
content: Quote from: Kilrah on April 24, 2016, 06:51:58 pmNot a bad idea... we already own a remote control boat... We also do dock walks each day, so a sensor on a stick would work as well.

author: miguelvp
author_rank: Super Contributor
timestamp: April 25, 2016, 04:33:21 pm
content: Not sure this will work because electrolysis is done with DC power, but maybe electrified water does spew Hydrogen specially at low AC frequency, so I guess a detector of excess Hydrogen concentrations might work.I wouldn't try to look for O2 because depending on the water composition you might not get pure O2.Edit: it should be easy to test but it goes without saying that you should be very careful.Hydrogen detector modules are very cheap (under $5) and probably Arduino friendly if you don't have a lot of experience with MCU's

author: Ian.M
author_rank: Super Contributor
timestamp: April 25, 2016, 06:23:02 pm
content: A sensor on a long stick (say a fishing rod) would be useful once you have an indication of problems in a localised area so you can quickly locate and disconnect the offending vessel, but for finding problems in the first place, it would be tedious enough that it is likely to be underutilised, as for reliable detection you need to dip the sensor within a surface distance of no more than a couple of times the depth, with no immersed pontoon metalwork (or concrete floats) between the dip point and the live metalwork on the offending vessel.

author: ianxtreem
author_rank: Contributor
timestamp: April 26, 2016, 02:16:17 pm
content: How about this for a sensor.... A current will be induced in a wire that is in the presence of an alternating electromagnetic field... So, I run an insulated wire down the length of a dock, attached to the under water infrastructure, and back up the opposite side of the dock. If there is an EM field anywhere along the length of wire I should be able to detect it, right? This places my sensor next to the dock ( the most likely place that someone will fall in) and near the stern of most boats (the most likely place for electricity leakage). Granted it only tells me that something is wrong, not the location, but if I know something is wrong then I can track it down via other means.

author: Ian.M
author_rank: Super Contributor
timestamp: April 26, 2016, 02:35:39 pm
content: No joy. It will only couple well to currents that flow parallel to it and a lot of the parallel component of the current in the water will cancel out either side of the nearest point on the wire to the fault location. Close proximity of the grounded dock metalwork will further reduce the sensitivity. Also, stray fields from power posts, lighting and power distribution wiring will swamp the tiny induced current you are trying to monitor.