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I had an issue recently where my cat turned on a laundry tub faucet, flooding the basement with municipal water (due to the floor drain being clogged; 1930 house in the Toronto area).

There was a live extension cord plug (connected to the clothes washer; off) fully submerged in 4 inches of water. I was surprised that the submerged extension cord plug didn't trip the breaker. It actually would have been preferable if the breaker had tripped, because otherwise, I had to wade through the water (possibly electrified) in rubber boots to get to the breaker to cut the power, which seemed risky, and then wade over to turn the tap off.

Why didn't the live extension cord plug short to ground, tripping the breaker? For example, I would have thought it would have shorted, possibly shorting to ground through the cast iron drain pipe in the floor.

(I don't have any experience with electrical stuff; feel free to correct my terminology.)

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    The circuit breaker is designed to trip with current above a certain amount. Fresh water, with no salt in it, doesn't conduct electricity very well. Also, the "ground" that would complete a short circuit is the "equipment ground", the third wire in a 3-prong outlet, not the actual dirt/earth. I suspect your drain pipes are not connected by wire(s) to your electrical system's ground (although your cold/hot water pipes if metal likely are).
    – Armand
    Dec 31, 2023 at 7:32
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    When you say "fully submerged" do you actually mean at the end? The cable itself is waterproof but the connectors aren't. Do you have an earth leakage breaker (GFCI)? That will trip on a small fault to ground and while common in wet locations they're by no means universal. A normal circuit breaker will trip on overcurrent, with the speed depending on the amount of overcurrent
    – Chris H
    Dec 31, 2023 at 8:04
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    @ChrisH "When you say "fully submerged" do you actually mean at the end?" Yes, at the end, at the connector. No, I don't have a GFCI.
    – User1974
    Dec 31, 2023 at 8:41
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    I once waded into a flooded Bank to turn off some servers on a table, perhaps ankle deep. I hit the wall switch and they didn't go off but there started a click and beeping. Turns out there was a UPS on the floor, half submerged. That was a time-slowing moment, realising that there was probably mere centimetres between the dirty water and the energised electrics inside. After considering my options, I slowly moved to the UPS and held down its power button with a plastic pen from my pocket. It went off along with the computers. Phew!
    – Criggie
    Dec 31, 2023 at 21:39
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    @Armand You are incorrect. There is a relationship between the literal ground/earth and the equipment ground. Buildings connect that ground (to which the third prongs go) into the earth with a metal stake. A flooded extension cord connected to ground via mildly conducting water will likely trip a GFCI.
    – Kaz
    Jan 2 at 2:36

3 Answers 3

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Good thinking on the rubber boots, but next time call the power company, or find some other way to turn off the power.

Without a GFCI municipal water will not conduct enough current to trip a breaker, but will still conduct enough to paralyze you. (and then you drown) So you only get one chance, if you slip on something and fall in the water, you're toast (or perhaps soup)

As mentioned in comments installing GFCI outlets (or GFCI breakers if the outlets are located below the flood line) is probably a good idea. NEC requires GFCI outlets in new-build laundry areas.

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    This would be a good time to install GFCI receptacles in the basement, which will trip if this happens again.
    – Mark
    Dec 31, 2023 at 16:32
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    @Mark That may not help much if the receptacle itself gets submerged, as there'll still be contact with the live wires leading up to it.
    – Bob
    Jan 1 at 23:46
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    Better still - don't connect your washer to the mains via an extension lead. Arrange a GFCI protected socket to be near the appliance.
    – D Duck
    Jan 2 at 0:15
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    It does go to every path, proportional to resistance - to some extent. Lights and toaster show a similar path, but the short trip through two leads vs the long trip through the person do not. Jan 2 at 16:29
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    To be clear, I am not at all advocating the idea of going through potentially electrified water - it is just that touching it is most probably not going to do anything to you, but there are a thousand other things that can go wrong. Jan 2 at 16:32
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It probably did short to ground (and to neutral). But that doesn’t actually trip the breaker reliably unless it’s a GFCI breaker or the short draws enough current to hit the trip point on the breaker, which it almost certainly did not.

Given that you mention the device plugged in is a washing machine, it’s probably a NEMA 5-15 or NEMA 5-20 plug. That means hot has 12.7mm of water to cover to short to neutral, and equivalent to ground. Good tap water typically has a resistance on the order of about 2 kΩ per meter. That gives us roughly 25.4 Ω of resistance, which at 120 V translates to just short of 5 A across the ‘short’ between hot and neutral, and the same to ground. Leakage beyond that is probably negligible in this case, so we’re looking at around 10-12 A. But your washing machine should be on a dedicated 15 A or 20 A circuit, and that’s not enough to trip the breaker for such a circuit.

To actually trip a 15 A breaker you need a short with a resistance of 8 Ω or less, and a 20 A breaker needs a short with a resistance of 6 Ω or less. That’s actually possible with tap water in some places, but it’s rather uncommon in more populous parts of North America or Europe.

Now, this does not mean that wading through the water was safe, even with well insulated boots. Water’s conductivity is very closely related to what’s dissolved in it and how much, your skin has plenty of stuff on the surface to dissolve into the water to raise that conductivity. Factoring that in, if you got close enough to the end of the extension cord (or to an outlet in the wall) and fell into the water, you very likely would have been paralyzed, and probably drowned as a result.

In the future, it’s much safer to call the power company for a temporary shutoff. Also, you probably should take the time to install GFCI breakers for all the basement circuits (not just this one) as they would have tripped in the described situation, and possibly look into better drainage to help avoid such scenarios.

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    Which all points to the benefit (though up-front cost can be significant) of an outside whole-service disconnect switch. Jan 1 at 2:27
  • So, another method would have been to throw some salt in the water...
    – Toffomat
    Jan 1 at 21:05
  • @Toffomat In theory yes, but with the volume of water likely involved, it would have had to be a lot of salt. Jan 2 at 2:34
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    "That’s actually possible with tap water in some places, but it’s rather uncommon in more populous parts of North America". A very good point, especially regarding "more populous". I rather suspect that my well water, pre-treatment, is in fact able to conduct that much current: so if I had a leak at between the entry to the house and the treatment system, I'd be at risk. Fortunately, 21st century electrical codes and whole house GFCI.
    – Auspex
    Jan 2 at 21:09
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    @AustinHemmelgarn Of course, this wasn't serious, but now you somewhat nerd-sniped me. The resistivity data for salt water seems disorganised and inconcistetnt, but a concentration of 1% would certainly suffice for good enough conductivity. For a plausible basement of 10*10 m^2, flooded to 1 m (so you can wade through with high boots), this requires a ton of rock salt, which costs only about 60$, so likely cheaper than an electrician (but shipping not included)...
    – Toffomat
    Jan 3 at 8:29
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I worked with an electrician who serviced a lot of commercial installations, so I got to learn a little about the difference between things like GFCI / C/AFCI but this guy explains it very well:

https://www.youtube.com/watch?v=E3rTqsL-CRU

Moreover I've lived in a house where a breaker remained engaged during a dead short and the wiring began to burn up inside of a wall and it almost burned down the house. The cost of good breakers is rather prohibitive:

https://www.bogleheads.org/forum/viewtopic.php?t=371755

For the most part what people are suggesting elsewhere in this thread about GFCI outlets, they're absolutely correct, but your breakers are also designed to operate a particular way depending on what you have and there are different kinds. Based on what you've described the water despite completing a circuit between hot and neutral didn't sink enough current to trip the breaker; my understanding is that a C/AFCI would absolutely fault if you completed a direct circuit between hot and ground; a qualified electrician can (and should be) the one to confirm that for you.

I would get the models of all of my breakers and find out what kind they are, and if you kinda understand the theory so far about different kinds of breakers and their operational characteristics maybe even cross check what is code. Moreover what is code is not necessarily the same thing as what is safe; code can be a minimum.

Ultimately I would have an electrician make an assessment and just know that if they're reasonable it's unlikely that they're going to recommend anything that they couldn't personally justify for themselves--not out of necessity; most of their clients probably can't understand or don't care that much. Absolutely ask questions and if possible have your own opinions because ultimately it's your house.

But again I can't emphasize this enough; find a qualified professional for an assessment.

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