Another sad reminder of why we require GFCI's

[zog]

http://www.startribune.com/462/story/1582594.html

 

[iwire]

Before the link expires.....

HUDSON, Wis. - The death of a 6-year-old girl in a bathtub offers a sad lesson about the dangers of using electrical appliances near water, officials say.

Chelsea Joe (Princess) Helland was found with a hair dryer in the water-filled tub, and a medical examiner's report shows a high probability she died from electrocution, said interim Police Chief Eric Atkinson.

That is really sad, my youngest girl turned 7 last tuesday......I can't imagine losing her.


I agree entirely of the importance of GFCIs, however it should be pointed out a GFCI may not trip when an appliance is dropped into a tub.

 

[LawnGuyLandSparky]

Must've been an old hair dryer - as they've all had integral GFCIs built into their plugs for over 20 years now.

 

[iwire]

Must've been an old hair dryer - as they've all had integral GFCIs built into their plugs for over 20 years now.

If it had a GFCI it might not trip, it would require a path to ground for it to trip.

Fiberglass tub with a plastic plumbed house could very well be isolated from ground paths.

If it had a LCDI it would trip.

 

[iaov]

If it had a GFCI it might not trip, it would require a path to ground for it to trip.

Fiberglass tub with a plastic plumbed house could very well be isolated from ground paths.

If it had a LCDI it would trip.

We've discussed this many times before. A GFIC does not require a path to ground to trip. They look at the hot and the neurtal currents. If they are not within a few milli-amps of each other they trip. Ground current is assumed , as if the current isn't going hot to neutral it must be going some place, namely ground. Also a fiber glass tub that did not provide a path to ground might also have prevented the tradgedy. You can hold on to an un-grounded conductor (hot) and if there is no complete path you will not be hurt.

 

[iwire]

We've discussed this many times before. A GFIC does not require a path to ground to trip.

It needs a path to back to the source that is not on the circuit conductors.

Typically that is to ground.

They look at the hot and the neutral currents. If they are not within a few milli-amps of each other they trip.

Thats right, and the only way those currents can become un-equal is for current to flow another way back to the source.

Again, that is typically ground.


Bottom line is a two wire device dropped into an electrically isolated body of water will not trip the GFCI.

 

[masterelect1]

It needs a path to back to the source that is not on the circuit conductors.

Typically that is to ground.




Thats right, and the only way those currents can become un-equal is for current to flow another way back to the source.

Again, that is typically ground.


Bottom line is a two wire device dropped into an electrically isolated body of water will not trip the GFCI.

Apparently, there was current flow through the girls' body, hence the electrocution. I would surmise this is where the unbalance would occur and if there was a GFCI involved it would trip regardless of grounded vs. non-grounded.

 

[charlie b]

It needs a path to back to the source that is not on the circuit conductors. Typically that is to ground. . . . Bottom line is a two wire device dropped into an electrically isolated body of water will not trip the GFCI.

I agree with the first two sentences, but not with the third. You do need an additional path back to the source. But it need not be a wire. Current can flow from the hot conductor of the hair dryer, to the bath water (this path includes the person in the tub), through the water pipes (or even the water itself) to the point at which the water pipe is used as a grounding electrode, then via the GEC to the main panel.

 

[LarryFine]

Current can flow from the hot conductor of the hair dryer, to the bath water (this path includes the person in the tub), through the water pipes (or even the water itself) to the point at which the water pipe is used as a grounding electrode, then via the GEC to the main panel.

But that would not be "an electrically isolated body of water" if current could flow from the water into piping.

 

[charlie b]

But that would not be "an electrically isolated body of water" if current could flow from the water into piping.

Sorry, Larry, but I do not understand what you are trying to say. Are you agreeing with me :smile: or not ?

 

[dlhoule]

I think he was agreeing with you, but pointing out that would not be an isolated body of water. If it is an isolated body of water the chances of tripping the GFCI are not good. The water with the girl in it will provide a parrallel path with the dryer itself, which I believe could easily be enough to cause electrocution.

The current will be the same at the GFCI where it is being monitored.

 

[winnie]

Apparently, there was current flow through the girls' body, hence the electrocution. I would surmise this is where the unbalance would occur and if there was a GFCI involved it would trip regardless of grounded vs. non-grounded.

If the current were to flow from hot, through the girls body, and then back through the neutral, there would be no imbalance, and no trip of the GFCI.

It doesn't matter what path the current follows in going between hot and neutral when downstream of the GFCI. The only thing that will trip the GFCI is current that somehow bypasses the GFCI's sensor. As iwire notes, current bypassing the GFCI is commonly caused by current flowing to 'ground'.

If you had a totally electrically isolated container of water, and dropped an appliance into it, then any current flow through the water would have to eventually make it back to the appliance supply cord. This would not trip a GFCI.

-Jon

 

[masterelect1]

Sorry, Larry, but I do not understand what you are trying to say. Are you agreeing with me :smile: or not ?

Supposition: the hair dryer is using 7.2 amps and is dropped into the tub. The poor girls body takes a hit of 100 ma. The return to the gfci is 7.2 minus 100ma. Typical GFCI's made to trip @ 5ma imbalance.
The GFCI must trip due to this imbalance of outgoing amps vs. return amps, ground reference not required.

 

[winnie]

Supposition: the hair dryer is using 7.2 amps and is dropped into the tub. The poor girls body takes a hit of 100 ma. The return to the gfci is 7.2 minus 100ma.

Yes, but where does that 100ma go after passing _through_ the person. You can't simply have current entering someone without exiting again (excluding capacitive effects, which are negligible for a human body at 120V).

If that current goes back through the appliance cord, then as far as the GFCI is concerned, there is no imbalance. The same current goes in as goes out, with a bit going through the unfortunate girl.

For the GFCI to trip, that 100mA has to go someplace other than the appliance cord.

-Jon

 

[pfalcon]

Supposition: the hair dryer is using 7.2 amps and is dropped into the tub. The poor girls body takes a hit of 100 ma. The return to the gfci is 7.2 minus 100ma. Typical GFCI's made to trip @ 5ma imbalance.
The GFCI must trip due to this imbalance of outgoing amps vs. return amps, ground reference not required.

(7.2A - .1A) around the girl and (.1A) through the girl. Total 7.2A back to the circuit. The (.1A) does not go away; it is the part of the total 7.2A that passes through that resistor in the circuit.

Ideal transport through ideally isolated water means 100% current from and to the GFCI. Balanced circuit means no trip.

 

[charlie b]

Was my description of the current path not valid: Current passing through the person's body, then via the water/water pipe to the connection point of the GEC, then up the GEC to the N-G bond point, and thus having reached the source without passing through the appliance's grounded conductor? Would that path not result in a GFCI trip?

 

[winnie]

Was my description of the current path not valid: Current passing through the person's body, then via the water/water pipe to the connection point of the GEC [...] Would that path not result in a GFCI trip?

That should cause the GFCI to trip. But arguably that means that you do have a ground reference.

-Jon

 

[pfalcon]

Was my description of the current path not valid: Current passing through the person's body, then via the water/water pipe to the connection point of the GEC, then up the GEC to the N-G bond point, and thus having reached the source without passing through the appliance's grounded conductor? Would that path not result in a GFCI trip?

Valid.

Common water hazard path is from the hot, through the water and victim, to some other grounded or bonded object. The current then returns to the source through the system bonding in a manner such as you described.

Whether the GFCI will trip under the conditions you describe depends on what portion of the current fails to return through the neutral - and how long you wait. GFCI tripping is time dependant.

edit: what portion of the current fails to return through the neutral

 

[LarryFine]

Sorry, Larry, but I do not understand what you are trying to say. Are you agreeing with me :smile: or not ?

I was disagreeing. If the tub water was truly isolated, which would require non-metallic plumbing, etc., the only current pathway would be within the dryer itself.

In other words, the electrocution would have been prevented with use of a properly-wired and -operational GFCI device.

 

[don_resqcapt19]

Larry,

In other words, the electrocution would have been prevented with use of a properly-wired and -operational GFCI device.

I don't understand how we can say this. We have no idea if the piping to the tub was metallic or non-metallic. If it is non-metallic it may have enough isolation so that the GFCI does not trip.
Don