pool saftey idea - Page 1
Forum section: electronics / projects

author: sarepairman2
author_rank: Frequent Contributor
timestamp: January 30, 2016, 12:18:43 am
content: watching that indian man on youtube conduct dangerous experiments gave me an idea.a pool accessory that is basically a little blinker circuit that can only be turned on if there is dangerous electricity in the water. powered by the electrodes it has in the water.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 30, 2016, 12:29:49 am
content: He's Iranian actually... but whatever

author: rs20
author_rank: Super Contributor
timestamp: January 30, 2016, 12:43:26 am
content: Are pools normally earthed, either deliberately or incidentally?Because if so, the RCDs thatshouldbe connected to any outdoors outlet (and possibly your entire house) should cut the power to whatever is energizing the pool the moment it happens.Prevention is better than warning, after all.You also need to define your problem more precisely. By "there is dangerous electricity in the water", do you mean "the water is at high voltage with respect to Earth?" Because the latter actually means something, and requires one leg connected to the water and another connected to earth to do its job. Two electrodes just sitting in the water can't do anything, there's no reason the two electrodes would be at different potentials (unless they were made of different metals, but then it'd generate voltage regardless of the "safety" of the water).

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: January 30, 2016, 12:49:57 am
content: Quote from: rs20 on January 30, 2016, 12:43:26 amThey are assumed to be earthed, but I don't think we have a requirement to earth them.That said you would only have extra low voltage lights these days and the pumps and any metal piping would be earthed

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 30, 2016, 02:18:12 am
content: Quote from: sarepairman2 on January 30, 2016, 12:18:43 amAre electrified pools a big problem? Where would the earth or neutral be for the gizmo's reference? Cuz it's not going to detect much of a potential difference IMHO if it's literally floating by itself in the middle of the pool?You know, like a bird on a wire?

author: Nerull
author_rank: Frequent Contributor
timestamp: January 30, 2016, 02:46:38 am
content: If there is a voltage gradient across the pool and the device has two electrodes spaced apart within that gradient, you could detect it. The reason birds don't get electrocuted sitting on a single wire is because the wire is very conductive. The voltage gradient across a few inches of wire is essentially zero, so there is no risk of shock. With water, this is not the case. Water is a conductor, but a pretty poor one, so there is substantial voltage drop across a few inches of it, so if anything more conductive - such as you - is placed in the water across the gradient, current will flow through it. For this to be a problem, you need to be located somewhere between the voltage source and a ground.This is what happens in cases like this:http://lakeexpo.com/news/lake_news/swimmer-electrocuted-at-lake-of-the-ozarks/article_25de24fe-1929-11e5-8ca0-0ff78a16476d.htmlI've never heard of this happening in a pool, but I suppose it would be possible. You need a live wire in contact with the water, and a ground some distance away, so that a gradient is created that someone could potentially enter. Your detection device also needs to be in this gradient, and aligned such that its electrodes would sense a measurable voltage difference.It would probably be simpler and better to make sure that any place where high voltage could potentially enter the water - such as the writing to a pump - also has a good ground, so that the shortest path can never be through the pool.

author: rrinker
author_rank: Super Contributor
timestamp: January 30, 2016, 03:54:36 am
content: Quote from: rs20 on January 30, 2016, 12:43:26 amThey certainly are in the US. GFCI is required anywhere there is water - so kitchen and bathroom outlets near sinks also must have them. My in ground pool has one at the main box where the sub panel splits off to go underground to the box located by the filter equipment. When it comes down to it, there's very little chance of mains power getting to the pool - the only electrical element in the system for my pool is the pump motor, and while the motor casing is metal (and has an earth wire attached), the pump impeller and housing are some sort of reinforced plastic material. All the piping from the filter to the pool is PVC. So it again comes down to the conductivity, or lack thereof, of the water.Small non-permanent pools that are big enough to use filters, the filter will have a GFCI built in to the plug, in case your house is older and the outdoor outlet is not a GFCI. Other portable appliances that might be used in a wet environment, like hair dryers, also have this sort of arrangement.

author: Xplode
author_rank: Contributor
timestamp: January 30, 2016, 06:41:39 am
content: You could, in theory, use a probe in the water to compare against the electrical service's earth ground. If the water became energized, it shouldn't be that hard to detect.However, most times the pools are now protected by GFCI circuits with <15mA trip settings If my memory serves me right.Accidents do happen though, so a buzzer (instead of the light) might be a good backup safety. I remember seeing a video online a year or two ago about a hotel pool in the USA that became electrified suddenly and electrocuted a bunch of people. Especially when they touched the metal railings/ladders.