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 Philly Master 04-17-2013 05:53 PM

Question ??????

here is a question ... FUN one ..

your standing in a bathtub full of water.... naked ... you put your right hand "IN" the neutral side of the GFI ...and your Left hand in the Hot side ( for the DIY ) would the GFI trip ...or would you get electrocuted ??

AND WHY !!!

 jeffnc 04-17-2013 06:22 PM

I'm not an electrical engineer, but I believe the breaker would trip. The electricity sees far less resistance flowing through your body to the neutral side of the circuit than through your body and then the water, however that should simply mean that less current should flow through the water - but not zero. This of course assumes your plumbing is metal and goes to ground.

Interestingly, if you take the water out of the equation, you get electrocuted (because the GFCI sees you as a normal electrical appliance.) So in this case standing in water is safer than not! An apparent paradox, but that is how GFCI is meant to work.

Good question.

(The above is my guess at a hypothetical question, not the definitive answer, in case some idiot at home wants to try this.)

 AllanJ 04-17-2013 06:24 PM

Depends on how "good" a contact was made at each of the 3 points, fingers on receptacle slot contacts (2 places), and feet through water to metal drain fitting to plumbing system to gounding electrode conductor back to panel..

Some current will flow through your body between hot and neutral, and some current will flow through your body between hot and ground. If the latter is less than a few milliamperes, the ground fault interrupter unit will not trip and you could be electrocuted by the hot to neutral flow.

 jeffnc 04-17-2013 06:33 PM

Hmm, I like Allan's answer too. Very thought provoking....

 mpoulton 04-17-2013 06:46 PM

The equivalent circuit for this is approximately three resistors in a wye arrangement. Two of them are your arms going to the receptacle slots, and the third is your body going into the bathtub. If the bathtub is grounded, then two points are at zero potential (right hand and feet) while the third is at 120V (left hand). So the result is that current flows in the left hand, and out both the right hand and the feet. The current out of the right hand would be similar to the current out of the feet (depends on the relative resistances of those body parts). This would trip the GFCI since a substantial amount of the current leaving the hot terminal does not return through the neutral, but instead goes to ground through the bathtub.

If the bathtub is fiberglass with a PVC drain line, the result may be different. The water in the tub is isolated from ground. Now the circuit is just hand-to-hand, and all current returns through the GFCI so it doesn't trip. You get electrocuted, but the bathtub has nothing to do with it.

One thing will definitely not happen: the breaker will not trip. There's no conceivable way that more than 15A will flow in this scenario. That would require a total resistance of 8 ohms or less, but body resistance is on the order of hundreds of ohms even neglecting skin resistance.

 jeffnc 04-17-2013 06:52 PM

Quote:
 Originally Posted by mpoulton (Post 1161458) The current out of the right hand would be similar to the current out of the feet (depends on the relative resistances of those body parts).
I don't understand why you're saying this, since the resistance of water must be more significant than the difference of the resistances of your hand and foot paths.

 Philly Master 04-17-2013 06:54 PM

Quote:
 Originally Posted by mpoulton (Post 1161458) The equivalent circuit for this is approximately three resistors in a wye arrangement. Two of them are your arms going to the receptacle slots, and the third is your body going into the bathtub. If the bathtub is grounded, then two points are at zero potential (right hand and feet) while the third is at 120V (left hand). So the result is that current flows in the left hand, and out both the right hand and the feet. The current out of the right hand would be similar to the current out of the feet (depends on the relative resistances of those body parts). This would trip the GFCI since a substantial amount of the current leaving the hot terminal does not return through the neutral, but instead goes to ground through the bathtub. If the bathtub is fiberglass with a PVC drain line, the result may be different. The water in the tub is isolated from ground. Now the circuit is just hand-to-hand, and all current returns through the GFCI so it doesn't trip. You get electrocuted, but the bathtub has nothing to do with it. One thing will definitely not happen: the breaker will not trip. There's no conceivable way that more than 15A will flow in this scenario. That would require a total resistance of 8 ohms or less, but body resistance is on the order of hundreds of ohms even neglecting skin resistance.

bathtub and water is the trick of the question ...LMAO
I was posed in a class and the answer given was no trips and ZIT ZIT ZIT

 Philly Master 04-17-2013 06:55 PM

Quote:
 Originally Posted by jeffnc (Post 1161464) I don't understand why you're saying this, since the resistance of water must be more significant than the difference of the resistances of your hand and foot paths.

body is 90% water ??

 ddawg16 04-17-2013 06:57 PM

Allan pretty much covered the points....

The kicker is that if your bathtub is a newer fiberglass tub with all ABS drains....chances are nothing will happen if you touch just the neutral or hot....the tub is effectively 'floating' (voltage wise), hence, no path to ground. In fact, you could be in the tub....drop a hot wire into the tub....and as long as you don't touch anything outside of it....your fine....

Now...when you touch both the hot and neut.....your a\$\$ is getting zapped....and I doubt the breaker will trip....should wake you up....

 Speedy Petey 04-17-2013 07:23 PM

Quote:
 Originally Posted by jeffnc (Post 1161429) I'm not an electrical engineer, but I believe the breaker would trip.
What does being an EE have to do with it??? I'd bet most EE's don't even know the principle of how a GFI works.

And no, the breaker would NOT trip. :no: Not for a while at least.

 jeffnc 04-17-2013 08:56 PM

Quote:
 Originally Posted by Speedy Petey (Post 1161501) What does being an EE have to do with it??? I'd bet most EE's don't even know the principle of how a GFI works.
Hopefully they'd understand the principles of how electricity flows, which is what this question is mostly about.

So you are saying no electricity would flow through the water? Why not?

 jeffnc 04-17-2013 08:58 PM

Quote:
 Originally Posted by Philly Master (Post 1161468) body is 90% water ??
Again, the difference between your hand and foot paths is going to be very small. The resistance of water is going to be much higher than the amount of that difference.

 jeffnc 04-17-2013 09:00 PM

Quote:
 Originally Posted by Philly Master (Post 1161466) I was posed in a class and the answer given was no trips and ZIT ZIT ZIT
But you said "and why?" So why is it that no electricity would flow through the water?

 mpoulton 04-17-2013 09:04 PM

Quote:
 Originally Posted by jeffnc (Post 1161464) I don't understand why you're saying this, since the resistance of water must be more significant than the difference of the resistances of your hand and foot paths.
I don't really know what you mean by that. I assumed roughly the same resistance hand-to-hand as hand-to-foot. That's an approximation, and actually ignores skin resistance which is more significant than body tissue resistance. The contact point resistance at each hand will be much higher than the "contact" resistance between the feet and the water. In reality, I would expect more current to exit the feet than the neutral hand, assuming the tub water is grounded and the water is conductive.

The water itself might be non-conductive if it's very pure, but that's not likely. Tap water is plenty conductive enough, although not as conductive as the inside of a person.

 ddawg16 04-17-2013 09:11 PM

Electricity needs a path to flow.....

If the bathtub is fiberglass with all plastic plumbing....there is not electrical path to ground.

Ever see the guys who do the power line maint? Helicopter deposits them on the power line and the scoot down it without an issue....even though they are sitting at over 100K volts....no path between their body and ground.

As for tripping the breaker....while your body typically has a lower resistance than water....the amount of current flow is dependent on several factors...if the bathtub is 'floating' (not grounded)....you can touch either conductor but no current will flow. But, if you touch both of them...current will flow through your body.

It does not take much current for you to die....once again, several factors...your health...surface area of the contact between your fingers and the conductors, how much salt is in your body and on your skin...etc. But that current is really no where near the breaker trip point....so, grab both conductors with both hands and enjoy the ride....

Side note....grab both those wires with the same hand....it's going to hurt...could burn your fingers....but it's not going to kill you....not going through your heart....and it still won't trip the breaker...

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