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Author Topic: Earth's natural electrical current?  (Read 8793 times)

Ed Hall

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Earth's natural electrical current?
« on: July 14, 2017, 07:55:43 PM »

While vacationing my children said the felt a tingle while climbing into the outdoor hot tub. I opened the breaker to the hot tub and had them climb out. I stuck my hand in the tub with the breaker open and felt a slight tingle. I was standing in a puddle that had formed when the kids climbed out.

I checked it with my NCVT and it didn't show a voltage present. I tried again with the breaker closed and still no voltage. I grabbed my VOM and stuck one lead in the crack in the concrete in the puddle and threw the other lead in the tub. It showed about 6 volts AC. I tried again with the breaker open and still 6VAC.  I tried to find a current and it did not register any current regardless of breaker position.  So I was the party pooper and told them they could not use the hot tub because of the stray voltage.

A few days later I saw this article in the booklet left by the rental company that manages the property. It claimed that some properties will experience a mild ground current and implied that it's normal.

My thought is that if the electrical system for the hot tub is grounded properly there shouldn't be a ground current even if the Earth's natural electrical current is high. It would be the same potential as the property grounded tub.

My question is this normal or are they just trying to avoid service calls and refunds?

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Pete Erskine

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Re: Earth's natural electrical current?
« Reply #1 on: July 14, 2017, 08:24:02 PM »

My question is this normal or are they just trying to avoid service calls and refunds?


Earth is a return circuit for every ground rod.  if some of them have significant voltage you might be able to sense it.  It probably is the result of poor power distribution planning in your electrical grid.

Having an electrician install a local ground rod for your power feed might lessen the level.
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Frank Koenig

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Re: Earth's natural electrical current?
« Reply #2 on: July 14, 2017, 08:56:23 PM »

A few sources of parasitic current or potential difference that come to mind:

*Ground leakage, as already mentioned.

*Capacitive or inductive coupling to nearby (high voltage) power lines.

*Reception and rectification of RF from transmitters.

*Static electricity. (The tendency for certain dielectrics to get a surface charge when rubbed together.)

*Galvanic effects. (Inadvertent batteries.)

*Thermoelectric effects. (As thermocouples.)

*Triboelectric effects. (Dissimilar metals transferring electrons from one to another when rubbed together.)

*Piezoelectric effects, (Certain crystals exhibiting a potential difference in response to mechanical strain.)

The earth has a radial electric field of about 100 V/m (if I recall correctly) but it's hard to observe. You won't see it by holding the probes of your voltmeter 1 m apart :)

I'm sure there are more. Add your own.

As for the "earth's natural current". Never heard of such a thing.

-F

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Stephen Swaffer

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Re: Earth's natural electrical current?
« Reply #3 on: July 14, 2017, 11:02:48 PM »

There is a whole section of code -680.26 Equipotential Bonding- dedicated to the proper way to build an equipotential grounding plane around "swimming pools,  fountains and similar installations." 

I am fairly certain you experienced the reason for those grounding planes-as I am certain that hot tub is "similar" to a pool installation.

I am not judging or intending to meddle in politics.  A quick scan through Currituck Counties website leaves a big question mark in my mind about electrical code enforcement and whether licensing is required for electrical installs.  Proper equipotential grounding plane installation is beyond the abilities of many licensed electricians (including myself).  If the resort company is taking shortcuts that routinely result in stray currents causing routine complaints and concerns this is a huge red flag.  Outer Banks?  Shouldn't be difficult to get a good ground-get a ground rod down to the water table-but an equipotential groundng plane is a lot more than a ground rod-or even a bunch of them.

You made the right call, fortunately or unfortunately depending on your POV.
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Peter Morris

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Re: Earth's natural electrical current?
« Reply #4 on: July 15, 2017, 04:42:01 AM »

While vacationing my children said the felt a tingle while climbing into the outdoor hot tub. I opened the breaker to the hot tub and had them climb out. I stuck my hand in the tub with the breaker open and felt a slight tingle. I was standing in a puddle that had formed when the kids climbed out.

I checked it with my NCVT and it didn't show a voltage present. I tried again with the breaker closed and still no voltage. I grabbed my VOM and stuck one lead in the crack in the concrete in the puddle and threw the other lead in the tub. It showed about 6 volts AC. I tried again with the breaker open and still 6VAC.  I tried to find a current and it did not register any current regardless of breaker position.  So I was the party pooper and told them they could not use the hot tub because of the stray voltage.

A few days later I saw this article in the booklet left by the rental company that manages the property. It claimed that some properties will experience a mild ground current and implied that it's normal.

My thought is that if the electrical system for the hot tub is grounded properly there shouldn't be a ground current even if the Earth's natural electrical current is high. It would be the same potential as the property grounded tub.

My question is this normal or are they just trying to avoid service calls and refunds?



Telluric currents ...

https://en.wikipedia.org/wiki/Telluric_current

https://en.wikipedia.org/wiki/March_1989_geomagnetic_storm

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John Roberts {JR}

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Re: Earth's natural electrical current?
« Reply #5 on: July 15, 2017, 09:13:19 AM »

While vacationing my children said the felt a tingle while climbing into the outdoor hot tub. I opened the breaker to the hot tub and had them climb out. I stuck my hand in the tub with the breaker open and felt a slight tingle. I was standing in a puddle that had formed when the kids climbed out.

I checked it with my NCVT and it didn't show a voltage present. I tried again with the breaker closed and still no voltage. I grabbed my VOM and stuck one lead in the crack in the concrete in the puddle and threw the other lead in the tub. It showed about 6 volts AC. I tried again with the breaker open and still 6VAC.  I tried to find a current and it did not register any current regardless of breaker position.  So I was the party pooper and told them they could not use the hot tub because of the stray voltage.

A few days later I saw this article in the booklet left by the rental company that manages the property. It claimed that some properties will experience a mild ground current and implied that it's normal.

My thought is that if the electrical system for the hot tub is grounded properly there shouldn't be a ground current even if the Earth's natural electrical current is high. It would be the same potential as the property grounded tub.

My question is this normal or are they just trying to avoid service calls and refunds?


I'd be very interested if that AC voltage was at 60 Hz....?

JR
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Frank Koenig

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Re: Earth's natural electrical current?
« Reply #6 on: July 15, 2017, 12:43:30 PM »

Telluric currents ...

Peter, I always learn something from you, whether audio related or not. Geomagnetic effects had occurred to me (exploding transformers) for my somewhat silly list, but I knew nothing of telluric currents.

Seriously, as for the tingling tubs, it almost certainly is a leakage problem due to a bad light, heating element, pump motor, beer fridge, etc. A good starting point would be to turn off the power as far upstream as possible, turn on all devices, open the neutral, and use an Ohmmeter to check the resistance from hot and neutral to ground. Chances are that would find it.

I once fixed a friend's hot tub that was tripping its GFCI by narrowing it down to the heating element. A bridge of corrosion products had formed on the dry side between one terminal and the housing. I cleaned up the corrosion and all was good.

Best,

--Frank
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Stephen Swaffer

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Re: Earth's natural electrical current?
« Reply #7 on: July 15, 2017, 08:35:38 PM »

The reason I mentioned (and code requires) an equipotential bonding grid is very simple.

How many birds have you seen sitting very calmly on power wires energized with 10's or 100's of thousands of volts and many amps flowing-but no ill effects.  On youtube you can see men working quite safely on the same live wires.  You DO NOT feel current flowinf through the earth.  You feel a tingle because two parts of your body are at a different potential, thus there is a current flowing through YOU.

The purpose of a bonding grid is to keep everything that a person can touch while wet and most likely bare footed at the same potential so that nothing can flow through the person-just like if you were standing on an aluminum wire.  It shouldn't matter that there is electricity flowing through the ground under your feet.
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Lyle Williams

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Re: Earth's natural electrical current?
« Reply #8 on: July 17, 2017, 06:02:58 PM »

So we all are thinking improper grounding?

How do we close the safety loop and save a life?  Email to AHJ?

Or do we just start a thread in ten years time titled "Hey, remember that hot tub thread, you'll never guess what..."

See something?  Say something.

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Stephen Swaffer

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Re: Earth's natural electrical current?
« Reply #9 on: July 17, 2017, 07:30:21 PM »


So we all are thinking improper grounding?



Others have repeated theselves  :D so may I?  Not improper grounding, but improper bonding..

An equipotential bonding grid requires a copper #8 connection between these:

1.  Re enforcing steel or #8 copper grid on 12" centers bonded at every crossing
2.  Perimeter surfaces-same as shell
3.  Metallic components
4.  Underwater lighting
5.  Metal fittings
6.  Electrical equipment
7.  Fixed metal parts (within 5' of pool)
8.  Pool water.

Interestingly,  this bonding doesn't have to be extended back to a panel-short of other bonding requirements for electrical equipment.  It is intended to make evryting you can touch essentially one "wire".  If you can't touch parts (including water) at different potentials you can't get shocked.  (With modern plumbing, water can be completely isolated with plastic piping-so water is a 2017 addition-probably not enforced hardly anywhere-but the OPs experience may illustrate the purpose for the new rule).

This is obviously an extreme synopsis-don't use this to design from!  The biggest issue I have is the property owners characterization of this as "normal".  Lightning is "normal" too!

I took the time to type this because it is an illustration of what should happen in any sound/entertainment scenario-albeit without the extreme copper mesh.
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Steve Swaffer

ProSoundWeb Community

Re: Earth's natural electrical current?
« Reply #9 on: July 17, 2017, 07:30:21 PM »


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