Bath tub GFI
- Thread starter domnic
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- Placerville, CA, USA
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- Retired PV System Designer
Plastic drain too, I presume.
The GFI may trip if there is an EGC in the cord to the hair dryer which is connected to metal.
If it is purely a two wire connection, the GFI will not trip. Lots of illustrations of this on the Internet.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If your water system is not a well then at some point the water will likely be in contact with a grounded metal water pipe. It would depend on the resistance of that connection to determine whether or not you would have the 4-6 ma needed to open the GFCI device.
jxofaltrds
Inspector Mike®
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- Mike P. Columbus Ohio
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- ESI, PI, RBO
Is it plugged in? :happyno:
I bet it would trip. Gut feeling.
Try it but don't be in the tub.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It will not trip unless there is an equipment grounding conductor on the hair blower or metallic drains. I did this with a bucket of water (plastic bucket) and dropped a wp flood bulb attached to a keyless socket. The gfci did not trip the light stayed lit and I even put my hand in the water.
rlundsrud
Senior Member
- Location
- chicago, il, USA
ok, I could be wrong about this as I have never actually dropped a hair dryer in a bucket of water on a hot/grounded conductor only GFCI protected circuit but I was taught that you needed only a hot/grounded conductor for a 120 volt GFCI. The way a GFCI operates is based on Faraday's law. The hot/grounded conductor are surrounded by a sensing coil, during normal operation the currents in the wires are in equal and opposite directions and of equal magnitude, there is no magnetic field surrounding the wires and the net magnetic flux in the sensing coil is zero. If the return current in the grounded conductor changes so that the two currents are not equal, circular magnetic field lines will exist around the pair of wires. This magnetic flux will induce an emf in the sensing coil and trigger the GFCI to trip before the current reaches a harmful level. So in my opinion it should work without a ground. If I learned this incorrectly, please let me know.
- Location
- Illinois
- Occupation
- retired electrician
The only way you would have a path back to the metal water pipe is if the water is running, and even in that case I doubt that the GFCI would trip.
We have very hard city water, about 17 grains, without treatment. My cold water is not treated, and all of the water piping in my house is copper. I cannot get a GFCI to trip if connect a wire to the hot of a GFCI receptacle and put the other end into the running water.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The problem with your idea is that the only current flow will be from the hot wire to the neutral wire through the water, so that there will be no imbalance for the GFCI to sense.
The GFCI does not detect current that goes "to ground", it detects current that goes out one wire and does not all come back on the other.
In the ungrounded tub, where would that alternate destination be?
If it goes through the heater wire or the water, the result is just the same.
So, the GFCI will work just fine without having a ground connection at its end, but the hair dryer in the tub will not trip it.
rlundsrud
Senior Member
- Location
- chicago, il, USA
one other thing....
one other thing....
I actually want to add one other point to this. In order for the net flux to not be zero, current would have to be leaking into ground system somewhere or put another way, not all of the return current would be in the grounded conductor. If you did this in a 5 gallon bucket and there was no path to ground, all the current would have to return on the grounded conductor. If a person put their hand in the bucket and they were grounded, that would create the secondary path to ground, the GFCI would sense the non-zero flux and trip the GFCI thereby protecting the person from dangerous currents. I wouldn't try this at home, but I feel that it should still work as designed.
Golddigger, you are quick on the draw. I was adding this update when you posted that. I completely agree with you, that is why I added this post.
one other thing....
I actually want to add one other point to this. In order for the net flux to not be zero, current would have to be leaking into ground system somewhere or put another way, not all of the return current would be in the grounded conductor. If you did this in a 5 gallon bucket and there was no path to ground, all the current would have to return on the grounded conductor. If a person put their hand in the bucket and they were grounded, that would create the secondary path to ground, the GFCI would sense the non-zero flux and trip the GFCI thereby protecting the person from dangerous currents. I wouldn't try this at home, but I feel that it should still work as designed.
Golddigger, you are quick on the draw. I was adding this update when you posted that. I completely agree with you, that is why I added this post.
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John120/240
Senior Member
- Location
- Olathe, Kansas
A little Off Topic but related: In the movie The Postman Always Rings Twice with Jessica Lange & Jack Nicholson they have a similar situation with a bath tub & water. Seems like they were trying to do somebody harm but the details are fuzzy. Too long ago
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
In that situation we have to assume a metal tub with metal drain piping. Or just note that it was only a movie. 
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- Location
- New Jersey
- Occupation
- Journeyman Electrician
mgookin
Senior Member
- Location
- Fort Myers, FL
In that situation we have to assume a metal tub with metal drain piping. Or just note that it was only a movie.
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I'll buy the movie part. Notice in movies how they pull a fire alarm pull station and all the sprinkers go off? It doesn't work that way (unless you have a deluge which is not how common area sprinklers operate).
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