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My wife has recently taken to running a cord out near our pool to watch TV. She's very careful, but I was thinking of doing what I can to make it safer, since the outlet in question is NOT a GFCI outlet (It's a standard US 110v outlet).

One obvious solution is an inline GFCI (or installing a GFCI outlet)

The other more expensive idea that occurred to me is using a 5ah 40v lithium battery that I can purchase a 300w inverter for.

My guess here is that if the wired TV were to go into the water, a GFCI would be better than nothing, but unsafe...whereas the battery would be practically speaking likely to be completely safe. Can anyone enlighten me as to which approach would be the safest, and if either or both is actually "safe"?

The water is typical "saline-pool" water.

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    An inverter is also taking the voltage back to 120 VAC. You can still deal enough current (2.5 A) to kill with a 300W inverter (death can occur with significantly less than 1 A). – statueuphemism Jan 21 at 3:56
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    @user253751 This is not true. An isolation transformer's secondary circuit is not grounded, but if you put both poles into water, there will be an electric field in the water which will not only form directly between the poles, but also within a certain range. – glglgl Jan 21 at 14:12
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    40v DC in water can be dangerous. – Hot Licks Jan 21 at 19:29
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    I'd love to hear your thinking of why the battery and inverter would add any safety at all. You'll still be delivering potentially lethal 110 AC with no mechanism to shut the power off should a circuit complete through a person. – David Schwartz Jan 21 at 21:22
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    @DavidSchwartz - No thinking. My intuition, which I know to be often wrong when it comes to electricity, which is why I asked. I don't really understand electricity well enough to think about it. Very glad I asked. – zzxyz Jan 21 at 21:50
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It doesn't need to be a GFCI outlet. It needs to be GFCI protected. GFCI protection is conferred by having any particular outlet obtain power power from the LOAD side of a GFCI device somewhere. On most string-topology circuits, a single well-placed GFCI device will protect the whole circuit.

If you stick a GFCI tester in there, push the button and the outlet goes dead, you're sympatico.

The bigger problem is the temptation to bring cords to the pool area

Your #1 safety risk is the fact that people wanting to plug things in, in the pool area, feel a need to run an extension cord from some distant location. This requires a social-engineering solution. You need to rearrange your home to suppress that desire.

So either put GFCI protection on every outlet they might ever dream to tap... or, install a plethora of outlets, actually poolside, that are protected by a GFCI device somewhere. I prefer to have my GFCI devices indoors, so I make extensive use of the LOAD feature of GFCIs. Now there's no reason for someone to run an extension cord to the pool area; there are outlets all over the place.

GFCI is safe as you're going to get

A properly installed GFCI setup, with the protection device some distance from the outlet, is as safe as things can be. It will trip the GFCI if hot or neutral current takes a path other than the normal one.

Higher DC voltages bite. HARD.

Electronics and car people tend to believe DC is docile and harmless. It is at 12V, yes. However, somewhere in the 20s it starts getting a personality, and by about 60 volts it goes full honey-badger. Can 40V bite you? Oh, yes it can! And it won't let go, either. So ixnay on the 40V battery pack. I encourage you to develop a little bit of fear of it.

TVs are 12 volts, anyway

Besides, now that TV tubes are gone, lot of TVs these days actually use a low voltage, typically 12 volts. Better off just using a battery pack that size than do a double conversion.

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    Also: lithium batteries are liable to explode violently if they fall in water. Is that better or worse than the GFCI? – user253751 Jan 21 at 10:41
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    @user253751 A small explosion is preferable over electrocution, but I'd prefer to avoid both. – Mast Jan 21 at 12:09
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    I recall many years ago being stung by a POTS line, gave it more respect after that. – Gary Bak Jan 21 at 13:10
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    It's going to be hard to forget the image of the full honey-badger battery pack! – Cort Ammon Jan 21 at 15:03
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    "TVs are 12 volts" LCD panel with CCFL backlight contains an high-voltage circuit to power it (probably low-current but still couple thousand volts). Only LED-backlit TV are full low voltage outside the main transformer. – zakinster Jan 21 at 17:18
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High voltages may be present inside the TV, and eliminating ground does not make the electricity harmless in water.

When energized electrodes are applied to water, an electric field is created which extends far from the electrodes. Depending on the voltage, whether there's pulsing or AC, and current this can induce muscle contractions and make people and animals unable to leave the water, or maintain a safe posture above the water.

So, in short, no - a battery and inverter combination is not safe, and certainly not safer than a GFCI protection unit.

While a properly used GFCI will stop the current very quickly once a wire or electrical appliance drops into the water - it will only do so if the appliance doesn't have an isolated power supply. Most electronics, however, do have voltage converters that isolate internal power from the power line, which means it's possible for a partially submerged electronic device to create an electric field in the water without causing the GFCI to trip.

The only adequate solution is to mount the TV and all wiring in a permanent fashion so it cannot come into contact with the water, and to GFCI protect it. If the TV is mounted to the wall, for instance, and connected via a short cord to a GFCI outlet mounted high on the wall with a tamper evident cover and lock (to discourage others plugging in extension cords which could reach to the water) then you'll achieve a reasonable level of safety. You may need a larger TV to make up for the distance from the water, and you may need more weather proofing if this is outdoors.

Any solution where it's possible for the electronics or wires to come into contact with the water is inadequate, regardless of the care of those using the equipment, or the protections you might put in line.

An alternative is using a tablet in a waterproof case, or one of the many newer waterproof or rugged tablets. It will probably be cheaper and more flexible than the TV, and if you have cable or satellite service you can use it with online streaming to get essentially the same content without having to use a real TV. If you already have a suitable tablet, the waterproof case would be cheaper than hiring an electrician to mount the TV and wire in a GFCI outlet.

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  • (Very bad) 9" Tablets pretty much start around $80, which was the price of this TV. Mounting the TV is not possible (there's no wall). However using GFCI is not at all a problem and the TV itself can be kept well away from the water and untouched when plugged in if desirable (and it sounds like it is). That would leave the only potential contact with water being the cord itself with nothing plugged into it, or an unplugged TV. – zzxyz Jan 21 at 19:28
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How about bolting the TV set to the wall permanently (above the possible splashes) AND employing GFCI for all circuits that go somewhere near the pool? It is just a matter of time someone to bring a hair dryer.

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